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—conformations of cyclohexanol and cyclohexandiols

Infrared spectra of cyclohexanol and the trans and cis forms of cyclohexandiols with 1,4-, 1,3- and 1,2-OH groups in solution in CCl₄, CDCl₃ and in low temperature matrices in argon are reported for the OH stretching region. Band splittings are observed in the matrix state and the components are assigned to equatorial and axial OH groups. These are not split in spectra of solutions because of the greater band width in this state. Bands from hydrogen bonded forms are observed for favourable spatial arrangements.     

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—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 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.     

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 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.     

Structural information from OH-stretching vibrations—XIV. The influence of local interactions on the OH-stretching frequency in alcohols with an α-triple bond

The effect on the OH-stretching vibration of changes in the π-character of alcohols with an α-triple bond has been studied by means of the i.r. absorption band. It is demonstrated that in the investigated alcohols the OH … π interaction causes an increase of the OH-frequency as a result of the position of the OH-group with respect to that of the triple bond. Changes in the charge on the triple bond are reflected in the frequency: the larger the negative charge the higher the OH-frequency. Compared to saturated tertiary alcohols the accessibility of the hydroxyl for solvent molecules and hence the OH … solvent interaction is increased due to the absence of two (shielding) β-H-atoms. It turns out that the raising of the frequency caused by the triple bond is overruled by the lowering effect of the solvent.     

Infrared and Raman studies of hydrogen bonded complexes involving acetone,acetophenone and benzophenone—I. Thermodynamic constants and frequency shifts of the νOH and νCO stretching vibrations

The hydrogen bonded complexes between phenol derivatives and acetone (I), acetophenone (II) and benzophenone (III) have been studied in carbon tetrachloride solution by i.r. spectroscopy. The formation constants, the enthalpies of complex formation, the Δν_OH and Δν_CO values have been determined. For a given phenol derivative, the thermodynamic constants and Δν_OH are ordered according to I > II > III and the influence of a substituent implanted on the phenolic ring can be expressed by the Hammett relationship. The ϱ coefficients of the Hammett equation are related to the complexation enthalpies. The Badger—Bauer relation is valid for the three bases. The comparison with complexes involving other carbonyl bases allows to precise the influence of the substituent implanted on the carbonyl group. The Δν_OH values obey the dual substituent parameter equation using σ_I and σ⁺_R; the ϱ_I/ϱ_R ratio is higher than one. The Δν_CO values are shown to depend on the complexation enthalpy and on the delocalization effect of the substituents.     

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.     

Some features of the incorporation of oxygen in different oxidation states in the apatitic lattice—II On the synthesis and properties of calcium and strontium peroxiapatites

New apatites: peroxiapatites, containing in their lattices oxygen in an oxidation state — I, are found with calcium and strontium phosphate apatites. The oxygen (-I) containing groups are peroxide ions, which are associated with vacancies. Peroxiapatites are formed at high temperatures by a reaction involving O²⁻ of the oxyapatites and molecules of oxygen, provided the treatment atmosphere is sufficiently free of water. The peroxiapatite formation must be correlated with the very high reactivity of oxyapatites, which has been shown in the first part of this paper.When peroxiapatites are heated, in air, inert gases or vacuum, the peroxide ions disproportionate: molecular oxygen originating from this disproportionation reaction, is practically retained till 350°C by the lattice of strontium apatites, while it is released on formation from calcium apatites.     

On the sol–gel preparation of different tungstates and molybdates

The preparation and characterization of the M′–M′′–O nitrate–tartrate (M′ = Ca, Ba, Gd and M′ = W, Mo) precursor gels synthesized by simple, inexpensive, and environmentally benign aqueous sol–gel method is reported. The obtained gels were studied by thermal (TG/DSC) analysis. TG/DSC measurements revealed the possible decomposition pathway of synthesized M′–M′′–O nitrate–tartrate gels. For the synthesis of different metal tungstates and molybdates, the precursor gels were calcined at different temperatures (650, 800, and 900 °C). According to the X-ray diffraction (XRD) analysis data, the crystalline compounds CaMo_1-x W _x O₄ doped with Ce³⁺ ions, BaMo_1-x W _x O₄ doped with Eu³⁺ ions and Gd₂Mo₃O₁₂ were obtained from nitrate–tartrate gels annealed at 650–900 °C temperatures. The XRD data confirmed that the fully crystalline single-phase powellite, scheelite, or Gd₂(MoO₄)₃ structures were formed already at 650 °C. Therefore, the suggested sol–gel method based on the complexation of metal ions with tartaric acid is suitable for the preparation of mixed tungstates–molybdates at relatively low temperature in comparison with solid-state synthesis.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—II

