Heterocyclic aromatic compounds valence electrons

Quinoline is a base since, as for pyridine, the lone pair of electrons on the nitrogen atom is not utilized in its internal resonance. Although it is an aromatic compound, the valence bond description of quinoline shows two of the neutral contributors, A and C (see Scheme 3.1), to the resonance hybrid as quinonoid in character, whereas in B either the carbo-cycle or the heterocycle must exist in the form of a 1,3-diene. The presence of the pyridine nucleus is reflected by the inclusion of doubly charged canonical forms. 

Generalized valence bond interaction energies were computed for mono/poly-nitrogenous five- and six-membered heterocycles.203 Results that diverged from those obtained by other methods were obtained only for poly-nitrogenous systems such as pyridazine, benzotriazole, and tetrazole, which may confirm Bird s earlier finding123 204 that electron delocalization is not a stand-alone and direct measure of aromaticity for nitrogenous heterocyclic compounds. 

In 1975 the anion of T was observed in a mass spectrometer, indicating a positive valence-state Ea for T. In 1990 the Ea of AGCUT were predicted using substitution, replacement, and conjugation effects [10-14], In order to estimate the Ea of substituted compounds, that of the parent compounds is required. In 1974 I. Nenner and G. J. Schulz estimated the AEa of quinoline (0.36 eV), pyradazine (0.40 eV), pyrimidine (0.00 eV), pyrazine (0.40 eV), and s-triazine (0.45 eV) from electron transmission spectra and half-wave reduction potentials [15]. No adiabatic electron affinities of aromatic nitrogen heterocyclic compounds were measured in the gas phase before 1989 [16]. 

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