Aromaticity/Antiaromaticity in Cyclic Conjugated Hydrocarbons

The physical reason for aromaticity/antiaromaticity was determined. The conclusion was reached after interpreting Hobey's mathematical results that were given in the study of the energy difference between the one-dimensional linear and cyclic particles-in-a-box models. We first revealed that the Huckel theory and particles-in-a-box model are simply different ways of solving the same Schr6dinger equation. Then, we pointed out that appearance of the zero-kinetic energy orbital as the lowest one in a cyclic conjugated system is the determining factor of aromaticity/antiaromaticity: Thirdly, reasons of such appearance double degeneracy m the higher ones and therr splitting by changing into the linear system were discussed. Finally, it was ascertained that what happens in the cyclic particles-in-a-box model really takes place in actual JT orbitals obtained by an ab initio molecular orbital (MO) method in cyclobutadiene and benzene. C 2002 John Wiley & Sons. Inc. Int J Quantum Chem 87: 135-144, 2002