Structural information from OH stretching frequencies—V. On the presence of different rotamers in substituted tertiary cyclohexanol compounds

The presence of different hydroxyl rotamers in a number of saturated aequatorial and axial tertiary cyclohexanols has been studied by means of the i.r. spectra of the OH stretching band. Band resolving experiments indicate that an OH positioned over a cyclohexylring contributes appreciably to the overall band. Frequencies have been assigned and the existence of some kind of non-bonding lone-pair effect has been established. Evidence has been found for a special type of rotamer in t,t,t-perhydrophenalen-9-ol.     

Structural information from OH stretching frequencies—VII. Preferential OH-rotamers in saturated tertiary alcohols

The presence of preferential OH-rotamers in tertiary alcohols dissolved in CCl₄ has been studied by means of the infrared absorption of the OH-stretching band. It appears that the position of the OH group in these molecules is related to the presence and the orientation of α- and β-alkyl groups. The oxygen lone pairs play a role as well. In some compounds the preferred rotamer proves to be the only one present.     

Structural information from OH stretching frequencies—XI. The orientation of the hydroxyl group in tertiary α-ethynyl alcohols

The presence of different OH-rotamers in 11 tertiary α-ethynyl alcohols dissolved in CCl₄ has been studied by means of the i.r. absorption band. In all compounds the hydroxyl appears to be present only in a position next to the triple bond. It is demonstrated that this phenomenon arises from OH…π interactions. The existence of OH…π hydrogen bonding could not unambiguously be established. Like in saturated compounds the orientation of the OH proves to be influenced by β- and γ-CH₃ groups.     

Structural information from OH stretching frequencies—IX. The influence of γ-alkyl substituents on the different OH rotamers in saturated axial cyclohexanols

The sensitivity of the OH-vibration in saturated axial cyclohexanols for γ-alkyl substituents has been studied. It appears that axial γ-substituents considerably influence both, the frequency and the presence of the rotamers. Besides the OH-vibration proves to be sensitive to the type of α-alkyl substituent. At least two types of intramolecular interaction affect the OH-frequency: (i) repulsive lone pair … β- and γ-alkyl interaction and (ii) β-methyl … axial β-H interaction.     

Structural information from OH stretching vibrations—XVII. On the different conformers in benzylalcohols and anthracylmethanols

The presence of conformers and corresponding OH rotamers in benzylalcohol and nine related compounds, dissolved in CCl₄ and CS₂, was studied by means of the i.r. OH stretching band. It is demonstrated that in the benzyalcohols at least two conformers are present differing in the position of the CO bond with regard to the plane of the ring, viz. at torsion angles ω of 0° and approximately 60°. The existence of a third conformation with ω = 90° cannot be excluded. The presence of different OH rotamers appears to be affected by the strength of the OH … π interaction. Effects on the distribution of conformers could not be proved.     

Structural information from OH stretching frequencies—VI. On the presence of different rotamers in alkyl substituted tertiary adamantanol-2 and bicylo[3.3.1]nonanol-9 compounds

The presence of different hydroxyl rotamers in alkyl substituted tertiary adamantanol-2 and bicyclo[3.3.1]nonanol-9 compounds has been studied in CCl₄, solution by means of the i.r. absorption of the OH-stretching band. The rotamer with the OH positioned over the ring skeleton proves to be sensitive to the alkyl substituent. Furthermore it is found that the adamantanol compounds behave differently from the corresponding cyclohexanol derivatives. It is demonstrated that information regarding the special orientation of the alkyl substituent can be derived from the OH-band.     

Studies of isolated GeH stretching frequencies—II. Substituent and inductive effects

v^is GeH data from the preceding paper I are examined for the additivity of substituent effects and for correlation with Taft σ* values. It is essential to correct for conformational variations in v^isGeH and the evidence indicates that gas based values are preferable to condensed phase one. α effects of Cl, Me, Et, i-Pr are roughly additive, but successive fluorination increases the increase in vGeH, whereas for other groups effects diminish with further substitution. For alkyl germanes and GeH₄ v^isGeH correlates well with Σσ* according to v = 2037 + 47Σσ*, but data for all other substituents are incompatible and no single correlation is possible, in contrast to earlier findings in this field. Possible reasons for the very different behaviour of alkyl [+I] groups and electronegative [-I] ones are considered. Attempts to evaluate dπ-pπ bonding contributions from vGeH data should be abandoned.     

