Aromatic C-nitroso compounds. Mechanism and kinetics of the hindered internal rotation of dimeric o-nitrosotoluene

Abstract

Using complete n.m.r. band shape analysis, the mechanism and kinetics of hindered rotation in dimeric o-nitrosotoluene (o,o′-azodioxytoluene) was studied. Theoretical fits to experimental spectra were obtained over a temperature range from –60 to +5 °C. Activation parameters for rotation around the Ar–N bond are ΔH^‡ 48.5 ± 2.1 kJ mol^–1 and ΔS^‡ 16 ± 13 J mol^–1 K^–1. The thermodynamic parameters are ΔH° 2.1 ± 0.3 kJ mol^–1 and ΔS° 2.9 ± 0.4 J mol^–1 K^–1. For cis⇄trans isomerization the values are ΔH° 10.4 ± 0.6 kJ mol^–1 and ΔS° 34.3 ± 2.6 J mol^–1 K^–1.