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Evidence for extended π,n‐participation in solvolysis of some benzyl chlorides
Author(s) -
Jurić Sandra,
Filipović Anita,
Kronja Olga
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.687
Subject(s) - solvolysis , chemistry , aryl , medicinal chemistry , aqueous solution , hammett equation , reaction rate constant , organic chemistry , hydrolysis , kinetics , alkyl , physics , quantum mechanics
Chlorides 3 (1‐aryl‐1‐chloro‐4‐methyl‐7‐methoxy‐4‐heptene) and 4 (1‐aryl‐1‐chloro‐4‐methyl‐4‐hexene) with various phenyl substituents were prepared (Y= p ‐OCH 3 , p ‐CH 3 , H and m ‐Br) and the solvolysis rates were measured in 80% (v/v) aqueous ethanol. The rate constants of 3 correlate well with σ + , and the ϱ + value obtained is −1.45±0.15, whereas with 4 breakdown of the Hammett plot occurs, and the ϱ + value without the p ‐anisyl group is −2.55±0.20, indicating extended π,n‐participation in 3 and simple π‐participation in 4 . The drastically smaller activation parameters obtained with 3 than with 4 are consistent with the proposed mechanism in which the high degree of order required in the transition state (large negative Δ S ‡) is overcompensated by a small Δ H ‡. Copyright © 2003 John Wiley & Sons, Ltd.