1,3-Dipolar cycloaddition of cyclic α-methoxynitrones, derivatives of 2H-imidazole 1-oxide and 4H-imidazole 3-oxide

The reactions of cyclic aldo- and -methoxynitrones of the 2H-imidazole-1-oxide and 4H-imidazole 3-oxide series with isocyanates, phenyl isothiocyanate, N-phenylmaleimide, and dimethyl acetylenedicarboxylate were studied. The reactions give the corresponding 1,3-dipolar cycloaddition products. 2,2-Dimethyl-4-phenyl-2H-imidazole 1-oxide does not enter into a similar reaction with isocyanates or phenyl isothiocyanate.     

Reaction of Β-oxonitrones — Imidazoline and pyrroline derivatives — With nucleophilic reagents

The reaction of -oxonitrones — imidazoline derivatives — with hydroxylamine, phenylhydrazine, and semicarbazide takes place at the carbonyl group with retention of the nitrone group. Stable nitroxyl radicals — spiroimidazoisoxazole derivatives — are formed in the oxidation of -hydroximinonitrones. The recyclization of the -oxonitrones, which takes place in an acidic medium, as well as by the action of hydrazine and thiosemicarbazide, leads, respectively, to pyrroline and pyrazole derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 912–919, July, 1991.     

The vibrational spectra of germane and silane derivatives—XI. Vibrational spectra and normal co-ordinate analyses of some thiogermanes

The i.r. and Raman spectra of the thiogermanes, (CH₃)_nH_3-n, GeSCH₃(n = 0–3) are reported and the fundamentals assigned. A normal co-ordinate analysis based on a modified valence force field supports the a priori assignments for all of the fundamental frequencies except the torsional modes.     

Raman spectra of gases—XX. Disilylsulfide and disilylsulfide-d6

The Raman spectra of gaseous, liquid and solid S(SiH₃)₂ and S(SiD₃)₂ have been recorded from 50 to 3500 cm⁻¹, and the infrared spectra of the gas and solid have also been investigated. A vibrational assignment is proposed and a normal coordinate calculation carried out using a modified valence force field.     

The vibrational spectra of germane and silane derivatives—XII. A reassignment of the dimethylhalosilanes

The i.r. and Raman spectra of the dimethylhalosilanes, Me₂SiHZ and Me₂SiDX (X = F, Cl, Br, I) have been recorded and the fundamental vibrations assigned. Analysis of the spectra of the deuterated compounds indicate that existing assignments for Me₂SiHX are in error.     

Vibrational spectra of 1,3,5-hexatriene and methylated derivatives—II. The coupling pattern for lateral methylation

The vibrational spectra of E-2-methyl-hexatriene (E2MH), 4-d-E-2-methyl-hexatriene (dE2MH), and E-3-methyl-hexatriene (E3MH) were measured and interpreted using semi-empirical QCFF/π calculations and empirical valence force field (VFF) calculations. The vibrational patterns of E2MH and E3MH are discussed on the basis of the VFF calculations. It is found that the vibrational pattern of E3MH resembles that of E-1,3,5-hexatriene whose normal modes to a high degree can be described by global symmetry coordinates, whereas the pattern of E2MH resembles that of isoprene whose normal modes are more influenced by local symmetry coordinates. The effect of steric hindrance on methyl group conformation and the coupling of the methyl group vibrations with those of the polyene chain are discussed.     

Vibrational spectra of benzene derivatives—XX Substituted benzoate ions and benzoic acids

The vibrational (principally i.r.) spectra are presented and assigned for some benzoate ions, for benzoic acid, and for twenty-five of the compounds: o-, m- or p-XC₆H₄CO₂Na, XC₆H₄CO₂H; X = CH₃, F, Cl, Br or I.     

NMR study of some diastereomeric nucleoside-3′-thiophosphate derivatives in solution

The conformational properties of diastereomeric P-modified nucleotides are reported as reflected by different NMR parameters. Some conformational trends can be rationalized by consideration of the ³J(C4,P) and ³J(C2,P) coupling values of the isomers and the nature of the substituent on the phosphorus. Configurational assessment of the phosphorus is inferred from NOE experiments. The effects of temperature, solvent and size of substituents are presented.     

