Aromaticity Concepts Derived from Experiments

Abstract

Aromaticity, a very important term in organic chemistry, has never been defined unambiguously. Various ways to describe it come from different phenomena that have been experimentally observed. The most important examples related to some theoretical concepts are presented here.

Fullerenes, carbon nanotubes and graphene as tetrel bond donors and acceptors of electrophiles

“…The delocalization index for the carbon-carbon pairs of the C 5 and C 6 rings of C 44 ranges from 1.0 to 1.52. Assessing the aromatic nature of these rings is not straightforward without performing robust analysis involving HOMA (harmonic oscillator model of aromaticity) [80][81][82] and other indices, 83,84 which is beyond the course of this study. Nevertheless, the MESP model calculations suggest that the sign of the potential of the centroid regions of all the carbon rings are positive (V S,max > 0) regardless of their type (Fig.…”

Nuclear quantum and H/D isotope effects on aromaticity: path integral molecular dynamics study

“…Even though the aromaticity is a very important concept, it is defined in various ways. [2][3][4][5] Thus, there are several methods for assessing the degree of aromaticity. Theoretical calculations have been used for a long time to evaluate the degree of the aromaticity.…”

HOMER: a reparameterization of the harmonic oscillator model of aromaticity (HOMA) for excited states

“…where R S and R D are the lengths of the pure single and double CC bonds in ethane and ethylene. 16 Perhaps the most appealing feature of the HOMA index is the ease with which its values can be obtained, 18,19 requiring only information about molecular geometry (R i ) that oftentimes is accessible from both experiments and quantum-chemical calculations. Throughout the years, various extensions of the original model have been proposed.…”