(The) transition states studies of $C_2H_5X$ and $CH_2CHNO$ with semiempirical and ab initio MO methods반경험과 순이론적 분자궤도 방법을 이용한 에틸 할라이드와 니트로소에텐의 전이상태에 관한 연구
The transition states of ethyl halides and nitrosoethene are studied with semiempirical (MINDO/3, MNDO, AM1, PM3) and ab initio (Gaussian $86,631G^{**}$) MO methods, respectively. When we calculate the transition states of ethyl halides with semiempirical MO methods, the optimized geometrical structures are good agreement with ab initio results, but the activation energies do not agree with experimental and ab initio results. The activation energies and optimized geometrical structure of ethyl fluoride with semiempirical MO methods show large deviation from experimental and 4-31G values.
$6-31G^{**}$ calculations for nitrosoethene and nitrosoethyne show them unstable. Nitrosoethene is only 20.2 kcal/mol more stable than it``s radicals ($C_2H_3$ + NO) and nitrosoethyne is only 27.6 kcal/mol more stable than it``s radicals(C$_2$H + NO) with $6-13G^{**}$ calculation. Thus these molecules nitrosoethene and nitrosoethyne) will react even at low temperature. In our studies, nitrosoethene decompose to it``s radicals and then reacts via cyclic intermediate proposed by Sherwood.