Organic chemistry is a discipline within
chemistryChemistry is the science concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions...
which involves the
scientificScience is in its broadest sense to any systematic knowledge-base or prescriptive practice that is capable of resulting in a prediction or predictable type of outcome...
study of the structure, properties, composition,
reactionsA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
, and preparation (by
synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
or by other means) of
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s that contain
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
. These compounds may contain any number of other elements, including
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
,
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
,
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
, the halogens as well as
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
,
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
and
sulfurSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
.
Because of their unique properties, multi-carbon compounds exhibit extremely large variety and the range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (
paintPaint is any liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.-History:...
s,
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
s,
foodFood is any substance, usually composed of carbohydrates, fats, proteins and water, that can be eaten or drunk by an animal, including humans, for nutrition or pleasure. Items considered food may be sourced from plants, animals or other categories such as fungus or fermented products like alcohol...
, explosives,
drugA drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
s,
petrochemicalPetrochemicals are chemical products made from raw materials of petroleum or other hydrocarbon origin. Although some of the chemical compounds that originate from petroleum may also be derived from coal and natural gas, petroleum is the major source...
s, to name but a few) and (apart from a very few exceptions) they form the basis of all earthly life processes.
Current (as of 2008) trends in organic chemistry include
chiral synthesisAsymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is organic synthesis which introduces one or more new and desired elements of chirality...
,
green chemistryGreen chemistry, also called sustainable chemistry, is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous substances. Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant...
,
microwave chemistryMicrowave chemistry is the science of applying microwave irradiation to chemical reactions. Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent or conducting ions in a solid...
,
fullereneA fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbon nanotubes or buckytubes...
s and
microwave spectroscopyRotational spectroscopy or microwave spectroscopy studies the absorption and emission of electromagnetic radiation by molecules associated with a corresponding change in the rotational quantum number of the molecule...
.
Historical highlights
At the very beginning of the nineteenth century chemists generally thought that compounds from living organisms were too complicated in structure to be capable of artificial
synthesisIn chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
from non-living things, and that a 'vital force' or
vitalismVitalism, as defined by the Merriam-Webster dictionary, is#a doctrine that the functions of a living organism are due to a vital principle distinct from biochemical reactions...
conferred the characteristics of living beings on this form of matter. They named these compounds 'organic', and preferred to direct their investigations toward inorganic materials that seemed more promising.
Organic chemistry received a boost when it was realized that these compounds could be treated in ways similar to
inorganic compoundTraditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin...
s and could be created in the laboratory by means other than 'vital force'. Around 1816
Michel ChevreulMichel Eugène Chevreul was a French chemist whose work with fatty acids led to early applications in the fields of art and science. He is credited with discovering margarine and designing an early form of soap made from animal fats and salt...
started a study of
soapSoap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid....
s made from various
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s and
alkaliIn chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Alkalis are best known for being bases that dissolve in water. Bases are compounds with a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base, especially for...
. He separated the different acids that, in combination with the alkali, produced the soap. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats (which traditionally come from organic sources), producing new compounds, without 'vital force'. In 1828
Friedrich WöhlerFriedrich Wöhler was a German chemist, best-known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, nowadays a district of Frankfurt am Main...
first manufactured the organic chemical
ureaUrea or carbamide is an organic compound with the chemical formula
2CO. The molecule has two amine residues joined by a carbonyl functional group....
(carbamide), a constituent of
urineUrine is a liquid waste product of the body secreted by the kidneys by a process of filtration from blood called urination and excreted through the urethra. Cellular metabolism generates numerous waste compounds, many rich in nitrogen, that require elimination from the bloodstream...
, from the inorganic
ammonium cyanateThe cyanate ion is an anion consisting of one oxygen atom, one carbon atom, and one nitrogen atom, [OCN]
−, in that order, and possesses 1 unit of negative charge, borne mainly by the nitrogen atom...
NH
4OCN, in what is now called the
Wöhler synthesisrightThe Wöhler synthesis is the conversion of ammonium cyanate into urea. This chemical reaction was discovered in 1828 by Friedrich Wöhler in an attempt to synthesize ammonium cyanate. It is considered the starting point of modern organic chemistry. Although the Wöhler reaction concerns the...
. Although Wöhler was, at this time as well as afterwards, cautious about claiming that he had thereby destroyed the theory of vital force, most
have looked to this event as the turning point.
A great next step was when in 1856 William Henry Perkin, while trying to manufacture
quinineQuinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , and anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine....
, again accidentally came to manufacture the organic
dyeA dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber....
now called Perkin's mauve, which by generating a huge amount of money greatly increased interest in organic chemistry. Another step was the laboratory preparation of
DDTDDT is one of the most well-known synthetic pesticides. It is a chemical with a long, unique, and controversial history....
by Othmer Zeidler in 1874, but the
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
properties of this compound were not discovered until much later.
