Critical evaluation of HOMA and MBL as local aromaticity indices

The harmonic oscillator model of aromaticity (HOMA) index is an excellent structural indicator of aromaticity. We found that HOMA values for internal benzene rings in large pericondensed polycyclic aromatic hydrocarbons are often overestimated because of the local aromaticity of adjacent benzene rings. The occurrence of this phenomenon was confirmed by comparing the HOMA with the corresponding SSE(LA) values; SSE(LA) is a graph-theoretical index of local aromaticity not disturbed by the aromaticity of the adjacent benzene rings. Mean bond length values were likewise assessed by comparing them with the corresponding HOMA and SSE(LA) values.