Frequencies and integral intenstities of the lactone and ester carbonyls of natural guaianolides

The frequencies and integral intensities of the IR bands of the stretching vibrations of lactone and acyclic ester carbonyls at C-8 of ten natural guaianolides and their derivatives, and of three model compounds have been studied. The most probable interpretation of the change in the value of A_C=O and _C=O of the lactone carbonyl have been suggested. In elegin and some of its derivatives, acroptilin, chlorohyssopifolin B, and eleganin, a lowering of the values of A_C=0 and _C=0 in comparison with dihydroelegin, hexahydroelegin, and the hydroxylactone of cynaropicrin is caused by nonvalent interactions of the lactone carbonyl with the -exocyclic double bond. The increase in A_C=O and _C=O in dihydroelegin, hexahydroelegen, and the hydroxylactone of cynaropicrin is due to the angular strain of the -lactone ring. It has been shown that in an acyclic side chain at C-8 an increase in the integral intensity and in the frequency of the ,-unsaturated ester carbonyl relative to guaianolides in which the terminal vinyl group at C-17 is absent is due to a conjugation effect.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 805–811, November–December, 1987.     

Die IR-Spektren von B-Methoxy- und B-Trideuteromethoxyborazinen und-boroxinen und Tri[methoxy(d3)boran

Zusammenfassung In Methoxyverbindungen des Bors tritt eine Verminderung der Frequenz der B—O-Valenzschwingung gengenüber den entsprechenden Trideuteromethoxyverbindungen auf. Dies wird durch zufällige Entartung von B—O und CH₃ erklärt, die zu einer Abstoßung und zur Vermischung des Schwingungscharakters dieser beiden Schwingungen führt. Hiedurch werden die B—O-Valenzschwingungen zu tieferen und die CH₃-Deformationsschwingungen zu höheren Wellenzahlen verschoben. Ähnliche Erscheinungen sind auch in Methoxyborazinen durch Wechselwirkung von BN und CH₃ zu beobachten. Diese Deutung gibt auch Hinweise für Zuordnungen in den Spektren von N-Methylborazinderivaten.

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In methoxy substituted boron compounds bands arising from B—O stretching and (O)–CH₃ deformation modes show accidental degeneracy. The frequency of the CH₃ absorption is increased whereas BO is decreased compared to the corresponding CD₃-compounds. The spectra of B-methoxyborazines show similar effects between BN and (O)–CH₃ bands, which is analogous to interference between BN and (N)–CH₃ in N-methylborazines.

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IR-Spektroskopische Untersuchungen an 1,3-Dioxa- und 1,3-Diaza-2-boracyclopentanderivaten

Zusammenfassung Die IR-Spektren von mehreren Dioxa- und Diazaboracyclopentanderivaten wurden zusammen mit jenen von C-deuterierten Verbindungen untersucht. Besonderer Wert wurde auf die Klärung von Kopplungen zwischen BN-, BO- und CH₃-Schwingungen im Bereich zwischen 1550 bis 1300 cm^–1 gelegt.

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IR-spectra of several dioxa- and diaza-boracyclopentanes have been studied together with those of some C-deuterated analogues. Special attention has been given to coupling effects of BN-, BO-, and CH₃-modes in the 1550–1300 cm^–1 region.

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Free Hydrogen Bonds in Alcohol Solutions with Inert Solvents

Raman spectra were obtained for alcohol solutions with inert solvents such asCCl₄, CHCl₃, etc. The frequency of the OH stretching vibrations[_OH(free) band]due to free hydrogen bonds varies with change in either alcohol or inert solvent.It is shown that the frequency of the _OH(free) band is sensitive to the shape ofthe head group of an inert solvent. The main cause for the frequency change ofthe _OH(free) band with change in alcohol is ascribed to the change of effectivemass of the vibrating unit (RO-H, R = alkyl group).     

Some anomalies in the vibrational spectra of α, β-unsaturated ketones

Summary Some anomalies in the intensities of the bands of the C=C and C=O bonds in the vibrational spectra of , -unsaturated ketones have been explained by a difference in the sequence of the frequencies of the in-phase (_s) and out-of-phase (_as) vibrations of the multiple bonds in their cis (_s<_as) and trans (_s>_as) arrangements.     

