The reaction mechanism of the aminolysis of alkanesulfmyl chloride (and fluoride) have been investigated theoretically for their structure and energies of the zwitterionic intermediates in forming during the reaction at the level of RHF/6-31G**,B3LYP/6-31G**,and B3LYP/6-311+G**.In all cases,the zwitterions show a kind of pseudo-trigonal bipyramidal (Ψ-TBP) structure indicating an addition-elimination pathway is involved in the gas phase as well as in the aqueous solution.The reorganization to a TBP structure in the gas phase,and that to a solution phase structure explicitly solvated by 5 water molecules,required substantially lower energy approximately 5 kcal/mol than the reorganization energy from sp2 to sp3 carbon center in the aminolysis of carbonyl compounds about 35 kcal/mol.