Aldehyde

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Aldehyde

An aldehyde is an organic compound containing a terminal carbonyl group. This functional group

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
, which consists of a carbon

Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
atom bonded to a hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
atom and double-bonded to an oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
atom (chemical formula O=CH-), is called the aldehyde group. The aldehyde group is also called the formyl or methanoyl group.

The word aldehyde seems to have arisen from alcohol dehydrogenated.

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Encyclopedia

An aldehyde is an organic compound containing a terminal carbonyl group. This functional group
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
, which consists of a carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
atom bonded to a hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
atom and double-bonded to an oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
atom (chemical formula O=CH-), is called the aldehyde group. The aldehyde group is also called the formyl or methanoyl group.

The word aldehyde seems to have arisen from alcohol dehydrogenated. In the past, aldehydes were sometimes named after the corresponding alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
s, for example, vinous aldehyde for acetaldehyde
Acetaldehyde

Acetaldehyde is an organic compound with the chemical formula CarbonHydrogen3CHOxygen or MeCHO. It is a flammable liquid with a fruity smell....
. (Vinous is from Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
vinum = wine, the traditional source of ethanol
Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
; compare vinyl
Vinyl

A vinyl compound is any organic compound that contains a vinyl group , −CarbonHydrogenCovalent bondCH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group....
.)

The aldehyde group is polar. Oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, more electronegative than carbon, pulls the electrons in the carbon-oxygen bond
Carbon-oxygen bond

A carbon-oxygen bond is a covalent bond between carbon and oxygen and one of the most abundant in organic chemistry and biochemistry. Oxygen has 6 valence electrons and prefers to share two electrons in bonding with carbon, leaving the remaining 4 nonbonding electrons in 2 lone pairs....
towards itself, creating an electron deficiency at the carbon atom.

Owing to resonance stabilization of the conjugate base, an a-hydrogen in an aldehyde is more acidic than a hydrogen atom in an alkane, with a typical pKa
PKA

PKA or pKa may be:* Protein kinase A, a cAMP activated protein kinase* pKa, the symbol for Acid dissociation constant...
of 17.

Nomenclature

IUPAC names for aldehydes

IUPAC prescribes the following nomenclature for aldehydes:
Acyclic aliphatic
Aliphatic compound

In organic chemistry, compounds composed of carbon and hydrogen are divided into two classes: aromatic compounds, which contain benzene rings or similar rings of atoms, and aliphatic compounds , which do not contain aromatic rings....
aldehydes are named as derivatives of the longest carbon chain containing the aldehyde group. Thus, HCHO is named as a derivative of methane, and CH₃CH₂CH₂CHO is named as a derivative of butane. The name is formed by changing the suffix -e of the parent alkane
Alkane

Alkanes, 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 ....
to -al, so that HCHO is named methanal, and CH₃CH₂CH₂CHO is named butanal.
In other cases, such as when a -CHO group is attached to a ring, the suffix -carbaldehyde may be used. Thus, C₆H₁₁CHO is known as cyclohexanecarbaldehyde. If the presence of another functional group demands the use of a suffix, the aldehyde group is named with the prefix formyl-. This prefix is preferred to methanoyl-.
If the compound is a natural product or a carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
, the prefix oxo- may be used to indicate which carbon atom is part of the aldehyde group; for example, CHOCH₂COOH is named 3-oxopropanoic acid.
If replacing the aldehyde group with a carboxyl group
Carboxyl group

A carboxyl group is a set of four atoms bonded together and present in carboxylic acids, including amino acid. Usually abbreviated as either CO2H or COOH, this set of atoms constitutes a functional group....
(-COOH) would yield a carboxylic acid with a trivial name, the aldehyde may be named by replacing the suffix -ic acid or -oic acid in this trivial name by -aldehyde. For example:

HCHO may be called formaldehyde
Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
.
CH₃CHO may be called acetaldehyde
Acetaldehyde

Acetaldehyde is an organic compound with the chemical formula CarbonHydrogen3CHOxygen or MeCHO. It is a flammable liquid with a fruity smell....
.
C₆H₅CHO may be called benzaldehyde
Benzaldehyde

Benzaldehyde is a chemical compound consisting of a benzene ring with an aldehyde substituent. It is the simplest representative of the aromatic aldehydes and one of the most industrially used members of this family of compounds....
.

