ISOMERS ON THE C2H2CL- CALCULATED ENTHALPIES OF FORMATION FOR UNSATURATED-HYDROCARBONS AND MONOCHLORO DERIVATIVES( SURFACE )

Ab initio molecular orbital calculations are reported for structures a t minima and at saddle points on the C2H2Cl+ surface. At SCF/6-31G(d,p ), the 1-chlorovinyl cation (1), the chlorenium ion (2), the 2-chlorov inyl cation (3), and chlorine-protonated chloroacetylene (4) are all a t minima, but inclusion of electron correlation at MP2/6-311G(d,p) eli minates the 2-chlorovinyl cation as a minimum and the transition struc ture for interconversion of 1 and 2 has a structure similar to 3. At M P4/6-311G(2df,p)//MP2/6-311G(d,p) 1 lies 19.4 kcal mol-1 below 2, and the barrier is 10.7 kcal mol-1 above 2. The calculated proton affinity of chloroacetylene is 169.0 kcal mol-1. For unsaturated molecules C2H 4, C2H3Cl, C2H3+, C2H5+, and C2H4Cl+ (two isomers), enthalpies of form ation from MP4SDTQ/6-311G(2df,p) calculations are within 2 kcal mol-1 of experimental values. At the same level of theory, the calculated DE LTAH(f,298)-degrees for the 1-chlorovinyl cation is 248.1 kcal mol-1, and for the chlorenium ion it is 268.1 kcal mol-1.