O.H. Ellestad

Substituted propanes: VI. The vibrational spectra and conformations of 1,3-dichloro-, 1,3-bromochloro-, 1,3-dibromo- and 1,3-diiodo-propane

Abstract The infrared and Raman spectra of 1,3-dichloro-, 1,3-bromochloro-, 1,3-dibromo- and 1,3-diiodopropane were recorded as liquids and in the crystalline state at low temperatures. Crystals of 1,3-dibromo- and 1,3-diiodopropane formed under ca. 20 kbar pressure at ambient temperature were studied by infrared technique. No evidence was found for the GG 1 conformer (parallel C-halogen bonds), but the other three staggered conformers ( GG , AA , and AG ) (four for 1,3-bromo-chloropropane) were observed in the liquid. In all the stable low temperature crystals the GG conformers were present, at high pressure 1,3-dibromopropane crystallized in GG and 1,3-diiodopropane in the AA conformation. The C-halogen stretching vibrations have been interpreted in detail. A complete list of fundamentals have been proposed for the GG conformers in each compound, for 1,3-diiodopropane the additional AA fundamentals have been assigned whereas some AG bands were interpreted for each compound.

Substituted propanes: V. The vibrational spectra, dipole moments and conformations of 1,2-dichloro-, 1-chloro-2-bromo- and 1,2-dibromopropane

Abstract The infrared and Raman spectra of 1,2-dichloro-, 1-chloro-2-bromo- and 1,2-dibromopropane were recorded as liquids, in polar and non-polar solvents and in the crystalline state at low temperatures. The infrared spectrum of a high pressure crystal of 1,2-dibromopropane was recorded at ambient temperature. Dipole measurements were carried out in CCl 4 and C 6 H 6 solutions. Each of the 1,2-dihalopropanes existed as a mixture of three conformers in the liquid state, the one with the halogens in the anti position was in large abundance. Spectral and dipole measurements revealed a comparatively larger concentration of the two polar gauche conformers in polar solvents. All the compounds crystallized in the anti form. The C-halogen stretching vibrations have been interpreted in detail. Vibrational analyses of the anti conformers have been carried out and a tentative assignment of the majority of the gauche bands has been proposed.

Infrared study of CO adsorbed on Co/γ-Al2O3 based Fischer–Tropsch catalysts; semi-empirical calculations as a tool for vibrational assignments

The n adsorption of CO(g) on a Co/γ-Al2O3 catalyst has been studied by diffuse reflectance infrared spectroscopy. n The effects of pressure, temperature and the addition of O2(g) and H2(g) have been investigated. Vibrational n bands can be assigned to specific carbonyl species on the reduced Co catalyst, at low surface concentration, n via a theoretical model. The basis for the model is an empirical relation between the number of valence electrons n in transition metal carbonyl complexes and the corresponding carbonyl stretching frequency. This relation has n been extended n to metallic n surfaces and combined n with results from extended Huckel calculations.

Substituted profanes: VII The vibrational spectra and conformations of 1,2,3-trichloro- and 1,2,3-tribromopropane

Abstract The infrared, far-infrared and Raman spectra of 1,2,3-trichloro- and 1,2,3-tribromopropane were recorded in the liquid state, in polar and non-polar solvents and in the crystalline state at low temperature. Crystals were formed under ca. 20 kbar pressure at ambient temperature and the infrared spectra recorded. Dipole measurements were carried out in CCl 4 and C 6 H 6 solutions. The existence of three or possibly four conformers in the liquids at room temperature was verified. Combined with independent electron diffraction measurements of the vapours, the spectra demonstrated an anti-gauche conformer (relative to the halogens) to be present in the low temperature and high pressure crystals of both compounds. This conformer was not the one suggested by earlier authors. The C-halogen stretching vibrations for the conformers do not agree with the predicted values.

The vibrational spectra of trans-1,4-dichlorocyclohexane and trans-1,4-dibromocyclohexane

Abstract The infrared and Raman spectra of trans-1,4-dichloro- and trans-1,4-di-bromocyclohexane were recorded in the region 4000-45 cm−1 as melts, as solutes in various solvents, as amorphous solids at −180 °C and in the crystalline state at various temperatures from −180 °C to 100 °C. Additional infrared studies of the vapours (140–190 °C), the solids under high pressure (1–50 kbar at ambient temperature) and dichroism of oriented polycrystalline films were carried out. Finally, Raman polarization ratios of the samples were measured in different solutions. Equilibrium mixtures of the trans-1,4-dichloro- and dibromo cyclohexanes in nearly equal amounts of ee and aa conformations were observed in the vapour phase, in the melts, in solutions and in the amorphous solids. In the crystals formed at room temperature both molecules existed predominantly in the ee conformation, with the chloro compound having a stable phase below and a disordered phase above 12 °C. When the chloro compound was evaporated onto a CsI window at −180 °C, both conformers were present in the amorphous solid. When annealed at temperatures below 10 °C, a crystal with molecules in the aa conformation was formed, above 12 °C, the crystal had molecules in the ee conformation. For the bromo compound no “aa crystal” was formed. When the “ee crystals” were exposed to high pressure the concentration of the aa conformer increased for both compounds and was almost exclusively present at 50 kbar and 50 °C. The spectra were interpreted in terms of C2h symmetry. The fundamental frequencies for both conformers were assigned and checked by the sum rule, and the rotational and vibrational partition functions were derived.