Other nomenclature
The carbon atom adjacent to a carbonyl group is called the a carbon. Carbon atoms further away from the group may be named ß for the carbon atom bonded to the a carbon, ? for the next, and so on. Hydrogen atoms bonded to these carbon atoms are named likewise: an a hydrogen is a hydrogen atom bonded to the a carbon and so on.

A reaction that introduces an aldehyde group is known as a formylation reaction
Formylation reaction

A formylation reaction in organic chemistry is the catch-all name for any organic reaction in which an organic compound is functionalized with a formyl group ....
.

Chemistry

Synthesis
There are several methods for preparing aldehydes:
Reacting a primary alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
with an oxidizing agent
Oxidizing agent

An oxidizing agent can be defined as either:#a chemical compound that readily transfers oxygen atoms, or#a substance that gains electrons in a redox chemical reaction...
. In the laboratory, this may be achieved by heating the alcohol with a chromium(VI) reagent an acidified solution of potassium dichromate
Potassium dichromate

Potassium dichromate, K2Cr2O7, is a common inorganic compound chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications....
, which is reduced
Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
to green Cr³⁺ during the reaction. Excess dichromate will further oxidise the aldehyde to form a carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
, so either the aldehyde is distilled
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
out as it forms (if volatile
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
) or milder methods and reagents such as PCC
Pyridinium chlorochromate

Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize the alcohol to the carboxylic acid as does the Jones reagent....
oxidation, IBX acid, Dess-Martin periodinane
Dess-Martin periodinane

Dess-Martin periodinane is a chemical reagent used to oxidation primary alcohols to aldehydes and secondary alcohols to ketones. This periodinane has several advantages over chromium- and dimethyl sulfoxide-based oxidants that include milder conditions, shorter reaction times, higher yields, and simplified workups....
, or Swern oxidation
Swern oxidation

The Swern oxidation, named after Daniel Swern, is a chemical reaction whereby a primary or secondary alcohol is redox to an aldehyde or ketone using oxalyl chloride, dimethyl sulfoxide and an organic base, such as triethylamine....
are used. The reaction is illustrated below with propan-1-ol
Propan-1-ol

Propan-1-ol is a primary alcohol with the formula CH3CH2CH2OH. It is also known as 1-propanol, 1-propyl alcohol, n-propyl alcohol, or simply propanol....
being oxidised to form propionaldehyde
Propionaldehyde

Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturate 3-carbon aldehyde and is a structural isomerism of propanone....
, and again with pentan-1-ol being oxidized to form pentanal
Pentanal

Pentanal, also called pentanaldehyde or valeraldehyde, is an alkyl aldehyde, molecular formula C5H10O. It is used in flavorings, resin chemistry, and rubber accelerators....
.

CH₃CH₂CH₂OH —? CH₃CH₂CHO
Reacting an alkene
Alkene

In organic chemistry, an alkene, olefin, or olefine is an Saturation chemical compound containing at least one carbon-to-carbon double bond....
(if there is a vinyl
Vinyl

A vinyl compound is any organic compound that contains a vinyl group , −CarbonHydrogenCovalent bondCH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group....
ic hydrogen) with ozone
Ozone

Ozone or trioxygen is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O2....
will form an ozonide (an unstable, explosive intermediate), which yields an aldehyde upon reduction with zinc and acid at reduced temperatures. This process is called ozonolysis
Ozonolysis

Ozonolysis is the cleavage of an alkene or alkyne with ozone to form organic compounds in which the multiple carbon-carbon bond has been replaced by a double bond to oxygen....
.

