The role of carbonyl and thiocarbonyl groups in the conformational isomerism of haloacetones and halothioacetones

The presumable, but not well-known parallelism between carbonyl and thiocarbonyl groups as electron acceptors in conformational analysis is reported. Our theoretical investigation was carried out for model compounds, namely mono-haloacetones and mono-halothioacetones. Furthermore, the donor ability of C–H and C–halo bonds has been evaluated on the basis of natural bond orbital (NBO) analysis and orbital levels calculations, and the conformational isomerism discussed in terms of classical and hyperconjugative interactions. It has been found that the conformational behavior of the titled compounds is strongly dependent on the π donor/acceptor behavior, which differs substantially between C=O and C=S systems, as well as on the steric/electrostatic and non-Lewis-type interactions involving the series of halogens.