Effect of monosubstitution on the stability of phenylnitrene: A density functional theory study

Abstract

The effect of the substituent on the stability of phenylnitrenes has impact in their application of the synthesis de aza compounds and novel materials. The energy gaps ΔE_1A1–3A2, ΔE_1A2–3A2 and ΔE_1A1–1A2 for the 3A2, 1A2 and 1A1 states of para-, meta- and ortho-monosubstituted phenylnitrene with a set of electron-withdrawing or electron-donating substituents in the benzene ring were calculated at the DFT (M062X and B3LYP) and MP2 levels of theory and showed that the stability was 3A2>1A2>1A1. The ΔE trends ΔE_1A1–3A2 > ΔE_1A2–3A2 > ΔE_1A1–1A2 and ΔE_1A1–3A2 > ΔE_1A1–1A2 > ΔE_1A2–3A2 obtained for the electron-donating and electron-withdrawing substituents, respectively, indicated that the difference of stability between 3A2, 1A2 and 1A1 decreases as the substituent changes from electron-withdrawing to electron-donating. Electron-withdrawing substituent on para-, meta- and ortho-monosubstituted phenylnitrene causes its closed-shell singlet 1A1 to become less stable than its open-shell singlet 1A2 compared to those of phenylnitrene. The sensitive of the para-monosubstituted phenylnitrene to the effect of the electron-donating and electron-withdrawing substituents follows the trend ΔE_1A1–1A2 > ΔE_1A1–3A2 > ΔE_1A2–3A2. Correlation analysis between the Hammett constant (σ) with the ΔE_1A1–3A2 and ΔE_1A2–3A2 reveals that substituents produce energy changes that are linearly additive, and the resonance effects are more important than inductive effects.