Hydrogen, heats of formation

It has been shown experimentally (heats of hydrogenation, heats of formation) that there is significant homoaromatic stabilization in cycloheptatrienes such as 1, 7, 8, 9, 12 (in the latter three there is additional classical Huckel aromaticity), as well as in norcaradienes such as 2, 3, 10, 11. In cases where other energetic factors of the pair of valence tautomers 1 2 are very similar, the relative homoaromaticity determines the equilibrium position. ... 

Benchmark Studies on Small Molecules Enthalpies of Hydrogenation Heats of Formation M0ller-Plesset Perturbation Theory Proton Affinities. 

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