Substituent
Substituent (from latin substituere "replace") particularly referred in the organic chemistry an atom or an atomic group ( organyl radical or any other radical), which one (s) in a molecule replaces a hydrogen atom, so this substituted. It is also possible for several hydrogen atoms of a basic body to be replaced by other atoms or groups of atoms. Several substituents are then bound to the base body.
Various substituents
The individual substituents can be categorized according to various criteria.
nomenclature
The atoms that are often found as substituents include, for example, the halogens . The atomic groups that are regarded as substituents include the organyl radicals ( alkyl radicals (see also article: side chain ), aryl radicals, alkylaryl radicals, heteroaryl radicals, etc.), the formyl group , the hydroxyl group , alkoxy groups , the Acetyl radicals, amino radicals, the mercapto group , the nitro group , and countless other radicals.
Influence on the electronic situation
Substituents often affect the polarization in a molecule. As a result, the chemical, physical, sensory and pharmacological properties of the molecule are often permanently changed. The substituents can be divided into electron donating and electron withdrawing .
Substituents on aromatics
First substituents on aromatic rings are classified as follows for pragmatic reasons:
- First order substituents and
- Second order substituents
First-order substituents direct a radical that is newly entered by electrophilic aromatic substitution in the ortho and para positions. Second-order substituents, on the other hand, direct a radical in the meta -position that occurs as a result of electrophilic aromatic substitution .
Steric Effects
The chemical reactivity of the basic body can be influenced by geometrically space-filling substituents ( tert-butyl group or the like).
literature
- H. Kaufmann, A. Hädener: Fundamentals of organic chemistry , Birkhäuser Verlag, 10th edition, 1996, ISBN 3-7643-5232-9 .