title: The azine bridge as a conjugation stopper: an NMR spectroscopic study of electron delocalization in acetophenone azines.
abstract: Dipole parallel-alignment of organic molecular crystals of azines has been achieved with a design that was based on the hypothesis that the azine bridge is a conjugation stopper. This hypothesis has now been tested in detail, and (1)H and (13)C NMR spectroscopic data of symmetric and asymmetric acetophenone azines are presented in support of this design concept. Previous structural, ab initio, and electrochemical studies have shown that the azine bridge largely inhibits through-conjugation in molecules with the general structure DPhC(Me) [double bond] N [bond] N [double bond] C(Me)PhA, where D is a donor group and A is an acceptor group. NMR spectroscopy is an excellent tool to probe the degree of conjugation through the azine bridge. The NMR results reported here for nine symmetrical and 18 asymmetrical azines show in a compelling fashion that the hypothesis holds. Varying the donor group does not change the chemical shifts of the aromatic hydrogen and carbon atoms on the acceptor-substituted phenyl ring. Likewise, varying the acceptor group does not change the chemical shifts of the atoms in the donor-substituted phenyl ring.
authors.affiliation: Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Lewis
authors.forename: Rainer
authors.initials: R
authors.lastname: Glaser
mesh_terms: D000098:Acetophenones / Q000737:chemistry; D001391:Azo Compounds / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D004563:Electrochemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure
chemical_list: D000098:Acetophenones; D001391:Azo Compounds; D001555:Benzene Derivatives