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.     

Rotational isomerism in fluorinated compounds: 1,3-Difluoro-2-chloropropane

Infrared spectra were obtained for 1,3-difluoro-2- chloropropane in the solid, liquid and vapor states and in solutions with nonpolar solvents. Comparisons of the spectra show the probable presence of three conformations in the liquid, two in the solid, and only one in the vapor. Changes in relative intensities of several bands in non-polar solvents show the less polar conformation to be the one present in the vapor state.     

Spectres de vibration et structure du chlorure de furoyle - isomères de rotation

The infrared and Raman spectra of various physical states of furoyl chloride have been studied. The spectral analyses show the existence of the OO-cis and OO-trans rotational isomers; the compound exists as a mixture of these rotamers in the liquid state, but the OO-trans form is shown to be the more stable in the solid state. An assignment of the observed fundamentals for these rotamers is proposed with a C_s symmetry. The maxima observed in the carbonyl region are interpreted as a combination of the two v(CO) vibrations and Fermi resonances.     

The vibrational spectra and rotational isomerism of monochloromethyl acetate and methyl oxalyl chloride

The IR spectra of monochloromethyl acetate and methyl oxalyl chloride have been studied for the vapour, liquid and solid states. For the first ester only one conformation is present and it has a planar arrangement of heavy atoms with the chlorine directed away from the carbonyl group and with a s-cis arrangement for the basic ester framework. For methyl oxalyl chloride, evidence is presented for the presence of two rotamers, the more stable of which is probably planar with a trans arrangement of carbonyl groups.     

Isomérie de rotation et spectres de vibration du chlorure et du bromure d'allyle

Infrared and Raman spectra (3500-30 cm⁻¹) of the allyl halides (chloride and bromide) in the vapor, liquid and solid states were obtained. From the data obtained in the vitreous phase at −180 °C, vibrational assignments for each isomer, cis and gauche, are proposed. The energy difference between the two isomers of allyl chloride was found to be approximatively 500 cal. The potential barrier of these compounds in the gaseous state has been calculated from the torsional frequencies.     

间甲基苯甲醚分子旋转异构体的质量分辨阈值电离光谱

间甲基苯甲醚分子有顺式和反式两个转动异构体.利用单光共振双光子电离技术和质量分辨阈值电离技术,研究了间甲基苯甲醚分子顺反异构体的基态到第一电子激发态(S1←S0)的跃迁和阈值电离.得到顺式、反式间甲基苯甲醚分子S1态的激发能(E1)分别为(36049±2)和(36117±2)cm-1,绝热电离能(Ip)分别为(64859±5)和(65110±5)cm-1.结合从头算法和密度泛函理论的量子化学计算,解释了顺式、反式间甲基苯甲醚分子E1和Ip存在差异的原因,并且对S1态和离子基态D0态出现的谱峰进行了标识.间甲基苯甲醚分子顺反异构体在S1态和D0态的活性振动主要是甲基转动、面内环的运动和与取代基相关的弯曲振动.间甲基苯甲醚分子的S1态振动光谱、D0态离子光谱以及理论计算均表明这两个转动异构体在D0态的几何构型与S1态的中性几何构型相比有较大改变,取代基与取代基、取代基与苯环间的相互作用强度高低次序为:S0S1D0.     

Vibrational and conformational analysis of chloromethyldifluorophosphine,ClCH2PF2

The vibrational spectra of chloromethyldifluorophosphine have been recorded in the different physical states. Both gauche and trans conformers are identified in the spectra. Temperature dependent studies and calculated dipole moments (CNDO/2) indicate that the gauche conformer is more stable in the gas-phase while the trans is more stable in the liquid phase. In the solid phase, both conformers are present, although the trans strongly dominates.     

Vibrational analysis of ethyl and n-propyl fluorides

Infrared spectra of n-propyl fluoride in the gas and solid states were obtained that confirm the presence of two molecular conformations in the gas and unannealed solid. Only one conformation identified as the gauche form is present in the annealed solid. Raman spectra were obtained for the solid. Normal coordinate calculations were made simultaneously for ethyl fluoride, gauche n-propyl fluoride, and trans n-propyl fluoride, and the resulting force constants and vibrational assignments are given.     

UV-, VIS- and IR-light-induced isomerization of HSNO in a low-temperature matrix

An infrared spectroscopic investigation has been performed on the trans and cis isomers of thionitrous acid (HSNO) and their D- and ¹⁵NO-isotopic modifications in argon matrices at 12 K. The substances were prepared photolytically from thionylimide (HNSO) isotopes in the matrix. With UV (250 nm), VIS (585 nm), and IR irradiation the cis → trans or the trans → cis isomerization of HSNO was induced, allowing an unequivocal distinction between the closely resembling IR spectra of the trans and cis isomers. Complete sets of fundamental frequencies of both rotamers were obtained and assigned by normal coordinate analysis using the transferable valence force field (TVFF) approach. Parallel to this analysis ab initio calculations on the SCF- and CI-levels were performed to predict energy, geometry, and barrier of internal rotation for the two HSNO rotamers.     

