Whereas in an @A00441@ molecule there is continuous overlap of p-orbitals over a cyclic array of atoms, in a homoaromatic molecule there is a formal discontinuity in this overlap resulting from the presence of a single \(\text{sp}^{3}\) hybridized atom at one or several positions within the ring; p-orbital overlap apparently bridges these \(\text{sp}^{3}\) centres, and features associated with @A00442@ are manifest in the properties of the compound. Pronounced homoaromaticity is not normally associated with neutral molecules, but mainly with species bearing an electrical charge, e.g. the 'homotropylium' @C00907@, (C8H9+):
In bis, tris, (etc.) homoaromatic species, two, three, (etc.) single \(\text{sp}^{3}\) centres separately interrupt the π-electron system.
See also:
homoconjugation (Note. 2)
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1121 [Terms] [Paper]