A theoretical study of atomic sulfur reactions with alkanes, alkenes, and alkynes

The results of an MNDO study of the potential energy surface for reaction of sulfur in its ground S(/sup 3/P) and first excited state S(/sup 1/D) with alkanes, alkenes, and alkynes are reported. In agreement with experiments, S(/sup 1/D) inserts into CH bonds of alkanes (CH/sub 4/ and C/sub 2/H/sub 6/) but S(/sup 3/P) does not. MNDO provides a reasonable explanation for the observed differences in S(/sup 1/D) and S(/sup 3/P) addition to ethylene. The stereoselectivity of S(/sup 3/P) addition is postulated to result from rapid intersystem crossing rather than from a high methylene rotational barrier in the triplet biradical. Ethenethiol is predicted to result from isomerization of hot thiirane rather than from sulfur insertion into the CH bond. In the addition of sulfur to acetylene, S(/sup 3/P) is predicted to yield thioketocarbene while thiirene, thioketene, and ethynethiol are predicted from S(/sup 1/D) addition.