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Polar Effects in the Solvolysis of 4‐Substituted Bicyclo [2.2.2]octyl p ‐Nitrobenzenesulfonates. Polar effects. VII
Author(s) -
Grob Cyril A.,
Rich Roland
Publication year - 1979
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19790620829
Subject(s) - chemistry , inductive effect , solvolysis , substituent , bicyclic molecule , hyperconjugation , medicinal chemistry , reaction rate constant , polar , carbocation , yield (engineering) , cyclohexane , stereochemistry , computational chemistry , hydrolysis , organic chemistry , kinetics , molecule , physics , quantum mechanics , astronomy , materials science , metallurgy
Hydrolysis of bicyclo[2.2.2]octyl p ‐nitrobenzenesulfonate ( 14a , X = p ‐NO 2 C 6 H 4 SO 3 ), and nineteen 4‐R‐substituted derivatives 14b–14t in 70% aqueous dioxane yield the corresponding bicyclo[2.2.2]octanols 14 (X = OH), exclusively. The 7‐center fragmentation to 1,4‐dimethylidene‐cyclohexane ( 15 ) is not observed. The logarithms of most of the rate constants, measured in 80% ethanol, correlate well with the corresponding inductive substituent constants σ 1 qof R. Hence, in these cases ionization rate is controlled by the inductive effect of R only. Poor correlations result when the substituents are potentially electrofugal groups, such as COO − , CH 2 OH, CH 2 NH 2 , CONH 2 and H, the deviations from the inductive regression line corresponding to rate enhancements of 1.6 to 8. These exalted substituent effects are tentatively ascribed to extended hyperconjugation involving two σ‐bonds. This study corroborates previous evidence that the inductive effect alone does not fully account for the polar effect of some substituents in reactions involving carbocations.