P. Klaboe

The vibrational spectra of piperidine and morpholine and their N-deuterated analogs

Abstract The i.r. spectra of piperidine (pentamethylene imine) and morpholine (diethyleneimide oxide) as vapours, liquids and as amorphous and crystalline solids at −180°C were recorded between 4000 and 200 cm−1. Additional far i.r. spectra (400-50 cm−1) of hexane solutions were obtained. Raman spectra of the liquids (including semiquantitative polarization measurements) and the crystalline solids at −180°C were recorded. Infrared and Raman spectra of the N-deuterated piperidine and morpholine were observed in the liquid state. Both compounds existed in an equilibrium between the NH equatorial and axial conformers for all the states of aggregation, including the crystalline solid. Most of the fundamentals belonging to the equatorial conformer coincided with the corresponding fundamentals of the axial conformer, with some notable exceptions. The fundamental frequencies for both molecules were assigned from i.r. vapour contours, Raman polarization measurements and close similarities with the spectra of dioxan, penta-methylene oxide, cyclohexane and other six membered heterocyclic systems. Force fields were derived for the NH(D) equatorial and axial conformers of both molecules and the calculated frequencies of the parent molecules and the N-deuterated species were correlated with the experimental data.

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.

Spectroscopic studies of glycolaldehyde

Abstract The infrared spectrum of glycolaldehyde in the vapour phase, as a melt, in solution and as a crystalline solid were recorded between 4000 and 200 cm −1 . Raman spectra were obtained of the solid glycolaldehyde, of a supercooled liquid and of a saturated aqueous solution. The spectra have been interpreted in terms of monomeric molecules in the vapour phase at 95°. In the crystalline state glycolaldehyde forms dimers having a centre of symmetry, probably of 1,4-dioxane structure. As a melt at 100°, as a supercooled liquid at 30° or when dissolved in water or polar organic solvents, glycolaldehyde apparently exists as an equilibrium between monomer and dimer molecules, the latter predominating.

The vibrational spectra of maleimide and N-D maleimide

Abstract The infrared spectra of maleimide as a vapour (160°C), melt (100°C), oriented polycrystalline film, pellet and when dissolved in various solvents were recorded between 4000 and 400 cm −1 . Also certain spectra in the far infrared region 400-40 cm −1 were obtained. Raman spectra of the crystalline solid, melt and as a saturated solution in acetonitrile were recorded and semiquantitative polarization measurements carried out. For N-D maleimide infrared and Raman spectra of the solid compound were recorded. The fundamental frequencies have been assigned in terms of C 2v , symmetry on the basis of infrared vapour contours and dichroism of the oriented film as well as on Raman polarization data. A force field was derived for maleimide, by initially transferring force constants from maleic anhydride and subsequent refinement of the force constants. The agreement between observed and calculated frequencies for the in-plane modes was satisfactory whereas certain large discrepancies remained for the out-of-plane vibrations.

The vibrational spectra of 2-chloro, 2-bromo, 2-iodo and 2-cyanopropane

Abstract The infrared spectra of 2-chloro, 2-bromo, 2-iodo and 2-cyanopropane (the isopropyl halides and isopropyl cyanide) were recorded in the gaseous and liquid states in the region 5000–200 cm −1 . Raman spectra of the liquids were obtained using He-Ne laser excitation and semiquantitative polarization data are reported. The vibrational spectra of these substances are very closely related and the spectra are interpreted in terms of C s , symmetry for all the molecules. A tentative assignment of the fundamental frequencies for each compound is proposed.

The vibrational spectra of maleic anhydride and its deuterated species

Abstract The infrared spectra of maleic anhydride and its mono- and dideuterated species were recorded in the region 5000-50 cm −1 in the vapour phase and in solution. Raman spectra of the solids and supercooled melts were obtained. Assignments of the fundamental vibrational frequencies are given, based upon semiquantitative polarization data and the infrared vapour contours as well as on the product rule and complete isotopic rule for the three compounds.

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.

The vibrational spectra of 1,4-dioxan-d0 and 1,4-dioxan-d8

Abstract The infrared spectra of 1,4-dioxan-d0 and 1,4-dioxan-d8 have been recorded in the vapour phase and as liquids in the region 4000-80 cm−1. Raman spectra of the liquids were obtained and polarization measurements have been carried out. Based upon the infrared vapour contours and the Raman polarization data, the vibrational spectra of both molecules have been assigned in terms of C2h symmetry and the results checked by the product rule. A normal coordinate calculation has been carried out, the thermodynamic functions and the root mean square amplitudes of vibration have been calculated.

The vibrational spectra of 1,4-dithiane and 1,3,5-trithiane

Abstract The infrared spectra of 1,4-dithiane have been recorded in the region 5000–200 cm −1 as a vapour at 150°, as a solid and dissolved in various solvents. Raman spectra of this compound were obtained as a solid and in solution and semiquantitative polarization data are presented. 1,3,5-trithiane was studied in the crystalline state and as a melt at 220°, and infrared and Raman spectra were recorded under these conditions. Approximate polarization values for the strong Raman bands were calculated from the melt-spectra. The strongest infrared bands were observed in the vapour at 230° as well as in solution. A tentative assignment of the fundamental frequencies for both molecules have been proposed.

Pressure effects on conformational equilibria. Difference in volume between conformers of 1,1,2‐trichloroethane

The effect of pressure on the equilibrium between conformers of 1,1,2‐trichlorocyclohexane has been studied using infrared spectra obtained with the diamond anvil cell. Changes in relative intensities of infrared bands show that the population of the more polar conformer (Cs symmetry) increases relative to that of the less polar conformer (C1 symmetry) with increasing pressure. Volume differences for converting the less polar to the more polar conformer are −3.8 cm3/mol in pure liquid and −1.8 cm3/mol in CS2 solution. These results are in agreement with values calculated by K. R. Crook and E. Wyn‐Jones [J. Chem. Phys. 50, 3445 (1969)].