Nucleus independent chemical shifts and side dependent aromaticity of phospholes and their anionic silicon counterparts

The nucleus independent chemical shifts (NICS) on the two sides of the five membered rings in phospholes and the corresponding silolyl anions are found to be numerically not same. It is reflected in their chemical reactivity. It is concluded that the frontier molecular orbitals on the two sides in phospholes and their anionic silicon counterparts are different. So far, it has never been necessary to invoke such a concept in the molecular orbital theory.