The objective of this article is investigation of the normal modes of vibrations of molecules containing amide or urethane groups. Comparison between methyl-N-methylcarbamate (MMC) and N-methylacetamide (NMA) has been discussed. Density functional (DFT) calculations at B3LYP/6-31G(d) level have been employed to investigate the normal modes of MMC and several simple urethanes. This level was used as a compromise between accuracy and applicability to larger systems. The obtained results are in good agreement with experimental spectra. Finally, we have confirmed that the use of “amide terminology” is correct when addressing urethane molecules.

Restricted Hartree–Fock and density function calculations (B3LYP), using 6-311++G(d,p), have been used to investigate the far infrared spectra of aromatic urethanes, synthesized on the basis of 2,4-and 2,6-toluene diisocyanate (2,4-TDI, 2,6-TDI), and the spectrum of ethylphenylurethane. It is shown, that the region of frequencies of 100–200cm−1 is associated primarily with torsional vibrations of methyl groups. For almost all studied urethanes, the bands are observed in the region 385–340cm−1, which is associated with in plane deformations of angles CCNC, COC and CNC of the urethane groups according to the calculations. The bands, observed at 300–320 and 260–280cm−1, are assigned to in plane and out of plane deformations of the urethane skeleton, which are mixed with vibrations of methyl group connected to the benzene ring.

Based on the Fourier transform IR spectroscopy together with the published NMR and X-ray data, it was shown that cyclic co-operative intramolecular hydrogen bond in calix[n]arene (n = 4, 6, 8) molecules is mainly responsible for their conformational state irrespective of the presence or absence of bulky substituents at the upper rim of the molecules. In accordance with the size of a macrocycle (n = 4, 6, 8), the stable conformation, secured by such a hydrogen bond, constitutes a cone, a pinched cone, and a pleated loop, respectively. The new, potentially competing system of hydrogen bonds in calix[6]arenes with 3-carboxymethyl-1-adamantyl substituents does not affect the conformational state of the macrocycle and its H-bonding. Six carboxy groups at the upper rim form in pairs three cyclic dimers, which does not disturb the hydrogen bonds of the hydroxy groups and the conformation of the macrocycle. In addition, the cavity of the molecule is considerably enlarged. The removal or rearrangement of the guest molecules in the solid calixarene by heating up to 180 °C only slightly affects the conformational state of macrocycles bearing bulky substituents, whereas in calixarenes devoid of such substituents, the similar procedure leads to somewhat of a distortion of the macrocycles (judging from the IR spectral indications of hydrogen bonding).

The equilibrium geometries and IR frequencies of methyl-N-methylurethane (MU) and methyl-N-(α)-naphthylurethane (MNU) were calculated by various quantum-mechanical methods: ab initio using the HF/6-31G* basis set, AM1 and PM3 semiempirical methods, and density functional theory (DFT) at the PBE/TZ2P level using MOPAC 6.0, GAMESS, and PRIRODA software. The experimental and calculated frequencies in the range 4000-60 cm-1 are compared and analyzed. The comparison was performed based on well-studied characteristic urethane bands: Amide A, Amide I, Amide II, Amide III, Amide IV, and Amide V. The calculated frequencies of MU and MNU were compared with the experimental frequencies; the best agreement was obtained by using the DFT method. Other methods require scaling factors. For ab initio calculations, only one linear multiplier, a = 0.889, may be introduced. To obtain agreement with experiment in AM1 and PM3 methods, one must take different scaling factors for different spectral regions. All calculations confirm the previous conclusions that urethane fragment vibrations are characteristic and weakly interacting with methyl group and naphthyl ring vibrations.

A comparative analysis of the IR spectra in the region of 3000–400 cm−1 of four urethanes (methyl-(N-(1-naphthyl) carbamate, ethyl-N-(1-naphthyl) carbamate, dimethyl-N,N′-(1,5-naphthylene) dicarbamate, and diethyl-N,N′-(1,5-naphthylene) dicarbamate) with known molecular and crystal structures was carried out. The assignment of the bands related to the vibrations of the urethane and naphthyl fragments was refined on the basis of the study of the crystalline samples, melts, solutions, and deuterated analogs. The effect of the degree of conjugation of the urethane group with the naphthalene ring on the Amide II vibration frequency in the crystals was shown. It was suggested that the stretching vibrations of the C(Ar)−N bond in naphthylurethanes (unlike aliphatic derivatives) make a considerable contribution to the Amide II vibration, while the planar deformation vibration of the N−H bond was proved to be more significant for Amide III than for Amide II. In addition, strong nonspecific intermolecular interactions in the crystal can weaken valent bonds.

Products of the chemical degradation of cast-molded polyurethanes based on aromatic diisocyanate and various oligoesters were studied by IR spectroscopy. The degradation proceeds according to the mechanism of transesterification of the urethane and ester groups. The possibility of obtaining secondary polyurethanes with good mechanical properties by using the degradation products is demonstrated.

Amorphous oligobutadiene urethanes with various distribution of urethane fragments were studied by SAXS and IR spectroscopy. Oligomers with a terminal urethane fragment were found to show a higher degree of association than those with an urethane fragment between the two polybutadiene chains. They differed in the degree of hydrogen bonding, the hydrogen bond energy in the former case being twice as large as in the latter one. Terminal urethane fragments displayed a higher tendency to association

IR spectroscopy, NMR and dielectric relaxation have been employed to study the features of structuring and molecular mobility of polymeric systems based on epoxycyclocarbonate composites with an amine curing agent. Shortening of the induction period of the reaction was observed with increase in the rate of rise in the dynamic rigidity of the system as compared with the usual epoxyamine composite. The hydroxyurethane fragments reduce the molecular mobility of the polymer in the glassy state. Rise in the strain-strength characteristics of the epoxypolyurethanes was observed on combining in the structure of the polymer rigid and flexible blocks.

Crystallization of reactive and model urethane oligomeric systems based on polytetramethyleneoxide, and the character of hydrogen bonds formed in this process, were studied by vibrational spectroscopy, X-ray diffraction and DTA. Crystallization kinetics was described by the Avrami equation, and conclusions concerning nucleation and growth of crystalline structures could be reached.