Structure Of N-methylacetamide Research Articles

Effect of Temperature and Concentration on the Structure of N-Methylacetamide−Water Complexes: Near-Infrared Spectroscopic Study

Generalized two-dimensional (2D) FT-NIR correlation spectroscopy and chemometric methods have been used to study temperature-dependent spectral changes in pure N-methylacetamide (NMA) and NMA-water mixtures. We also examined the effect of varying water content on the structure of the mixture. It has been found that the extent of self-association of NMA in CCl4 is very high; the association occurs even at concentration of 0.001 M. In the pure liquid NMA, the population of the monomers is negligible and the structure is dominated by the linear associates. An increase in temperature reduces the number of hydrogen bonds, but in contrast to alcohols their strength remains nearly the same. This reflects a difference in the mechanism of thermal breaking of the associates of NMA and alcohols. The present results reveal that the interaction between NMA and water in the NMA-rich region (X(H2O) < 0.1) does not have a significant effect on the intrinsic structure of NMA. The structure of NMA is dominant, and the molecules of water do not form separate clusters but are dispersed and incorporated into the structure of NMA. We did not observe the presence of the free OH groups in the mixture. This led to the suggestion that each molecule of water forms two hydrogen bonds to two different molecules of NMA. An analysis of the asynchronous spectra reveals that most of the peaks observed in the asynchronous spectra, constructed from the temperature-dependent data, simply result from the frequency shift. This assumption is supported by the simulation studies.

Vibrational Spectroscopy of N-Methylacetamide Revisited

Although a lot of work has been performed on the vibrational analysis of N-methylacetamide (NMA), some uncertainties and even contradictions remain, mainly due to the fact that the structure of NMA at room temperature is not stable due to traces of water or due to the fact that the authors only studied the infrared or the Raman spectra. On the basis of the infrared and Raman spectra in the −196 °C to +100 °C temperature range, we have shown that the effects of temperature on the structure and the changes in the strength of the hydrogen bonding within a structure elucidate a lot of the complexity of the solid state vibrational spectra of NMA. Force field calculations on the monomer and multimers (n = 6) and solution spectra of NMA and the N-deuterated compound are used to provide a better understanding of the influence of hydrogen bonding on the typical amide fundamentals. Nine typical so-called “amide bands” have been further characterized.

Study of the structure of N-methylacetamide associates by vibrational spectroscopy

Study of the structure of N-methylacetamide associates by vibrational spectroscopy