Structures of pyrido[1,2a]pyrazinium and pyrido[1,2c][1,4]oxazinium bromides studied by 1H, 13C and 15N NMR, FTIR, X-ray and DFT methods

2-R-Pyridines (RaCN, CHaNOH and COMe) with phenacyl bromide gave the corresponding quaternary bicyclic ring system containing one ring junction nitrogen and one extra nitrogen or oxygen atom (1–3). Their structures were confirmed by 1H, 13C and 15NMR spectra in DMSO-d6 solution using 2D NMR techniques (COSY, NEOSY, HETCOR and HMBC). The structure of 1-oxo-3-phenylpyrido[ 1,2a]pyrazinium bromide monohydrate, 1, was unambiguously confirmed by X-ray crystallography. The crystals of 1 are monoclinic, space group P21/n, with aZ7.730(2) A ° , bZ14.094(3) A ° , cZ12.553(3) A ° , bZ106.18(3)8, VZ1311.3(5) A ° 3 and ZZ4 (at 110 K). The isolated entities of 1–3 were analyzed by the B3LYP/6-31G(d,p) level of theory in order to get information on the electrostatic interaction between the oppositely charged groups. q 2005 Elsevier B.V. All rights reserved