Rates of Solvolysis of the Alkylphenyldimethylcarbinyl Chlorides. Evidence for the Importance of Carbon-to-Carbon Hyperconjugative Contributions in Alkyl Groups^1,2

Abstract

Phenyldimethylcarbinol and its o-, m-and ^-monoalkvl (methyl, ethyl, isopropyl and Z-butyl) derivatives were synthesized. With one exception, these carbinols were converted readily to the corresponding tertiary chlorides by treatment with hydrogen chloride. The failure of o-Z-butylphenyldimethylcarbinol to yield the expected tertiary chloride is attributed to the large strains to be expected in this molecule, a homomorph of the unknown y-di-Z-butylbenzene. The rates of hydrolysis of the various tertiary chlorides in 90% aqueous acetone were measured at several temperatures. The small increase in rate (25°) observed in the meta alkyl derivatives ( , 1.00; m-Me, 2.00; w-Et, 1.94; m-i-Pr, 1.87; m-Z-Bu, 1.85) is attributed primarily to the inductive effect of the substituent. The minor decrease in effect with increased branching is attributed to a small hyperconjugative contribution transmitted to the ortho position of the aromatic ring and relayed to the reaction center by induction. The much larger effect of the para alkyl groups (p-Me, 26.0; p-Et, 22.0; p-i-Pr, 18.8; p-t-Bu., 14.4) is attributed to hyperconjugation stabilization of the electron deficient center by the alkyl group. From the observation that both in the meta and para positions methyl and Z-butyl groups have similar effects, it is concluded that carbon-to-carbon hyperconjugation must be nearly as important as carbon-to-hydrogen hyperconjugation. A methyl group in the ortho position (o-Me, 3.63) is far less important than a methyl group in the ^-position (p-Me, 26.0). This is attributed to steric hindrance of resonance in the transition state. With increasing bulk of the ortho substituent, the effect increases (c-Et, 2.07; o-i'-Pr, 0.847). The rate data obey the empirical relationship, log p¡ = c log (pi!mi), previously developed for the substitution reactions of toluene.

Formation and mechanism for reactions of ring‐substituted phenonium ions in aqueous solution

“…For example, a Yukawa–Tsuno treatment of rate constants for acetolysis of 2‐phenylethyl tosylates X‐3‐OTs through phenonium reaction intermediates (Scheme B) gives values of ρ = 3.9 and r = 0.63 . The values for the Hammett ρ and the Yukawa–Tsuno parameter r are smaller than for the reference solvolysis reactions of cumyl chlorides . This is consistent with a transition state for solvolysis of X‐3‐OTs , where electron donation from 4‐X is attenuated and the effective positive charge “seen” by the ring substituents reduced in comparison with the reference S N 1 solvolysis …”

Studies on hydroperoxide-dependent substrate hydroxylation by purified liver microsomal cytochrome P-450

“…(27). Cumyl chloride was prepared by the method of Brown et al (28). a-Hexylhydroperoxide was made by the reaction of n-hexyl tosylate with alkaline hydrogen peroxide according to a general published procedure (29).…”

Solvolysis of 2‐chloro‐2(3,4‐disubstituted) phenylpropanes: Validity of Hammett–Brown σ+ constants in assessing additive effects of substituents

“…The parent alcohol ( 2a ) was prepared in 80% yield by the reaction between acetone and phenylmagnesium bromide 28,30. The alcohols 2b–2e (Table I) were prepared by reacting the corresponding meta‐substituted methyl p ‐toluate esters ( 1b–1e ) with 2 molar equiv of methylmagnesium bromide or iodide 29.…”