Reacting an ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
with diisobutyl aluminium hydride (DIBAL-H) or sodium aluminium hydride can cause reduction, yielding an aldehyde.
Reduction of an acid chloride using the Rosenmund reduction
Rosenmund reduction

The Rosenmund reduction is a chemical reaction that redox an acid halide to an aldehyde using hydrogen over palladium-on-carbon catalyst poisoning with barium sulfate....
or using lithium tri-t-butoxyaluminium hydride (LiAlH(O-t-C₄H₉)₃).
Reaction of ketones with methoxymethylenetriphenylphosphine
Methoxymethylenetriphenylphosphine

Methoxymethylenetriphenylphosphine is a Wittig reagent with used as an reagent in the homologization of aldehydes and ketones to extended aldehydes, an organic reaction first reported in 1958 ....
in a modified Wittig reaction
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
.
Various formylation reaction
Formylation reaction

A formylation reaction in organic chemistry is the catch-all name for any organic reaction in which an organic compound is functionalized with a formyl group ....
s, such as the Vilsmeier-Haack reaction
Vilsmeier-Haack reaction

The Vilsmeier-Haack reaction is the chemical reaction of a substituted amide with phosphorus oxychloride and an activating group arene to produce an aryl aldehyde or ketone ....
, can be used to introduce an aldehyde group.
In the Nef reaction
Nef reaction

The Nef reaction is an organic reaction describing the acid catalysis hydrolysis of a salt of a primary or secondary nitroalkane to an aldehyde or a ketone and nitrous oxide ....
, aldehydes form by hydrolysis of salts of primary nitro compounds.
Zincke aldehyde
Zincke aldehyde

Zincke aldehydes, or 5-amino-2,4-pentadienals, are the product of the reaction of a pyridinium salt with two equivalents of any secondary amine, followed by basic hydrolysis....
s form by reaction of pyridinium salts with secondary amines followed by hydrolysis.
In the Stephen aldehyde synthesis
Stephen aldehyde synthesis

Stephen aldehyde synthesis, a named reaction in chemistry, was invented by Henry Stephen . This reaction involves the preparation of aldehydes from nitriles using tin chloride , hydrochloric acid and quenching the resulting iminium salt with Water ....
aldehydes form from nitrile
Nitrile

A nitrile is any organic compound which has a -Carbon=Nitrogen functional group. The -C=N functional group is called a nitrile group....
s, tin(II) chloride
Tin(II) chloride

Tin chloride is a white crystalline solid with the formula 2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot....
, and hydrochloric acid
Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
.
In the Meyers synthesis
Meyers synthesis

The Meyers synthesis is an organic synthesis for the preparation of unsymmetrical aldehydes via hydrolysis of an oxazine . The reaction is named after the American chemist Albert I....
they form by hydrolysis of an oxazine.
The McFadyen-Stevens reaction
McFadyen-Stevens reaction

The McFadyen-Stevens reaction is a chemical reaction best described as a base-catalyzed thermal decomposition of acylsulfonylhydrazides to aldehydes....
is a base-catalyzed thermal decomposition of acylsulfonylhydrazides

Keto-enol tautomerism
Aldehydes can exist in either the keto or enol
Enol

Enols are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond. Enols and carbonyl compounds are in fact isomers; this is called keto-enol tautomerism:...
tautomers. Keto-enol tautomerism
Keto-enol tautomerism

In organic chemistry, keto-enol tautomerism refers to a chemical equilibrium between a keto form and an enol. The enol and keto forms are said to be tautomers of each other....
is catalyzed by either acid or base.

Common reactions

Reduction and oxidation

The aldehyde group can be reduced to the group -CH₂OH, changing the aldehyde into a primary alcohol
Primary alcohol

A primary alcohol is an alcohol which has the hydroxyl radical connected to a primary carbon. It can also be defined as a molecule containing a ??CH2OH? group....
.
The aldehyde group can be oxidized to the group -COOH, yielding a carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
. Suitable oxidizing agents include potassium permanganate
Potassium permanganate

Potassium permanganate is the inorganic chemical compound potassiummanganeseoxygen4, a water soluble salt consisting of equal Mole amounts of potassium and permanganate ions....
, nitric acid
Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
, chromium(VI) oxide
Chromic acid

Chromic acid generally refers to a collection of chemical compound generated by the acidification of solutions containing chromate and dichromate ion or the dissolving of chromium trioxide in sulfuric acid....
, and acidified potassium dichromate
Potassium dichromate

Potassium dichromate, K2Cr2O7, is a common inorganic compound chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications....
.
The combination of manganese dioxide, acetic acid
Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
and methanol
Methanol

Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula carbonhydrogen3oxygenhydrogen ....
will convert the aldehyde to a methyl ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....

