Magnitude of bond energies

In a previous discussion4 it was pointed out that there is some arbitrariness in the choice of bond energies, arising from uncertainty in the experimental data, lack of constancy of bond energies from compound to compound, and other causes. Because of differences in the data used and their treatment, the values given in that paper and the present one differ somewhat the difference in no case exceeds 0.1 v.e., however, which is of the order of magnitude of the errors inherent in the data. 

With radicals of the benzyl type, 11 through 18, the dimerization equilibrium depends on the relative magnitudes of the energy gain arising from the C-C bond formation and of the ir-electron energy loss which results from a reduction of the conjugated system. 

Present quantum chemistry is mainly concerned with the calculation of bond energies. Accordingly, for the rest of this chapter we shall concentrate mainly on solvation enthalpies. The latter, being magnitudes composed of a lot of strongly interwoven effects, do not allow a simple separation of bulk and outer-shell influences. 

Aside from NMR, general spectroscopic data have not had great impact on either the bond fixation or the reactivity question. This is probably because the magnitude of the energy necessary to cause either the reaction selectivities or bond fixation is close to the error in these methods. The NMR studies stand out from this generalization. Chemical shift data have been useful in demonstrating that the effects of strained annelations are localized to the C - and tpjo-carbons. Coupling constant... 

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