Structure and conformation of 2,3-diethoxycarbonyl-1-methylpyridinium iodide studied by NMR, FTIR, Raman, X-ray diffraction and DFT methods.

Abstract Computational and spectroscopic properties of 2,3-diethoxycarbonyl-1-methylpyridinium iodide, 1, were studied. The crystal structure of 1 was analyzed by X-ray diffraction. Molecular geometry of title compound has been calculated using the density functional theory (DFT) at B3LYP/6–311G(d,p) level of theory and was compared with the experimental data. Iodide anion interacts electrostatically with the positively charged pyridinium nitrogen atom and via weak C H⋯I − hydrogen bonds. In crystals the N-methyl and ethoxycarbonyl groups are disordered in two orientations. The structures of 2 (in vacuum), 3 (in CHCl 3 ) and 4 (in DMSO) optimized by the B3LYP/6-311G(d,p) approach are different than that in crystal 1 . The experimental 13 C and 1 H chemical shifts ( δ exp ) of the investigated ester in CDCl 3 and DMSO-d 6 correlate linearly with GIAO/B3LYP/6-311G(d,p) magnetic isotropic shielding constants calculated according to the screening solvation model (COSMO), δ exp  =  a  +  b σ calc . The FTIR and Raman spectra of the solid compound are consisted with the X-ray structure.