Energetics of intramolecular hydrogen bonds and conformations of ω-diphenylphosphoryl- and ω-diphenylthiophosphoryl-substituted aliphatic alcohol molecules

A series of conformationally heterogeneous and energetically multilevel -diphenylphosphoryl- and -diphenylthiophosphoryl-substituted aliphatic alcohols, whose molecules are capable of five-, six-, and seven-membered ring closure due to the OH...O=P or OH...S=P intramolecular hydrogen bond (IHB), was studied by IR spectroscopy and molecular mechanics. The data obtained confirm the previous assumption that the energy of IHB (E _IHB) differs substantially from the difference of enthalpies of conformers with and without IHB (–H ), which is experimentally determined by the temperature dependence of the intensity of IR (OH) absorption bands. The measured –H values can be positive, zero, or negative at significant IHB effects, i.e., at high (OH) and E _IHB values.     

Infrared spectroscopy of hydrogen bond and substituent effects in electron donor molecules

The frequency shift, , of the O—H stretching mode in the IR spectra of the H-complexes of phenol with electron donor molecules BX_i (B is the n- or -donor center and X_i are substituents; a total of eight series), the change in the Gibbs free energy, G, due to H-complexation, and the parameter (a measure of the ability of BX_i molecules to donate an electron pair; two series) are determined by both the electrostatic interaction and charge transfer in the formation of H-complex. The , G, and values depend not only on the inductive and resonance effects, but also the polarizability of substituents characterized by the parameters.     

Charge control of phenol complexation with unsaturated compounds containing organosilicon substituents. Thiophene derivatives

The frequency shifts of the O-H stretching modes and the resonance components _R of these shifts in the IR spectra of H-complexes of phenol with thiophene derivatives having organic and organosilicon substituents have been analyzed. Relationship of and _R parameters to values calculated by nonempirical methods that characterize the electronic effect of organic substituents on the effective charges of the thiophene ring atoms has been established. It has been shown that in the complexation of phenol (hard acid) with thiophene derivatives charge control prevails over frontier orbital control. The changes in the effective charges of the thiophene ring atoms due to the effect of organosilicon substituents have been calculated.For the previous publication of this series see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2163–2168, December, 1994.This work was supported by the Russian Foundation for Basic Research, Project No. 93-03-18725.     

Atranes

The infrared absorption spectra over the range 400–1700 cm^–1 of ten organyl- and organoxysilatranes, p-CH₃C₆H₄O] are investigated. The SiN coordinate link in these compounds is largely unreflected in the fundamental vibration frequencies of the bonds of the central silicon atom or the internal vibration frequencies of the substituents X linked to that atom. However, all the IR spectra have an absorption band in the 570 cm^–1 region, related to the valence vibrations (SiN), or manifesting itself as the frequency (Si-O) of the XSi (O)₃ group, substantially lowered because of interaction between the Si-O and Si-N bonds. Evidence in favor of this bond is shift of the (Si-H) frequency in the spectrum of silatrane(X=H).For Part V see [1].     

Influence of solvent on ir spectra of aroyl(hydroxymethyl)trifluorosilanes

Conclusions Dipole-dipole interaction of the solvent with molecules of aroyl (hydroxymethyl) trifluorosilanes 4-XC₆H₄COOCH₂SiF₃ is responsible for changes in frequency of the stretching vibrations of groups included in a five-membered ring, containing an intramolecular coordination bond Si 0 (the frequencies C=O and SiF _a , are lowered, and the frequencies _asCOC are raised). The value of the orientation-induction parameter in the Buckingham equation, reflecting the dependence of C=O and SiF _a on the parameters of the medium (, n), increases with increasing electron-donor capability of the substituent X, indicating an increase in the strength of the coordination bond. The coefficient in the Hammett equation is determined by the polar properties of the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2251–2254, October, 1984.     

