X-ray, MP2 and DFT studies of the structure, vibrational and NMR spectra of homarine

Homarine (1-methyl-2-carboxy-pyridine), HOM, has been characterized by single crystal X-ray diffraction, MP2 and B3LYP calculations, FTIR, Raman, 1H and 13C NMR spectra. The crystals of HOM at room temperature are monoclinic, space group P21/c, with a = 7.095(3), b = 7.648(2), c = 12.059(4) Å, β = 91.55(3)°, V = 654.0(4) Å3, and Z = 4. The calculated bond lengths and bond angles at MP2 and B3LYP level of theory with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets are in good agreement with the X-ray data. The difference between calculated and X-ray values of N(1)···O(1) distances and N(1)–C(2)–C(8)–O(1) dihedral angle can be explain by electrostatic interactions between the positively charged nitrogen atom and the negatively charged carboxylate group. The tentative assignments for the experimental FTIR solid state spectrum has been made on the basis of MP2 and B3LYP calculated frequencies. Correlations between the experimental 1H and 13C NMR chemical shifts for HOM and GIAO calculated magnetic isotropic shielding tensors (σ), δexp = a + b σcal, are reported.