Vibrational spectrum of nitroethylene

Conclusions On the basis of the infrared and Raman spectra of normal and isotope-substituted nitroethylenes, the authors offer an interpretation of the frequencies of nitro-groups conjugated with a multiple C=C bond.Translated from Izvestiya Akademii Nauk SSR, Seriya Khimicheskaya, No. 8, pp. 1870–1871, August, 1968.We are grateful to E. F. Ponizovtsev and S. S. Bulakov for their help with the experiments.     

Vibrational spectrum and structure of dimethylamino-dichloroarsine

The infrared spectra of solid and gaseous dimethylaminodichloroarsine have been recorded from 4000 to 33 cm⁻¹. The Raman spectra of the liquid and solid phases have also been recorded. A comparison of the Raman spectra of the liquid and solid indicates that there is a change in conformational composition between the two phases. The isomer present at room temperature in the liquid and gas phases is assigned to the trans form. A study of the temperature dependence of the intensities of the Raman spectrum indicates that the trans form is converted to a second isomer which is believed to be the gauche isomer as the temperature is decreased. At −190°C, the Raman intensities indicate that the molecule still exists as a mixture of these two isomers. A vibrational assignment is presented and discussed in detail.     

Vibrational spectroscopic studies of conformation of poly(oxyethylene). II. Conformation–spectrum correlations

Detailed normal-coordinate analysis has been carried out on a large number of conformers of model molecules of poly(oxyethylene); the model molecules treated are CH₃(OCH₂CH₂)_nOCH₃ with n = 2,3, and 6. The systematic treatment provides well-defined correlations between conformation and vibrational spectra of poly(oxyethylene). The vibrations in the region 1050–800 cm^?1, which are associated with the C? O and C? C stretching and CH₂ rocking modes, are highly dependent on the conformation of the polymer chain. On the basis of these correlations, the infrared and Raman spectra of the molten state and of the aqueous solution are interpreted in terms of the conformational states. The analysis indicates that the following conformational fragments are present in these phases: GT-TG (T: trans; G: gauche), TT-TG, GT-GG, TT-TT, and TT-GG for the CH₂? CH₂? O? CH₂? CH₂ group, and TGT and TGG for the O? CH₂? CH₂? O group. Conformational fragments GT-TG′ and GT-G′G′ are also possible in the analogy to GT-TG and GT-GG.     

Vibrational spectrum of glycine molecule

The infrared and Raman spectra of glycine molecule has been studied in spectral region 400-4000 cm(-1) in solid form as well as in water. The vibrational frequencies for the fundamental modes of the glycine in neutral and its zwitterionic form have also been calculated using AM1 semiempirical method as well as ab initio method with minimal basis set. The reliability of the minimal basis set and AM1 method with higher basis sets, for IR spectra of the neutral glycine conformers were examined. We find that the 6-21G basis set calculation yields structural parameters, rotational constant and dipole moment of glycine conformers, which are very similar to those obtained from extended basis set calculation as well as experimental values. IR frequencies for glycine conformer I are also calculated in water using SCRF=PCM model and compared with experimental values. A comparison between calculated frequencies for neutral glycine, and its zwitterionic form with observed IR and Raman bands have been made. The total energies for gas phase glycine and its zwitterionic form along with those of hydrated forms were also calculated. It is found from the calculations that in the gas phase neutral glycine is more stable as compared to its zwitterionic form.     

Vibrational spectrum of crystalline cyclopentanone

Infrared and Raman spectra of liquid and solid cyclopentanone have been studied. Spectroscopic evidence shows that the molecule undergoes a solid state phase transition at 168°K. The crystalline form stable below this temperature is ordered and close-packed; its infrared and Raman spectra have been interpreted assuming that cyclopentanone crystallizes in the C⁵_2h or C¹₁ centrosymmetric space groups.     

Vibrational analysis and solid state conformation of monothiobiuret hydrate

The i.r. assignments for monothiobiuret(Mtb)-hydrate and its deuterated compound have been made from normal coordinate analyses carried out for Mtb and Mtb-d₅ using a chosen molecular model containing a trans-cis —CONHCS— group for Mtb (H₂NCONHCSNH₂). The i.r. spectra of anhydrous Mtb in solid and in solution and of Mtb · H₂O at liquid nitrogen temperature have also been studied.     

Microwave spectrum and conformation of n-propyltrifluorosilane

The conformational properties of gaseous n-propyltrifluorosilane (CH₃CH₂CH₂SiF₃) have been investigated by microwave spectroscopy and high-level quantum chemical calculations. The microwave spectrum was investigated in the 20–62 GHz spectral range at a temperature of −78 °C. The spectra of the ground vibrational state and three vibrationally excited states of one conformer having an antiperiplanar conformation of the C–C–C–Si chain of atoms were assigned. No evidence for the existence of the synclinal (gauche) conformer was seen in the microwave spectrum. It is concluded that the synclinal form is at least 3.5 kJ/mol less stable than the antiperiplanar conformer in the gas phase. Density functional theory calculations have been performed for the system mainly to predict the effects of centrifugal distortion. The G3 quantum chemical method has been used to test the ability of this method to predict the energy difference between the synclinal and antiperiplanar conformers.     

