Study of Cyclic Quaternary Ammonium Bromides by B3LYP Calculations, NMR and FTIR Spectroscopies

N,N-dioctyl-azepanium, -piperidinium and -pyrrolidinium bromides 1-3, have been obtained and characterized by FTIR and NMR spectroscopy. DFT calculations have also been carried out. The optimized bond lengths, bond angles and torsion angles calculated by B3LYP/6-31G(d,p) approach have been presented. Both FTIR and Raman spectra of 1-3 are consistent with the calculated structures in the gas phase. The screening constants for C-13 and H-1 atoms have been calculated by the GIAO/B3LYP/6-31G(d,p) approach and analyzed. Linear correlations between the experimental H-1 and C-13 chemical shifts and the computed screening constants confirm the optimized geometry.