Vibrational spectra of cyclobutanecarbonyl chloride and bromide and their α-deuterated compounds

The IR spectra of cyclobutanecarbonyl chloride and bromide and their α-deuterated compounds have been recorded in the vapor, liquid and crystal states. The Raman spectra have also been measured in the liquid state. Comparison of the spectra in the liquid phase with those in the crystal phase reveals that these acyl halides exist in a conformational equilibrium in the liquid state. Tentative vibrational assignments are proposed on the basis of the isotope effect and previous published results for other simple cyclobutane compounds.     

Vibrational spectra of 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane

Infrared and Raman spectra are obtained for 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane. The former compound exists as a mixture of P_C and P_H' conformers in the liquid and unannealed solid states, but only the P_C conformer is present in the crystalline solid. Vibrational assignments are made for both conformers of 1-chloro-2-methylpropane and for 1-chloro-2,2-dimethylpropane with the aid of normal coordinate calculations.     

Vibrational analysis of 2-fluoropropane and 2-fluorobutane

Vibrational spectra were obtained for 2-fluorobutane in the vapor, liquid, and solid states. The S_HH and Spy conformers are present in the solid, and the S_HH conformer is present in the liquid and in lower concentration in the vapor. Vibrational assignments were made with the aid of normal coordinate calculations that fit thirty-six frequencies of 2-fluoropropane and S_HH 2-fluorobutane with an average error of 3.7 cm^?1. Only a few vibrations of 2-fluorobutane seem to be dependent on conformation. The “C—F stretching” frequency cannot be used to distinguish the conformers because of extensive interaction between this coordinate and others.     

间甲基苯甲醚分子旋转异构体的质量分辨阈值电离光谱

间甲基苯甲醚分子有顺式和反式两个转动异构体. 利用单光共振双光子电离技术和质量分辨阈值电离技术,研究了间甲基苯甲醚分子顺反异构体的基态到第一电子激发态（S₁←S₀）的跃迁和阈值电离. 得到顺式、反式间甲基苯甲醚分子S₁态的激发能（E₁）分别为（36049±2）和（36117±2）cm^-1,绝热电离能（I_p）分别为（64859±5）和（65110±5）cm^-1. 结合从头算法和密度泛函理论的量子化学计算,解释了顺式、反式间甲基苯甲醚分子E₁和I_p存在差异的原因,并且对S₁态和离子基态D0态出现的谱峰进行了标识. 间甲基苯甲醚分子顺反异构体在S₁态和D₀态的活性振动主要是甲基转动、面内环的运动和与取代基相关的弯曲振动. 间甲基苯甲醚分子的S₁态振动光谱、D₀态离子光谱以及理论计算均表明这两个转动异构体在D₀态的几何构型与S₁态的中性几何构型相比有较大改变,取代基与取代基、取代基与苯环间的相互作用强度高低次序为：S₀<S₁<D₀.     

Vibrational spectra and structure of cis- and trans-1,2- dimethoxyethylenes

The vapor, liquid and CCl₄ solution infrared spectra of cis- and trans-1,2-dimethoxyethylene were recorded in the region 250–4000 cm^?1. The laser-Raman spectra were obtained in the liquid state only. The vibrational spectra show that at least two rotational isomers exist for each molecule. Further, the spectra indicate that for both the cis- and trans molecules, one of the rotational isomers has at least one planar conformer. Some vibrational assignments are made for the observed infrared and Raman bands of the cis- and trans- 1,2-dimethoxyethylenes.     

Δ-2 thiazoline et alkyl-2 Δ-2 thiazolines: etude vibrationnelle infrarouge et Raman.conformation

Raman spectra (liquid state) and infrared spectra of 2-Δ thiazoline and its 2-alkyl derivatives (vapor, liquid, solution and solid states) have been analysed between 4000 and 200 cm⁻¹. The assignments proposed for the fundamental vibrations of these heterocycles agree with a planar or a very little distorted conformation of the cycle.     

A proton spin–lattice relaxation rate and nuclear Overhauser effect investigation of the stereochemistry of some 1-aryl derivatives of 1,2-dihydro-s-triazines

Proton spin–lattice relaxation rates (R₁ values) have been measured, at 400 MHz, for a number of 2-methyl- and 2,2-dimethyl-substituted 4,6-diamino-1-aryl-1,2-dihydro-S-triazines. These compounds have high barriers to internal rotation about the aryl C? N bond, and exist in solution as mixtures of enantiomeric or diastereomeric rotational isomers. Diastereotopically related 2-methyl groups in enantiomeric rotamers, and 2-methyl and 2-methine protons in diastereomeric rotamers, typically have different relaxation rates. In favourable circumstances this information may be used to identify the individual rotamers. Unequivocal direct identification of rotamers may be obtained from nuclear Overhauser effect difference spectra.     

