Structure of methyl 3-(trimethylammonium)benzoate iodide studied by X-ray diffraction, DFT calculations, NMR and FTIR spectra

The structure of methyl 3-(trimethylammonium)benzoate iodide, 3-(Me)3N+C6H4CO2MeI−, (1a) has been determined by X-ray diffraction, DFT calculations and characterized by FTIR and NMR spectroscopy. The crystals are orthorhombic, space group Pnma and the structure is stabilized by interaction of I anion with the N, O(1) and O(2) atoms. The N⋯I distances vary between 4.541(3) and 7.752(3) Å. The correlation between the atomic distances and the Mulliken atomic charges is linear. Charge on the quaternary nitrogen atom depends on options used for generating electrostatic potential-derived charges. The interpretation of 1H and 13C NMR spectra in DMSO-d6 has been based on 2D experiments and calculated GIAO/B3LYP/6-311G(d,p) magnetic isotropic shielding constants. The FTIR spectrum of the solid compound is consistent with the X-ray results. The probable assignments of the anharmonic experimental vibrational frequencies of the investigated ester (1a) based on the calculated harmonic frequencies are proposed.