title: C-H bond strengths and acidities in aromatic systems: effects of nitrogen incorporation in mono-, di-, and triazines.
abstract: The negative ion chemistry of five azine molecules has been investigated using the combined experimental techniques of negative ion photoelectron spectroscopy to obtain electron affinities (EA) and tandem flowing afterglow-selected ion tube (FA-SIFT) mass spectrometry to obtain deprotonation enthalpies (Δ(acid)H(298)). The measured Δ(acid)H(298) for the most acidic site of each azine species is combined with the EA of the corresponding radical in a thermochemical cycle to determine the corresponding C-H bond dissociation energy (BDE). The site-specific C-H BDE values of pyridine, 1,2-diazine, 1,3-diazine, 1,4-diazine, and 1,3,5-triazine are 110.4 ± 2.0, 111.3 ± 0.7, 113.4 ± 0.7, 107.5 ± 0.4, and 107.8 ± 0.7 kcal mol(-1), respectively. The application of complementary experimental methods, along with quantum chemical calculations, to a series of nitrogen-substituted azines sheds light on the influence of nitrogen atom substitution on the strength of C-H bonds in six-membered rings.
authors.affiliation: JILA and Department of Chemistry and Biochemistry, University of Colorado, 440 UCB, Boulder, Colorado 80309, USA.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Wren
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Vogelhuber
authors.forename: John M
authors.initials: JM
authors.lastname: Garver
authors.forename: Shuji
authors.initials: S
authors.lastname: Kato
authors.forename: Leonid
authors.initials: L
authors.lastname: Sheps
authors.forename: Veronica M
authors.initials: VM
authors.lastname: Bierbaum
authors.forename: W Carl
authors.initials: WC
authors.lastname: Lineberger