Spectroscopic electronegativities of alkyl groups. A method for estimating ionization potentials of di- and triradicals (original) (raw)

A set of alkyl group parameters that are transferable and additive has been derived from the ionization potentials of the corresponding radicals. These parameters, which are related to spectroscopic electronegativities, have been correlated with 13C NMR data of (a) alkyl halides, (b) aliphatic hydrocarbons, (c) aromatic hydrocarbons, (d) p-alkyl-substituted acetophenones, (e) olefinic compounds, (f) secondary alcohols, (g) aldehydes and ketones, and (h) 2,6-alkyl-substituted p-benzoquinones. Sequences of 13C chemical shift data of monohalogen derivatives of acyclic, monocyclic, and bicyclic hydrocarbons are shown to be interrelated, a fact that permits the estimation of electronegativities of di-and trivalent alkyl substituents and ionization potentials of di-and triradicals. For example, the ionization potential of the triradical l l b derived by 'homolytically removing" the CX fragment from 1-haloadamantanes was estimated as 30.7 eV, from the fluoride, 29.3 eV, from the chloride, 29.2 eV, from the bromide, and 28.98 eV from the iodide, a range of 1.72 eV. In general, the estimated ionization potentials range between 0.23 and 1.72 eV for triradicals and 1.08 and 5.14 eV for diradicals. Correlations are also reported between sequences of 13C chemical shift data and the corresponding thermochemical data, as a corollary of the correlations between spectroscopic electronegativities and 13C chemical shift data.