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A linear relation between delta-H(super degree) (sub acid)(HX), EA[X(sub .)], and BDE(HX) is shown for specific classes of compounds and only one of these quantities is needed to determine the others. The intercepts obtained from plots of delta-H(super degree) (sub acid)(HX) vs EA[X(sub .)] provide bond energies which correspond to BDE(HX) when EA[X(sub .)] = 0.

The α-C-H bond dissociation energy (BDE) of phenylcyclopropane (1) was experimentally determined using Hess' law. An equilibrium acidity determination of 1 afforded ΔH°acid = 389.1 ± 0.8 kcal mol-1, and isotopic labeling established that the α-position of the three-membered ring is the favored deprotonation site. Interestingly, the structure of the base proved to be a key factor in correctly determining the proper ionization site (i.e., secondary amide ions are needed, and primary ones and OH- lead to incorrect conclusions since they scramble the deuterium label). An experimental measurement of the electron affinity of 1-phenylcyclopropyl radical (EA = 17.5 ± 2.8 kcal mol-1) was combined with the ionization energy of hydrogen (313.6 kcal mol-1) to afford BDE = 93.0 ± 2.9 kcal mol-1. This enabled the effect of the phenyl substituent to be evaluated and compared to other situations where it is attached to an sp³- or sp²-hybridized carbon center. M06-2X, CCSD(T), G4, and W1BD computations were also carried out, and a revised C-H BDE for cyclopropane of 108.9 ± 1.0 kcal mol-1 is recommended. [ABSTRACT FROM AUTHOR]

Bridgehead C-H bond dissociation enthalpies of 105.7 ± 2.0, 102.9 ± 1.7, and 102.4 7plusmn; 1.9 kcal mol-1 for bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane, and adamantane, respectively, were determined in the gas phase by making use of a thermodynamic cycle (i.e., BDE(R-H) = ΔHºacid(H-X) - IE(H) + EA(X)). These results are in good accord with high-level G3 theory calculations and the experimental values along with G3 predictions for bicyclo[1.1.1]pentane, bicyclo[2.2.1]hexane, bicyclo[3.1.1]heptane, and bicyclo[4.2.1]nonane the gas found to correlate with the flexibility of the ring system. Rare examples of alkyl anions in the gas phase are also provided. [ABSTRACT FROM AUTHOR]