CH stretching frequencies and vicinal CHCH stretching interaction constants in ethyl and isopropyl halides

New i.r. data are reported for the CH stretching regions of deuterated ethyl and isopropyl halides including the species CH₃CD₂X, CD₃CH₂X, CHD₂CHDX, (CHD₂) (CD₃)CHX, (CH₃)₂CDX and, where necessary, the normal compounds. These are analysed to obtain vicinal CH stretch—stretch interaction force constants in addition to force fields for the separate CH₃ and CH₂ groups. In the chloride, bromide and iodide compounds, ⨍′_t is consistently larger (in the range 0.024–0.030) and of opposite sign to ⨍′_g (0–0.018 mdyn/Å). Several intensity observations indicate that ⨍′_t is negative, ⨍′_g positive. Ethyl and isopropyl fluorides are anomalous in that ⨍′_t is smaller than ⨍′_g.     

Structural information from OH-stretching vibrations—XIII. Bandshape and bandmaximum of phenols in CCl4 and CS2

The bandwidth(s) of the OH-stretching vibration of 15 para- and ortho-substituted phenols dissolved in CCl₄ and CS₂ have been studied. The half-bandwidth (HBW) proves to be sensitive not only for changes in the intra- and intermolecular environment but also for ⨍_OH and for the mobility of the OH with respect to its intramolecular surroundings. The parameter ΔHBW seems to be uniquely related to the difference between the inhomogeneous broadening in CS₂ and CCl₄. A bulk and a local contribution could be established in the solvent effect on the bandmaximum. It is demonstrated that intra- and intermolecular interactions take place predominantly via the proton of the hydroxylgroup.     

Normal coordinate analysis of the molybdenum—oxygen stretching frequencies in the infrared and Raman spectra of 16O- and 18O-dioxomolybdenum(VI) complexes

The Raman and i.r. spectra of the dioxomolybdenum(VI) complexes, MoO₂[NH₂CH₂C(CH₃)₂S]₂, 1, MoO₂[CH₃NHCH₂C(CH₃)₂S]₂, 2, MoO₂[(CH₃)₂NCH₂C(CH₃)₂S]₂, 3, and MoO₂[(SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂], 4, have been investigated in the region of the MoO₂ stretching frequencies. ¹⁸O substitutions for the oxygen atoms in these complexes gave rise to complicated patterns in their vibrational spectra. A normal coordinate analysis has been applied to interpret the vibrational modes of complex 1 in terms of coupling the symmetric and antisymmetric OMoO stretches. Where the O atoms are inequivalent, the frequency differences between pairs of coupled modes varied with the site(s) of the isotopic substitution(s). The particular pattern of frequency differences was then used to aid in the spectral assignments of the remaining complexes.     

N–H stretching frequencies and the conformation of substituted ureas: an ab initio MO study

The dependence of N–H stretching-mode frequencies in representative di- and trialkyl ureas on the conformational state of the ureido group has been studied by ab initio MO calculations using HF/3-21G and HF/6-31G** basis sets. The molecules studied were 1,3-dimethylurea, 1-methyl-3,3-dimethylurea and 1-methyl-3,3-di-iso-propylurea. The principal conclusions from the ab initio results are:

• 1.the trans–trans conformer (N–H bonds trans to the CO bond) has N–H stretching bands with about 20–30 cm⁻¹ higher frequency than the respective cis–cis structure, in accord with earlier literature assignments based on experimental data;
• 2.the N–H stretching frequency interval in tri-substituted ureas is 15–20 cm⁻¹ higher than the N–H band position in the 1,3-disubstituted molecule studied, the effect being determined mostly by the higher N–H stretching force constant;
• 3.in the absence of the steric hindrance the stable rotameric forms of the ureido grouping are almost planar at HF/3-21G level of calculations, while HF/6-31G** calculations predict a slightly pyramidal structure at the nitrogen atoms in the trans–trans conformer;
• 4.in 1-methyl-3,3-di-iso-propylurea the steric influence of the two bulky iso-propyl groups cause a deviation from planarity of the N–H bond. The non-planar conformation is accompanied by a shift of the N–H stretching mode frequency towards higher values; and
• 5.the variations of the theoretically estimated N–H stretching-mode frequencies appear to be principally determined by changes in the N–H stretching force constants in the different molecules.

© 1997 Elsevier Science B.V.     

