Amide resonance in thio- and seleno- carbamates: A theoretical study

The potential energy surfaces of carbamic acid HO(CO)NH2 (C1), thiocarbamic acid HS(CO)NH2 (T1) and selenocarbamic acid HSe(CO)NH2 (S1) and corresponding methyl derivatives have been searched using the ab initio MO and density functional methods to study the conformational preferences and to understand the amide resonance. Amide resonance has been found to increase in the same order as indicated by nN → π*C-O delocalization. The observed trend in the increase in the amide resonance can be attributed to decrease in the competitive nX → π*C-O delocalization rather than electronegativity of X.