GAS-PHASE CHEMISTRY OF THE NEGATIVE-IONS DERIVED FROM AZOBENZENE AND HYDRAZOBENZENE

The proton affinities of the azobenzene radical anion and the conjugate base of hydrazobenzene have been determined to be 1465 kJ mol-1 and 1514 kJ mol-1, respectively, with the use of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an external ion source. The proton affinities lead in combination with a measured electron affinity of azobenzene (55 kJ mol-1) to a N-H bond dissociation energy (BDE) of 306 kJ mol-1 for hydrazobenzene while the N-H BDE of the PhNHNPh radical is estimated to be 208 kJ mol-1. The difference between the N-H BDE values of 98 kJ mol-1 approximates the pi-bond energy of the nitrogen-nitrogen bond in azobenzene. The reaction of the PhNNBARPh and PhNHNBARPh ions with derivatives of trifluoroacetic acid are characterized. The occurrence of dissociative electron transfer instead of S(N)2 substitution in reactions of the azobenzene radical anion with halogen-substituted methanes is discussed.