MINDO/3研究胞嘧啶异构体间异构化反应——Ⅰ. N1-氢-4-氨基-2-羰基胞嘧啶与4-亚氨基-2-羰基胞嘧啶异构反应

本文报导用半经验方法研究N_1-氢-4-氨基-2-羰基胞嘧啶与4-亚氨基-2-羰基胞嘧啶异构化反应。用MINDO/3能量梯度法优化了孤立体系的全部自由度, 计算结果表明氨型比亚氨型稳定, △E=33.85 kJ mol~(-1); 限定分子体系在同一平面, 用Powell法优化过渡态几何构型, 计算所得正反应活化势垒为168.87 kJ mol~(-1), 逆反应活化势垒为135.02 kJ mol~(-1)。从IRC途径分析了该异构化反应的物理实质。

MINDO/3 STUDY OF THE TAUTOMERIC REACTIONS OF THE TAUTOMERS OF CYTOSINE Ⅰ. The Tautomeric Reaction of N1-H-4-NH2-2-oxo-cytosine and 4-NH-2-oxo-cytosine

A MINDO/3 MO method has been applied to study the tautomeric reaction of the N_1-H-4-NH_2-2-oxo-cytosine and 4-NH-2-oxo-cytosine. The geometries of the molecules involved in the tautomeric reaction are optimized by energy gradient method using MINDO/3 program. The results show that the amino-tautomer is more stable than imino-tautomer by △E=33.85 kJ mol~(-1).The geometry of the transition state is optimized by Powell's method. The reaction path of the tautomeric reaction is presented, based on Fukui's IRC theory. The physical nature of the reaction is revealed by analysing the intramolecular charge transfer as the tautomeric reaction is occurring. The activation arrier of the forward reaction is 168.87 kJ mol~(-1), while it is 135.02 kJ mol~(-1) for the backward reaction.