Assessment of Nucleophilicity and Electrophilicity of Radicals, and of Polar and Enthalpy Effects on Radical Addition Reactions1

Abstract

Principal component analysis (PCA) was performed on experimental rate constant and theoretical barrier height data of radical addition reactions involving various carbon- and sulfur-centered radicals and vinyl-type alkenes. Altogether six data sets were analyzed. In three cases the reactivity data were completed by certain descriptors, i.e., the electron affinity (EA) and negative ionization potential (−IP) of alkenes, as well as the exothermicity (−ΔHr) of reactions. It was found that in each case the first two principal components account for more than 93% of the total variance in the data. The scores of the first principal component correlate with EA and (−ΔHr), whereas those of the second principal component with (−IP). It is concluded that PCA is able to decompose both experimental and theoretical reactivity data into nucleophilic and electrophilic components, as well as into polar and enthalpy terms. In the plots of component loadings the radicals form significant groups depending on their character...