The Substituent Effect. VIII. Solvolysis of m- and p-Substituted α-Methylbenzyl Chlorides

Abstract

The rates of solvolysis of twenty-two m- and p-substituted α-methylbenzyl chlorides were determined in 80% aqueous acetone. The relative rates at 45 °C are not correlated linearly with σ0 or σ. The use of Brown’s σ+ improves the fit but the resulting correlation is still concave. An excellent correlation, logk⁄k0=−4.950(σ0+1.147Δ\barσR+), was obtained by applying the LArSR equation. The r value 1.15 suggests that the π-electronic contribution relative to the inductive contribution of −R para substituents at the transition states differs with reaction, and is more important in the present α-methylbenzyl than Brown’s t-cumyl solvolysis (r=1.00 by definition). A set of Δ\barσ+ and σ+ corresponding to the substituent constants for unit r were calculated. The calculated σ+ values are in precise agreement with Brown’s primary σ+ values. The generality of the LArSR equation and some new substituent constants are illustrated.

Electrocatalytic reduction of arylethyl chlorides at silver cathodes in the presence of carbon dioxide: Synthesis of 2-arylpropanoic acids

“…Tetraethylammonium perchlorate (Fluka >98%) was crystallised twice from ethanol and dried in a vacuum oven at 60°C. The arylethyl chlorides 1-3 were prepared by reduction of the corresponding acetyl derivatives followed by reaction of the resulting alcohols with HCl according to published procedures [28,29]. The 2-arylpropanoic acids used as authentic samples for the identification and quantification of the electrocarboxylation products were of commercial origin and were used without further purification.…”

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

“…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 rate of solvolysis of 1,2‐diphenylethyl chloride in 80% aqueous acetone is 26 times less than that of 1‐phenylethyl chloride in the same solvent. The enthalpy of activation is higher by 11.6 kJ mol −1 and entropy of activation is lower by 11.5 J mol −1 K −1 41. 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.…”

Solvent and structural effects in tautomeric 2(6)-hydroxy-4-methyl-6(2)-oxo-1-(substituted phenyl)-1,2(1,6)-dihydropyridine-3-carbonitriles: UV, NMR and quantum chemical study

“…In the second step, the initial approximation of the band intensities and band widths, as well as the assignment to the appropriate tautomeric form were performed. The final refinement is performed by simultaneous resolution of the whole set of spectra according to literature procedures [25,29,30,46]. TD-DFT calculations have shown (Tables S6 and S7; Figs.…”

“…The UV-Vis and NMR data were analyzed by the use of LSER and LFER models, respectively, in order to evaluate influences of solvent/solute interactions and substituent effects on tautomeric equilibria and the extent of ICT. Due to overlapping of the absorption bands, applied methodology for resolution of UV-Vis spectra was based on certain approximations [30]. The algorithm applied for evaluation of the state of tautomeric equilibria was described elsewhere [25,31].…”