Vibrational analysis of C-H stretching overtones in pyridine and 2,6-lutidine

Year: 1991

Authors: Bini R., Foggi P., Della Valle R.G.

Autors Affiliation: LENS (European Laboratory for Non-Linear Spectroscopy), Largo E. Fermi 2, I-50125 Firenze, Italy; Dipartimento di Chimica, Università di Firenze, Via Gino Capponi 9, I-50121 Firenze, Italy; Dipartimento di Chimica Fisica, Università di Venezia, Calle Larga S. Marta, Dorsoduro 2137, 30123 Venezia, Italy

Abstract: Aryl and methyl C-H stretchings of pyridine and 2,6-lutidine in the liquid phase have been studied in the region of the fundamentals and of the overtones up to the fifth. Standard spectrometers were used to investigate IR and near-IR regions. Thermal lensing laser spectroscopy was used in the visible region. ?n = 1, 2 spectra show a complex pattern that becomes simpler on going to higher ?n values. In this case, the interpretation of the spectra can be made by using the local-mode approach. Stretching frequencies are mainly perturbed by the local environment of bonds, and then new details on molecular structures can be obtained. The observation of the double bands in high-overtone spectra of pyridine is due to differences between properties of the C-H bonds in the 2,6- and 3,4,5-positions. The lower frequency structures in 2,6-lutidine are attributed to conformationally nonequivalent C-H bonds of the methyl groups. Nonnegligible interactions between methyl C-H bonds and the nitrogen atom are responsible for a smaller anharmonicity of the in-plane C-H stretching.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY

Volume: 95 (8)      Pages from: 3027  to: 3031

KeyWords: Local mode picture; Morse oscillator; Spectra
DOI: 10.1021/j100161a017

Citations: 15
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