In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. The terms substituent, side-chain, group, branch, or pendant group are used almost interchangeably to describe branches from a parent structure, though certain distinctions are made in the context of polymer chemistry. In polymers, side chains extend from a backbone structure. In proteins, side chains are attached to the alpha carbon atoms of the amino acid backbone.
The suffix yl is used when naming organic compounds that contain a single bond replacing one hydrogen; -ylidene and -ylidyne are used with double bonds and triple bonds, respectively. In addition, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent attaches to when such information is needed to distinguish between 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.
Other articles related to "ylidene, ylidenes":
... However, Arduengo's group later obtained an imidazol-2-ylidene in which the bulky N-adamantyl groups were replaced with smaller methyl groups ... was not the predominant stabilising factor, and that imidazole-2-ylidenes were thermodynamically stable ... was disproved in 1995 by Arduengo's group, who obtained a derivative of dihydroimidazol-2-ylidene, lacking the double bond ...
... -ylidene means that two hydrogens are replaced by a double bond between parent and substituent ... sporadically, and is often used synonymously with -ylidene.The spelling "-ylidine" seems to be a rare usage in some contexts, but it appears in manufacturer's ...
... stable nucleophilic carbene, a thiazol-2-ylidene derivative, was involved in the catalytic cycle of vitamin B1 (thiamine) that yields furoin from furfural ... through the generation of a stable thiazol-2-ylidene intermediate ... Wanzlick and co-workers conjectured that carbenes derived from dihydroimidazol-2-ylidene were produced by vacuum pyrolysis of the corresponding 2-trichloromethyl ...