- Gas-Phase Chemistry of the Negative Ions Derived from Azo- and Hydrazobenzene
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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 PhNHN.Ph radical is estimated to be 208 kJ mol-1.The difference between the N-H BDE values of 98 kJ mol-1 approximates the ?-bond energy of the nitrogen-nitrogen bond in azobenzene.The reaction of the PhN.N-Ph and PhNHN-Ph ions with derivatives of trifluoroacetic acid are characterized.The occurrence of dissociative electron transfer instead of SN2 substitution in reactions of the azobenzene radical anion with halogen-substituted methanes is discussed.
- Ingemann, Steen,Fokkens, Roel H.,Nibbering, Nico M. M.
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p. 607 - 612
(2007/10/02)
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- Gas-Phase Generation of Phenylnitrene Anion Radical - Proton Affinity and ΔHf0 of PhN-. and Its Clustering with ROH Molecules
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Phenylnitrene anion radical (PhN-.) was prepared in a flowing afterglow apparatus by dissociative electron attachement of phenyl azide (PhN3).PhN-. undergoes a very slow reaction with PhN3, producing PhN4Ph-. and PhN2Ph-. in a ratio of 4:1.The proton affinity pf PhN-. was bracketed from kinetic studies with various potential proton donors, PA(PhN-.) = 372 +/- 2 kcal mol-1, from which ΔHf0(PhN-.) = 60 +/- 2 kcal mol -1 was calculated.With alcohols which are too weakly acidic to directly protonate PhN-. , a sequence of bimolecular reactions is observed involving ROH; PhN-. -> PhN-.(HOR) -> PhNH. + RO-(HOR) -> RO-(HOR)x.Although the first step of the sequence is slow, the second step, a cluster-to-cluster transformation, is fast.The related reaction sequence of PhN-. reacting with HOH involves the ions PhN-. -> PhN-.(HOH) -> PhN-.(HOH)2 -> PhNH. + HO-(HOH)2 -> HO-(HOH)x with the third reaction as the fast step.The relationship of these sequential processes to acidities and basicities found in solution is discussed.Of the five observed reaction channels for PhN-. with CH3CN, the major channel yields the adduct m/z 132 and a minor channel produces the M-1 species, m/z 131.Additions by PhN-. to Cα or N or CH3CN are considered to account for these product anions.The reaction of PhN-. with (CH3)3CCN also yields its adduct.
- McDonald, Richard N.,Chowdhury, A. Kasem,Setser, D. W.
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p. 6599 - 6603
(2007/10/02)
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