An energy decomposition analysis approach to the rotational barriers of amides and thioamides

•Energy decomposition analysis (CMOEDA) can describe the rotational barriers of amides and thioamides.•The rotational barrier is increased by polarization and electrostatic components, and decreased by exchange-repulsions.•The difference between the two transition states is mainly determined by repulsive interations.•Larger electrostatic and polarization interactions in the ground state increases the rotational barrier of thioformamide relative to formamide.•Destabilization of the ground state due to repulsions decreases the rotational barrier of acetamide relative to formamide.