The structures and isomerization of silylenoid Ph2SiLi(OBu-t) were studied by density functional theory at B3LYP/6-31G(d) level. Four equilibrium structures and four isomeric transition states were located. Based on the B3LYP/6-31G(d) optimized geometries, the corresponding harmonic vibrational frequencies of transition states were obtained. The stability, reactivity and existence of various equilibrium structures were discussed.

The alcoholysis of N-methyl-1,2-thiazetidine-1,1-dioxide has been investigated using ab initio and density functional theory. The geometries, energies and frequencies of reactants, intermediates, transition states and products are calculated. Our results indicate the alcoholysis of N-methyl 1,2-thiazetidine 1,1-dioxide proceeds via two reaction channels. Channel Ⅰ is the cleavage of bond C-S and producing N-methyl-N-ethyl amino-methyl sulfonate (P1, in Fig. 1) in which attacking of CH3OH and breaking of bond C-S are concerted. Channel Ⅱ is the cleavage of bond S-N and producing 2-(N-methyl) taurine methyl ester (P2, in Fig. 1) in which there are two reaction processes with two different mechanism: concerted and stepwise. The most favorite pathway for alcoholysis of N-methyl 1,2-thiazetidine 1,1-dioxide was found. The energy barrier of the cleavage of C-S bond and producing P1 is the highest among them. We think that this may be the possible reason of having no experimental evidence on the formation of product P1.

The alcoholysis of 1,2-thiazetidine 1,1-dioxide has been investigated using ab initio and density functional theory at HF/6-31G*, MP2/6-31G*//HF/6-31G* and B3LYP/6-31G* levels. The geometries, energies and frequencies of all stationary points were calculated in detail. Solvent effects have been considered by means of a polarizable continuum model (PCM). Our results indicate the lcoholysis of 1,2-thiazetidine 1,1-dioxide proceeds via concerted mechanism and stepwise mechanism. In the stepwise mechanism, two possible reaction pathways can be followed whilst one possible reaction pathway can be followed in the concerted mechanism. The most favorite pathway for lcoholysis of 1,2-thiazetidine 1,1-dioxide was found.

One-carbon unit transfer from l-aceyl-3-methylimidazolinium to 1,2-diaminobenzene has been studied using PM3 method. The structures of the intermediates and transition states have been optimized. The results show that there are two pathways to transfer the one-carbon unit, and each pathway consists of six steps. They are the combination of two reactants, proton migration, splitting of five-membered ring, formation of benzimidazole ring, another proton migration and separation of C-N bond. And the proton migrating step is the rate limiting step.