Determination of N—NO Bond Dissociation Energies of N-Nitrosoindoles and Their Radical Anions in Acetonitrile

The heterolytic and homolytic N-NO bond dissociation energies of seven N-nitrosoindole derivatives were evaluated by using titration calorimetry and relative thermodynamic cycles.The energetic scales of the heterolytic and homolytic N-NO bond dissociation energies of N-nitrosoindoles cover the ranges from 206.1 to 246.2 kJ/mol and from 119.1 to 124.6 kJ/mol,respectively,which indicates that N-nitrosoindoles are much easier to release a NO radical(NO\5) rather than a NO cation(NO+).The estimation of the heterolytic and homolytic(N-NO)-\5 bond dissociation energies of the N-nitrosoindoles radical anions gives the energetic ranges from 25.5 to 33.4 kJ/mol and from 5.0 to 40.5 kJ/mol for the(N-NO)-\5 bond homolysis and heterolysis,respectively,which means that N-nitrosoindole radical anions are unstable at room temperature.