The ¥á-Effect and Mechanism of Reactions of Y-Substituted Phenyl Benzenesulfonates with Hydrogen Peroxide Ion

Bulletin of the Korean chemical society

Li Ra Im¹  Ik Hwan Um¹ 

关键词: The ¥á-Effect;    Br©ªnsted-type plot;    Hammett plot;    Intramolecular H-bonding;    Solvent effect;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

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 Br┆nsted-type plot is linear with モlg = -0.73. The Hammett plot correlated with with �?^- constants results in much better linearity than ヲo 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 �?-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 �?-effect). TS stabilization through intramolecular H-bonding interaction has been suggested to be irresponsible for the �?-effect shown by HOO^- ion, since the magnitude of the �?-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 �?-effect found in the this study.

【 授权许可】

Unknown