Another oxidation reaction is the silver mirror test. In this test, an aldehyde is treated with Tollens' reagent
Tollens' reagent

Tollens' reagent is usually ammoniacal silver nitrate, but can also be other compounds, as long as there is an aqueous solution Ammonia#Ammonia as a ligand complex ....
, which is prepared by adding a drop of sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
solution into silver nitrate
Silver nitrate

Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula silverNitrogenOxygen3. This compound is a versatile precursor to many other silver compounds, such as those used in photography....
solution to give a precipitate of silver(I) oxide, and then adding just enough dilute ammonia
Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
solution to redissolve the precipitate in aqueous ammonia to produce [Ag(NH₃)₂]⁺ complex. This reagent will convert aldehydes to carboxylic acids without attacking carbon-carbon double-bonds. The name silver mirror test arises because this reaction will produce a precipitate of silver whose presence can be used to test for the presence of an aldehyde.
If the aldehyde can not form an enolate (e.g. benzaldehyde), addition of strong base causes the Cannizzaro reaction
Cannizzaro reaction

The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical reaction that involves the base -induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position....
to occur, producing a mixture of alcohol and carboxylic acid.

Nucleophilic addition reactions
In nucleophilic addition reactions a nucleophile
Nucleophile

In 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 ....
can add to the carbon atom in the carbonyl group, yielding an addition compound in which this carbon atom has tetrahedral molecular geometry
Tetrahedral molecular geometry

In a Tetrahedral molecular geometry a central atom is located at the center with four substituents that are located at the corners of a tetrahedron....
. Together with protonation of the oxygen atom in the carbonyl group (which can take place either before or after addition); this yields a product where the carbon atom in the carbonyl group is bonded to the nucleophile, a hydrogen atom, and a hydroxyl group.

In many cases, a water molecule is removed after the addition takes place; in this case, the reaction is classed as an addition
Addition reaction

An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one....
-elimination
Elimination reaction

An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism ....
or addition
Addition reaction

An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one....
-condensation reaction
Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule....
.

There are various examples of nucleophilic addition reactions.
In the acetalisation
Acetalisation

Acetalisation is an organic reaction that involves the formation of an acetal or ketal. One way of acetal formation is the nucleophilic addition of an alcohol to a ketone or an aldehyde....
reaction, under acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ic or basic
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
conditions, an alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
adds to the carbonyl group and a proton is transferred to form a hemiacetal
Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
. Under acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ic conditions, the hemiacetal and the alcohol can further react to form an acetal
Acetal

An acetal is a molecule with two single bonded oxygens attached to the same carbon atom.Traditional usages distinguish ketal from acetal . Current accepted terminology classifies ketals as a subset of acetals....
and water. Simple hemiacetals are usually unstable, although cyclic ones such as glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
can be stable. Acetals are stable, but revert to the aldehyde in the presence of acid.
Aldehydes can react with water (under acidic or basic conditions) to form hydrate
Hydrate

Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
s, R-C(H)(OH)(OH), although these are only stable when strong electron withdrawing groups are present, as in chloral hydrate
Chloral hydrate

Chloral hydrate is a sedative and hypnotic approved drug as well as a chemical reagent and precursor. The name chloral hydrate indicates that it is formed from chloral by the addition of one molecule of water....
. The mechanism is identical to hemiacetal formation.
In alkylimino-de-oxo-bisubstitution
Alkylimino-de-oxo-bisubstitution

Alkylimino-de-oxo-bisubstitution in organic chemistry is the organic reaction of carbonyl compounds with amines to imines . The reaction name is based on the IUPAC Nomenclature for Transformations....
, a primary or secondary amine adds to the carbonyl group and a proton is transferred from the nitrogen to the oxygen atom to create a carbinolamine. In the case of a primary amine, a water molecule can be eliminated from the carbinolamine to yield an imine
Imine

