Dissection of methyl internal rotational barrier in thioacetone

The nature of methyl internal rotational barrier in thioacetone has been investigated by relaxation effect, natural bond orbital (NBO) analysis and Pauli exchange interactions and compared with its parent molecule acetone. Flexible calculation correlates well with the experimental barrier compared to that of rigid rotational model. NBO analysis provides individual contribution of bond, antibond, lone pair and Pauling exchange interaction energy towards the rotational barrier. The lengthening of bonds is explained by charge transfer interaction between different bonding and antibonding orbitals