Theoretical study of cyclopropenones and cyclopropenethiones: decompositionvia intermediates

Abstract

The mechanism of the decomposition of cyclopropenones and cyclopropenethiones giving acetylenes (R¹–CC–R² with R¹ = R² = H, F) plus carbon monoxide and carbon monothioxide, respectively (CX, X = O, S) has been probed using DFT (B3LYP/6-311G(d,p)) and MO (CCSD(T)/6-31G(d)) calculations. It turns out that the decomposition is stepwise, forming first an intermediate which has the properties of a semi-carbene, semi-zwitterion, whose structure is best described in both cases as a resonance hybrid between a carbene and a zwitterion. Using the PCM model, study of the solvent effect on the reactions in three continua (water, acetonitrile and benzene) shows that solvents do not affect the shape of the potential energy surfaces but tend to stabilize all the isomers. Estimation of the first vertical excited states by CIS and TD-B3LYP methods suggests that the photochemical reactions are likely to take place in the ground state rather than in an excited state. Hardness and polarizability profiles along the reaction paths show that there is a maximum in the polarizability profile besides an inverse relationship between hardness and polarizability. Fluorine substitution tends to stabilize the intermediate making it a genuinely detectable moiety.