Vibrational spectrum and structure of nitrosothiocarbamylcyanomethanide ion

The IR spectra (400–4000 cm^–1) of the sodium salt of the nonlinear nitrosocontaining acido ligand of a methanide type Na[ONC(CN)C(S)NH₂], as well as of the deutero-derivative compound were studied. The frequencies and the forms of the normal vibrations of NaL (the H-form) and NaL (the D form) were calculated in the harmonic approximation of the valence-force field; a theoretical IR spectrum of compound NaL(H) was obtained from the quantum-chemical calculation. The frequencies observed in the spectrum were assigned from the results of the calculation, the force constants of the bonds were analyzed, and were compared with those for the salt of the oxo anion Na[ONC(CN)C(O)NH₂]. Various Cu²⁺ and Ni²⁺ complexes with a thio ligand were synthesized and the type of coordination of the nonlinear anion was established from the IR spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 312–317. May–June, 1988.     

Vibrational spectrum of the tropylium cation

Russian Chemical Bulletin -     

Microwave spectrum and conformation of isopropyl fluoroformate

The microwave spectrum of isopropyl fluoroformate is characterized by intense a-type R-branch transitions from one conformational species. The rotational constants of the ground state, A₀ = 4967.0(8) MHz, B₀ = 1704.69(2) MHz, C₀ = 1468.86(1) MHz and κ = −0.8651(2) are consistent with a τ₁ (O=COC) = 0°, τ₂(COCH) ˜35° structure. This structure can be viewed as a combination of the two conformational species found in ethyl fluoroformate. Two vibrational satellites having rotational constants A₀ = 4963(5) MHz, B₀ = 1694.11(7) MHz. C₀ = 1471.43(4) MHz and A₀=4998(6) MHz, B₀ = 1705.21(7) MHz, C₀ = 1471.10(4) MHz have been assigned.     

Vibrational spectrum and force field of trimethyl- methoxysilane

The IR and Raman spectra of (CH₃)₃SiOCH₃, (CH₃)₃SiOCD₃, (CD₃)₃SiOCH₃ and (CD₃)₃ SiOCD₃ are presented together with results of normal coordinate calculations. Numerical values of certain force constants and effects of mechanical coupling between Si-O-C bridge vibrations and some of internal vibrations of (CH₃)₃Si and OCH₃ groups are briefly discussed.     

Vibrational spectrum of 3-methyl and 4-methylpyridine

The assignments of the vibrational spectra of the 3-methyl and 4-methylpyridine molecules have been carried out following the SQMFF methodology (scaled quantum mechanical force field). The theoretical frequencies have been obtained by calculating the RHF/3-21G force field, using the scale factors for pyridine and 2-methylpyridine and are correlated in a satisfactory manner with the frequencies recorded in the IR and Raman of these methyl derivatives.     

Vibrational circular dichroism studies of molecular conformation and association of dipeptides

Vibrational circular dichroism (VCD) and infrared (IR) absorption spectra in the NH stretching region have been measured for the dipeptides, R′COAANHR′'(R′ = Me and tertBu; AA = Ala, Leu, Val and Phe; R′' = Me, isoBu and neoPe). Analyses of the VCD and absorption spectra indicated that the VCD bands for the NH stretching are quite sensitive to the state of hydrogen bonding as well as the local conformation of oligopeptides. VCD spectra exhibit a negative VCD band at 3420-3405 cm⁻¹ due to the C₅ conformer with an intramolecularly hydrogen-bonded five-membered ring. The intermolecularly hydrogen-bonded NH stretching vibration exhibits a characteristic negative—positive couplet from the high wavenumber side due to the antiparallel C₅C₅ dimer formation. Hydrogen-bonded oligomers beyond the dimer formed in highly concentrated solutions give rise to an additional negative VCD band on the lower wavenumber side of the hydrogen-bonded absorption band.     

Vibrational spectrum and internal rotation in 2,5-dimethylpyrazine

The infrared and Raman spectra of 2,5-dimethylpyrazine have been recorded and assigned on the basis of a C_2h molecular geometry previously determined by MINDO/3. The potential energy function corresponding to the internal rotation of both methyl groups has been used to solve the Schrödinger equation, and to obtain the energy levels of that motion on the basis of a molecular symmetry G₃₆. The rotation of each substituent is found to be almost independent of the other.