Sulfine, CH2SO: Determination of Its Heat of Formation, Basicity, and Bond Strengths by Quantum Chemistry †

Ab initio calculations executed at the CAS-SDCI/CASSCF/DZ(2df,2d,p)+f(S) level of theory have been employed to determine the heat of formation, ΔH f, of the parent sulfine, CH2SO, 1, relative to six experimentally well-known anchors: ΔH f(1) = −3 ± 14 kJ/mol (0 K). The standard G2 and G2(MP2) methods yield lower values, −18 and −30 kJ/mol, respectively. It is inferred that the geometry optimization procedure in G2, which uses MP2(FULL)/6-31G*, does not accurately reproduce the experimental structure of 1. A larger basis set (MP2/6-311 + G(2df,2p) leads to the correct structure and to a ΔH f(1) = −2 kJ/mol (0 K). Our recommended value at 298 K, ΔH f(1) = −9 kJ/mol, represents a significant revision upwards of a previously estimated value (−50 ± 22 kJ/mol). The proton affinity of 1 (to generate CH2SOH+) is calculated to be 787 kJ/mol (298 K).