The crucial breakthrough for the theory of organic chemistry was the concept of chemical structure, developed independently and simultaneously by Friedrich August Kekule and
Archibald Scott CouperArchibald Scott Couper was a Scottish chemist who proposed an early theory of chemical structure and bonding...
in 1858. Both men suggested that
tetravalentIn chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element...
carbon atoms could link to each other to form a carbon lattice, and that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.
The history of organic chemistry continues with the discovery of
petroleumPetroleum or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.The term "petroleum" was first used in the treatise De Natura Fossilium, published in...
and its separation into
fractionA fraction in chemistry is a quantity collected from a sample or batch of a substance in a fractionating separation process. In such a process, a mixture is separated into fractions, which have compositions that vary according to a gradient. A fraction can be defined as a group of chemicals that...
s according to boiling ranges. The conversion of different compound types or individual compounds by various chemical processes created the petroleum chemistry leading to the birth of the
petrochemicalPetrochemicals are chemical products made from raw materials of petroleum or other hydrocarbon origin. Although some of the chemical compounds that originate from petroleum may also be derived from coal and natural gas, petroleum is the major source...
industry, which successfully manufactured artificial
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
s, the various organic
adhesiveAdhesive or glue is a compound in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry...
s, the property-modifying petroleum additives, and
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
s.
The pharmaceutical industry began in the last decade of the 19th century when acetylsalicylic acid (more commonly referred to as
aspirinAspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
) manufacture was started in Germany by
BayerBayer AG is a German chemical and pharmaceutical company founded in Barmen, Germany in 1863. Today it is headquartered in Leverkusen, North Rhine-Westphalia, Germany. It is well-known for its original brand of aspirin...
. The first time a drug was systematically improved was with
arsphenamineArsphenamine, also known as Salvarsan and 606, is a drug that was used to treat syphilis and trypanosomiasis. It was the first modern chemotherapeutic agent.-History:...
(Salvarsan). Numerous derivatives of the dangerously toxic
atoxylArsanilic acid is the organoarsenic compound also called p-aminophenylarsenic acid. This colourless solid was used as a drug in the late 19th and early 20th centuries but is now considered prohibitively toxic. Arsanilic acid is a derivative of phenylarsonic acid with an amine in the 4-position...
were systematically synthesized and tested by
Paul EhrlichPaul Ehrlich was a German scientist in the fields of hematology, immunology, and chemotherapy, and Nobel laureate. He is noted for curing syphilis and for his research in autoimmunity, calling it "horror autotoxicus"...
and his group, and the compound with best effectiveness and toxicity characteristics was selected for production.
Early examples of organic reactions and applications were
serendipitousSerendipity is the effect by which one accidentally discovers something fortunate, especially while looking for something entirely unrelated. The word has been voted as one of the ten English words that were hardest to translate in June 2004 by a British translation company...
, such as Perkin's accidental discovery of Perkin's mauve. However, from the 20th century, the progress of organic chemistry allowed for synthesis of specifically selected compounds or even molecules designed with specific properties, as in
drug designDrug design, also sometimes referred to as rational drug design, is the inventive process of finding new medications based on the knowledge of the biological target. The drug is most commonly an organic small molecule which activates or inhibits the function of a biomolecule such as a protein which...
. The process of finding new synthesis routes for a given compound is called total synthesis.
Total synthesisIn principle a total synthesis is the complete chemical synthesis of complex organic molecules from simpler pieces, usually without the aid of biological processes....
of complex natural compounds started with
ureaUrea or carbamide is an organic compound with the chemical formula
2CO. The molecule has two amine residues joined by a carbonyl functional group....
, increased in complexity to
glucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
and
terpineolTerpineol is a naturally occurring monoterpene alcohol that has been isolated from a variety of sources such as cajuput oil, pine oil, and petitgrain oil. There are three isomers, alpha-, beta-, and gamma-terpineol, the last two differing only by the location of the double bond...
, and in 1907, total synthesis was commercialized the first time by
Gustaf KomppaGustaf Komppa was a Finnish chemist best known for a world-first in commercializing total synthesis, that of camphor in 1903.Komppa was born in Viipuri in 1867. He graduated from the University of Helsinki in 1891 and subsequently worked for a while in Switzerland before obtaining his Ph.D...
with
camphorCamphor is a waxy, white or transparent solid with a strong, aromatic odor. It is a terpenoid with the chemical formula C
10H
16O. It is found in wood of the camphor laurel , a large evergreen tree found in Asia and also of Dryobalanops aromatica, a giant of the Bornean forests...
. Pharmaceutical benefits have been substantial, for example
cholesterolCholesterol is a lipidic, waxy steroid found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes, where it is required to establish proper membrane permeability and fluidity...
