Determination of Reactivity by MO Theory (￥1￥1). An MO Theoretical Study on Mechanism of Thiocarbonyl Addition

摘要

Ab initio molecular orbital calculations have been performed in an effort to determine which types of chemical interactions play essential roles for the system, OH- + CH2S, H2O + CH2SH+, and H2O + CH2S. The most important contribution to the interaction energy in controlling reaction path is the exchange repulsion energy, EX, which is largely responsible for the shape of the total interaction energy curve. In the ion-molecule reaction, prior protonation of thioformaldehyde or prior deprotonation of water leads to formation of the corresponding ionic adducts (H2O+CH2SH and HOCH2S-), with no barrier to reaction, simulating specific acid and base catalysis, respectively, as in the case of formaldehyde. Otherwise, approach of water to thioformaldehyde gives rise to a completely repulsive interaction.