BDEs

Bond dissociation energy (BDE) is the minimum energy required to break a chemical bond homolytically in a molecule, producing two radicals. It is typically expressed per mole of bonds (kJ/mol or kcal/mol). For example, the BDE of a C–H bond is the energy needed to convert RH into R• and H•. The BDE depends on the specific bond and the surrounding molecular environment; substituents, resonance, and hybridization can raise or lower the energy required. Higher-order bonds (double, triple) generally have higher BDEs than single bonds, and bonds near electronegative atoms can exhibit different values.

In practice, BDEs are measured for isolated molecules in the gas phase, or estimated from thermochemical data. Environmental factors such as solvent, temperature, and phase can alter the effective bond strength. Units are kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

Determination can be experimental or computational. Experimental methods include calorimetry and spectroscopic data combined via thermochemical cycles (Hess’s law) to derive bond energies from standard enthalpies of formation. Computational approaches use quantum chemistry methods (for example, DFT or high-level ab initio calculations) to estimate BDEs and related properties.

Applications of BDE data span reaction mechanism analysis, prediction of radical formation and reactivity, assessment of radical stability, and modeling in combustion and polymerization. They also serve as benchmarks for the evaluation and development of computational methods and can aid in synthetic planning and materials design.