NIR vibrational overtone spectra of toluidines-evidence for steric and electronic effects in o-toluidine.

The near infrared vibrational overtone absorption spectra of liquid phase toluidines are reported. The analysis of the observed CH and NH local mode mechanical frequency values shows that there exists steric and electronic interaction between the amino and methyl groups in o-toluidine. This observation supports the conclusions drawn from structural studies of toluidines by resonance two-photon ionization (R2PI) spectroscopy, ab initio calculations and laser induced fluorescence studies reported earlier.

CH overtone spectrum of nitromethane: a C3V coupled oscillator analysis using local mode parameters.

The near infrared overtone absorption spectrum of liquid phase nitromethane in the spectral region deltaV = 2-5 is reported. The observed spectrum is analysed using local mode model. It is shown that the observed CH local mode overtones and local-local combinations are well predicted by a C(3V) coupled oscillator Hamiltonian.

NIR vibrational overtone spectra of N-methylaniline, N,N-dimethylaniline and N,N-diethylaniline--a conformational structural analysis using local mode model.

In aniline, the lone pair electrons on the nitrogen atom in the amino group interact with the pi electrons of the ring and the mechanical frequency of the ring CH oscillator shows a red shift from that of benzene. This happens because of the parallel orientation of the pi electrons in the two molecules. This effect is observed in N-methylaniline also. But in N,N-dimethylaniline, the addition of two alkyl group to the amino group changes the parallel orientation of pi electrons of the nitrogen. This changes the electron donating nature of the amino substituent and as a result, a blue shift is observed in the mechanical frequency of the ring CH oscillator from that of benzene. The same effect is observed in the ring CH oscillator frequency of N,N-diethylaniline also.