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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 20, Number 10
BKCSDE 20(10)
October 20, 1999 

Kinetics and Mechanism of the Pyridinolysis of Benzyl Bromides in Dimethyl Sulfoxide
Sung Wan Hong, Han Joong Koh, Hai Whang Lee, Ikchoon Lee
Nucleophilic substitution reaction of Y-benzyl bromide with X-pyridines are investigated in DMSO at 45.0℃. Biphasic rate dependence is observed on varying the substituents in the substrate (Y) as well as in the nucleophile (X). The two well-defined straight lines in the Hammett (ρy) and Bronsted ( βx) plots are interpreted to indicate the changes in transition-state structure, a decrease in bond cleavage as the substituent on the substrate is changed from electron-donors ( ρy < 0) to electron-acceptors ( ρy > 0), and an increase in the extent of bond formation with the corresponding changes of the substituent on the pyridine. A Jencks' type analysis of separate polar (ρ) and resonance (ρr) effects can also be accounted for by the change of the transition-state structure, not by the variable combination of polar and resonance effects.
1172 - 1176
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