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 (RCN, CHNOH 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-phenyl-pyrido[1,2a]pyrazinium bromide monohydrate, 1, was unambiguously confirmed by X-ray crystallography. The crystals of 1 are monoclinic, space group P21/n, with a=7.730(2) Å, b=14.094(3) Å, c=12.553(3) Å, β=106.18(3)°, V=1311.3(5) Å3 and Z=4 (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.