Ionized Benzonitrile and Its Distonic Isomers in the Gas Phase

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2001-09, Vol.105 (37), p.8579-8587
• Main Authors: Flammang, Robert, Barbieux-Flammang, Monique, Gualano, Emmanuel, Gerbaux, Pascal, Le, Hung Thanh, Nguyen, Minh Tho, Turecek, Frantisek, Vivekananda, Shetty
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp011702t

The dehydrobenzonitrilium distonic radical cations a − c, isomers of benzonitrile radical cation d, were prepared by collisional dehalogenation of protonated halogenobenzonitriles and characterized by tandem mass spectrometry (MS/MS/MS experiments and ion−molecule reactions) making use of a hybrid mass spectrometer of sector−quadrupole−sector configuration. These experimental results were further supported by density functional theory calculations at the B3LYP/6-311++G(3df,2p) level, indicating that although the distonic ions are less stable than ion d by ca. 45−50 kJ mol-1, they are protected against isomerization by relatively large energy barriers. Relative energies of benzonitrile and its isomers as well as their proton affinities and ionization energies were also evaluated. N-protonation in benzonitrile is about 120 kJ mol-1 more exothermic than ring protonation.