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The far infrared (50-370-cm -1 ) and low frequency Raman (70-300-cm -1 ) spectra of gaseous 1,2-difluoroethane have been recorded. The fundamental asymmetric torsional frequencies of the more stable gauche (two fluorine atoms oriented gauche to one another) and the high energy trans conformations have been observed in the far infrared spectrum of the gas at 147.0 and 116.7 cm -1 , respectively. For the trans conformer, four Q-branches arising from transitions between excited torsional vibrational states have also been observed

The far infrared (50-370-cm -1 ) and low frequency Raman (70-300-cm -1 ) spectra of gaseous 1,2-difluoroethane have been recorded. The fundamental asymmetric torsional frequencies of the more stable gauche (two fluorine atoms oriented gauche to one another) and the high energy trans conformations have been observed in the far infrared spectrum of the gas at 147.0 and 116.7 cm -1 , respectively. For the trans conformer, four Q-branches arising from transitions between excited torsional vibrational states have also been observed

A fiber-optic sample cell designed for use in the near-infrared region is described. For Fourier transform (FT) Raman spectroscopy, Nd:YAG laser radiation is transmitted to the sample through one fiber bundle, while a second fiber bundle collects and transfers the scattered light to the source compartment of an infrared interferometer equipped with a CaF2 beam splitter and an InGaAs detector. Because the two fiber bundles are mounted in the aluminum body of the cell, virtually no optical alignment is required. In addition to its utility in FT-Raman spectroscopy, the cell may be used for obtaining near-infrared absorption spectra of liquids and reflectance spectra of solids without changing its configuration. Examples of the many uses of the cell are provided, and modifications which would potentially improve its efficiency and expand its capabilities are discussed.

The Raman spectra (4000–100 cm−1) of liquid and solid cyclohexylphosphine were recorded, together with the infrared spectra (4000–400 cm−1) of the vapor and solid. Both the Raman and infrared spectra indicate the existence of axial conformers, presumably with gauche and trans orientations of the PH2 group, in addition to the more stable equatorial form. The likelihood of the existence of two equatorial forms of cyclohexylphosphine is discussed, although such a result has not been confirmed experimentally. Variable-temperature experiments monitoring the very weak Raman lines for the axial conformers give enthalpy differences in the range 1.6–1.8 kcal mol−1· A complete set of vibrational assignments is proposed based on data from the PD2 species and analogy with related substituted cyclohexanes.

The infrared and Raman spectra of solid, liquid and gaseous epifluorohydrin have been recorded. For the fluid phases, there are a number of spectral triplets which can be interpreted as arising from a cis and two nonequivalent gauche conformations. The number of bands which disappear as the solid sample is annealed indicates that a single conformation exists in the crystalline state. The temperature dependence of the intensities of Raman lines for the liquid state is consistent with enthalpy differences of approximately 0.6 and 0.4 kcal mol−1 between the most stable and each of the less stable conformers. The existence and identities of the less stable conformers are discussed.

The gas-phase Fourier transform infrared spectrum (4000-400 cm−1) of chlorocyclopropane was recorded at a resolution of 0.5 cm−1. For the first time, gas-phase Raman and solid-phase infrared and Raman spectra were obtained for this molecule. Liquid-phase Raman and infrared spectra were also recorded and, on the basis of all the data, a complete assignment of the 21 normal modes of vibration of chlorocyclopropane was made. The proposed assignment is in excellent agreement with assignments for other substituted cyclopropanes and, in particular, other chlorine-substituted cyclopropanes.

Utilisation d'une postcolonne avec du dimethoxy-2,2 propane pour enlever l'eau avant spectrometrie IR

Infrared and laser‐Raman spectra of 1,2‐difluoroethane (FH2CCH2F) have been recorded from 4000 to 50 cm−1. Whereas the Raman spectra were measured for all three physical states, the infrared data were recorded for the gaseous and crystalline phases. Spectral transitions associated with the predominant gauche conformer have been assigned with confidence on the basis of clearly defined infrared band contours and Raman depolarization ratios. Although several fundamentals have also been assigned for trans‐1,2‐difluoroethane, the majority of the normal modes associated with trans‐C2F2H4 appear to be unresolved or coincident with bands assigned to gauche‐C2F2H4. The magnitude of ΔH separating the two conformers was determined to be 1.98±0.08 kcal/mole by measuring the temperature dependence of the Raman bands assigned to the F–C–C–F bending modes for gauche (503 cm−1) and trans (461 cm−1) C2F2H4, respectively. An overall potential function describing the torsional barriers and ΔH will be discussed on the basis ...

