posted on 2007-10-04, 00:00authored byPrasenjit Seal, Swapan Chakrabarti
Density functional theoretical investigation has been performed to explore the reliability of the nucleus-independent chemical shift (NICS) scheme in assessing aromatic behavior of some planar six-membered
heteroatomic systems. It has been observed that the NICS scan and the diamagnetic and paramagnetic
contributions of the in-plane and out-of-plane components are quite reliable in assessing any aromatic or
antiaromatic behavior in borazine. However, for boraphosphabenzene, the aromatic stabilization energy is
too small to consider it as an aromatic system but the NICS scans and the homodesmotic reactions suggest
an opposite trend. Interestingly, in the case of alumazene, a very shallow minimum is observed for the out-of-plane component, which suggests the presence of weak diamagnetic ring current. However, the diamagnetic
and paramagnetic contribution curves to the out-of-plane component for alumazene clearly reveal a net
paramagnetic contribution. Thus we may surmise that apart from the single NICS value, the NICS scan also
is not a very authentic tool for the assessment of aromaticity of planar six-membered heteroatomic systems.