The sequence of C-H bond dissociation energies from ethane to C 2 provides a more interesting bond energy analysis (Figure ). The C-H bond dissociation energies vary by almost 100 kcal/mol (from 34.25 kcal/mol to 131.44 kcal/mol), but the C-H bond energies are almost constant (from -102.42 kcal/mol to -106.81 kcal/mol). The principal variation in bond orders and thus bond energies resides in the C∼C bonds. The large increase in C∼C bond energy (and resulting small C-H BDE) when a new π-bond forms is hardly a revelation, but it is not generally appreciated that the large C-H BDE of acetylene is a consequence of the much weaker C≡C bond in ethynyl radical, rather than an especially strong C-H bond in acetylene.