Solvolyses of aryldineopentylcarbinyl, aryl-tert-butylneopentylcarbinyl, and aryldi-tert-butylcarbinyl p-nitrobenzoates. Effects of the bulky alkyl groups at the reaction center and substituents in the aryl ring

The leaving group dependence in the rates of solvolysis of 1,2‐diphenylethyl system

“…The backside attack by a nucleophile or solvent is difficult in a sterically hindered substrate and it is shown that when bulky groups replace the α ‐alkyl group in 1‐phenylethyl chloride the mechanism of the reaction shifts more towards S N 1 side in S N 1–S N 2 spectrum 44. The steric inhibition of resonance suggested for S N 1 reaction21, 41, 45–48, 52 is a more plausible explanation for the change in thermodynamic parameters observed for the solvolysis of 1,2‐diphenylethyl chloride compared to 1‐phenylethyl chloride. The m value and the kinetic parameters observed for 1‐phenylneopentyl chloride which is analogous to 1,2‐diphenylethyl chloride are explained due to the steric inhibition of resonance 44.…”

“…The substitution of β ‐hydrogen by phenyl group can retard the rate by the reduction in hyperconjugative contribution by a hydrogen atom; also the benzyl group is electron withdrawing with σ * value +0.22. The steric effect of α ‐alkyl substituent has much more influence in the retardation of rate of solvolysis in aralkyl systems 41–48. It is reported43, 49 that the substitution of the methyl group by bulky alkyl groups in 1‐phenylethyl chloride retards the rate; a substitution of the isopropyl group in the place of methyl retards the rate by 20 times.…”

“…The steric effect due to benzyl is slightly smaller than the isopropyl group and retardation of the order of 10–15 times is thus expected if a benzyl group replaces the methyl. The steric effect of the bulky groups favours S N 1 reaction by the relief of steric strain42, 46, 48, 51 during the formation of transition state but it retards the rate of reaction in S N 2 reaction by preventing the backside nucleophilic attack. The backside attack by a nucleophile or solvent is difficult in a sterically hindered substrate and it is shown that when bulky groups replace the α ‐alkyl group in 1‐phenylethyl chloride the mechanism of the reaction shifts more towards S N 1 side in S N 1–S N 2 spectrum 44.…”

Biogenetic-Type Rearrangements of Terpenes

“…A study of the effect of solvent upon the products resulting from deamination of isobutyl amine indicates that cyclopropane formation is enhanced in non-polar solvents (182). 1,3-hydrogen elimination to cyclopropanes has also been found in the solvolysis (183) and pyrolysis (184) of highly hindered p-nitrobenzoates. …”

Theoretical Gas‐Phase Stabilities of α‐Trimethylsilyl‐Substituted Tertiary Carbenium Ions

“…The differences were ascribed to steric effects. [6,8,9] Gas-phase experiments by Schwarz showed that α-silyl carbenium ions easily undergo 1,2-methyl and 1,2-H shifts to the β-silylcarbenium ions, [10,11] a fact which further complicates the situation. In theoretical studies, the SiMe 3 group effect is often extrapolated from the simple SiH 3 model calculations, while the influence of several silyl groups on the stability of an adjacent tertiary carbenium ion has not been explored so far.…”