IR Spectroscopic Study of Alkane Interaction with the Brønsted Acid Sites of Hydrogen-Exchanged Zeolites

Diffuse-reflectance IR spectroscopy is used to study the interaction of C₃ and C₆ alkanes (propane, n-hexane, 3-methylpentane, and cyclohexane) with the Brønsted acid sites of hydrogen-exchanged mordenite, ferrierite, ZSM-5, and faujasite. It is found that a shift of the absorption band of the stretching vibrations of acidic Si(OH)Al groups toward lower frequencies (OH) due to the formation of a hydrogen bond with adsorbed alkanes increases in the following series: OH(propane) < OH(n-hexane) = OH(3-methylpentane). The accessibility of Si(OH)Al groups to alkane molecules is determined by the dimension of rings through which molecules enter zeolite channels and cavities. It follows from the measured OH values that the strength of Brønsted acid sites decreases in the following series: HZSM-5 > H-mordenite H-ferrierite HY. The difference between the three high-silica zeolites is not great. The results obtained are compared with the published IR data on Si(OH)Al groups of zeolites with adsorbed alkanes and other weak bases.     

IR-Untersuchungen an B-Tris (dimethylamino) boroxin und B-Tris[dimethylamino (d6)] boroxin

Zusammenfassung In B-Tri(dimethylamino)boroxin zeigt — im Gegensatz zum B-Trimethoxyboroxin — die B–O-Hauptbande nur geringe Kopplung mit CH₃-Deformationsschwingungen. Die B–N-Valenzbande tritt hingegen mit _sCH₃ in Wechselwirkung, wodurch Banden mit gemischtem Schwingungscharakter entstehen. In der deuterierten Verbindung liegt BN verkoppelt mit BO bei 1461 cm^–1

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In B-Tri(dimethylamino)boroxin coupling between the B–O ring stretching main-band and CH₃ is weak in contrast to B-trimethoxyboroxine. Interference between BN and CH₃ leads to bands of mixed character, one of them is above 1500 cm^–1. In [(CD₃)₂NBO] BN coupled with BO is at 1461 cm^–1.

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Effect of quantization of molecular rotations on the rate of capture in the ion-linear dipole system

The version of transition state theory that accounts for quantization of the rotational energy of a dipole gives ion-dipole capture rate constants in good agreement with the statistical adiabatic channel model and, in the region , gives results more accurate than those obtained by numerical trajectory calculations.

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, , - . , .

     

Far infrared spectra (500–50 cm−1) of the 2,2′-bipyridine complexes of palladium and platinum halides

Summary The far-i.r. spectra of the title complexes have been examined. Band assignments are based on the shifts induced by ligand deuteration and halide substitution. Deuteration of bipyridine causes large shifts ( >10 cm^–1) in internal ligand modes, intermediate shifts between 2 and 9 cm^–1) in metal-nitrogen stretching and bending modes and small to zero shifts in metal-halide stretching and bending vibrations. Generally, the requirements for square planarC _2v synanetry [two (M–N) and two (M–X) bands] are observed. Previous ambiguities in the assignment of the (M–N) bands have been resolved by the isotopic labelling technique employed in this study.     

Liquid phase oxidation of acrolein catalyzed by Co and Mo complexes

Liquid phase catalytic oxidation of acrolein in the presence of Co(III) and Mo(VI) complexes was investigated. The addition of a Mo(VI) complex was found to accelerate the reaction at higher, and retard it at lower, Co(III) concentrations.

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Co(III) Mo(VI). Mo(VI) Co(III) Co(III).

     

Gas phase hydrogenation of m-xylene on palladium catalysts

Gas phase hydrogenation of m-xylene on palladium supported catalysts was studied and compared with the hydrogenation of o-xylene. The modification in the stereoselectivity of palladium due to an increase in the acidity of the support is explained in terms of an increased residence time of the reactive species on the active surface, leading to a product composition closer to that predicted by thermodynamics.

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- -. , , .

