Theoretical studies on the relative reactivities of aryl thiol, thiono and dithio carbonates and carbamates

Abstract

RHF, MP2 and DFT calculations were carried out for the unhydrated and explicitly solvated (by five water molecules) putative zwitterionic complexes formed in the aminolysis of oxo {(O, O)} and thio {(O, S), (S, O) and (S, S)} carbonates [MeO‒ C(˭Y)‒ Y′Ar] and carbamates [NH2‒ C(˭Y)‒ Y′Ar, where Y and Y′ are O or S] with ammonia. The reorganization energy of the carbonyl carbon from an sp2 to an sp3 center, i.e., the energy needed to form a zwitterionic tetrahedral intermediate, was inversely related to the experimental rate of the aminolysis of carbonates as Y and Y′ are varied, (O, S)<(O, O)<(S, S)<(S, O). For carbamates the reorganization energy is the highest and the solvation energy is the lowest among ester, carbonate and carbamate series, which is suggestive of the difficulty of zwitterionic intermediate formation and changeover to a concerted mechanism found experimentally for the aminolysis of the carbamates.