Experimental and Computational Bridgehead C–H Bond Dissociation Enthalpies

Bridgehead C–H bond dissociation enthalpies of 105.7 ± 2.0, 102.9 ± 1.7, and 102.4 ± 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) = ΔH°_acid(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[2.1.1]­hexane, bicyclo[3.1.1]­heptane, and bicyclo[4.2.1]­nonane were found to correlate with the flexibility of the ring system. Rare examples of alkyl anions in the gas phase are also provided.