The Raman spectra of gaseous, liquid and solid S(SiH 3 ) 2 and S(SiD 3 ) 2 have been recorded from 50 to 3500 cm −1 , and the infrared spectra of the gas and solid have also been investigated. A vibrational assignment is proposed and a normal coordinate calculation carried out using a modified valence force field.

Infrared and Raman spectra of (bromomethyl)cyclopropane and epibromohydrin have been recorded. Reversible spectral changes which accompany changes in temperature indicate the existence of an equilibrium mixture of gauche and cis conformers for (bromomethyl)cyclopropane. The gauche form is more stable, and from the variable temperature studies an enthalpy difference of 2.0±0.2 kcal mol−1 has been obtained for the liquid phase. For epibromohydrin, two non-equivalent gauche conformers have been identified, and the gauche-1 form is more stable than the gauche-2 by 0.80±0.20 kcal mol−1 in the liquid phase. Additionally there is evidence for a third conformer, presumably the cis form, but characterization of this conformer has been limited by the complexity of the spectra associated with the gauche-1 and gauche-2 forms. Consequently, only a lower limit can be given for the ΔH separating the cis and gauche-1 conformers. The results are consistent with previous observations for similar molecules.

The infrared and Raman spectra of 1,3-dithietane have been recorded with the sample in the solid state and trapped in an argon matrix at 18K. The number of coincidences between the infrared and Raman spectra of the matrix-isolated sample is consistent with C2v molecular symmetry in which the ring has a puckered conformation. In the solid state a number of bands disappear upon annealing, and the observed mutual exclusion for the annealed solid can be interpreted in terms of D2h, symmetry. Whereas the matrix probably represents the “free” molecule, the planarity of the ring in the annealed solid can be attributed to crystal packing.

The infrared spectra (4000–400 cm−1) of gaseous, liquid and solid (cyanomethyl) cyclopropane have been recorded for the first time. Additionally, the Raman spectra (3500–50 cm−1) of condensed phases of this substance have also been obtained. ‘Extra’ Q branches have been observed in the gas-phase infrared spectrum, and six liquid-phase Raman doublets (two of which are also seen in the infrared spectrum of the liquid) have also been observed, wherein one member of each doublet vanishes once the polycrystalline solid state spectrum is obtained. These data have been interpreted in terms of a two conformer (gauche/cis) fluid-phase equilibrium for (cyanomethyl)cyclopropane, with only the gauche conformer remaining in the solid phase. The temperature behavior of the 774/756 and 835/855 cm−1 liquid-phase Raman doublets yields an enthalpy difference between conformers of 0.72±0.10 kcal mol−1, with the gauche conformer the more stable. This ΔH value implies a room-temperature conformational equilibrium for (cyanomethyl)cyclopropane composed of 87% gauche and 13% cis rotamers in the liquid phase. In addition, a vibrational assignment for the 33 normal modes of (cyanomethyl)cyclopropane has been proposed, and it is in excellent agreement with the previously published vibrational assignments for three (halomethyl)cyclopropanes.

The Raman and IR spectra of diallyl sulfide and diallyl disulfide in the liquid and solid state are reported and examined in order to determine their most stable conformations. In both the liquid and solid state, the allyl moieties in both molecules are in a “gauche” conformation in which the sulfur atoms and the terminal vinyl carbons probably form a dihedral angle of between 105° and 120°. In the liquid state, there are two possible S-S rotational conformers of diallyl disulfide. The “gauche” conformer with a C-S-S-C dihedral angle of approximately 70° is 242±24 cal mol−1 more stable than the “near-cis” conformer which probably has a C-S-S-C dihedral angle of approximately 25°. Only the “gauche” S-S rotational conformer of diallyl disulfide exists in the solid state. Additionally, in the liquid state, there are two C-S rotational conformers for each molecule. The “gauche” conformer corresponds to a C-C-S-C (diallyl sulfide) or C-C-S-S (diallyl disulfide) dihedral angle of 70° and the “trans” conformer corresponds to a C-C-S-C or C-C-S-S dihedral angle of 180°. For diallyl sulfide the “trans” C-S conformer is 260±26 cal mol−1 more stable than the “gauche” C-S conformer while for diallyl disulfide the “gauche” C-S conformer is 358±20 cal mol−1 more stable than the “trans” C-S conformer. In the solid state, both C-S conformers exist for diallyl sulfide but only the “gauche” C-S conformer exists for diallyl disulfide.

