Pyrido pyrazine spectra

Nucleophilic attack of pyrido[2,3-6]pyrazine (3-deazapteridine) by the KNH2-NH3 system occurs at position 3 and leads to the formation of adduct 65, which has been characterized by its 13C-NMR spectrum.118 Large upheld shifts are observed at C-3, which experiences hybridization change, and at C-7, where much of the electronic charge is accommodated by delocalization (resonance structure 65a). Analogous spectral changes are observed in the reaction with 2-tert-butyl-6-chIoropyrido[2,3-6]pyrazine, yielding adduct 66.119... 

Our understanding of the physicochemical properties of pyrazines has deepened. The internal rotation and IR spectrum of 2,5-pyrazinedicarboxamide were studied by quantum chemical calculations <05TC73>, and ab initio MO calculations at the MP2/6-3r G( ) level were used to explain the electronic and vibrational properties of complexes of pyrazine and HX linear acids <05JMS2822>. MM and MO calculations were used to investigate the conformational and electronic properties of odor-active pyrazines <05JMS169>, and NMR, IR, X-ray, and DFT methods were used to examine the structures of pyrido[l,2-a]pyrazinium bromide <05JMS7>. 

The Pariser-Parr-Pople method, self-consistent molecular orbital calculations, and the Huckel approach have been applied to the theoretical calculation of transition energies and intensities in the ultraviolet spectra of pyrido[2,3-ft]pyrazine and other azanaphthalenes. Good agreement with experimental data was obtained. The infrared spectra of the parent heterocycle" and its 8-hydroxy derivative have been discussed the 0X0 form is preferred to the hydroxy form both in chloroform solution and in the solid state. As with other a-hydroxyazines, the oxo form is also favored in the 2-, 3-, and 6-hydroxy compounds. Ultraviolet spectra have been measured for the parent heterocycle and various substituted compounds. The spectrum of the parent is substantially similar to other azanaphthalenes. In ethanol the principal bands are at ca. 260,300, and 350 nm. Both the infrared and ultraviolet spectra of about 60 derivatives of the ring system have been assembled. ... 

Molecular orbital calculations have been performed on pyrido[3,4-fojpyrazine using several approaches. Along with pyrido[2,3- )]pyrazine and other azanaphthalenes, these calculations provide good estimates of the transition energies and intensities of the ultraviolet spectrum of the parent heterocycle. The infrared spectra of the parent and other azanaphthalenes have been determined and discussed. Infrared data for several a- and y-hydroxy compounds confirm their existence, in solution and in the solid state, as oxo compounds. The visible and ultraviolet spectrum of the parent has been analyzed. In 95% ethanol the principal peaks are at 232 and 309 nm. The spectrum is substantially the same as that of quinoxaline, and analogous derivatives of the two heterocycles also possess similar spectra. Comparative ultraviolet data have been used to differentiate between amino derivatives of pyrido[3,4-b]pyrazine and pyrido[2,3-fc]pyrazine and between isomeric dihydro and tetrahydro derivatives of the [3,4-b]system. PMR data are available for certain... 

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