Bond Dissociation Energies and Kinetic Methods

Throughout this work, we will refer to the heats of reactions and the methods used for the kinetic determinations. We have collected background information for discussion in this section. A list of important bond dissociation energies is followed by brief descriptions of the more important kinetic methods used for determining radical reaction rate constants discussed in this review. 

Knowledge of homolytic bond dissociation energies (BDEs) is critically important for understanding radical chemistry. The bond energies of organic compounds have been reviewed extensively, but we will use recommended R-H BDE values for organic compounds given in a recent excellent 

Bond Dissociation Energies (BDEs) in kcal/mola 

The photoacoustic calorimetry technique employs photolysis by laser pulses of a mixture containing di-im-butyl peroxide, an appropriate metal hydride, and solvent. Photolysis of the peroxide gives i-BuO radicals that abstract a hydrogen atom from the hydride, and the measured photoacoustic signal is proportional to the overall reaction enthalpy. After calibration, 

Rate constants can be determined directly or by indirect techniques. The latter approach involves competition between the reaction with an unknown rate constant and another reaction (the basis reaction) with a known rate constant. Indirect methods can be highly precise, but at some point the kinetics must be placed on an absolute scale by comparison to directly measured rate constants. Therefore, indirect methods incorporate the absolute errors of the calibrated basis reaction as well as the random errors of the competition study and those of any preceding competition studies used in calibration of the basis reaction. 

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