-related compounds have opened ways to synthesis of complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increasing, with examples such as
lysergic acidLysergic acid, also known as D-lysergic acid and -lysergic acid, is a precursor for a wide range of ergoline alkaloids that are produced by the ergot fungus and some plants. Amides of lysergic acid, lysergamides, are widely used as pharmaceuticals and as psychedelic drugs...
and
vitamin B12Vitamin B12 is a water soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
. Today's targets feature
tens of stereogenic centers that must be synthesized correctly with asymmetric synthesis.
BiochemistryBiochemistry is the study of the chemical processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
, the chemistry of living organisms, their structure and interactions
in vitroA procedure performed in vitro is performed not in a living organism but in a controlled environment, such as in a test tube or Petri dish...
and inside living systems, has only started in the 20th century, opening up a brand new chapter of organic chemistry with enormous scope. Biochemistry, like Organic Chemistry, primarily focuses on compounds containing carbon as well.
Description and nomenclature
Classification is not possible without having a full description of the individual compounds.
In contrast with
inorganic chemistryInorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
, in which describing a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
can be achieved by simply enumerating the chemical symbols of the
elementsA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
present in the compound together with the number of these elements in the molecule, in organic chemistry the relative arrangement of the atoms within a molecule must be added for a full description.
One way of describing the molecule is by drawing its
structural formulaThe structural formula of a chemical compound is a graphical representation of the molecular structure, showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly. There are three common representations used in publications: text,...
. Because of molecular complexity, simplified systems of chemical notation have been developed. The latest version is the line-angle formula, which achieves simplicity without introducing ambiguity. In this system, the endpoints and intersections of each line represent one carbon, and hydrogens can either be notated or assumed to be present by implication. Some disadvantages of chemical notation are that they are not easily described by words and they are not easily printable. These problems have been addressed by describing molecular structures using organic nomenclature .
Because of the difficulties arising from the very large number and variety of organic compounds, chemists realized early on that the establishment of an internationally accepted system of naming organic compounds was of paramount importance. The Geneva Nomenclature was born in 1892 as a result of a number of international meetings on the subject.
It was also realized that as the family of organic compounds grew, the system would have to be expanded and modified. This task was ultimately taken on by the International Union on Pure and Applied Chemistry (IUPAC). Recognizing the fact that in the branch of biochemistry the complexity of organic structures increases, the IUPAC organization joined forces with the
International Union of Biochemistry and Molecular BiologyThe International Union of Biochemistry and Molecular Biology is an international non-governmental organisation concerned with biochemistry and molecular biology...
, IUBMB, to produce a list of joint recommendations on nomenclature.
Later, as the numbers and complexities of organic molecules grew, new recommendations were made within IUPAC for simplification. The first such recommendation was presented in 1951 when a cyclic benzene structure was named a
cyclophaneA cyclophane is a hydrocarbon consisting of an aromatic unit and an aliphatic chain that forms a bridge between two non-adjacent positions of the aromatic ring. More complex derivatives with multiple aromatic units and bridges forming cagelike structures are also known...
. Later recommendations extended the method to the simplification of other complex cyclic structures, including heterocyclics, and named such structures
phanesPhanes are sub-structures of highly complex organic molecules introduced for simplification of the naming of these highly complex molecules.Systematic nomenclature of organic chemistry consists of building a name for the structure of an organic compound by a collection of names of its composite...
.
For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations are not always followed in practice except when it is necessary to give a concise definition to a compound, or when the IUPAC name is simpler (viz.
ethanol versus
ethyl alcohol). Otherwise the
common or
trivial nameIn chemistry and biology, a trivial name is a non-systematic name or non-scientific name. That is, the name is not recognised according to the rules of any formal system of nomenclature. Many trivial names continue to be used because their sanctioned equivalents are considered too cumbersome...
may be used, often derived from the source of the compound.
In summary, organic substances are classified by their molecular structural arrangement and by what other atoms are present along with the chief (carbon) constituent in their makeup, while in a structural formula, hydrogen is implicitly assumed to occupy all free valences of an appropriate carbon atom which remain after accounting for branching, other element(s) and/or multiple bonding.
Hydrocarbons and functional groups
Classification normally starts with the hydrocarbons: compounds which contain only carbon and hydrogen. For sub-classes see below. Other elements present themselves in atomic configurations called functional groups which have decisive influence on the chemical and physical characteristics of the compound; thus those containing the same atomic formations have similar characteristics, which may be:
miscibilityIn chemistry, miscibility is the property of liquids to mix in all proportions, forming a homogeneous solution. In principle, the term applies also to other phases , but the main focus is on the solubility of one liquid in another...
with water, acidity/
alkalinityAlkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity of a solution and ANC is often incorrectly used to refer to alkalinity.The alkalinity is...
, chemical
reactivityReactivity refers to the rate at which a chemical substance tends to undergo a chemical reaction in time. In pure compounds, reactivity is regulated by the physical properties of the sample. For instance, grinding a sample to a higher specific surface area increases its reactivity. In impure...
, oxidation resistance, and others. Some functional groups are also
radicalsIn chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions...