Structural Characterization and Chemical Modification of a Glucan from Spores of Ganoderma lucidum

The fungus of Ganoderma lucidum (Fr.) Karst has been viewed a folk medicine in China and its medical effects on cancer, hypertension, hepatitis and hyperglycemia were demonstrated by pharmacological studies in the last two or three decades1,2. On the other hand, interesting biological activities and physico-chemical properties have been reported for the polyelectrolytes derived from neutral polysaccharides, including anti-tumor, anti-HIV and formation of charged hydrogels. In the previous …     

Optical investigation of the conformations of cyclopentanone and α-chlorocyclopentanone

Summary Cyclopentanone exists in two conformations — with a quasi-axial (V) and a quasi-equatorial (VI) position for the carbonyl group. -Chlorocyclopentanone exists in four conformations: (VIDtrans-la'-2a(VIII) trans-le'2e, (DC) cis-la'2a=(X) cis-1a'2e.     

NMR studies of conformations and molecular recognition of pyridinio-appended and nicotinamide-appended β-cyclodextrin

Abstract

The conformations of pyridinio-appended β-cyclodextrin (CDP⁺) and nicotinamide-appended β-cyclodextrin (CDNA⁺) were studied by NMR spectroscopy. The orientations of the pyridine residue of CDP⁺ and the nicotinamide residue of CDNA⁺ were determined by using a combination of NMR spectroscopic techniques. NMR spectra indicate that the shapes of the cavities of CDP⁺ and CDNA⁺ were changed after forming complexes. This change depended on the shape of the guest. CDNA⁺ could separate the ¹H resonances at the Cβ position of racemic tryptophan into two sets of resonances for each enantiomer.     

Ab initio/empirical potential energy functions and stretching vibrational frequencies of the X̃ 2Π and à 2Π states of the chloroacetylene cation

Anharmonic potential energy functions for the stretching vibrational motions of the two lowest doublet states of chloro-acetylene cation have been constructed using ab initio RHF SCF calculations and some experimental information. Stretching vibrational frequencies are calculated variationally for four different isotopomers. The ν₁ vibrations of H¹²C₂³⁵Cl⁺ are predicted to occur at 3176 (X̃ ²Π) and 3231 (à ²Π) and the ν₂ vibration of the à state at 2081 cm⁻¹.     

Borosulfates—Synthesis and Structural Chemistry of Silicate Analogue Compounds

Borosulfates are oxoanionic compounds consisting of condensed sulfur- and boron-centered tetrahedra. Hitherto, they were mostly achieved from solvothermal syntheses in SO₃-enriched sulfuric acid, or from reactions with the superacid H[B(HSO₄)₄]. The crystal structures are very similar to those of the corresponding class of silicates and their substitution variants, especially regarding the typical structural motif of corner-sharing tetrahedra. However, the borosulfates are supposed to be even more versatile, because (BO₃) units might also be part of the anionic network. The following article deals with detailed reports on the different synthesis strategies, the crystal chemistry of borosulfates in comparison to silicates, and their hitherto identified properties.     

Overview of Special Session B—Compositional and Structural Analysis of Biomass

Special Session B at the 29th Symposium on Biotechnology for Fuels and Chemicals was the first invited session at this symposium devoted to analytical methods. The special topic was added in response to numerous requests for information on new and innovative methods that could be applied in the growing renewable fuels industry. Presentation topics include analytical methods for the characterization and analysis of maize traits, tools for investigating cell wall limitations to enzymatic degradation, methods for customizing enzyme cocktails for biomass, new techniques for the analysis of carbohydrates, analytical methods that enhance our understanding of pretreatment, improved methods for monitoring process intermediates, and published standard analytical methods for biomass conversion processes.     

Steroids of the spirostan and furostan series from plants of the genus Allium. XXVII. Alliosterol and allosides A and B from Allium suvorovii and Allium stipitatum — Structural analogs of furostanols

Two new glycosides of the cholestane series (allosides A and B) have been isolated from the fruit of the cocultivatedAllium suvorovii Rgi. andAllium stipitatum Rgl. (family Liliaceae, local name anzur). The acid hydrolysis of both compounds gave a sterol not previously described, which has been called alliosterol and has the structure of (22S)-cholest-5-ene-1, 3, 16, 22-tetraol, and the product of its dehvdration, which is (16S, 22S)-furost-5-ene-1, 3-diol. Alloside A is the 16-O--D-galactopyranoside, and alloside B the 16-O--D-galactopyranoside 1-O--D-glucopyranoside of alliosterol.Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 231–241, March–April, 1991.