Dependence of amide vibrations on hydrogen bonding.

摘要: The effect of hydrogen bonding on the amide group vibrational spectra has traditionally been rationalized by invoking a resonance model where impacts functional stabilizing its [(-)O-C=NH (+)] structure over [O=C-NH] structure. However, Triggs and Valentini's UV-Raman study solvation effects epsilon-caprolactum, N, N-dimethylacetamide (DMA), N-methylacetamide (NMA) ( Triggs, N. E.; Valentini, J. Phys. Chem. 1992, 96, 6922-6931) casts doubt validity this demonstrating that, contrary to prediction, carbonyl does not impact AmII' frequency DMA. In study, we utilize density theory (DFT) calculations examine C=O N-H groups NMA, which is typically used as simple peptide bond. Our indicate expected, dependence AmI vibration predominantly derives from group, whereas AmII primarily bonding. contrast, conformation-sensitive AmIII band equally both thus, responsive at or site. work shows that clear understanding normal mode composition vibrations crucial for an accurate interpretation frequencies.