, similar to those in inorganic chemistry, defined as
polarIn chemistry, polarity refers to a separation of electric charge leading to a molecule having an electric dipole. Polar molecules can bond together due to dipole–dipole intermolecular forces between one molecule with asymmetrical charge distribution and another molecule also with asymmetrical...
atomic configurations which pass during chemical reactions from one chemical compound into another without change.
Some of the elements of the functional groups (O, S, N, halogens) may stand alone and the
group name is not strictly appropriate, but because of their decisive effect on the way they modify the characteristics of the hydrocarbons in which they are present they are classed with the functional groups, and their specific effect on the properties lends excellent means for characterisation and classification.
Referring to the hydrocarbon types below, many, if not all of the functional groups which are typically present within aliphatic compounds are also represented within the aromatic and alicyclic group of compounds, unless they are dehydrated, which would lead to non-reacting co-optional groups.
Reference is made here again to the organic nomenclature, which shows an extensive (if not comprehensive) number of classes of compounds according to the presence of various functional groups, based on the IUPAC recommendations, but also some based on
trivial nameIn chemistry and biology, a trivial name is a non-systematic name or non-scientific name. That is, the name is not recognised according to the rules of any formal system of nomenclature. Many trivial names continue to be used because their sanctioned equivalents are considered too cumbersome...
s. Putting compounds in sub-classes becomes more difficult when more than one functional group is present.
Two overarching chain type categories exist: open chain aliphatic compounds and closed chain
cyclic compoundIn organic chemistry, a cyclic compound is a compound in which a series of carbon atoms are connected to form a loop or ring. Benzene is a well known example...
s. Those in which both open chain and cyclic parts are present are normally classed with the latter.
Aliphatic compounds
The aliphatic hydrocarbons are subdivided into three groups of
homologous seriesIn chemistry, a homologous series is a series of organic compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass...
according to their state of
saturationIn chemistry, saturation has five different meanings:#In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of it will appear as a precipitate...
: paraffins
alkaneAlkanes, also known as paraffins, are chemical compounds that consist only of the elements carbon and hydrogen , wherein these atoms are linked together exclusively by single bonds without any cyclic structure...
s without any double or triple bonds, olefins
alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s with double bonds, which can be mono-olefins with a single double bond, di-olefins, or di-enes with two, or poly-olefins with more. The third group with a triple bond is named after the name of the shortest member of the homologue series as the acetylenes
alkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
s. The rest of the group is classed according to the functional groups present.
From another aspect aliphatics can be straight chain or branched chain compounds, and the degree of branching also affects characteristics, like octane number or
cetane numberCetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality.- Definition :...
in petroleum chemistry.
Aromatic and alicyclic compounds
Cyclic compounds can, again, be saturated or unsaturated. Because of the bonding angle of carbon, the most stable configurations contain six carbon atoms, but while rings with five carbon atoms are also frequent, others are rarer. The cyclic hydrocarbons divide into alicyclics and aromatics (also called arenes).
Of the alicyclic compounds the
cycloalkaneCycloalkanes are types of alkanes which have one or more rings of carbon atoms in the chemical structure of their molecules. Alkanes are types of organic hydrocarbon compounds which have only single chemical bonds in their chemical structure...
s do not contain multiple bonds, whilst the
cycloalkeneA cycloalkene or cycloolefin is a type of alkene hydrocarbon which contains a closed ring of carbon atoms, but has no aromatic character. Some cycloalkenes, such as cyclobutene and cyclopentene, can be used as monomers to produce polymer chains....
s and the cycloalkynes do. Typically this latter type only exists in the form of large rings, called
macrocycleA macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of seven or more atoms to be a macrocyle...
s. The simplest member of the cycloalkane family is the three-membered
cyclopropaneCyclopropane is a cycloalkane molecule with the molecular formula C
3H
6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms....
.
Aromatic hydrocarbons contain
conjugatedA conjugated system occurs in an organic compound where atoms covalently bond with alternating single and multiple bonds and influence each other to produce a region called electron delocalization. In this region electrons do not belong to a single bond or atom, but rather a group...
double bonds. One of the simplest examples of these is
benzeneBenzene, or benzol, is an organic chemical compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point...
, the structure of which was formulated by
KekuléKekule can refer to a German chemist, his son, or the various things named after them :*Friedrich August Kekulé von Stradonitz , German organic chemist*Non-Kekulé molecule...
who first proposed the
delocalizationIn chemistry delocalized electrons are electrons in a molecule that are not associated with a single atom or to a covalent bond. Delocalized electrons are contained within an orbital that extends over several adjacent atoms. Classically, delocalized electrons can be found in conjugated systems of...
or
resonanceResonance in chemistry is a key component of valence bond theory used to graphically represent and mathematically model certain types of molecular structures when no single, conventional Lewis structure can satisfactorily represent the observed structure or explain its properties...
principle for explaining its structure. For "conventional" cyclic compounds, aromaticity is conferred by the presence of 4n + 2 delocalized pi electrons, where n is an integer. Particular instability (
antiaromaticityAntiaromatic molecules are cyclic systems containing alternating single and double bonds, where the pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart. Therefore antiaromatic compounds are unstable and highly reactive; often antiaromatic compounds...
