Dehydrative Cyclocondensation Mechanisms of Hydrogen Thioperoxide and of Alkanesulfenic Acids

Structural features of hydrogen thioperoxide (oxadisulfane, H–S–O–H) and of alkanesulfenic acids (R–S–O–H; R = CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, C(CH3)3, CF3, CCl3) and the mechanisms of their dehydrative cyclocondensation to the respective sulfinothioic acid (H–(S═O)–S–H) and alkyl alkanethiosulfinates (R–(S═O)–S–R) have been studied using coupled cluster theory with single and double and perturbative triple excitations [CCSD(T)] and quadratic configuration interaction with single and double and perturbative triple excitations [QCISD(T)] with the cc-pVDZ basis set and also using second-order Moller-Plesset perturbation theory (MP2) and the hybrid density functionals B3LYP, B3PW91, and PBE1PBE with the 6-311+G(d,p) basis set. The concerted cyclodehydration mechanisms include cyclic five-center transition states with relatively long distance sulfur–sulfur bonding interactions. Attractive and repulsive nonbonding interactions are predicted in the sulfenic acids, transition states, and thiosulfinates. In the...