The infrared spectra of gaseous and solid vinyloxirane have been recorded, while Raman spectra of all three physical states have been obtained. The vibrational data for the liquid and vapor phases are consistent with the presence of three conformations, the s-trans and two nonequivalent gauche forms. The energy separations between the most stable s-trans and each of the other confromers have been determined for the liquid state to be 1.1 ± 0.2 and 0.8 ± 0.2 kcal mol−1 by measuring the temperature dependence of sets of Raman lines. A complete vibrational assignment is proposed for the s-trans conformer, and the identities of the less stable conformers are discussed in terms of previous studies of related molecules.

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 (Cs symmetry) from a hypothetical cis/cis (C2υ) 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 Cs 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.

The ν 1 , ν 2 , and ν 3 fundamentals of nitrosyl chloride, ON 35 Cl, have been recorded with a Fourier transform interferometer at an apodized resolution of 0.004 cm −1 . The data have been analyzed together with previous microwave data for the ground vibrational state to yield improved molecular parameters for the (100), (010), and (001) vibrational states. The main results (in cm −1 ) are: v 1 = 1 v 2 = 1 v 3 = 1 A 2.892513(18) 2.941109(9) 2.931514(12) B 0.1922820(7) 0.1906560(8) 0.1904847(9) C 0.1800373(7) 0.1783946(8) 0.1784287(8) ν i 1799.7316(2) 595.8518(2) 331.9707(2) Additionally, the values for a number of the centrifugal distortion constants have been obtained for each of these normal modes.

The low frequency (500–80 cm−1) Raman spectra of gaseous methylcyclobutane, c‐C4H7CH3, and methyl‐d3‐cyclobutane have been recorded. A series of Q branches beginning at 161 cm−1 for the light molecule and 154 cm−1 for the d3 compound with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fitted to an asymmetric potential function of the form: V(cm−1)=(4.78±0.10)×105X4−(3.08±0.04)×104X2 +(2.18±0.1)×104X3 with an assumed reduced mass of 160 amu for the light compound. Utilizing this potential the difference between the puckering angles for the two conformers was calculated to be 4.3° with the equatorial conformer having the larger value of 20.7°. A similar potential was obtained for the d3 molecule. The energy difference between the equatorial and axial forms was found to be 247±20 cm−1 (706 cal/mol) and a barrier of 641±20 cm−1 (1.83 kcal/mol) was found for the inte...

Because of the throughput, multiplex, and calibration advantages of Fourier transform (FT) infrared spectroscopy, renewed interest has arisen in developing FT-Raman techniques for extended applications in the chemical, physical, and biophysical areas. The ability to use a single interferometer with the appropriate accessories for obtaining either infrared or Raman spectra adds further to the allure and potential of this new spectroscopic approach. As a result of the broad frequency range accessible to an interferometer, FT-Raman spectra can be collected with the use of a variety of laser excitation sources ranging from the visible (488 nm and 647.1 nm, for example) to near-infrared (1064 nm) wavelengths. Excitation at longer wavelengths often provides the significant advantage of yielding Raman spectra which are free from fluorescence effects.

The i.r. (4000-200 cm −1 ) and Raman (4000-50 cm −1 ) spectra of gaseous and solid 2-fluoroethylamine have been recorded along with the Raman spectra of the neat liquid and a TMS solution. These data have been interpreted on the basis of at least four conformations in the gas phase and one conformation in the crystalline solid. Conformers identified as Gg ′ and Gt which exhibit intramolecular hydrogen bonds are the most stable forms in the gas phase and coexist with the Gg and Tg conformers. In the condensed phases, intermolecular hydrogen bonding becomes a dominant factor, and only the Gg conformer remains in the solid. The conformer stabilities determined here are discussed in terms of theoretical calculations and experimental data for similar molecules.

The Raman spectra of gaseous, liquid and solid cyclopentylamine and the infrared spectra of the gaseous and solid phases have been recorded. Raman depolarization ratios and infrared band contours in the gas phase indicate that cyclopentylamine exists primarily with a gauche orientation of the —NH2 group, and the torsional fundamental for this conformer has been observed at 232 cm−1. In the solid state the temperature characteristics in certain spectral regions are consistent with the existence of two low temperature phases, and the higher temperature phase appears to exist over a range of approximately only 7°C. A complete vibrational assignment is proposed, and the structural features of cyclopentylamine are discussed.

