The α-Effect in Hydrazinolysis of 4-Chloro-2-Nitrophenyl X-Substituted-Benzoates: Effect of Substituent X on Reaction Mechanism and the α-Effect

Bulletin of the Korean chemical society

Min-Young Kim¹  Jieun Lee¹  Ik-Hwan Um¹  Tae-Eun Kim¹ 

关键词: The -effect;    Hydrazinolysis;    Ground-state destabilization;    Transition-state stabilization;    Yukawa-Tsuno plot;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants (kN) have been measured spectrophotometrically for the reaction of 4-chloro-2- nitrophenyl X-substituted-benzoates (6a-6h) with a series of primary amines including hydrazine in 80 mol % H2O/20 mol % DMSO at 25.0 oC. The Brønsted-type plot for the reaction of 4-chloro-2-nitrophenyl benzoate (6d) is linear with βnuc = 0.74 when hydrazine is excluded from the correlation. Such a linear Brønsted-type plot is typical for reactions reported previously to proceed through a stepwise mechanism in which expulsion of the leaving group occurs in the rate-determining step (RDS). The Hammett plots for the reactions of 6a-6h with hydrazine and glycylglycine are nonlinear. In contrast, the Yukawa-Tsuno plots exhibit excellent linear correlations with ρX = 1.29-1.45 and r = 0.53-0.56, indicating that the nonlinear Hammett plots are not due to a change in RDS but are caused by resonance stabilization of the substrates possessing an electron-donating group (EDG). Hydrazine is ca. 47-93 times more reactive than similarly basic glycylglycine toward 6a-6h (e.g., the α-effect). The α-effect increases as the substituent X in the benzoyl moiety becomes a stronger electronwithdrawing group (EWG), indicating that destabilization of the ground state (GS) of hydrazine through the repulsion between the nonbonding electron pairs on the two N atoms is not solely responsible for the substituent-dependent α-effect. Stabilization of transition state (TS) through five-membered cyclic TSs, which would increase the electrophilicity of the reaction center or the nucleofugality of the leaving group, contributes to the α-effect observed in this study.

【 授权许可】

Unknown