     

Kinetic Study of the Chemiluminescence Spectrum of Rarified Flame in Dichlorosilane Oxidation in the Near IR Region

Electronically excited HO ₂ ^. radicals (A ² A"–X ² A"), OH^.radicals (= 2 – 0), and HCl molecules (= 3 – 0) are identified using the emission spectra at 0.8–1.6 m in the rarefied flame in dichlorosilane combustion at 293 K and low pressures. The spectrum also contains the composite bands of the H₂O (0.823 m) and H₂O₂(0.854 m) molecule vibrations. The maximum intensity of emission of these species is attained behind the front of the active chemical transformation, and the equilibrium between the vibrational and translational degrees of freedom is established in the region of the regular thermal regime of cooling. SF₆additives act as a reservoir that accumulates the vibrational energy in developed ignition. The processes responsible for the inhibition of dichlorosilane oxidation by SF₆additives are considered.     

Infrarotspektren von Nickel- und Kobaltphosphit

Zusammenfassung Es wurden Infrarotabsorptionsspektren von NiHPO₃·4 H₂O und den - und -Isomeren von CoHPO₃·2 H₂O im Bereich von 700 bis 3600 cm^–1 aufgezeichnet und die Banden entsprechend zugeordnet. Aus den Spaltungswerten der Absorptionsbande der antisymmetrischen Valenzschwingung _as der PO₃-Gruppe folgt, daß durch den Einfluß der Kationen die Symmetrie des Phosphitanions verringert ist, und am besten mit Punktgruppe C_s beschrieben werden kann. Dies wird durch Vergleich der Wellenzahl der symmetrischen Valenzschwingung _s (PO₂) mit dem nach derRobinsonschen Beziehung ermittelten Wert bestätigt. Aus den Wellenzahlen der Valenzschwingungen _s (PO₂), _as (PO₂) und (PO) wurden die Kraftkonstanten und Längen der PO-Bindungen berechnet, die den beim Kupferphosphit und Magnesiumphosphit mittels Röntgenstrukturanalyse ermittelten Werten entsprechen. Aus der Form der Absorptionsbande der Valenzschwingung der OH-Gruppe wurde die Möglichkeit des Vorkommens einer Wasserstoffbindung über ein Wassermolekül diskutiert.

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Infrared spectra of nickel and cobalt phosphite

The IR spectra of NiHPO₃·4 H₂O and of the -and -isomers of CoHPO₃·2 H₂O have been recorded in the 700–3600 cm^–1 region and frequencies assigned. From splitting values of _as (PO₃) a symmetry decrease of the phosphite anion due to the influence of the cation was found. The symmetry of the phosphite anion therefore is best described under point group C_s. A confirmation was possible by comparing the experimentally obtained symmetric stretching mode _s (PO₂) with the value calculated from Robinson's equation. Stretching vibration wave numbers were used to calculate force constants and PO-bond lengths; these agree with bond lengths found by X-ray analysis of Cu- and Mg-phosphites. The possible existence of a hydrogen bond due to the presence of a water molecule was discussed on the basis of the shape of the _OH bond.

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FT-Raman Spectra of o-, m-, and p-Nitrophenol Included in Cyclodextrins

FT-Raman spectra of o-, m-, and p-nitrophenol included in -cyclodextrin (CD), -CD, hydroxypropyl (HP) -CD, andsulfated -CD were recorded. The phenyl (C=C) band of o- and p-nitrophenol in the CD inclusion complexes was shifted to higher wavenumber thanthat of pure o- and p-nitrophenol,whereas the phenyl (C=C) band of m-nitrophenol in the CD inclusion complexes was shifted to lower wavenumber than that of pure m-nitrophenol. The ring CH peak of o-nitrophenol in the CD complexes was shifted to higher wavenumber than that of pure o-nitrophenol, whereas the ring CH peak of m- and p-nitrophenol in the CD complexes was shifted to lower wavenumber than that of pure m- and p-nitrophenol.     

Vibrational spectra of the hexaalkyldielementooxanes-derivatives of the group IVB elements

Conclusions On the basis of the calculation of the frequencies and form of the normal vibrations for hexaalkyldielementooxanes (C₂H₅)₃MOM(C₂H₅)₃ (M is an element from the Group IVB) and the existence of a correlation between _as ^MOM and k_MO and _OH, it is shown that a change in the frequency of the antisymmetrical valence vibrations for the M-O-M group is mainly due to dynamic effects in the M-O-M system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1042–1044, May, 1976.