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化学学报
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化学学报 ›› 1994, Vol. 52 ›› Issue (3): 217-222. 上一篇    下一篇

研究论文

N-烯基硝酮分子内环加成反应区域选择性的理论研究IV. N-4-己烯基硝酮分子内环加成反应的区域选择性

马思渝;傅孝愿   

  1. 北京师范大学化学系
  • 发布日期:1994-03-15

Theoretical study on the regioselectivity of intramolecular N-alkenylnitrone cycloaddition. IV. the regioselectivity of intramolecular N-4-hexenyl nitrone cycloaddition

MA SIYU;FU XIAOYUAN   

  • Published:1994-03-15

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本文用AM1 MO方法和过渡状态理论研究N-4-己烯基硝酮分子内环加成反应的机理, 计算两个平行反应(a, b)的速率常数的比值, 得到与实验吻合的结果。计算结果还表明, 由于N-5-甲基的电子效应, 使得反应b的活化焓降低, 同时, N-5-甲基引起的构型变化, 使得反应b的活化熵增高(绝对值变小), 这使得K~b/K~a值明显增长, 是区域选择性发生较大改变的原因。

关键词: 反应机理, 环加成反应, 过渡态理论, 区域选择性, 国家教委高等学校博士学科点专项科研基金, 烯基硝酮, 己烯基硝酮

The regioselectivity of intramol. N-4-hexenyl nitrone cycloaddn. has been investigated by AM1 MO method and transition state theory. Two isomeric products and corresponding transition states were located by energy gradient technique. The ratio of the rate constants of these two parallel reaction (kb/ka) is calculated to be 25.46, which is in good agreement with experiments In comparison of this ratio with that of N-4-pentenyl nitrone cycloaddn., which is 1.21, it is realized that N-5-Me substituent changes the regioselectivity notably. The main reason is that the electronic effect of N-5-Me makes the activation enthalpy of reaction b reduced and the configuration change by introducing an N-5-Me group makes the activation entropy of reaction b increased.

Key words: REACTION MECHANISM, CYCLOADDITION REACTION, TRANSITION STATE THEORY, REGIOSELECTIVITY

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