Kinetics of Proton Transfer from 2-Nitro-4-X-phenylacetonitriles to Piperidine and Morpholine in Aqueous Me<sub>2</sub>SO. Solvent and Substituent Effects on Intrinsic Rate Constants. Transition State Imbalances
作者:Claude F. Bernasconi、Philip J. Wenzel
DOI:10.1021/ja961837q
日期:1996.1.1
consistent with a transition state in which delocalization of the negative charge into the 2-nitrophenyl moiety lags behind proton transfer. A consequence of this imbalance is that the intrinsic rate constant decreases with increasing electron withdrawing strength of X. For π-acceptor substituents (NO2, SO2CH3, CN) there is a further decrease in ko due to a lag in the delocalization of the charge into X. The
哌啶和吗啉对 2-硝基-4-X-苯基乙腈、2-X(X = NO2、SO2CH3、CN、CF3、Br 和 Cl)进行去质子化的速率常数 ( ) 以及逆反应 ( ) 的速率常数 ( )在 90% Me2SO−10% 水、50% Me2SO−50% 水和水(仅 X = NO2、SO2CH3、CN)中测定。Bronsted βB 值 (dlog /dp )、Bronsted αCH 值 (dlog /dlog ) 和固有速率常数 (log ko = log(k1/q) for p − p + log(p/q) = 0) 由这些计算得出数据。αCH 小于 βB,这意味着不平衡与过渡状态一致,其中负电荷离域到 2-硝基苯基部分滞后于质子转移。这种不平衡的结果是固有速率常数随着 X 吸电子强度的增加而降低。 对于 π 受体取代基(NO2、SO2CH3、