Title: The origin and nature of the π-electron steric effect
Abstract: The existence of conformational or steric proximity substituent effects involving π-electrons has been demonstrated in a number of recent reports but the question of whether this effect is due simply to the size of the substituent or to lone pair electrons on the substituent has not been investigated. Relative to this question, pKa's for an extensive series of 2'- and 4'-substituted-4-aminobiphenyls and for a series of 4'-substituted-2-amino-biphenyls have been determined. The results of this study demonstrate that a π-electron steric effect is operative in the 2'-substituted-4-aminobiphenyls and that it occurs primarily (when possible) via lone pair electron-π electron interactions and not simply via a steric size effect. The pKa data for the 4'-substituted-2-aminobiphenyls reinforce this conclusion and further demonstrate that 2,4'-resonance is possible in appropriately substituted 2,4'-disubstituted biphenyls. In addition, the relativity of the concept of substituent size and of electron withdrawing or donating character of various groups is illustrated.
Publication Year: 1977
Publication Date: 1977-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 2
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