The IR and Raman spectra (4000–50 cm−1) of (chloromethyl)cyclopropane and epichlorohydrin have been recorded in all three physical states. It has been concluded from the spectroscopic data and from variable temperature studies that (chloromethyl)cyclopropane exists as an equilibrium mixture of gauche (95%) and cis (5%) conformers in the liquid state, while only the gauche form persists in the solid phase. The enthalpy difference between these two rotamers was found to be 1.40±0.10 kcal mol−1. Similarly, epichlorohydrin has also been shown to exist as an equilibrium mixture of gauche-1 (70%), gauche-2 (21%) and cis (9%) conformers in the liquid state, with only the gauche-1 form remaining in the solid phase. Enthalpy differences among these conformers were determined to be 1.2±0.2 kcal mol−1 (gauche-1 vs. cis) and 0.70±0.10 kcal mol−1 (gauche-1 vs gauche-2). Apparently steric repulsions between the chlorine atom and β ring-hydrogens destabilize the cis conformation in each molecule. For each molecule, a vibrational assignment has also been proposed.

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 C 2 and C s gauche/gauche rotational isomers, with the C 2 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 C 2 conformer of DCPM is more stable than the C s conformer by 0.93 ± 0.10 kcal/mole. In addition, it appears that the C 2 rotamer of DCPM also predominates in the gaseous phase. Tentative assignments of the major spectral bands of DCPM have also been proposed.

General advantages and potential limitations of Fourier transform (FT) Raman spectroscopy using Nd:YAG laser excitation at 1064 nm have been considered for both routine analysis and specific biophysical applications. Optical design and operating parameters which affect the quality and reproducibility of the data are discussed. Moderately high resolution spectra (0.25 cm−1) of liquids are obtained with relative ease, and the results are compared with dispersive spectra. Particular emphasis has been placed on applications to biological systems where intrinsic fluorescence has traditionally limited the use of dispersive Raman spectroscopy. As an example of a biophysical study, we demonstrate the utility of FT-Raman spectroscopy in elucidating the interactions of polyene antibiotics with model membrane lipid bilayers as a means of understanding novel drug/membrane interactions at the molecular level.

The Raman spectra of liquid and solid dl-bisoxirane and the infrared spectra of all three phases have been recorded. The microwave spectrum has been studied in the X- and R-band frequency regions. The vibrational data indicate that the molecule exists as a mixture of at least two conformations in the fluid state. The more stable conformer, which has a trans orientation of the two oxirane rings and persists as the only conformer in the crystalline solid state, has also been observed in the microwave spectrum of the vapor. The rotational constants of the ground vibrational state are (in MHz) A = 10998.186, B = 2340.413, and C = 2126.233. From Stark effect measurements, the dipole moment component μb (along the symmetry axis) is found to be 3.43 ± 0.01 D. Rotational transitions and the Stark effect for two excited vibrational states have also been measured and analyzed. A second conformer, which is 0.23 ± 0.08 kcal/mole (0.96 ± 0.33 kJ/mole) less stable than the trans conformer in the liquid state, is identified as a near-gauche conformer whose dihedral angle is probably between 40° and 50°. The possibility of an additional conformer is considered, and the structure of dl-bisoxirane is discussed in terms of similar molecules.

Etude des spectres IR et Raman des composes cites dans 3 etats physiques differents. Attribution des vibrations

The Raman (3500–20 cm−1) and infrared (3500–50 cm−1) spectra of gaseous and solid methylcyclobutane and methyl-d3-cyclobutane have been recorded. Additionally, the Raman spectra of the pure liquids have been recorded and qualitative depolarization values have been obtained. The spectra have been interpreted on the basis that both the axial and equatorial conformers are present in the fluid phases and that the equatorial form is thermodynamically preferred and the only form present in the annealed solid. All 39 of the normal vibrational modes have been assigned for both the d0 and d3 compounds. An abundance of spectral evidence is presented which indicates extensive coupling between the vibrations associated with the ring and those of the methyl group. The CH3 internal torsional mode has been observed in the Raman spectrum of the solid at 232 cm−1 and utilizing this frequency the periodic threefold barrier to internal rotation has been calculated to be 1190 cm−1 (3.40 kcal mol−1). The fundamental ring puckering mode has been assigned from the Raman spectra of the gases to weak features observed at 161 and 154 cm−1 for the d0 and d3 compounds, respectively. All of these results are compared with the corresponding quantities for some similar molecules.

The Raman spectrum of gaseous phosphaethyne (HCP) has been recorded, and the CH and CP stretching vibrations (ν1 and ν3) have been observed at 3218 and 1277 cm−1, respectively. These frequencies compare very favorably with those previously determined from IR and UV-visible spectra. The sample is stable for short periods of time under the required experimental conditions, and the vibrational data are discussed in terms of the stability and reactivity of HCP.

