THEORETICAL-STUDY OF THE BOND-DISSOCIATION ENERGIES OF PROPYNE (C3H4)

The C-C and C-H bond dissociation energies (BDEs) of propyne have been computed using the modified coupled-pair functional method. Due to hyperconjugation, the C-C and methyl C-H single bonds are stronger and weaker, respectively, than those in ethane. The acetylenic C-H and C=C BDEs are larger and smaller, respectively, than in acetylene, also as a result of the hyperconjugation. Our best estimate of 92.5 +/- 2 kcal/mol for the methyl C-H BDE in propyne in slightly larger than the experimental value. For the acetylenic C-H BDE in propyne we predict 135.9 +/- 2 kcal/mol.