A THEORETICAL INVESTIGATION ON THE ELECTRON-ACCEPTOR PROPERTIES OF POLAR CS BONDS OF CH3-NFNSH (N=0-3) THIOLS AND AND CH3-NFNSCH3-NFN (N=0-3) SULFIDES

The structures and stabilities of fluoro-substituted thiols and sulfid es of general formula CH3-nFnSH and CH3-nFnSCH3-sFn (n = 0-3), have be en calculated at the MP2/6-311G* and MP2/6-311 + + G** levels. The ro le of F-substitution in molecules and fragments resulting from CS and SH bond cleavage has been studied. In molecules, F-substitution does n ot bring about important changes of the CS bond lengths, and, accordin gly, no important change is observed in the energy of the vertical ani on species which remain much less stable than the neutral ground state . The same type of conclusion holds for the homolytic dissociation of neutral molecules (CS and SH bonds), yielding radical moieties, which exhibit only little variation upon F-substitution. When dealing with a nion fragments, the situation is more striking. It is noteworthy that the well-documented effect of methyl anions stabilization by halogen s ubstitution is appreciably increased in the new class of compounds of formula CH3-nFnS. For the latter, the EA rises from 1.47 eV in CH3S to 3.08 eV in CF3S. On the grounds of energy balance between (A(0) + B-) (infinity) and (A(-) + B-0)(infinity) it is proposed that CF3SH and CF 3SCH3 are good candidates for the adiabatic formation of stable 3-elec tron bonds.