Alkyl stabilization energies

Table 3 Radical stabilization energies (in kj/mol) of cyclic alkyl radicals at 0 K according to Eq. 1 ...

Table 8 Selected stabilization energies (5 /kcal mol" ) of alkyl radicals."...

Stone and coworkers determined the /3-silicon effect in w-alkyl- and aryl-substituted carbenium ions20 and vinyl cations21 by measuring in a high-pressure mass spectrometer the thermodynamic data for the association of various alkenes and alkynes with trimethylsilylium ion. From their measured thermodynamic data they calculated, by using equations 13 and 14, the /S-silyl stabilization energies listed in Table 1. 

The gain in stabilization by substituents is compared for radicals and cations in Table 6.8. For radicals the change from methyl to ethyl or even tertiary butyl is not linked to a large gain in stabilization energy. In cations, however, alkyl and alkoxyl substituents have a dramatic effect. Thus, the stabilizing effect of substituents on radical cations is mainly due to the stabilization of the cation and only to a small extent to that of the radical. 

Recent thermochemical determinations suggest that A = 14.21 kcal/mol and B 17.21 kcal/mol (llg). To obtain, for instance, benzylic C-X bond strengths, the stabilization energy calculated from equation 9 is subtracted from C-X bond strengths for corresponding saturated species. Recent studies of alkyl-benzene pyrolysis (117) imply that within current uncertainties in relative bond strengths this formula applies to secondary and... 

For ionization of alkyl halides, the fluorine-containing Lewis acids show exceptional ability, far exceeding those of A1C13 and other conventional Lewis acids. They also show a high tendency to form stable complex anions of MtF + i- or MtF OH- type. Thus, the following values of stabilization energy for formation of complex anions are reported [33] ... 

The polarizability effect index is based on the stabilizing energy Ex caused by the polarizability effect for a substituent X interacting with a point charge q [Cao and Li, 1998]. For alkyl and aliphatic alcohol substituents, the stabilizing energy Ex is defined as ... 

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