THEORETICAL-STUDIES OF ELIMINATIONS .6. THE REGIOCHEMISTRY AND STEREOCHEMISTRY OF THE GAS-PHASE REACTIONS OF 3-HALOCYCLOHEXENES WITH FLUORIDE - AN AB-INITIO STUDY

The gas phase reactions of fluoride with 3-chlorocyclohexene and 3-flu orocyclohexene have been investigated with ab initio calculations up t o the MP2/6-31+G* level. Transition states were located for 1,4-elimi nations and 1,2-eliminations as well as S(N)2 and S(N)2' substitutions . For each reaction, a variety of stereochemical outcomes was explored . For both systems, the preferred pathway is an anti 1,4-elimination, but syn 1,4-eliminations and anti 1,2 eliminations have transition sta tes that are nearly as stable. The two modes of substitution (S(N)2 an d S(N)2') have similar barriers, but are much less favorable than elim ination. The results are compared to recent experimental studies of re lated systems.