The vibrational spectra of germane and silane derivatives—X. Trifluoro(methyl)-silane and -germane revised

A reinvestigation of the vibrational spectra of CH₃SiF₃ has lead to a more complete assignment than is currently available. An extension of the methods used has prompted a reassignment of the skeletal modes of CH₃GeF₃ and is believed to have lead to a settling of the assignment of CH₃GeCl₃, for which several versions exist.     

The measurement of derivative i.r. spectra—II. Experimental measurements

The performances of the Butler and Hopkins, and Savitzky and Golay methods, used in conjunction with the Trott and Beynon smoothing technique, for generating derivative i.r. spectra have been assessed experimentally, primarily in the context of peak finding. The test bands used were tert.-butyl benzene (761 cm-⁻¹), 1,2,3-trimethylbenzene (764.5 cm⁻¹) and m-xylene (766.5 cm⁻¹), together with doublets from two component mixtures of these hydrocarbons and a computer-generated doublet from the 1,2,3-trimethylbenzene band. Measurements were made on Perkin-Elmer 577 and 580 spectrometers, with off-line data processing; very satisfactory second and fourth derivative spectra were obtained. Conditions for the optimum compromise between signal to noise ratio and resolution, in terms of the derivatization and smoothing parameters, were established and prove to be similar to those previously deduced from a study of synthetic Lorentzian peak systems. Of the two derivatization techniques the Butler and Hopkins method gives the somewhat superior performance.     

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.     

Hydrogen bonding in 3-azetidinol—3. Ab initio and experimental spectra of the hydrogen-bonded species

The IR and Raman spectra in the range 4000-10 cm⁻ of 3-azetidinol and the O,N-dideuterated derivative have been recorded in the solid state and in aqueous solution. The interpretation of the vibrational spectra has been based upon ab initio calculations in the STO-3G approximation. A model structure for the calculations has been adopted in which 3-azetidinol binds two molecules of water and two molecules of ammonia. The results obtained for the aqueous solution are in accordance with the occurrence of 3-azetidinol as a hydrated, stacked, intermolecularly hydrogen-bonded chain.     

Conformation of acetate derivatives of sugars and other cyclic alcohols. Crystal structures, NMR studies, and molecular mechanics calculations of acetates. When is the exocyclic C-O bond eclipsed?

[reaction: see text] A study of published crystal structures (of O-acetylated sugars for the most part) suggests that the exocyclic C-O bond in acetate esters of cyclic alcohols intrinsically prefers a staggered conformation, although the eclipsed conformation is only slightly less stable. When the acetate is flanked by two equatorial substituents the preferred conformation is close to eclipsed. Over 1500 C-OAc bonds have been analyzed. Diagnostic NMR criteria for torsion angles and MM3 calculations are reported and confirm these conclusions.     

Spectroscopic characterization of alkane radical cations—I. Electronic absorption spectra of 3-methylalkane radical cations

Radical cations of various 3-methylalkanes (C₆-C₁₄) have been produced and stabilized by γ-irradiation of the corresponding neutral compounds in saturated chloroflourocarbon (1,1-diflourotetra-chloroethane and 1,1,2-trichlorotriflouroethane) and perflourocarbon (perflourohexane and perfluoro-methylcyclohexane) matrices at 77 K. The perfluorocarbon matrices appeared more suitable for studies of the lighter radical cations, whereas the chlorofluorocarbon matrices were more suited for studies of the heavier radical cations; intermediary cations could be studied in both types of matrices. After irradiation, electronic absorptions associated with both the matrix and the alkane additive were observed. Pure spectra of the 3-methylalkane radical cations were obtained by difference spectrometry, after selective elimination of these cations by illumination. The electronic absorption spectra of the 3-methylalkane radical cations consist in all cases of a single broad absorption band. The spectral position of this band shifts to longer wavelengths with increasing chain length; the maximum of the absorption band was found to be situated at 490 nm for 3-methylpentane radical cations and at 940 nm for 3-methyltridecane radical cations. The results are most interesting because they give direct information on the electronic absorption of 3-methylpentane radical cations. It was found that the molar extinction coefficients of these cations are not very much smaller than those of other 3-methylalkane radical cations and thus must be of the order of 10³dm³·mol^-1·cm^-1. From this it is deduced that the majority of positive ions trapped in irradiated pure 3-methylpentane glasses at 77 K are not parent cations.     