NMR Studies of Solvent Effect on Internal Rotation in Some Non-Symmetrical 1,2-Disubstituted Ethanes

The A₂B₂ system of PMR spectra of 3-bromopropionic acid, 3-chloropropionic acid, 3-bromopropionitrile, and 3-chloropropionitrile exhibit appreciable solvent effect at room temperature. NMR spectroscopic parameters of A₂B₂ spectrum as well as physical parameters related to internal rotation, i. e. the highest energy barrier and the energy difference between rotamers, were determined for these compounds in the medium of various solvents. It was found that in the case of 3-bromopropionic acid, the trans rotamer is more stable than the gauche rotamers, and the energy difference decreases with increasing dielectric constant of solvent. While in the case of 3-bromopropionitrile, the gauche rotamers were found to be more stable than the trans rotamer and the energy difference increases with increasing dielectric constant of solvent. In the remaining two compounds, 3-chloropropionic acid and 3-chloropropionitrile, both trans and gauche rotamers are equally stable in a solvent of low dielectric constant, however in a solvent of higher dielectric constant, the gauche rotamers become more stable than the trans rotamer and the energy difference becomes more pronounced with increasing dielectric constant of solvent.     

Infrared and Raman spectra, conformational stability, ab initio calculations and vibrational assignments for trans-3-chloropropenoyl chloride

The infrared (3500-30 cm(-1)) spectra of gaseous and solid and the Raman (3500-200 cm(-1)) spectra of the liquid with quantitative depolarization ratios and solid trans-3-chloropropenoyl chloride (trans-ClCHCHCClO) have been recorded. These data indicate that both the anti (carbonyl bond trans to the carbon-carbon double bond) and syn conformers are present in the fluid states but only the anti conformer is present in the crystalline state. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (-55 to -100 degrees C) have been recorded. Utilizing conformer pairs at 870 and 725 cm(-1), 1215 and 1029 cm(-1), and 1215 and 1228 cm(-1), the enthalpy difference has been determined to be 136+/-5 cm(-1) (389+/-14 cal mol(-1)) with the anti conformer the more stable form. Optimized geometries and conformational stabilities were obtained from ab initio calculations at the levels of RHF/6-31G(d), MP2/6-31G(d), MP2/6-311 + + G(d,p), MP2/6-311 + + G(2d,2p) and MP2/6-311 + + G(2df,2pd) with only the latter two calculations predicting the anti rotamer to be the more stable form. The vibrational frequencies, harmonic force constants and infrared intensities were obtained from the MP2/6-31G(d) calculations, whereas the Raman activities and depolarization values were obtained from the RHF/6-31G(d) calculations. The spectra are interpreted in detail and the results are compared with those obtained for some related molecules.     

Ground-state, excited-singlet-state, and excited-triplet-state energy levels and photophysics of the three rotational isomers of isophthalaldehyde vapor

Emission, excitation, and absorption spectra of isophthalaldehyde (benzene-1,3-dicarboxaldehyde) vapor have been measured at different temperatures, along with the UV-vis and IR absorption spectra in solution. Analyses of the temperature dependence of the phosphorescence and excitation spectra of isophthalaldehyde vapor revealed the energetic relationships among the three rotational isomers in the T1(n, pi*), S1(n, pi*), and ground states. This appears to be the first example of the system where the S0, T1, and S1 energy levels are determined for the three rotational isomers. The phosphorescence, fluorescence, and excitation origins of the three rotamers were assigned on the basis of the results of the density functional theory (DFT) and semiempirical SCF-MO calculations and infrared data as well as on the basis of the temperature dependence of the emission and excitation spectra.     

Infrared, and Raman spectra, conformational stability, normal coordinate analysis, ab initio calculations, and vibrational assignment of 1-chlorosilacyclobutane

The infrared spectra (3500–40 cm⁻¹) of gaseous and solid and the Raman spectra (3500–30 cm⁻¹) of liquid and solid 1-chlorosilacyclobutane, c-C₃H₆SiClH, have been obtained. Both the axial and equatorial conformers with respect to the chlorine atom have been identified in the fluid phases. Variable temperature (−105 to −150°C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference has been determined to be 211±17 cm⁻¹ (2.53±0.21 kJ/mol), with the equatorial conformer being the more stable form and the only conformer remaining in the annealed solid. At ambient temperatures, approximately 26% of the axial conformers are present in the vapor phase. A complete vibrational assignment is proposed for the equatorial conformer, and many of the fundamentals of the axial conformers have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been determined for both rotamers by ab initio calculations employing the 6-31G(d) basis set at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. Structural parameters have also been obtained using MP2/6-311+G(d,p) ab initio calculations. The r₀ parameters for both conformers are obtained from a combination of the ab initio predicted values and the twelve previously reported microwave rotational constants. The results are discussed and compared to those obtained for some similar molecules.