Spectroscopic studies of 1,4-dibromobutyne-2

Abstract Infrared spectra of 1,4-dibromobutyne-2 have been recorded over the 4000-200 cm −1 region in the vapour, liquid, amorphous and crystalline states Raman spectra were extended to ca. 20 cm −1 in the same states of aggregation, except for the non-recorded vapour phase spectrum. The temperature was varied between −190 and 160 °C, and the pressure up to 10 kbar. A high proportion of the molecules exhibited free, internal rotation in the vapour and liquid phases, but to a smaller extent in the amorphous state at −190 °C. For those molecules not being excited beyond the potential barrier, an unsymmetric conformation was preferred, whereas in the crystalline state the molecules possessed the anti conformation ( C 2 h ) both at low temperature and at high pressure at ambient temperature. A vibrational analysis based upon force field calculations was carried out and the mean amplitudes of vibration computed. The data have been related to preliminary results from dipole moment and electron diffraction investigations.

DIFFUSE REFLECTANCE IR STUDIES OF BIMETALLIC FISCHER-TROPSCH CATALYSTS

Abstract The promoting effects of Re in a bimetallic Fischer-Tropsch catalyst, Co/Re on a γ-Al 2 O 3 support, has been studied by diffuse reflectance infrared spectroscopy. It is concluded (1) that Re promotes the reduction of Co, (2) that Re for the first time is observed in the surface layer, and (3) that Re most probably forms a tricarbonyl entity.

The conformation and vibrational spectra of trans-1,4-dihalocyclohexanes: Part II. trans-1,4-Chlorobromocyclohexane and trans-1,4-chloroiodocyclohexane

Abstract The IR spectra of trans -1,4-chlorobromo- and trans -1,4-chloroiodocyclohexane were recorded in the region 4000–30 cm −1 as solutes in various solvents, as KI and polyethylene pellets and as solids under high pressure (1–50 kbar at ambient temperature). Additional spectra of the melts, amorphous and annealed crystalline solids at 90 K and dichroism of oriented polycrystalline films were obtained above 200 cm −1 . Raman spectra of the compounds were recorded in the amorphous and crystalline states at 90 K, and polarization measurements were made in CCl 4 CS 2 and C 6 H 6 solution. The title compounds existed as an equilibrium mixture of ee and aa conformers in solution, in the melts and in the amorphous solids at 90 K. When heated to temperatures in the region 165–195 K the amorphous solids apparently crystallized into a metastable form containing the aa conformer, while above 200 K the solids were converted to a stable crystal containing the ee conformer. Under high pressure the concentration of the aa conformer increased and this form was almost exclusively present at ca. 50 kbar nominal pressure. The fundamental frequencies for both conformers were assigned in terms of C s molecular symmetry. An extensive normal coordinate analysis on six trans -1,4-dihalocyclohexanes was carried out using the overlay technique.

The conformation and vibrational spectra of trans-1,4-dicyanocyclohexane

Abstract The IR spectra of trans -1,4-dicyanocyclohexane as a melt, as a solute in various solvents, as KI and polyethylene pellets and as amorphous and annealed crystalline solids at 90 K have been recorded in the region 4000-50 cm −1 . Additional spectra at high pressures (1–50 kbar) have been recorded and the dichroic ratios of oriented polycrystalline films are obtained above 200 cm −1 . Raman spectra of the compound as a melt, as an amorphous and crystalline solid at 90 K and dissolved in acetone, chloroform and benzene have also been recorded. The compound exists as an equilibrium mixture of ee and aa conformers in solution, in the melt and in the amorphous solid at 90 K, but as one conformer only, apparently the ee form, in the crystalline state. Unlike the corresponding dihalocyclohexanes, trans -1,4-dicyanocyclohexane cannot be converted to an “ aa crystal” either by exposure to high pressure or by annealing to a metastable crystal. The fundamental frequencies of both conformers have been interpreted in terms of C 2h molecular symmetry and the assignments supported with a force constant calculation by the overlay technique transferring force constants from various related molecules.

Spectroscopic studies of ethyl thiocyanate

Abstract Infrared and Raman spectra of ethyl thiocyanate have been recorded over the 4000-50 cm −1 region in the vapour, liquid, amorphous and crystalline states. The temperature was varied between −180 and 180 °C. The spectra revealed only the gauche conformation. An assignment of the fundamental vibrations has been proposed.