Studies on nitramide and its methyl derivatives with ab initio calculations——Ⅳ.The harmonic force field and vibrational spectra of dimethylnitramine and its isotopic derivatives

The complete harmonic vibrational force field of dimethylnitramine has been calculatedat the Hartree-Fock level using 4-21G basis set.The harmonic force field was then scaled with scalefactors previously derived from N-methylnitramine,and the vibrational spectrum of dimethylnitraminewas computed.This apriori prediction,made with no reference to observations on dimethylnitramine,agrees with the experimental IR spectrum in gas phase with a mean deviation of 8.4 cm~(-1).Some of thescale factors were reoptimized by fitting of the computed force field to experimental data.The newset of scale factors reduced the mean deviation to 4.5 cm~(-1),and was used to predict the vibrationalspectrum of deuterated form of dimethylnitramine(-6D).Dipole moment derivatives were also cal-culated and used to predict infrared intensities which are comparable with experimental values.     

Vibrational spectra of carboxylato complexes—II. Some oxo-tetranuclear complexes

The i.r. and Raman spectra of the compounds Be₄O(OOCCH₃)₆, Be₄O(OOCCD₃)₆, Be₄O(OOCH)₆ and Zn₄O(OOCCH₃)₆ have been analysed and assigned in detail. In particular, the vibrational modes of the O(MO₃)₄ subunits, and their interactions with the carboxylate ligand vibrations, have been identified. The compound Zn₄O(OOCC₂H₅)₆ has the same oxo-centred structure as the others.     

Vibrational spectra of benzene derivatives—XIX. Pentafluoroiodobenzene,and pentafluoroderivatives of thiophenol,styrene, nitrobenzene,benzoate ions and aniline

Interpreted i.r. and Raman spectra are reported for C₆F₅X, XI, SH, CHCH₂, NO₂, CO₂^∼, NH₂. From measurements of the solvent dependence of the NH₂ stretching frequencies of C₆F₅NH₂ the value deduced for pK_a is −2.2±0.5.     

σ-Complexes of transition metals in organic synthesis. 9. Reactions of allyl organomanganese compounds with γ-bromine derivatives of esters of α, Β-unsaturated carboxylic acids

The allyl Mn(II) organic compounds R¹CH=C(R²)CH₂MnCl (R¹=H, Me; R²=H, Me, Bu), obtained in situ from Grignard reagents and Li₂MnCl₄, react with esters of 4-bromocrotonic, (2-bromobutylidene)-, (4-bromo-2-butenylidene)-, (2-bromoisobutylidene) malonic, and (2-bromoheptylidene)cyanoacetic acids in THF at –78 to +20C to give derivatives of substituted cyclopropanecarboxylic or cyclopropane-1, 1-dicarboxylic acids. These derivatives contain a fragment of the allyl type. When ethers of 2-(bromomethyl)acrylic, 4-bromo-2-methyl-, and 4-bromo-3-methyl-2-butenoic acids are used, cross-combination products result.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 656–663, March, 1991.     

Vibrational spectra of halogen substituted cyclopropanes—V. Trans-1,2-dichlorocyclopropane

The i.r. spectra of gaseous trans-1,2-dichlorocyclopropane were measured from 4000 to 400 cm⁻¹ and to 200 cm⁻¹ in the liquid phase. The Raman spectrum of the liquid was obtained from 4000 to 50 cm⁻¹. An assignment of all 21 normal vibrations was proposed on the basis of i.r. vapour phase band contours, Raman depolarization ratios, expected group frequencies and comparison with closely related molecules. There is excellent agreement with the normal modes previously assigned for the cis and trans isomers of the chloro, bromo and iodo analogues. The data indicate little interaction between the two CHCl moieties.