INDUCTIVE, HYPERCONJUGATIVE AND FRANGOMERIC EFFECTS IN SOLVOLYSIS OF 1-SUBSTITUTED 3-BROMOADAMANTANES

Three kinds of polar substitutent effects are observable in the solvolyses of 1‐R‐substituted 3‐bromoadamantanes (VI). This follows from the relationship between products, rate constants k in 80% ethanol, and the inductive substituent constants σ 1q of the substituent R. Alkyl groups and electron‐attracting substituents at C (1) control the rate by their inductive effects alone, since logk correlates closely with σ 1q. However, rates are higher than predicted on the basis of the respective σ 1q values when conjugating (+ M)‐substituents or electrofugal groups are attached to C(1). These exalted substituent effects are attributed to CC‐hyperconjugative relay of positive charge from the cationic center at C(3) to the substituent at C(1). When the substituent is a strong electron donor (e.g. O− and S−), accelerated substitution gives way to heterolytic fragmentation, rates and products then being controlled by the frangomeric effect. Copyright © 1978 Verlag GmbH & Co. KGaA, Weinheim