Vibrational spectra and conformational behavior of dicyclopropylmethane

Raman spectra of the condensed phases of dicyclopropylmethane have been recorded. In addition, i.r. spectra of this compound have been obtained for all three phases. From the appearance of spectral doublets in the liquid phase Raman (and i.r.) spectra, one member of each of which vanishes upon crystallization, it has been concluded that, in the liquid state, DCPM exists as an equilibrium mixture of at least two conformers. Based upon the spectral results for DCPM, and upon the conformational preferences of a number of related molecules, it has been concluded that these two conformers are the C₂ and C_sgauche/gauche rotational isomers, with the C₂ form being the one which remains in the solid phase. From a variable temperature study of liquid phase Raman peaks, it has been determined that the C₂ conformer of DCPM is more stable than the C_s conformer by 0.93 ± 0.10 kcal/mole. In addition, it appears that the C₂ rotamer of DCPM also predominates in the gaseous phase. Tentative assignments of the major spectral bands of DCPM have also been proposed.     

Vibrational spectra and conformational behavior of benzyl fluoride

Infrared and Raman spectra have been obtained for benzyl fluoride and a vibrational assignment has been made. The spectra indicate the presence of a large number of conformers that differ only in the orientation of the C-F bond, as a result of free or nearly free internal rotation.     

Vibrational spectra and conformational behavior of 1,1- diethylcyclopropane

Infrared spectra (from 4000 to 400 cm⁻¹) of solid, liquid and gaseous 1,1-diethylcyclopropane and Raman spectra of the condensed phases of this compound have been recorded. Evidence for two conformational isomers, one of which vanishes in the polycrystalline solid phase, is found in the spectral data for the liquid phase. It has been concluded that these two rotational isomers are the gauche/gauche conformers which arise when the two methyl groups are displaced in a conrotatory sense (C₂ symmetry) and a disrotatory sense (C_s symmetry) from a hypothetical cis/cis (C_2υ) structure. These conclusions are consistent with the conformational results previously obtained for ethylcyclopropane and ethyloxirane. In addition, from the variable temperature liquid phase Raman intensity measurements, the C₂ rotamer of 1,1- diethylcyclopropane has been calculated to be 1.1 ± 0.2 kcal/mole more stable than the C_s form, and is the sole conformer remaining in the solid phase. Tentative vibrational assignments, in agreement with those for related molecules, are proposed for the major spectral bands of 1,1-diethylcyclopropane.     

Vibrational spectra and conformations of chloromethyldimethyl- and tris(chloromethyl)phosphine oxides

A study was carried out on the IR spectra of (CH₃)₂P(O)CH₂Cl and (CH₂Cl)₂PO. The frequencies and forms of the normal modes were calculated. The molecular mechanics method was used to calculate the energy of the various conformations of these molecules. (CH₃)₂P(O)CH₂Cl in the liquid and solution is a mixture of trans and gauche conformations, while (CH₂Cl)₃PO is a mixture of trans,gauche,gauche, trans,gauche,gauche, and gauche,gauche,gauche conformations.S. M. Kirov Kazan Chemical Engineering Institute and A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 38–46, November–December, 1989.     

Alkylation of N-arylcyanamides and electron-deficient phenols with (chloromethyl)thiirane

Alkylation of N-arylcyanamides with (chloromethyl)thiirane in aqueous alkaline solution provides an easy synthetic approach to N-aryl-N-(thietan-3-yl)cyanamides. Yields vary from 34 to 76% and are lower in the case of electron-deficient aryl substituents. The reaction with phenols containing electron-withdrawing groups results in formation of 3-(aryloxy)thietanes in 19–45% yields.     

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 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 ethyl trichloroacetate

The IR and Raman spectra of ethyl trichloroacetate (E-TCA) and its deuterate (E-TCA-d₅) have been measured in the liquid, glassy and crystalline states. Vibrational assignment was made by referring to isotopic wavenumber-shift, characteristic group frequencies of related esters and with the aid of a normal coordinate calculation on E-TCA and E-TCA-d₅. It is suggested that in the liquid and glassy states there exist two molecular forms (trans—trans—trans and trans—trans—gauche) with regard to the internal rotations about the ClC---C---O---CH₂CH₃ axis, and that the former persists in the crystalline state. The band pairs of E-TCA and the other ethyl esters are discussed in relation to the nature and number of rotational axes, effect of the heavy trichloromethyl group, and enhancement of band intensity by vibrational coupling.     

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.     

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 conformational equilibrium of (CH3)2CClNO and (CD3)2CClNO

Conclusions A conformational equilibrium has been observed in (CH₃)₂CClNO, and it has been shown that the cis_Cl and trans conformers are present in solutions and in the gas phase, the more stable conformer being the cis_Cl. In n-C₆H₁₄, the energy difference amounts to 1.22 kcal/mole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1538–1544, July, 1989.     

Vibrational spectra and conformational analysis of 1,3-dithia-5,6-benzocycloheptenes

The equilibrium between the chair and boat forms of 1,3-dithia-5,6-benzocycloheptene and its 2-Me, t-Bu, and Ph derivatives has been established by Raman and IR spectroscopy, and their spectroscopic characteristics have been revealed. In liquids the chair forms of 1,3-dithia(or dioxa)-5,6-benzocycloheptenes have C_s symmetry for the ring, and the twist forms of the seven-membered acetals have C₂ symmetry.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2014–2019, September, 1989.