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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.

Griffiths and co-workers demonstrated that diffuse reflectance infrared spectroscopy (DRIFTS) can be used to study solids as mixtures with KCl and as samples deposited from solutions, and we have devised a sampling accessory for obtaining DRIFT spectra of multiple samples which is more convenient than making KBr pellets, cast films, or even thin films. Very often the analyst is required to obtain spectra of a large number of samples, and generally these samples must be prepared and analyzed one at a time. The multiple sample accessory shown in Fig. 1 enables us to complete the sample preparation prior to recording any spectra. In this way, valuable instrument time is more efficiently utilized, and the necessity of disruputing the instrument's purge between each sampling is minimized. The accessory is small enough to fit through a f

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 infrared spectra of gaseous vinylsilane, cyclopropylsilane, vinyltrichlorosilane, cyclopropyltrichlorosilane, and silacyclopentane have been recorded. Barriers to internal rotation have been calculated for vinylsilane and cyclopropylsilane from an analysis of combination and difference bands associated with the Si-H stretches. Vibrational assignments have been made for vinyltrichlorosilane and cyclopropylsilane. High resolution spectra of the combination and difference bands involving the Si-H stretches and the ring-puckering vibration in silacyclopentane have been analyzed, and the new assignment is found to be completely consistent with existing low-frequency data. The structural implications of the results are discussed.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laboratory mixtures of terpenoid compounds and crude fractions extracted from native plants have been subjected to analysis by GC-FTIR. Positive identification is relatively straightforward for compounds whose relative retention times are sufficiently different, and proper choice of the stationary phase in the GC column can ensure satisfactory results for this class of compounds. Preliminary work with capillary GC columns has also been carried out, and the results of the various experiments are discussed.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

Determining the number of methyl groups per 100 carbon atoms is used as a measure of the degree of chain branching, and this is measured using a computer-interfaced, infrared spectrophotometer.