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Substituent
 
 
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In organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
, a substituent is an atom or group of atoms substituted in place of 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 on the parent chain of a hydrocarbon
Hydrocarbon

In 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 or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded com...
. The suffix -yl (meaning "attached to") is used when naming organic compound
Organic compound

An 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 compound....
s that contain a substituent. Additionally, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent is attached to when such information is needed to distinguish between structural isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s.






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In organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
, a substituent is an atom or group of atoms substituted in place of 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 on the parent chain of a hydrocarbon
Hydrocarbon

In 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 or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded com...
. The suffix -yl (meaning "attached to") is used when naming organic compound
Organic compound

An 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 compound....
s that contain a substituent. Additionally, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent is attached to when such information is needed to distinguish between structural isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s. The polar effect
Polar effect

The Polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby chemical reaction center....
 exerted by a substituent is a combination of the inductive effect
Inductive effect

The inductive effect in chemistry is an experimentally observable effect of the transmission of charge through a chain of atoms in a molecule by electrostatic induction....
 and the mesomeric effect
Mesomeric effect

The mesomeric effect or resonance effect in chemistry is a property of substituents or functional groups in a chemical compound. The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M....
. Additional Steric effects
Steric effects

Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds , and this may affect the molecule's preferred shape and chemical reaction....
 result from the volume occupied by a substituent.

The phrases most-substituted and least-substituted are frequently used to describe molecules and predict their products. For example:

  • Markovnikov's rule
    Markovnikov's rule

    In organic chemistry, Markovnikov's rule or Markownikoff's rule is an observation based on Zaitsev's rule. It was formulated by the Russian chemist Vladimir Vasilevich Markovnikov in 1870 ....
     predicts that the hydrogen adds to the carbon of the alkene functional group that has the greater number of hydrogen substituents.
  • Zaitsev's rule
    Zaitsev's rule

    In chemistry, Zaitsev's rule, Saytzeff's rule or Saytsev's rule named after Alexander Mikhailovich Zaitsev is a rule that states that if more than one alkene can be formed by an elimination reaction, the more stable alkene is the major product....
     predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond.


Number crunching

One cheminformatics
Cheminformatics

Cheminformatics is the use of computer and Information science techniques, applied to a range of problems in the field of chemistry. These in silico techniques are used in pharmaceutical companies in the process of drug discovery....
 study identified 849,574 unique substituents up to 12 non-hydrogen atoms large and containing only C,H,N,O,S,P,Se and the halogens in a set of 3,043,941 molecules. 50 common substituents are found in only 1% of this set and 438 in 0.1%. 64% of the substituents are unique to just one molecule. The top 5 consists of the phenyl, chlorine
Chlorine

Chlorine...
, methoxy
Methoxy

In chemistry , methoxy refers to the functional group consisting of a methyl group bound to oxygen. It has the formula:The word is used in organic nomenclature usually to describe an ether....
, hydroxyl
Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
 and ethyl
Ethyl group

In chemistry, an ethyl group is an alkyl functional group derived from ethane . It has the chemical formula -Carbon2Hydrogen5 and is very often abbreviated -Et....
 substituent. The total number of organic substituents in organic chemistry is estimated at 3.1 million creating a total of 6.7×1023 molecules. OR since you can increase the carbon chain length of a substituent an infinite amount, provided it is not long enough to become part of the parent carbon chain (which can also be infinite in length), you can have an infite number of substituents, simply by increasing carbon chain length. For instance, the substituents methyl (-CH3) and pentyl (C5H11)

See also

  • 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....
    s are a subset of substituents
  • Side chain
    Side chain

    A side chain in organic chemistry and biochemistry is a part of a molecule that is attached to a core structure. The placeholder R is often used as a generic placeholder for side chains, the R historically being derived from radical or rest....


External links

  • and 49,000 linkers extracted from bioactive molecules