) is conferred by the presence of 4n conjugated pi electrons.
The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a heterocycle.
PyridinePyridine is a simple aromatic heterocyclic organic compound with the chemical formula C
5H
5N used as a precursor to agrochemicals and pharmaceuticals, and is also an important solvent and reagent. It is structurally related to benzene, wherein one CH group in the aromatic...
and
furanFuran, also known as furane and furfuran, is a heterocyclic organic compound. It is typically derived by the thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood. Furan is a colorless, flammable, highly volatile liquid with a boiling point close to room...
are examples of aromatic heterocycles while
piperidinePiperidine is an organic compound with the molecular formula
5NH. This heterocyclic amine consists of a six-membered ring containing five methylene units and one nitrogen atom...
and
tetrahydrofuranTetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use is however as a...
are the corresponding alicyclic heterocycles. The heteroatom of heterocyclic molecules is generally oxygen, sulfur, or nitrogen, with the latter being particularly common in biochemical systems.
Rings can fuse with other rings on an edge to give
polycyclic compoundIn organic chemistry, a polycyclic compound is a cyclic compound with more than one hydrocarbon loop or ring structures . The term generally includes all polycyclic aromatic compounds, including the polycyclic aromatic hydrocarbons, the heterocyclic aromatic compounds containing sulfur, nitrogen,...
s. The
purineA purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed
spiroA spiro compound is a bicyclic organic compound with rings connected through just one atom. The rings can be different in nature or identical. The connecting atom is also called the spiroatom, most often a quaternary carbon...
and are important in a number of
natural productA natural product is a chemical compound or substance produced by a living organism - found in nature that usually has a pharmacological or biological activity for use in pharmaceutical drug discovery and drug design...
s.
Polymers
One important property of carbon in organic chemistry is that it can form certain compounds, the individual molecules of which are capable of attaching themselves to one another, thereby forming a chain or a network. The process is called
polymerizationIn polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
and the chains or networks polymers, while the source compound is a
monomerA monomer is a small molecule that may become chemically bonded to other monomers to form a polymer...
. Two main groups of polymers exist: those artificially manufactured are referred to as
industrial polymersPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
or synthetic polymers and those naturally occurring as
biopolymerBiopolymers are polymers produced by living organisms. Cellulose and starch, proteins and peptides, and DNA and RNA are all examples of biopolymers, in which the monomeric units, respectively, are sugars, amino acids, and nucleotides....
s.
Since the invention of the first artificial polymer,
bakeliteBakelite , or polyoxybenzylmethylenglycolanhydride, is an early plastic. It is a thermosetting phenol formaldehyde resin, formed from an elimination reaction of phenol with formaldehyde, usually with a wood flour filler. It was developed in 1907–1909 by Belgian chemist Dr...
, the family has quickly grown with the invention of others. Common synthetic organic polymers are
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
or polythene,
polypropylenePolypropylene or polypropene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and...
,
nylonNylon is a generic designation for a family of synthetic polymers known generically as polyamides and first produced on February 28, 1935 by Wallace Carothers at DuPont...
,
teflonIn chemistry, polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene which finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
or PTFE,
polystyrenePolystyrene , sometimes abbreviated PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry...
,
polyesterPolyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
s, polymethylmethacrylate (commonly known as perspex or plexiglas) polyvinylchloride or PVC, and polyisobutylene an important artificial or synthetic
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
also the polymerised butadiene, a rubber component.
The examples are generic terms, and many varieties of each of these may exist, with their physical characteristics fine tuned for a specific use. Changing the conditions of polymerisation changes the chemical composition of the product by altering
chain lengthThe degree of polymerization, or DP, is the number of repeat units in an average polymer chain at time t in a polymerization reaction . The length is in monomer units. The degree of polymerization is a measure of molecular weight...
, or branching, or the
tacticityTacticity is the relative stereochemistry of adjacent chiral centers within a macromolecule . The practical significance of tacticity rests in the link between tacticity and the physical properties of the polymer...
. With a single monomer as a start the product is a homopolymer. Further, secondary component(s) may be added to create a heteropolymer (co-polymer) and the degree of clustering of the different components can also be controlled. Physical characteristics, such as hardness,
densityThe density of a material is defined as its mass per unit volume. The symbol of density is ρ .- Formula :Mathematically:where: is the density, is the mass, is the volume....
, mechanical or
tensile strengthTensile strength is indicated by the maxima of a stress-strain curve and, in general, indicates when necking will occur. As it is an intensive property, its value does not depend on the size of the test specimen...
, abrasion resistance, heat resistance, transparency, colour, etc. will depend on the final composition.
