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Lack of the neighboring group rate effect in solvolytic reactions that proceed via participation
Author(s) -
Jurić Sandra,
Kronja Olga
Publication year - 2008
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.1290
Subject(s) - chemistry , solvolysis , ethanol , solvation , solvent , solvent effects , medicinal chemistry , reaction rate constant , taft equation , chloride , computational chemistry , organic chemistry , kinetics , substituent , hydrolysis , physics , quantum mechanics
In order to investigate the influence of solvent polarity on the rate effect of double bonds in reactions that proceed via an extended π ‐participation mechanism, the solvolysis rates ( k U ) of the benzyl chloride derivative 1 and tertiary chloride 2 that have doubly unsaturated side chains were measured in absolute ethanol, 80% v/v. aq. ethanol and 97% wt. aq. trifluoroethanol. The rates of the corresponding saturated analogs 1S and 2S ( k S ) were measured in 80% aq. ethanol and 97% wt. aq. trifluoroethanol, while those in pure ethanol were calculated according to LFER equation log k = s f ( E f + N f ). In solvents with moderate ionizing power (ethanol and 80% aq. ethanol) the expected rate effects were obtained ( k U / k S >1), while in solvent with high ionizing power (2,2,2‐trifluoroethanol) absence of the rate effect was observed ( k U / k S ≈1), indicating that in the k S process the solvation of the transition state is very important, while in k Δ process the breaking of the CCl bond is not appreciably developed in the transition state and the solvent effect is marginal. Copyright © 2007 John Wiley & Sons, Ltd.