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A General Definition of Ring Substituent Positions
Author(s) -
Cremer Dieter
Publication year - 1980
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198000048
Subject(s) - substituent , ring (chemistry) , chemistry , orientation (vector space) , perpendicular , position (finance) , plane (geometry) , geometry , center (category theory) , steric effects , crystallography , stereochemistry , mathematics , organic chemistry , finance , economics
Starting from the concept of the mean plane of a general nonplanar N ‐membered ring, the substituent orientation angles α and β are derived. These angles define the position of a ring substituent in an unambiguous way, the angle α indicating the direction of the ring‐substituent bond relative to the mean plane (perpendicular, inclined or parallel) and the angle β revealing whether the bond vector is directed inward (towards the geometrical center of the ring) or outward (away from the geometrical center). The orientation angle α allows a generalization of the terms “axial” and “equatorial” including Barton's original specification of these terms and vivifying their semantics. Unlike earlier descriptions of ring substituent orientations the new definitions completely avoid terms like “quasi‐axial”, “quasi‐equatorial”, etc. Examples are given which show their usefulness in discussions of steric effects.