Biomolecules
Biomolecular chemistryA biomolecule is any organic molecule that is produced by a living organism, including large polymeric molecules such as proteins, polysaccharides, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products.As organic molecules,...
is a major category within organic chemistry which is frequently studied by biochemists. Many complex multi-functional group molecules are important in living organisms. Some are long-chain biopolymers, and these include proteins,
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
,
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
and the polysaccharides such as
starchStarch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds.Starch is produced by all green plants as an energy store and is a major food source for humans....
es in animals and
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
s in plants. The other main classes are
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
s (monomer building blocks of proteins), carbohydrates (which includes the polysaccharides), the nucleic acids (which include DNA and RNA as polymers), and the
lipidLipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others...
s. In addition, animal biochemistry contains many small molecule intermediates which assist in energy production through the Krebs cycle, and produces
isopreneIsoprene or 2-methyl-1,3-butadiene is a common organic compound with the formula CH2=CCH=CH2. It is present under standard conditions as a colorless liquid...
, the most common hydrocarbon in animals. Isoprenes in animals form the important
steroidA steroid is a terpenoid lipid characterized by its sterane core and additional functional groups. The core is a carbon structure of four fused rings: three cyclohexane rings and one cyclopentane ring. The steroids vary by the functional groups attached to these rings and the oxidation state of the...
structural (
cholesterolCholesterol is a lipidic, waxy steroid found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes, where it is required to establish proper membrane permeability and fluidity...
) and steroid hormone compounds; and in plants form
terpeneTerpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium....
s, terpenoids, some alkaloids, and a unique set of
structural hydrocarbons called biopolymer polyisoprenoids present in
latexLatex refers generically to a stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic. Latex as found in nature is a milky sap-like fluid within many plants that coagulates on exposure to air. It is a complex emulsion in which proteins, alkaloids,...
sap which is the basis for making
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
.
Small molecules
In pharmacology, an important group of organic compounds is
small moleculeIn the fields of pharmacology and biochemistry, a small molecule is a low molecular weight organic compound which is by definition not a polymer...
s, also referred to as 'small organic compounds'. In this context, a small molecule is a small organic compound that is biologically active, but is not a
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
. In practice, small molecules have a
molar massMolar mass, symbol M, is the mass of one mole of a substance . It is a physical property which is characteristic of each pure substance...
less than approximately 1000 g/mol.
Fullerenes
FullereneA fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbon nanotubes or buckytubes...
s are among the types of compounds engineered by organic chemists that have generated the most interest. The discovery of their unique electronic properties due to their spherical structure has stimulated new research into related fields such as
carbon nanotubeCarbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 28,000,000:1, which is significantly larger than any other material...
s.
Others
Organic compounds containing bonds of carbon to nitrogen, oxygen and the halogens are not normally grouped separately. Others are sometimes put into major groups within organic chemistry and discussed under titles such as organosulfur chemistry,
organometallic chemistryOrganometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, organophosphorus chemistry and
organosilicon chemistryOrganosilicon compounds are organic compounds containing carbon silicon bonds. Organosilicon chemistry is the corresponding science exploring their properties and reactivity.Like carbon, the organically bound silicon is tetravalent and tetrahedral...
.
Characteristics of organic substances
Organic compounds are generally
covalently bondedA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
. This allows for unique structures such as long carbon chains and rings. The reason carbon is excellent at forming unique structures and that there are so many carbon compounds is that carbon atoms form very stable covalent bonds with one another (
catenationCatenation is the ability of a chemical element to form a long chain-like structure via a series of covalent bonds. Catenation occurs most readily in carbon, which forms covalent bonds with other carbon atoms. Catenation is the reason for the presence of a large number of organic compounds in nature...
). In contrast to inorganic materials, organic compounds typically melt, boil, sublimate, or decompose below 300 °C. Neutral organic compounds tend to be less soluble in
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
compared to many inorganic salts, with the exception of certain compounds such as ionic organic compounds and low molecular weight alcohols and carboxylic acids where hydrogen bonding occurs.
Organic compounds tend to dissolve in organic
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water. Most other commonly-used solvents are organic chemicals. These are called organic solvents...
s which are either pure substances like
etherDiethyl ether, also known as ether, ethyl ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol...
or
ethyl alcoholEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
, or mixtures, such as the paraffinic solvents such as the various
petroleum etherPetroleum ether, also known as benzine, VM&P Naphtha, Petroleum Naphtha, Naphtha ASTM, Petroleum Spirits, X4 or Ligroin, is a group of various volatile, highly flammable, liquid hydrocarbon mixtures used chiefly as nonpolar solvents.Petroleum ether is obtained from petroleum refineries as the...
s and
white spiritWhite spirit, also known as Stoddard solvent, is a paraffin-derived clear, transparent liquid which is a common organic solvent used in painting and decorating. In 1924, an Atlanta dry cleaner named W. J. Stoddard worked with Lloyd E...
s, or the range of pure or mixed aromatic solvents obtained from petroleum or tar
fractionA fraction in chemistry is a quantity collected from a sample or batch of a substance in a fractionating separation process. In such a process, a mixture is separated into fractions, which have compositions that vary according to a gradient. A fraction can be defined as a group of chemicals that...
s by physical separation or by chemical conversion. Solubility in the different solvents depends upon the solvent type and on the functional groups if present. Solutions are studied by the science of
physical chemistryPhysical chemistry is the explanation of macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical concepts; sometimes using the principles, practices and concepts of physics like thermodynamics, quantum chemistry, statistical mechanics and...
