Infrared spectra of crystalline ethylenedinitramine and tetramethylenedinitramine and their N-deuterated analogs

Conclusions The IR spectra of cyrstalline ethylenedinitramine, tetramethylenedinitramine, and their deuterated deriyatives were obtained. The assignment of the frequencies for the NH valence and deformation vibrations was made.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 432–434, February, 1968.     

The rα-structures of partially oriented 1,2,4,5-and 1,2,3,4-tetrachlorobenzene determined from their proton magnetic resonance spectra with natural abundance 13C-satellites

By recording two spectra of the same molecule in different nematic liquid crystals, and analysing the data simultaneously, information has been obtained on the molecular structures of 1,2,4,5- (1) and 1,2,3,4-tetrachlorobenzene (2). Carbon–hydrogen and carbon–carbon internuclear distance ratios, as well as bond lengths and bond angles, were computed and corrected for harmonic vibrations. Only part of the molecular structure of 2 could be derived with reasonable precision; the reasons for this limitation are discussed. The spectra of the two isomers were also analysed in isotropic solvents in order to determine the indirect coupling constants. One- and two-bond ¹³C isotope effects on the chemical shifts of the protons were observed. The solvent effects of the different nematic liquid crystals on the structure were found to be small compared with the experimental error.     

Solid‐State NMR Correlation Experiments and Distance Measurements in Paramagnetic Metalorganics Exemplified by Cu‐Cyclam

We show how to record and analyze solid‐state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu‐cyclam complex as an example. Assignment of the ¹³C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the ¹H signals was done by means of ¹H–¹³C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct ¹H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic ¹H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording ¹H–¹H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the ¹H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu‐cyclam by means of ¹³C R₂ relaxation experiments combined with the electronic relaxation determined by EPR.     

Time‐Resolved FTIR Emission Spectroscopy of Transient Radicals

Fourier Transform spectroscopy with 10^?8 second time resolution for recording IR emission spectra has been developed as an efficient means for detecting previously unknown vibrational modes of transient radicals. 193 nm photodissociation of a precursor molecule is used to generate vibrationally excited radicals, from which IR emission is recorded with time and spectral resolution. Assignment of the spectra is performed using information obtained through multiple precursors, isotopic substitution, time dependence of emission intensity, theoretical calculations, and 2‐dimensional cross‐spectra correlation analysis. The radicals vinyl, cyanovinyl, and OCCN have been studied with many vibrational modes identified.     

Vibrational Spectra of the Molten Nitrate/Platinum Electrode Interfacial Region

Raman spectra and IR reflection-absorption spectra are measured for the interfacial region between a platinum electrode and molten NaNO₃, KNO₃, and binary eutectic LiNO₃–KNO₃. The design of high-temperature spectroelectrochemical cells used in recording vibrational spectra of the region is described. Effects of electrode potential on the NO^- ₃ion inner-vibrational spectra are studied.     

Multichannel analyzers of atomic emission spectra: Current state and analytical potentials

The structure and characteristics of a modern tool for recording and processing emission spectra, that is, multichannel analyzer of atomic emission spectra (MAES), based on multicrystal assemblies of photodiode arrays, as well as spectral parameters of the instruments equipped with these analyzers are presented. The analytical potentials of MAES spectrometers are considered.     

Use of the Anomeric Carbon-13 Proton One Bond Scalar Coupling Constant as a Tool for Detecting 1,2-Orthoester Formation in Oligosaccharide Synthesis

Abstract

The anomeric ¹J_C,J value has for some time been successfully used for structural elucidation of oligosaccharides. The first recorded spectra on unenriched carbohydrates were published by Bock et al. in 1973 and pointed out that the anomeric ¹J_C,J value could be used for assignment of the anomeric configuration since pyranoses with an axial H-1 have a ¹J_C,J value which is approximately 10 Hz lower than the corresponding value in compounds with an equatorial H-1.^1–3 Their method recording non decoupled ¹³C NMR spectra had the disadvantage of being insensitive and thereby time-consuming. Introduction of INEPT⁴ followed by technical developments, has overcome this disadvantage. Nowadays, with reverse detection techniques, technical skill instead of sensitivity is a limiting factor. In this communication I would like to emphasize that the anomeric ¹J_C,J value can be used for detecting 1,2-orthoester formation as well as for establishing a- or P-configuration.     

Factors affecting photoisomerization of 4-styrylpyridine

Photoisomerization of 4-styrylpyridine at different irradiation wavelengths (λ 365 and 254 nm) and in different solvents was studied by UV and ¹H NMR spectroscopy. A procedure for recording the UV spectra of 4-styrylpyridine dissolved in liquid crystalline films freely suspended within a frame. The results of quantum-chemical calculations of the geometry and UV spectra of 4-styrylpyridine isomers are presented.     

