Molecular hardness, polarizability and valency variation of formamide and thioformamide on internal rotation: A density functional study

The variations of hardness, polarizability, and valency of formamide and th ioformamide on internal rotation are studied through calculations using the Kohn-Sham version of spin-polarized density functional theory. It is obser ved that a minimum energy structure is associated with maximum hardness and maximum molecular valency. Also the calculated C-N bond order is found to be larger in thioformamide in the energetically more stable planar structur e which is consistent with its higher rotational, barrier. The observation that the preferable protonation site is at the oxygen (sulfur) atom and not the nitrogen atom in formamide (thioformamide) is explained through the ca lculated Fukui reactivity indices.