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

Abstract

1,2‐Diphenylethyl chloride undergoes solvolysis by SN1 mechanism in aqueous organic solvents. The α‐phenyl group of 1,2‐diphenylethyl chloride enters into conjugation with the developing carbocationic centre. The β‐phenyl group on the other hand was unable to extend its conjugation via neighbouring group participation due to steric inhibition of resonance in the formation of non‐classical carbocation. 1,2‐Diphenylethyl chloride thus behaves similar to 1‐phenylethyl chloride in its solvolysis pattern. The solvolytic rate studies of chloride and methanesulphonate of 1,2‐diphenylethyl alcohol in various aqueous organic solvents show that the dispersion observed in the Winstein–Grunwald plot is not due to a change in leaving group but due to the difference in solvation requirements of aromatic and aliphatic groups. Copyright © 2010 John Wiley & Sons, Ltd.

Kinetics of elimination reactions of 1,2‐diphenyl ethyl substrates in acetonitrile: A mechanistic change in the presence of a strong base

“…The possibility of A N D E + D N (E1cB) can be discarded on the account of the mass law effect shown by this substrate. A rate enhancement in the presence of weak bases like chloride ion is expected in an E1cB mechanism, whereas a rate deceleration with a characteristic mass law constant value of 11 (α = k −1 / k 2 ) is reported in the presence of added tetrabutyl ammonium chloride 5.…”

“…The preparation and kinetic measurements of 1‐chloro‐1‐(4‐methoxyphenyl)‐2‐phenylethane is reported earlier 5. The mesylates were prepared by the dropwise addition of methanesulfonyl chloride (3 mL) to the corresponding alcohols (5 g) in dry pyridine (25 mL) kept at 0°C.…”

“…In the unimolecular dehydrochlorination of 2‐chloro‐2‐phenylpropane (cumyl chloride) 4 and 1‐chloro‐1‐(4‐methoxyphenyl)‐2‐phenylethane (1‐ p ‐anisyl‐2‐phenylethyl chloride) 5 in acetonitrile, it is established that the added weak base pyridine does not enter into the rate equation. The pyridine merely abstracts the eliminated hydrogen chloride without involving in the abstraction of β‐hydrogen.…”

“…The possibility of substitution with a solvent 6 or base can be completely discarded 7–9 since the product analysis showed only the presence of alkene. In the pure E1 reaction, the product should be completely nonstereospecific, since the carbocation is free to adopt its most stable conformation before giving up the proton 1,5.…”

“…In methanolysis 12,13 as well as in aqueous organic solvolysis reactions 14–16, the possibility of various pathways that are difficult to be distinguished by kinetic and product analysis led to controversial suggestions without confirmative results. The E1 mechanism established recently 5 in the dehydrochlorination of 1‐chloro‐1‐(4‐methoxyphenyl)‐2‐phenylethane in acetonitrile, with a lone thermodynamically stable transproduct, is a promising system for the study of mechanistic changes in the presence of the added strong base.…”