. Like inorganic salts, organic compounds may also form
crystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography...
s. A unique property of carbon in
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
s is that its valency does not always have to be taken up by atoms of other elements, and when it is not, a condition termed unsaturation results. In such cases we talk about carbon carbon double bonds or
triple bondsAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
. Double bonds alternating with single in a chain are called
conjugatedA conjugated system occurs in an organic compound where atoms covalently bond with alternating single and multiple bonds and influence each other to produce a region called electron delocalization. In this region electrons do not belong to a single bond or atom, but rather a group...
double bonds. An aromatic structure is a special case in which the conjugated chain is a closed ring.
Molecular structure elucidation
Organic compounds consist of carbon atoms, hydrogen atoms, and functional groups. The
valenceIn chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element...
of carbon is 4, and hydrogen is 1, functional groups are generally 1. From the number of carbon atoms and hydrogen atoms in a molecule the
degree of unsaturationThe degree of unsaturation formula is used in organic chemistry to help draw chemical structures. The formula lets the user determine how many rings, double bonds, and triple bonds are present in the compound to be drawn...
can be obtained. Many, but not all structures can be envisioned by the simple valence rule that there will be one bond for each valence number. The knowledge of the
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
for an organic compound is not sufficient information because many
isomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. The word is derived from the Greek ισομερης, isomerès; isos = "equal", méros = "part"....
s can exist.
Organic compounds often exist as
mixtureIn chemistry, a mixture is when two or more different substances are mixed together but not combined chemically. The molecules of two or more different substances are mixed in the form of solutions, suspensions, and colloids....
s. Because many organic compounds have relatively low
boiling pointThe boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
s and/or dissolve easily in organic
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water. Most other commonly-used solvents are organic chemicals. These are called organic solvents...
s there exist many methods for separating mixtures into pure constituents that are specific to organic chemistry such as
distillationDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
,
crystallizationCrystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas...
and
chromatographyChromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
techniques.
There exist several methods for deducing the structure of an organic compound. In general usage are (in alphabetical order):
- Crystallography
Crystallography is the experimental science of determining the arrangement of atoms in solids. In older usage, it is the scientific study of crystals...
: This is the most precise method for determining molecular geometryMolecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...
; however, it is very difficult to grow crystals of sufficient size and high quality to get a clear picture, so it remains a secondary form of analysis. Crystallography has seen especially extensive use in biochemistry (for protein structure determination) and in the characterization of organometallic catalysts, which often possess significant molecular symmetryMolecular symmetry in chemistry describes the symmetry present in molecules and the classification of molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can predict or explain many of a molecule's chemical properties, such as its dipole moment...
.
- Elemental analysis
Elemental analysis is a process where a sample of some material is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualitative , and it can be quantitative...
: A destructive method used to determine the elemental composition of a molecule. See also mass spectrometry, below.
- Infrared spectroscopy
Infrared spectroscopy is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum. It covers a range of techniques, the most common being a form of absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify compounds or...
: Chiefly used to determine the presence (or absence) of certain functional groups.
- Mass spectrometry
Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds...
: Used to determine the molecular weight of a compound and from mass spectrum analysisMass spectrum analysis is an integral part of spectroscopy and mass spectrometry dealing with the interpretation of mass spectra . Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of every organic chemistry curriculum.-Basic...
its structure. High resolution mass spectrometry can often identify the precise formula of a compound through knowledge of isotopic masses and abundances; it is thus sometimes used in lieu of elemental analysis.
- Nuclear magnetic resonance (NMR) spectroscopy
Nuclear magnetic resonance is a property that magnetic nuclei have in a magnetic field and applied electromagnetic pulse, which cause the nuclei to absorb energy from the EM pulse and radiate this energy back out...
identifies different nuclei based on their chemical environment. This is the most important and commonly used spectroscopic technique for organic chemists, often permitting complete assignment of atom connectivity and even stereochemistry given the proper set of spectroscopy experiments (e.g. correlation spectroscopyCorrelation spectroscopy is one of several types of two-dimensional nuclear magnetic resonance spectroscopy. Other types of two-dimensional NMR include J-spectroscopy, exchange spectroscopy , and Nuclear Overhauser effect spectroscopy...
).
