烷基氟化物热消除反应的理论研究-1

用RHF从头计算法研究了氟代乙烷消除氟化氢反应的取代基效应．对所有构型均采用能量梯度法在3-21G基级水平上进行了优化，过渡态的构型用振动分析确认．计算结果表明，对所讨论的基团-F，-CH_3，－CN，－NH_2，在α位和β位取代，均对过渡态的结构有一定的影响，电荷分布表明，标题反应的过渡态为部分极化的四元环过渡态．－F在α位和β位的取代均使氟代烷1－2消除氟化氢反应的活化位垒升高，且前者的活化位垒高于后者；－CN在α位的取代使反应的活化位垒升高，在β位的取代使反应的活化位垒降低．－CH_3和-NH_2在α位的取代使反应的活化位垒降低，在β位的取代使反应的活化位垒升高，只是-NH_2的效应强于-CH_3．这些结果与由实验结果推测的结论一致表明，本消除反应与其它卤代烷的消除反应有显著的差别．

Theoretical Studies on the Elimination Reaction of Alkyl Fluorides-1

At the level of 3-21G basis set, the transition states of the titled reactions have been optimized by using the energy gradient method with GAUSSIAN 80 program.On this basis, a vibrational analysis has been performed with GAUSSIAN 86 program to make the transition states further confirmed.
It has been found that the substitution of -F, -CN, -NH_2 and -CH_3 at α or β carbon leads to the change of the structures of the transition states of the titled reactions. The charge distribution of the transition states shows that all of them are polarized fourmember ring structures.
It is shown that the substitution of -F at α or β carbon leads to a rising of the reaction arrier height and the barrier of the former is higher than that of the later. However, the substitution of -CN at α and β carbons lead to a rising and a lowering of the reaction barrier respectively. As for the -NH_2 and -CH_3 cases, α substitution always increases the barrier height, while β substitution decreases it, and the substitution effect of -NH_2 is stronger than that of -CH_3. These results are in accord with the conclusions derived from experiments.