The case of infrared carbonyl stretching intensities of 2-bromocyclohexanone: Conformational and intermolecular interaction insights

• Published in: Chemical physics letters 2010-07, Vol.494 (1), p.26-30
• Main Authors: Coelho, Jakelyne V., Freitas, Matheus P., Ramalho, Teodorico C., Martins, Carina R., Bitencourt, Michelle, Cormanich, Rodrigo A., Tormena, Cláudio F., Rittner, Roberto
• Format: Article
• Language: English
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2010.05.097

The infrared spectrum of 2-bromocyclohexanone in the vapor phase and theoretical calculations show that this important model compound experiences self-association and the molar absorptivities of conformers are different. [Display omitted] ► The first infrared spectrum of 2-bromocyclohexanone in the vapor phase. ► The IR behavior is different from expected theoretically for the isolated state. ► 2-Bromocyclohexanones experiences self-association even in the vapor phase. ► The difference of C O molar absorptivities between conformers is significant. The infrared spectrum of 2-bromocyclohexanone in the vapor phase was obtained for the first time, and the ν C O intensity for the more polar equatorial conformer was surprisingly found to be higher than for the axial form, suggesting its larger population, opposite to calculations. Theoretical data for dimeric models showed that attractive intermolecular interactions in the equatorial– equatorial dimer are dominant, but this is not enough to explain the spectroscopic behavior, since the axial– axial dimer remains more stable. The higher C O molar absorptivity in the equatorial form is therefore invoked to explain its more intense C O band, as confirmed by charge calculations.