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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 30, Number 10
BKCSDE 30(10)
October 20, 2009

Title	The α-Effect and Mechanism of Reactions of Y-Substituted Phenyl Benzenesulfonates with Hydrogen Peroxide Ion
Author	Li Ra Im, Ik Hwan Um*
Keywords	The α-Effect, Brønsted-type plot, Hammett plot, Intramolecular H-bonding, Solvent effect
Abstract	Second-order rate constants (k_HOO-) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted phenyl benzenesulfonates (1a-g) with HOO- ion in H₂O at 25.0 ± 0.1℃. The Brønsted-type plot is linear with βlg = -0.73. The Hammett plot correlated with with σ^- constants results in much better linearity than σo constants, indicating that expulsion of the leaving group occurs in the rate-determining step (RDS) either in a stepwise mechanism or in a concerted pathway. However, a stepwise mechanism in which departure of the leaving group occurs in the RDS has been excluded since HOO^- ion is more basic and a poorer leaving group than the leaving Y-substituted phenoxide ions. Thus, the reactions of 1a-g with HOO^- ion have been concluded to proceed through a concerted mechanism. The α-nucleophile HOO^- ion is more reactive than its reference nucleophile OH^- ion although the former is ca. 4 pKa units less basic than the latter (i.e., the α-effect). TS stabilization through intramolecular H-bonding interaction has been suggested to be irresponsible for the α-effect shown by HOO^- ion, since the magnitude of the α-effect is independent of the electronic nature of substituent Y in the leaving group. GS destabilization through desolvation of HOO^- ion has been concluded to be responsible for the α-effect found in the this study.
Page	2393 - 2397
Full Text	PDF

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