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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 19, Number 9
BKCSDE 19(9)
September 20, 1998 

Transition-State Variation in the Sovolyses of para-Substiuted Phenyl Chloroformates in Alcohol-Water Mixtures
In Sun Koo, Kiyull Yang, Keumduck Kang, Ikchoon Lee
Solvolyses of para-substituted phenyl chloroformates in water, D2O, CH3OD, 50% D2O-CH3OD, and in aqueous binary mixtures of acetone, ethanol, methanol are investigated at 25.0 ℃. Product selectivities are reported for a wide range of ethanol-water and methanol-water solvent compositions. These data are interpreted using the Grunwald-Winstein relationship, Hammett equation, and quantum mechanical model. Grunwald-Winstein plots of the first-order rate constants for phenyl chloroformates with YCl (based on 1-adamantyl chloride) show marked dispersions into three separate curves for the three aqueous mixtures with a small m value and a rate maximum for aqueous alcohol solvents. To account for these results, third-order rate constants, kww, kaw, kwa, and kaa were calculated from the observed kww and kaa values together with kaw and kwa calculated from the computer fit. The kinetic solvent isotope effects determined in water and methanol are consistent with the proposed mechanism of the general base catalyzed carbonyl addition-elimination for para-substituted phenyl chloroformates solvolyses based on mass law and stoichiometric salvation effect studies. This study has shown that the quantum mechanical model predicts transition state variation correctly for SN2 like SAN reaction mechanism of para-substituted phenyl chloroformates.
968 - 973
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