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本文采用MINDO/3方法研究N_3-氢-4-氨基-2-羰基胞嘧啶与异4-氨基-2-羟基胞嘧啶异构化反应途径。对所研究的分子体系运用能量梯度法,给出了计算优化的几何构型。用Powell法优化了过渡态几何构型,并给出了该异构化反应的IRC。计算表明,前者比后者在能量上稳定4.9 kcal mol~(-1),正反应与逆反应的活化势垒分别为43.4和38.5kcal_mol~(-1)。本文对几个胞嘧啶异构化反应的物理实质也作了总结,试图揭示该类反应的一致性规律。
In this paper, the MINDO / 3 method was used to study the isomerization reaction of N_3-hydro-4-amino-2-carbonylcytosine and iso-4-amino-2-hydroxycytosine. The energy gradient method is applied to the molecular system studied, and the optimized geometry is given. The geometry of the transition state was optimized by Powell method and the IRC of the isomerization reaction was given. Calculations show that the former is 4.9 kcal mol -1 more energetically than the latter, and the activation barriers of the positive reaction and the reverse reaction are 43.4 and 38.5 kcal_mol -1, respectively. In this paper, the physical essence of several cytosine isomerization reactions has also been summarized, trying to reveal the consistency of such reactions.