AB-INITIO STUDY OF DECOMPOSITION OF CARBAMIC ACID AND ITS THIO AND SILA DERIVATIVES

The ab initio molecular orbital method (at the 6-31G** level of theory) has been used to study the decomposition of carbamic acid, thiocarbamic O-acid, thiocarbamic S-acid, dithiocarbamic acid and silacarbamic acid. The total internal energy of the molecules investigated is calculated as a sum of the HF energy, the electron correlation (MP4(SDTQ) contribution and zero-point vibration energy. At the highest level of theory a negative decomposition energy results for the decarboxylation of carbamic acid, thiocarbamic O-acid, thiocarbamic S-acid and dithiocarbamic acid. The decarboxylation reaction for silacarbamic acid was, however, found to be highly endothermic. The fundamental vibrational frequencies allowed in the IR spectrum are computed for both reactants and reaction products.