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7936802 
Journal Article 
ALICYCLIC REACTION-MECHANISMS .7. SOLVOLYSIS REACTIONS AND FORCE-FIELD CALCULATIONS WITH EPIMERIC CYCLOHEXANE DERIVATIVES 
Schneider, HJ; Schmidt, G 
1986 
1 
Chemische Berichte
ISSN: 0009-2940 
119 
1 
65-73 
English 
WOS:A1986AYB6100006 
Reactions of the epimeric 4‐tert‐butylcyclohexyl tosylates in hexafluoroisopropyl alcohol (HFIP) (1e, 1a) allow for the first time to observe SN1‐type non‐stereospecific substitution, whereas conventional solvents including even trifluoroethanol yield SN2‐type inversion by solvent assisted pathway (≙ks). Large differences are found between the epimers in the solvent participation, measured kinetically by the Schleyer‐Bentley equation. This, as well as the even enhanced elimination with the equatorial isomer 1e as compared to 1a (98% vs. 96% in HFIP) points to the occurrence of non‐chair intermediates from 1e‐derivatives, and to more E2‐ than E1‐type reactions. Kinetic measurements, including those of cis‐3,5‐dimethylcyclohexane esters (2a, 2e) and 3α/3β‐(tosyloxy)androstanes (3a, 3e) show little differences between the equatorial esters in agreement with MM2 calculations, which establish small strain energy variations between the differently substituted twist‐boat intermediates. Large differences, however, of up to 500% are measured between the axial esters (1a, 2a, 3a), although the alkyl substituents are remote from the leaving group and do not alter the chair geometry. These variations, which demonstrate the severe limitation of the Winstein‐Holness equation for solvolysis reactions, are explained by MM2 calculated significant strain difference between the educts and the corresponding substituted cyclohexenes. Copyright 1986 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim