In organic chemistry
, a substituent
is an atom or group of atoms substituted in place of a hydrogen
atom on the parent chain
of a hydrocarbon
. The suffix -yl
(meaning "attached to") is used when naming organic compounds
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 isomers
. The polar effect
exerted by a substituent is a combination of the inductive effect
and the mesomeric effect
. Additional Steric effects
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 predicts that the hydrogen adds to the carbon of the alkene functional group that has the greater number of hydrogen substituents.
- Zaitsev's rule predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond.
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
substituent. The total number of organic substituents in organic chemistry is estimated at 3.1 million creating a total of 6.7×1023
- Cheminformatics Analysis of Organic Substituents: Identification of the Most Common Substituents, Calculation of Substituent Properties, and Automatic Identification of Drug-like Bioisosteric Groups Peter Ertl J. Chem. Inf. Comput. Sci.; 2003; 43(2) pp 374 - 380 Abstract Download reprint