Substituent

Substituent ( from Latin: substituere = replace ) referred especially in organic chemistry, an atom or group of atoms ( organyl residue or other residuals ), which one (s ) in a molecule replaces a hydrogen atom, so this substituted. It may be replaced by other atoms or groups of atoms and more hydrogen atoms of the basic body. Then to the basic body more substituents are attached.

Various substituents

One can categorize the individual substituents according to various criteria.

Nomenclature

The atoms that are frequently encountered as substituents include, for example, the halogens. To groups of atoms which are considered to be substituents organyl radicals include (alkyl - residues (see article: side chain), aryl radicals, alkylaryl radicals, heteroaryl radicals, etc.), formyl group, hydroxy group, alkoxy groups, the acetyl residue, amino acid residues, the mercapto group, the nitro group, and numerous other moieties.

Influence on the electronic situation

Substituents often influence the polarization in a molecule. Thus, the chemical, physical, sensory and pharmacological properties of the molecule are often changed significantly. It can be divided into electron-donating substituents and electron-withdrawing.

Substituents on the aromatic

Erstsubstituenten on aromatic rings are classified for pragmatic reasons as follows:

• Substituents of the first order and
• Secondary substituent

Substituents first order directing a by electrophilic aromatic substitution new entrants remaining in the ortho and para positions. In contrast, a second-order direct substituents by electrophilic aromatic substitution new entrants to rest in the meta position

Steric effects

Geometrically by bulky substituents ( tert-butyl group or the like) the chemical reactivity of the basic body can be influenced.