Vibrational spectra and rotational isomerism of fluoroacetone

Infrared spectra have been redetermined for fluoroacetone in the vapor, liquid, and solid states, and Raman spectra have been obtained for the liquid. There are two rotational isomers present in the liquid, but only the more polar form is present in the crystalline solid and only the less polar form is present in the vapor. Vibrational assignments were made for the two rotamers with the aid of normal coordinate calculations that utilized a twenty-five parameter valence force field.     

Vibrational spectra and rotational isomerism of triallyl amine

The infrared spectra of triallyl amine in the vapour and liquid phases (as solutions in CS₂, CCl₄, CH₃Cl and CH₃CN), and in the solid state at low temperature were measured from 250 to 4000 cm⁻¹. The Raman spectrum of the liquid was recorded and qualitative depolarization measurements were made. It is shown that in the liquid and vapour phases the molecule exists as a mixture of at least two rotational isomers, while in the crystalline phase it assumes a single configuration having point-group symmetry C₃. A vibrational assignment for the observed bands in the infrared and Raman spectra is proposed on the basis of the C₃ point group symmetry for the more stable form of the molecule.     

Vibrational spectra and rotational isomerism of 1,2-dimethyldisilane

The i.r. and Raman spectra of 1,2-dimethyldisilane and its Si-perdeuterated species have been measured for the liquid and solid states. Existence of rotational isomers about the SiSi bond was shown on the basis of the spectral examination and the normal coordinate treatment. The fundamental vibrations were assigned for the two possible rotational isomers.     

Vibrational spectra and rotational isomerism of 2,2-difluoropropyl chloride

Infrared spectra were obtained for 2,2-difluoropropyl chloride in the neat liquid, vapor, and solid states, and Raman spectra were obtained for the liquid. This compound exists as a mixture of trans and gauche rotamers in the vapor and liquid states, but only the trans form is present in the solid. Vibrational assignments were made for the two rotamers with the aid of zero-order normal coordinate calculations using force constants transferred from 2,2-difluoropropane and 1,1,1-trifluoroethyl chloride.     

Infrared spectra and rotational isomerism of ethyl fluoroformate and ethyl propiolate

The infrared absorption spectra of ethyl fluoroformate and ethyl propiolate have been examined in the vapour, solution and solid states. For both esters evidence is found of rotational isomerism arising from internal rotation about the O-C₂H₅ bond, in close agreement with previous work on other ethyl esters.     

Vibrational spectra and rotational isomerism of methyl methylsilyl sulphide

Infrared and Raman spectra of methyl methylsilyl sulphide are measured for the liquid and solid states. The fundamental vibrations are assigned and the normal vibrations calculated for two possible rotational isomers about the Si-S bond. Two different solid spectra are obtained, one corresponding to the trans form and the other to the gauche form; the liquid spectrum shows the presence of both forms. The gauche form is more stable than the trans form in the liquid state by 80 ± 50 cal mol^?1. The crystallization process indicates that the freezing and melting points of the trans form are slightly higher than those of the gauche form.     

Vibrational spectra and rotational isomerism of simple dialkyl dithioesters and N-acylglycine ethyl dithioesters,thiolesters, and dioxygenesters

Simple dialkyl dithioesters and N-acylglycine ethyl dithioesters have been investigated by Raman, resonance Raman and infrared spectroscopies. Based on the data of isotopic substituted derivatives and a normal coordinate analysis, vibrational assignments have been proposed for methyl dithioacetate. Raman spectra of ethyl dithioacetate(CH₃C(=S)S

CH₂CH₃) and methyl dithiopropionate (CH₃CH₂

C (=S)SCH₃) have provided fundamental knowledge on rotational isomerism about the bonds indicated. Raman, resonance Raman and FTIR spectroscopic studies on N-acylglycine ethyl dithioesters indicated the coexistence of three conformers in solution and a combined x-ray crystallographic-resonance Raman spectroscopic approach has been used to set up precise structure-spectra correlations for these conformers. The corresponding conformational states of N-acylglycine thiolesters and dioxygenesters are also discussed briefly.     

Vibrational spectra and rotational isomerism of bis(N-2-chloroethyl)nitramine

The IR and Raman spectra of bis(N-2-chloroethyl)nitramine (BCENA) in the liquid and crystalline states and in CCl₄ and CH₃CN solutions are studied. The spectra are compared, and it is concluded that BCENA exists as a mixture of conformers of different polarities in the liquid state and as one less polar conformer in the crystalline state. To determine the conformations corresponding to the total electron energy minima and interpret the vibrational spectrum of BCENA, we performed an ab initio quantum chemical calculation of the BCENA molecule in the Hartree-Fock approximation using the 3–21G* and 6–31G* basis sets. Out of twelve possible conformations five are stable; the most stable conformer is C₂(GG). The frequencies and forms of normal vibrations of stable conformers are calculated using scaled quantum chemical force fields. The calculated and experimental frequencies are compared, and the relations between the frequencies of skeletal stretching and bending vibrations are analyzed. It is concluded that the BCENA crystal is formed by the C₂ (GG) conformer. The vibrational spectrum is interpreted, and the frequencies are assigned to vibrations of conformers differing in form. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 303–317, March–April, 1997.     

Vibrational spectra of ethyl iodedes

The infrared spectra of CH₃CH₂I, CD₃CH₂I, and CH₃CD₂I of the vapors and the solids at 170°C have been recorded from 4000-200 cm^?1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH₃CH₂X molecules is presented.     