- Optical rotation
Optical rotation is the turning of the plane of linearly polarized light about the direction of motion as the light travels through certain materials. It occurs in solutions of chiral molecules such as sucrose , solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or...
: Distinguishes between two enantiomers of a chiral compound based on the sign of rotation of plane polarized light. If the specific rotationThe specific rotation of a chemical compound [α] is defined as the observed angle of optical rotation α when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample concentration of 1 gram per 1 millilitre. The specific rotation of a pure material is an...
of an enantiomer is known, the magnitude of rotation also gives the ratio of enantiomers in a mixed sample, though HPLC with a chiral column also can supply this information.
- UV/VIS spectroscopy: Used to determine degree of conjugation in the system. While still sometimes used to characterize molecules, UV/VIS is more commonly used to quantitate how much of a known compound is present in a (typically liquid) sample.
Additional methods are provided by
analytical chemistryAnalytical chemistry is the study of the chemical composition of natural and artificial materials. Properties studied in analytical chemistry include geometric features such as molecular morphologies and distributions of species, as well as features such as composition and species identity...
.
Organic reactions
Organic reactionOrganic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and redox reactions. In organic synthesis, organic reactions are used...
s are
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
s involving
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
s. While pure
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
s undergo certain limited classes of reactions, many more reactions which organic compounds undergo are largely determined by functional groups. The general theory of these reactions involves careful analysis of such properties as the
electron affinityThe electron affinity, Eea, of an atom or molecule is the amount of energy required to detach an electron from a singly charged negative ion, i.e., the energy change for the processAn equivalent definition is the energy released when an electron is attached to a neutral atom or...
of key atoms,
bond strengthIn chemistry, bond strength is measured between two atoms joined in a chemical bond. It is the degree to which each atom linked to a central atom contributes to the valency of this central atom...
s and steric hindrance. These issues can determine the relative stability of short-lived reactive intermediates, which usually directly determine the path of the reaction. An example of a common reaction is a
substitution reactionIn a substitution reaction, a functional group in a particular chemical compound is replaced by another group . In organic chemistry, the electrophilic and nucleophilic substitution reactions are of prime importance...
written as:
- Nu− + C-X → C-Nu + X−
where X is some
functional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part...
and Nu is a
nucleophileIn chemistry, a nucleophile is a reagent that forms a chemical bond to its reaction partner by donating both bonding electrons. Because nucleophiles donate electrons, they are by definition Lewis bases . All molecules or ions with a free pair of electrons can act as nucleophiles...
.
There are many important aspects of a specific reaction. Whether it will occur spontaneously or not is determined by the
Gibbs free energyIn thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from an isothermal, isobaric thermodynamic system...
change of the reaction. The heat that is either produced or needed by the reaction is found from the total
enthalpyIn thermodynamics and molecular chemistry, the enthalpy is a thermodynamic property of a thermodynamic system. It can be used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure...
change. Other concerns include whether side reactions occur from the same reaction conditions. Any side reactions which occur typically produce undesired compounds which may be anywhere from very easy or very difficult to separate from the desired compound.
Synthetic organic chemistry
Synthetic organic chemistry is an
applied scienceApplied science is the application of knowledge from one or more natural scientific fields to solve practical problems. Fields of engineering are closely related to applied sciences. Applied science is important for technology development. Its use in industrial settings is usually referred to as...
as it borders
engineeringEngineering is the discipline, art and profession of acquiring and applying technical, scientific and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or inventions.The American Engineers' Council...
, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a
carbonylIn organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom : C=O.The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex In organic chemistry, a carbonyl group is a functional group...
compound can be used as a
nucleophileIn chemistry, a nucleophile is a reagent that forms a chemical bond to its reaction partner by donating both bonding electrons. Because nucleophiles donate electrons, they are by definition Lewis bases . All molecules or ions with a free pair of electrons can act as nucleophiles...
by converting it into an enolate, or as an
electrophileIn chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. Because electrophiles accept electrons, they are Lewis acids...
; the combination of the two is called the
aldol reactionThe aldol reaction is a powerful means of forming carbon-carbon bonds in organic chemistry.Discovered independently by Charles-Adolphe Wurtz and Alexander Porfyrevich Borodin in 1872, the reaction combines two carbonyl compounds to form a new β-hydroxy carbonyl compound; Borodin observed the...
. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called
total synthesisIn principle a total synthesis is the complete chemical synthesis of complex organic molecules from simpler pieces, usually without the aid of biological processes....
.
There are several strategies to design a synthesis. The modern method of retrosynthesis, developed by E.J. Corey, starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed, because each compound and also each precursor has multiple syntheses.
See also
- Important publications in organic chemistry
- List of organic reactions
- Molecular modelling
Molecular modelling is a collective term that refers to theoretical methods and computational techniques to model or mimic the behaviour of molecules. The techniques are used in the fields of computational chemistry, computational biology and materials science for studying molecular systems ranging...
External links