The vibrational spectra of 1, 2-dif luoroethane , 1,1, 2-trif luoroethane , and 1,1, 2 , 2-tetra- fluoroethane have been recorded In the gaseous, liquid, and solid states. The conform- ational preferences have been studied as a function of temperature and physical state. Transitions arising from the torsional vibration for the stable form of each molecule have been observed in the far infrared. Using these and other data, torsional potential func­ tions have been developed. Trends In the conformational characteristics of the fluoroe­ thanes are discussed.IntroductionMultiple conformations can exist in ethane derivatives In which there Is partial sub­ stitution on each carbon atom. For example, the staggered forms of 1,2-difluoroethane and 1,1,2,2-tetraf luoroethane can exist in either the gauche (C2 ) or tj^an_s_ (C2h) conformations, and 1,1,2-trifluoroethane can assume conformations with either GI or Cs molecular symmetry.Very Often, differences in selection rules between infrared and Raman experiments provide information necessary for distinguishing between possible conformers. The ability to use these techniques to study solids, liquids, and gases can simplify the interpretation of spectral data if the conformational behavior Is dependent upon the physical state. Addi­ tional Information concerning conformational equilibria can be found In the far infrared and low-frequency Raman spectra of vapors. Transitions arising from torsional vibrations are found in this region of the spectrum, and the frequencies of these transitions are dictated by the form of the potential energy function which governs Internal rotation. A suitable model for the potential function Is V(e) = (h) £ Vn(l-cos n0), where 6 Is the internal rotation angle and the shape of the function is determined by the relative values of the individual n-fold terms, Vn. A knowledge of the potential function Is Important for fully understanding the conformational equilibrium.Results 1, 2-DIfluoroethaneThe infrared and Raman spectra of 1,2-difluoroethane exhibit a one-to-one correspondence which Is consistent with C2 molecular symmetry (gauche) for the most abundant form. Weak bands associated with the trans (C2h) conformer are discernable in the spectra of the gas and liquid states, but these bands are absent In the spectrum of the crystalline solid. The temperature dependence of bands In the liquid state Indicate that the gauche form is more stable by 2.0 kcal/mol.The fundamental torsional vibration for gauche 1,2-difluoroethane has been observed in the Raman spectrum as a Q branch and In the far Infrared spectrum as a B-type band centered at 147 cm"1 . A second transition seems to be centered at approximately 137 cm"1 . The torsion for the trans conformer exhibits a series of Q branches at 117^ 112, 106, 101, 100, and 93 cm"1 . The transitions for both conformers have been fitted to a periodic potential function, and the torsional transitions are satisfactorily reproduced by using potential constants Vi = 215. V2 = -554 V3 = 1184 and V6 = -19 cm"1 . This function Implies that the energy separation of the gauche and trans conformers is 1.2 kcal/mol, a value which Is similar In magnitude to that for the liquid state.1,1,2-TrifluoroethaneThe difference in selection rules for GI and Cs molecular symmetries are not very dis­ tinctive. However, the abundance of Q branches In the Ramari spectrum implies that the GI form is more stable than the Cs in the gas phase, and a variable temperature study Is con­ sistent with a AH value of 1.6 ± 0.4 kcal/mol. The reverse is true for the liquid state where the Cs conformer is more stable by 1.03 ± 0.10 kcal/mol. Additionally the Cs con- former Is the only one present In the crystallne solid state.Far Infrared spectra recorded at 0.25 cm" resolution exhibit a Q branch series for the GI conformer at 117, 115, 113, 110, 106, 101, and 96 cm."1 . These are assigned to the

The Raman spectrum of gaseous silacyclopentane has been recorded from 25 to 4000 cm−1. The series of Q branches observed at 264.5, 259.9, and 255.3 cm−1 have been assigned as the fundamental and hot bands of the radial vibration of a hindered pseudorotator. A two‐dimensional potential surface has been determined and indicates that the interconversion between equivalent twisted forms proceeds through a puckered intermediate. The barrier of 1414 cm−1 is of the same order as that found using a one‐dimensional treatment, and the two models are discussed.

The vibrational spectra of cyclopropylamine have been reconsidered; the results are consistent with our earlier studies describing a trans/gauche conformational equilibrium. The conformer having the amino protons trans to the ring CC bonds is more stable than the gauche conformer. The equilibrium in cyclopropylamine is discussed and contrasted with a recent report in which only one conformer was identified.