The theory of factor analysis developed in Part I [A. Muller and D. Steele, Spectrochim. Acta 46A, 817 (1990) [1] is extended to cases where m > 3, m being the number of factors. The effect of increasing the number of independent parameters by m(m-1) for T′ and the subsequent changes produced in the transformed eigenspectra, are investigated. Applications to actual spectra of mixtures of: (A) butan-2-one, ethyl ethanoate, cyclohexane and oct-1-ene (B) butan-2-one, ethyl ethanoate, cyclohexane and 2-methylpentane and (C) oct-1-ene, butan-2-one, ethyl ethanoate, cyclohexane and 2-methyl-pentane are presented. Using standard target techniques, an alternative approach is developed for the m> 3 case. This is based on transformation of the leading three eigenspectra, followed by identification and elimination of a component in a repetitive manner, until completion. The problems associated with the implementation of the Beer-Lambert Law are explored the need for accurate determination of a suitable wavenumber block to ensure the removal of the correct amount of each component, is examined. The ability to recognize at least one of the m component spectra per programme cycle is demonstrated.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—I

The theory of factor analysis is extended to permit the computer based extraction of the spectra of pure components from spectra of mixtures. A simultaneous linear, non-orthogonal transformation of the eigenspectra and eigenvectors is used to generate all positive absorbances and concentrations within noise level. Applications to actual spectra of mixtures of: (A) ethyl ethanoate, butan-2-one and oct-1-ene; (B) ethyl ethanoate, butan-2-one and cyclohexane; and (C) butan-2-one, cyclohexane and 2-methylpentane are presented. The effects of changes in signs of the constrained diagonal elements of the transformation matrix is investigated. To explore the ability of the software to cope with component spectra in which there are no wavenumbers at which one component dominates an artificial set of mixtures is examined. Recognizable spectra are extracted. It appears that, even when there are no wavenumbers at which one component dominates, the condition of finding “the sum of squares of negative absorbances/concentrations” near zero is adequate to yield useful spectra for library searches.     

Raman spectra of selectively deuterated tetramethylammonium ions—II. Fermi resonance in the methyl stretching region

The Raman spectra of six selectively deuterated Me₄N⁺ ions in the methyl stretching regions are reported and the Fermi resonance multiplets caused by interactions with methyl bending overtones are discussed. For the rather simple cases of a single CH₃ group in the d₉ ion and a single CD₃ group in Me₄N⁺-d₃ three independent methods for the evaluation of the unperturbed symmetric stretching frequency from the observed Fermi resonance triplet are compared, and the matrix elements W₁₂ and W₁₃, describing this interaction, are determined from the perturbed frequencies and intensities. It is shown that a simple procedure, which determines ν⁰_s from the centre of gravity of an observed Fermi resonance multiplet, can also be applied to more complex cases, e.g. the polarized multiplets of the isotopically pure ions Me₄N⁺ and Me₄N⁺-d₁₂. The origin of the complex Fermi resonance pattern in the latter species is discussed in relation to the increased complexity in the methyl bending region, that has been previously analysed.     

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.     

Energy and volume activation parameters of the retro-Diels—Alder reaction in different solvents

The temperature and pressure effects on the decay rate of an adduct obtained from 9-chloroanthracene and tetracyanoethene by a Diels—Alder reaction were studied. The rate constants (298.2 K) and the enthalpies, entropies, and volumes of activation were determined for the retro-Diels—Alder reaction in different solvents. The data obtained confirm a possible decrease in the molar volume of the solvated adduct upon partial bond cleavage on the way to the transition state. The reversal of the sign in front of the activation volume cannot be indicative of a changed reaction mechanism.     

Intermolecular vibrations and dynamics of the anisole—benzene complex studied by multi-resonance spectroscopy

The intermolecular vibrations of the anisole—benzene complex in the ground and excited electronic states have been observed by the LIF (laser-induced fluorescence) and fluorescence-dip techniques. Short progressions due to the intermolecular vibrations suggest a small structure change of the complex upon electronic excitation. The LIF excitation spectrum shows predominant progressions of 27 cm⁻¹, which is tentatively assigned to one of the intermolecular bending modes in the excited electronic state. On the other hand, the fluorescence-dip spectrum shows only a series of bands with irregular intervals due to the intermolecular modes in the ground electronic state. The decay rates of the vibrationally excited complex in the ground electronic state have also been measured with the SEP-LIF (stimulated emission pumping-laser-induced fluorescence) technique, where the complex vibrationally excited by SEP is probed by the delayed LIF measurements. The complex excited to its purely intermolecular mode stays in the initially prepared state after a delay time of 1 μs. On the other hand, the complex excited to the intramolecular vibrational states above 500 cm⁻¹ does not seem to stay in the prepared states. Neither the relaxed complex nor the dissociated monomer was detected. A possible reason for this observation is discussed.     

Substituent effects in infrared spectroscopy—carbonyl stretching frequency in substituted acetonaphthones,acetylfluorenes and acetylbiphenyls

The carbonyl stretching frequencies of several ring substituted acetonaphthones, acetylfluorenes and acetylbiphenyls have been measured in CCl₄/CHCl₃ solvent and correlated with the substituent constants. The data are also analysed by DSP equation to evaluate ϱ_I and ϱ_R. Compared to acetylfluorenes, acetylbiphenyls transmit substituent effects to a lesser extent, which is explained in terms of the noncoplanarity of the two phenyl rings in the later system.