E.T.G. Lutz

Structural information from OH stretching frequencies monohydric saturated alcohols

Infrared data have been recorded of the hydroxyl stretching band for about 70 monohydric saturated alcohols in dilute carbon tetrachloride solution. The wavenumber maximum, the half-bandwidth and the band pattern could be related to the structure of the molecules. Not only primary, secondary and tertiary alcohols can be distinguished but also β-branched and cyclic ones. Four effects seem to be connected with the OH stretching band; viz. substitution and fixation both lowering the frequency, and rotation and shielding both enhancing it. For identification purposes a table correlating structure, wavenumber and half-bandwidth is presented.

STRUCTURE AND VIBRATIONAL PROPERTIES OF TETRAGONAL SCHEELITE NABI(MOO4)2

The structure of the tetragonal NaBi(MoO4)2 crystal was determined. The space group is I4=S42 with cell dimensions a=5.267, c=11.565 A and Z=2. The molybdenum atoms occupy two different sites of 4 symmetry. The Na+ and Bi3+ cations are situated on two positions with different occupancy factors and are short-range ordered. The IR and Raman polarized spectra are discussed on the basis of the factor group analysis and phonon calculations. The modified Urey–Bradley force field and potential energy distribution were applied for three molecular models of local disorder. Polarization properties are explained and related to the crystal structure.

Hydrogen bonds in crystalline carbohydrates : a variable-temperature FT-IR study

Abstract FT-IR spectroscopy has been used to investigate the hydrogen-bonding systems in crystalline methyl-α- d -manno-, methyl-β- d -galacto- and methyl-α- d -glucopyranoside. The OH stretching region has been studied at subambient temperatures. Deuterium exchange has been carried out to check for vibrational coupling. Good correlation is found between the uncoupled ν OH frequency at 100 K and the ratio of OH bond length to O ⋯ O distance obtained from neutron diffraction data. This correlation can be used to assign peaks to the different OH ⋯ O systems in crystalline carbohydrates. The shift of ν OH with temperature, the wavenumber-temperature coefficient (WTc), also proves to be useful in the assignment.

Vibrational characteristics of the double oxygen bridge in the NaIn(WO4)2 and NaSc(WO4)2 tungstates with wolframite structure

Abstract The normal coordinate analysis of the tungsten–oxygen core in NaIn(WO 4 ) 2 and NaSc(WO 4 ) 2 crystals was performed. The Urey–Bradley force field and potential energy distribution (PED) were applied in the internal and external phonon calculations for the W 4 O 22 Na 2 In 2 molecular system. The dynamics of the asymmetric WO 2 W oxygen bridge as well as terminal WO bonds were analyzed and discussed. The vibrational characteristics of the oxygen double bridge bond, i.e. vibration energy, symmetry, force constants, PED, atomic displacements, direction of the transition dipole moments and mean square amplitudes were obtained and discussed. The theoretical considerations were based on the polarized IR and Raman spectra of the materials studied.

2-Ethynyladamantan-2-ol: a model compound with distinct OH ··· π and CH ··· O hydrogen bonds

Abstract Vibrational spectroscopy has been used to demonstrate that the extremely short OH ··· π and ≡CH ··· O intermolecular contacts in crystalline 2-ethynyladamantan-2-ol are due to strong interactions, which may unambiguously be typified as hydrogen bonding in view of the behaviour of OH and ≡CH stretching and bending modes. The XH stretching vibration shifts to lower frequency, becomes broader and more intense and has a positive frequency-temperature coefficient, whereas the XH bending modes shift to higher values and show a negative frequency-temperature coefficient. Solution spectra of the title compound in apolar solvents served as a reference for the “free” molecule. Variable-temperature measurements together with deuteration experiments have been performed to establish the correct assignment of these characteristic modes.

