Abstract
A thermodynamic criterion for aromatic and conjugative interactions is proposed. Enthalpies of stepwise hydrogenation of, for example, three double bonds are compensated for strain energy changes during hydrogenation. Strain energies are calculated by molecular mechanics. If the compensated values show a monotonic increase from bond 3 to bond 1, the molecule is conjugatively stabilized. If the initial rise is sharp followed by a constant ΔH h for bonds 2 and 1 and the molecule is cyclic, stabilization is aromatic. If the compensated ΔH h decreases, the interaction is destabilizing. By this set of criteria, biquinacene is unstabilized, triquinacene is homoaromatically stabilized, hexaquinacene is homoconjugatively stabilized, and cis,cis,cis-1,4,7-cyclononatriene is homoaromatically destabilized. New experimental data are presented for the biquinacenes (bicycloocta-1,7-diene and its hydrogenation products) and the hexaquinacenes.
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Rogers, D.W., Loggins, S.A., Samuel, S.D. et al. Homoaromaticity and homoconjugation in the quinacenes: Biquinacene, triquinacene, and hexaquinacene. Struct Chem 1, 481–489 (1990). https://doi.org/10.1007/BF00671235
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DOI: https://doi.org/10.1007/BF00671235