A Theoretical Study of the Relationship between the Electrophilicity ω Index and Hammett Constant σ(p) in [3+2] Cycloaddition Reactions of Aryl Azide/Alkyne Derivatives

The relationship between the electrophilicity ω index and the Hammett constant σ(p) has been studied for the [2+3] cycloaddition reactions of a series of para-substituted phenyl azides towards para-substituted phenyl alkynes. The electrophilicity ω index—a reactivity density functional theory (DFT) descriptor evaluated at the ground state of the molecules—shows a good linear relationship with the Hammett substituent constants σ(p). The theoretical scale of reactivity correctly explains the electrophilic activation/deactivation effects promoted by electron-withdrawing and electron-releasing substituents in both azide and alkyne components.