An imine is a functional group or chemical compound containing a carbon?nitrogen double bond . Due to their diverse reactivity, imines are common substrates in a wide variety of transformations....
. This reaction is catalyzed by acid.
The cyano group in HCN
Hydrogen cyanide

Hydrogen cyanide is a chemical compound with chemical formula HCN. A solution of hydrogen cyanide in water is called hydrocyanic acid. Hydrogen cyanide is a colorless, extremely poisonous, and highly volatility liquid that boiling slightly above room temperature at 26 Celsius ....
can add to the carbonyl group to form cyanohydrin
Cyanohydrin

A cyanohydrin is a functional group found in organic compounds. Cyanohydrins have the formula R2CCN, where R is H, alkyl, or aryl. Cyanohydrins are industrially important precursors to carboxylic acids and some amino acids....
s, R-C(H)(OH)(CN).
In the Grignard reaction
Grignard reaction

The Grignard reaction, named after the French chemist Fran?ois Auguste Victor Grignard, is an organometallic chemistry chemical reaction in which alkyl- or aryl-magnesium halides , act as nucleophiles, attack electrophilic carbon atoms that are present within polar bonds to yield a carbon-carbon bond , thus altering hybridization about the r...
, a Grignard reagent adds to the group, eventually yielding an alcohol with a substituted group from the Grignard reagent. Related reactions are the Barbier reaction
Barbier reaction

The Barbier reaction is an organic reaction between an alkyl halide and a carbonyl group as an electrophilic substrate in the presence of aluminium, zinc, indium, tin or its salts....
and the Nozaki-Hiyama-Kishi reaction.
In the aldol reaction
Aldol reaction

The aldol reaction is a carbon-carbon bond formation chemical reaction in organic chemistry. In its usual form, it involves the nucleophilic addition of a ketone enolate to an aldehyde to form a Hydroxy ketone, or "aldol" , a structural unit found in many biomolecule and pharmaceuticals....
, the metal enolates of ketone
Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
s, ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
s, amide
Amide

In chemistry, an amide is one of three kinds of compounds:* the organic chemistry functional group characterized by a carbonyl group linked to a nitrogen atom , or a compound that contains this functional group ; or...
s, and carboxylic acids will add to aldehydes to form ß-hydroxycarbonyl compounds (aldol
Aldol

An aldol or aldol adduct is a beta-hydroxy ketone or aldehyde, and is the product of aldol reaction ....
s). Acid or base-catalyzed dehydration will then lead to a,ß-unsaturated carbonyl compounds. The combination of these two steps is known as the aldol condensation
Aldol condensation

An Aldol condensation is an organic reaction in which an enolate ion reacts with a carbonyl compound to form a ?-hydroxyaldehyde or ?-hydroxyketone, followed by dehydration to give a conjugated enone....
.
Hydroxylamine
Hydroxylamine

Hydroxylamine is a reactive chemical with chemical formula NH2OH. It can be considered a hybrid of ammonia and water due to parallels it shares with each....
(NH₂OH) can add to the carbonyl group. After the elimination of water, this will result in an oxime
Oxime

An oxime is one in a class of chemical compounds with the general formula R1R2carbonnitrogenoxygenhydrogen, where R1 is an organic compound side chain and R2 is either hydrogen, forming an aldoxime, or another organic group, forming a ketoxime....
.
An ammonia
Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
derivative of the form H₂NNR₂ such as hydrazine
Hydrazine

Hydrazine is a chemical compound with the chemical formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia....
(H₂NNH₂) or 2,4-dinitrophenylhydrazine
2,4-Dinitrophenylhydrazine

2,4-Dinitrophenylhydrazine is the chemical compound C6H32NHNH2. Dinitrophenylhydrazine is relatively sensitive to Shock and friction; it is a shock explosive so care must be taken with its use....
can add to the carbonyl group. After the elimination of water, this will result in the formation of a hydrazone
Hydrazone

A hydrazone is a class of organic compounds with the structure R2C=NNR2. They are related to ketones and aldehydes by the replacement of the oxygen with the NNR2 functional group....
. This forms the basis of a test for aldehydes and ketones.

