Exploring the reactivity of benzotriazole derivatives: Mayr's approach and density functional theory analysis

Abstract

σ-complexation reactions of 2-N-(4′-X-pheny1)-4,6-dinitrobenzotriazole 1-oxides 1a (X = CH3) and 1e (X = CF3) with a series of C-nucleophiles, as reference, have been investigated kinetically in aqueous solution at 20 °C. The reactions are second-order and exhibit electrophilicity parameter E = -10.25 for 1a and E = -11.66 for 1e. Comparison with other derivative benzotriazoles 1a, 1c, 1d, and 1f–i reported in preceding papers is discussed, and it is shown that the E vs. pKa plot is nonlinear. In this context, geometries optimization of electrophiles 1a–i were performed at density functional theory (DFT) with the B3LYP hybrid functional and the 6–31 g(d,p) and 6–31 + g(d,p) basis sets, in acetonitrile, using the Gaussian 09 package, in order to clarify the negative deviations observed for benzotriazoles 1h and 1i. Thus, the origin of the nonlinear E vs. pKa plot was interpreted in terms of strong steric compression of the adjacent ortho-nitro and N-oxide functions. In addition, Parr's electrophilicity indices ω for these series of benzotriazoles 1a–i were calculated from the electronic chemical potential μ and the chemical hardness η and compared to experimental electrophilicity parameters E. More importantly, it has been shown that such theoretical and experimental electrophilicity scales are linearly and directly related to the correlation parameters of r2 > 0.97.