Structural Information from the Integrated Intensity of the OH-Stretching Band of Saturated Alcohols

The integrated intensity, A, of the free OH-stretching band of a large number of noncyclic and six-membered cyclic saturated monohydroxy compounds has been studied as a possible source of structural information. The intensity of primary alcohols proves to be constant, viz., 16.8 ± 0.5 km/M. No factors have been found that influence this value. The standard A-value for secondary alcohols is 13.8 ± 0.4 km/M. OH-rotamers without trans-H-Oxygen-lone-pair interaction show a lower intensity; factors influencing the rotamer distribution might thus affect the overall A-value. A significant decrease is observed when a γ-methyl group is situated (very) close to and therefore strongly interacts with a lone pair of the oxygen atom. The standard A-value for tertiary alcohols is 11.2 ± 0.6 km/M. Initially all rotamers have the same A-value, but for the secondary ones a strongly interacting γ-methyl group may cause an appreciable intensity lowering. Besides, strong sterical interactions between the three alkyl substituents at the α-C-atom usually give rise to small changes in the intensity. The overall conclusion is that the integrated intensity proves to be a useful source of structural information.

The hydrophilic nature of water trees (in polyethene)

The water tree phenomenon is examined by investigating its hydrophilic nature. Experimental findings lead to a model which involves both the chemical composition and the physical structure of water trees. Carboxylate groups were found in all water trees considered. The concentration depended greatly on the type of polyethene; the carboxylate groups are thought to be end groups of the polymer. An interaction between water and carboxylate groups was assessed. This also was done for groups which absorb in the 1000-1200-cm/sup 1/ range; these groups are probably ionic sulfur-oxygen groups. It is shown that the hydrophilic nature of watertrees may be explained completely by the presence of chemically or physically bonded ionic groups. The oxidative stability of polyethene is reduced locally by water treeing. The results obtained support the idea of oxidation occurring during watertreeing if carboxylate groups and ionic sulfur-oxygen groups are regarded as possible oxidation products. Water trees can be selectively permeable to different entities; they seem to bear a close resemblance to ionomer membranes locally.<<ETX>>

A variable low-temperature FT-IR study of crystalline β-d-fructopyranose and deuterated analogues

Abstract FT-IR spectra have been recorded of β- d -fructopyranose and deuterated analogues at variable temperatures in the range between ambient and 100 K. The natural resolution enhancement showing up in the OH stretching region provides detailed information with respect to the system of H-bonds in the crystalline phase. Other spectral changes resulting from cooling have been studied in addition. The shift of the band maxima proves to be correlated with the H-bond geometry, i.e. the temperature sensitivity depends on the type(s) of H-bonding. The presence of vibrational coupling between some of the H-bonded OH groups has been demonstrated with deuterium exchange experiments. The peaks in the OH stretching region have been tentatively assigned based on the spectral information of the uncoupled vibrations at 100 K.

Solvent dependence of intramolecular hydrogen-bonds in ethylene glycol derivatives: an FT-IR study

Abstract A number of mono-methyl ethers of (poly) ethylene glycols have been investigated by FT-IR in the gas phase as well as in dilute solutions of CCl 4 , CS 2 , CHCl 3 and CH 3 I. It appears that both nucleophilic and electrophilic solvent interaction causes a decrease in the stretching frequency of an OH-donor. The behaviour of an OH-donor in a 5-RH-bond is similar to that of a monohydroxy-OH as both types of hydroxyl groups have an “open” character towards the solvent. As the OH-proton is strongly shielded in the 8-R and 11-R conformations, the frequencies in CCl 4 , CS 2 and CH 3 I are mainly determined by the positions of the acceptors and the bulk effect of the solvents. In solution, conformations are preferred in which the OH-proton exhibits a large accessibility to the solvent.

Structural information from OH stretching frequencies II. Spectral data and presence of conformers in primary, secondary and tertiary alcohols

Abstract The presence of conformers in non-phenolic alcohols in dilute CCl4 solution has been investigated. For some primary and secondary alcohols it is proved that the observed OH band can be composed of those of the contributing conformers. The spectral data of one of the conformers of propanol-1 could be calculated; the shielding effect of a β-gauche methyl group is established that way. It is shown that the orientation of the methyl groups in propanol-2 as well as in tert. butanol is different due to mutual non-bonding interaction. The normalized integrated intensity of the OH band is different for but fairly constant within the four types of alcohols and so it may be used for identification.