More complex reactions

If an aldehyde is converted to a simple hydrazone (RCH=NHNH₂) and this is heated with a base such as KOH
Potassium hydroxide

Potassium hydroxide is the inorganic compound with the formula potassiumhydroxide. Along with sodium hydroxide, this colourless solid is a prototypical "strong base"....
, the terminal carbon is fully reduced via the Wolff-Kischner reaction
Wolff-Kishner reduction

The Wolff-Kishner reduction is a chemical reaction that fully redox a ketone to an alkane.The method originally involved heating the hydrazone with sodium ethoxide in a sealed vessel at about 200 ?C....
to a methyl group. The Wolff-Kishner reaction may be performed as a one-pot reaction
One-pot synthesis

In chemistry a one-pot synthesis is a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor....
, giving the overall conversion RCH=O ? RCH₃.
Reaction of aldehydes with reducing agent
Reducing agent

A reducing agent is the element or compound in a redox reaction that reduces another Chemical species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox....
s such as magnesium
Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
gives diol
Diol

A diol or glycol is a chemical compound containing two hydroxyl groups Vicinal diols have hydroxyl groups attached to adjacent atoms. Examples of vicinal diol compounds are ethylene glycol and propylene glycol....
s in a Pinacol coupling reaction
Pinacol coupling reaction

A pinacol coupling reaction is an organic reaction in which a carbon-carbon covalent bond is formed between the carbonyl groups of an aldehyde or a ketone in presence of an electron donor in a radical process ....
.
The Wittig reaction
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
takes aldehydes to alkene
Alkene

In organic chemistry, an alkene, olefin, or olefine is an Saturation chemical compound containing at least one carbon-to-carbon double bond....
s and the Corey-Fuchs reaction
Corey-Fuchs reaction

The Corey-Fuchs reaction is a series of chemical reactions designed to transform an aldehyde into an alkyne. The formation of the 1,1-dibromoolefins via phosphine-dibromomethylenes was originally discovered by Desai and McKelvie....
takes aldehydes to alkyne
Alkyne

Alkynes are hydrocarbons that have at least one triple bond between two carbon atoms, with the formula CnH2n-2. The alkynes are traditionally known as acetylenes or the acetylene series, although the name acetylene is also used to refer specifically to the simplest member of the series, known as e...
s. Both use a triphenylphosphine
Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PhosphorusPhenyl group or Ph3P....
reagent. The Takai reaction also converts aldehydes to alkenes. The Corey-Chaykovsky reagent is a sulfonium ylide which converts aldehydes to epoxide
Epoxide

An epoxide is a cyclic ether with only three ring atoms. This ring approximately is an equilateral triangle which makes it highly ring strain....
s.

Examples of aldehydes

Methanal (Formaldehyde)
Ethanal (Acetaldehyde)
Propanal (Propionaldehyde)
Butanal
Butanal

Butyraldehyde, also known as butanal, is an organic compound that is the aldehyde analog of butane as well as an isomer of butanone. It is a colorless flammable liquid with an acrid smell....
(butyraldehyde)
Benzaldehyde
Benzaldehyde

Benzaldehyde is a chemical compound consisting of a benzene ring with an aldehyde substituent. It is the simplest representative of the aromatic aldehydes and one of the most industrially used members of this family of compounds....
Cinnamaldehyde
Cinnamaldehyde

Cinnamic aldehyde or cinnamaldehyde is the chemical compound that gives cinnamon its flavor and odor.Cinnamaldehyde occurs naturally in the bark of cinnamon trees and other species of the genus Cinnamomum like camphor and cassia....
Tolualdehyde

Related compounds
Other kinds of organic compounds containing carbonyl groups include
Dialdehydes
Ketone
Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
s
Carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
s
Amide
Amide

In chemistry, an amide is one of three kinds of compounds:* the organic chemistry functional group characterized by a carbonyl group linked to a nitrogen atom , or a compound that contains this functional group ; or...
s