Vibrational spectra of ethyl dihaloacetates

Vibrational spectra of ethyl dihaloacetates have been studied. Infrared spectra in vapour and liquid phases, solutions in different solvents, and Raman spectra of these compounds have been recorded in order to assign the fundamental bands. The existence of different rotamers about the CC bonds joining the dihalomethyl and carbonyl groups produces a splitting in some bands of the spectra. It yields a more complex profile but, to some extent, it allows an easier assignment of bands which present that splitting. A theoretical study of the potential barrier hindering free rotation about that bond has been made in order to predetermine the number and orientation of the rotamers in each compound.     

The vibrational spectra,rotational isomerism,normal coordinate analysis and mean amplitudes of ethyl formate,ethyl chloroformate and ethyl cyanoform

The infrared spectra of ethyl formate, chloroformate, and cyanoformate in the liquid phase have been recorded in the region 4000–4020 cm^?1, and in the solid and vapour phase and in solution in the region 4000–4200 cm^?1. Evidence is reported for the existence of two rotameric forms in each case.Normal coordinate calculations are reported for both rotameric forms of the first two esters, and assignments based on potential energy distributions are given. These assignments show considerable mixing of the normal modes and suggest the inadequacy of simple assignments made by comparison with related molecules.Calculated mean amplitudes are also reported for the first two molecules.     

Vibrational and NMR spectra of mono- and di-chlorothiolacetic acids in relation to rotational isomerism and hydrogen bonding

The vibrational spectra of mono- and di-chlorothiolacetic acids have been measured in liquid and gaseous states and solutions, and vibrational assignments have been proposed. The experimental material shows that these molecules are present as a mixture of two rotational isomers. The energy of the two isomers in the liquid state is almost the same.     

The vibrational spectra and rotational isomerism of methyl ethyl sulphone-d0, -d3 and -d5

The infrared and Raman spectra of methyl ethyl sulphone, methyl ethyl sulphone-1,1,1-d₃ and methyl ethyl sulphone- 1,1,1,3,3-d₅ have been presented with vibrational assignments. Two solid states have been identified in which the molecules are either the trans or the gauche rotational isomers: one solid, the A form, occurs in cooled KBr disks used for infrared spectra while the other was found in CsI disks under ambient conditions. A mixed crystal form has also been found. In the liquid state the enthalpy of the B rotational isomer is slightly less than that of the A isomer by 90 (± 140) J mol⁻¹     

The infrared carbonyl band of ethyl haloacetates and rotational isomerism

The integrated intensities of the carbonyl band components of the following ethyl haloacetates, R-COOFt (R = CH₂Cl, CH₂Br, CHCl₂ and CHBr₂), have been measured at different temperatures. From these intensities, values of ΔH° for the equilibrium between the $\text{cis}$ and $\text{gauche}$ rotamers have been estimated. Ethyl haloacetates have been studied in both CCl₄ solution and in gas phase. The absolute values of ΔH° in solution are lower than in gas phase. Results obtained in gas phase indicate that the stability of the $\text{gauche}$ rotamer increases with the size of the halogen atom.     

The vibrational spectra and rotational isomerism of 1,1,1-Trimethoxyethane

The liquid, vapour and solid-state infrared spectra of 1,1,1-trimethoxy-ethane were recorded in the region 250–4000 cm⁻¹. The laser-Raman spectrum with qualitative depolarization data was obtained for liquid only. The spectra show that there are at least two rotational isomers present in the liquid phase. The solution spectra reveal that the less polar form is the more stable in the liquid phase. The form playing an important role has GGG configuration. A vibrational assignment has been attempted for the observed infrared and Raman bands.     

Vibrational spectroscopic study of rotational isomerism in O,O-dimethylphosphorodithioic acid

In this paper, the IR and Raman spectra of (CH₃O)₂P(S)SH have been studied at room temperature and at lower temperature. It is found that the P = S stretching vibrational band consists of four sub-bands, which shows that there are four rotational isomers for (CH₃O)₂P(S)SH. With the aid of computer we have separated the P=S bands and measured the relative intensities of each sub-band at different temperatures, so the relation of interconversion between isomers was obtained. Moreover, there exists intermolecular hydrogen bond in this compound, which will impede the rotation of S-H about P-S bond. Therefore, the interconversion of isomers results only from the rotation of O-CH₃ about P-O bond.     

Infrared spectra and rotational isomerism of certain crystalline vinyl ethers

Conclusions In contrast to conformationally inhomogeneous liquid vinyl ethers, crystalline trialkylvinyloxyalkylammonium salts, according to the data of IR spectroscopy, exist practically only in the form of a flat (conjugated) conformation. An exception is trimethylvinyloxyethylammonium bromide, which crystallizes almost exclusively in a nonplanar form.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1457–1460, July, 1971.     

Infrared spectra and rotational isomerism of epifluorohydrin and other propene oxide derivatives

The infrared spectrum for the vapour, liquid and solid states of epifluorohydrin has been studied, and evidence has been obtained for the presence of rotational isomers. The dominant conformer in all phases corresponds to a gauche structure, which was the only form identified in the vapour by microwave spectroscopy [1]. Similar evidence for conformational equilibria has been found for the chloro, bromo and iodo derivatives, and the enthalpy differences between the rotational isomers of these compounds were measured respectively as 4580 ± 970, 3950 ± 400, and 2350 ± 170 J mol^?1 respectively. At low temperatures, epiiodohydrin was found to crystallize in one of two possible crystalline phases. These two phases correspond to the two rotational isomeric conformations of the molecule.