Coherent amplification in fluorescent dye solutions. II. The inverse pre-resonance Raman spectrum of rhodamine 6G

Inverse pre-resonance Raman spectra of rhodamine 6G in solution in methanol have been recorded over the concentration range 10^?1 to 10^?4 mol ?^?1. The solute and solvent transitions are found to display perfectly normal lorentzian profiles over the whole of this concentration range. Intensities and depolarization ratios of the pre-resonance Raman features are recorded. It is shown that the spectra arise from monomeric rhodamine 6G molecules in the singlet electronic ground state and the relative merits of the CARS and inverse Raman methods for recording resonance Raman spectra are discussed.     

Structures of the products of aminoalkylation of 5- and 7-hydroxyflavones

On the basis of the¹H NMR spectra, it is shown that 7-hydroxyflavone is aminoalkylated in the 8 position, and it was established by¹³C NMR spectroscopy that the aminomethylation of 5-hydroxyflavone takes place in the 6 and 8 positions to give both monosubstitution and disubstitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 609–612, May, 1978.The authors thank V. K. Voronov for recording and discussing the¹H NMR spectra of I and II.     

Coupling of chromatography and NMR. 3—study of flowing gas chromatographic fractions by proton magnetic resonance

A procedure is described which allows the recording of ¹H NMR spectra from gas chromatographic (GC) fractions flowing through the magnetic field with a velocity of c. 0.6 cm/s. The spectra are obtained by the pulse Fourier transform technique; the beginning and the termination of the pulse sequence is timed according to the chromatogram from a thermal conductivity detector. The line width of the signals in the NMR spectra is 2 Hz.     

Time‐Dependent Surface Plasmon Resonance Spectroscopy of Silver Nanoprisms in the Presence of Halide Ions

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl^?, Br^?, and I^? are about 3×10^?4 M , 1×10^?6 M , and 1.5×10^?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.     

High-resolution/higher-order derivative spectrophotometry for identification and estimation of synthetic organic pigments in artists' paints

Twenty-two pigments commonly used in artists' paints were investigated by recording the fourth-derivative (d⁴) ultraviolet-visible spectra. Dimethyl sulphoxide was used as a universal solvent. It was possible to distinguish pigments which were chemically very similar and of the same colour, and to quantify the components of binary mixtures without separation by using side-peak-side ratio computations. Acrylic or oil media had no influence on the derivative spectra. For mixtures of more than two components, the pigments were separated by thin-layer chromatography and the d⁴-spectra were recorded directly from the developed spots; 10 ng of each pigment in 5 μl of solvent was enough for the analysis.     

The Diels-Alder reaction between substituted 6,6-dimethyl-2-vinylnorpinenes and maleic anhydride

Cycloaddition of substituted 6,6-dimethyl-2-vinylnorpinenes with maleic anhydride occursvia the attack of a dienophile on diene from the less hindered side of the bicyclic fragment. IR, UV, CD, and¹H NMR spectra of adducts have been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1546–1548, August, 1995.The authors are grateful to I. E. Ismaev for recording several¹H NMR spectra.     

Coupling of HPLC and NMR 1—analysis of flowing liquid chromatographic fractions by proton magnetic resonance

A procedure is described which allows the recording of ¹H NMR spectra from high performance liquid chromatography (HPLC) fractions flowing through the magnetic field with a velocity of either 0.05 or 0.25 cm/s. The NMR spectra are obtained by the pulse Fourier transform technique; the beginning and the termination of the pulse sequence is timed according either to the chromatogram from a UV detector or to the free induction decay of the appropriate HPLC fraction. The linewidth of the signals in the NMR spectra is between 1.5 and 2.0 Hz.     

Improved Large‐Scale Liquid‐Phase Synthesis and High‐Temperature NMR Characterization of Short ­(F‐)PNAs

We report on a large‐scale synthesis of F‐PNA trimer 10 and PNA trimer 11 . The key improvement is the facile two‐step synthesis of (2,4‐difluoro‐5‐methylphenyl)acetic acid ( 2 ). Water solubility of the corresponding F‐PNA oligomer 10 was achieved by synthesizing solubility enhancer 5a , which is twofold positively charged and only consists of inherent structural elements of PNA. Protected and unpaired PNA n‐mers exist in a mixture of 2ⁿ conformers undergoing slow exchange and leading to complicated NMR spectra. Structure analysis was improved by recording ¹H‐ and ¹³C‐NMR spectra at elevated temperatures above the coalescence point. Fully protected backbone derivatives show sharp resonances where expected, and spectra of protected PNAs are remarkably simplified, thereby allowing an interpretation for the first time. Both trimers 10 and 11 are considered as building blocks for a self‐replicating system based on PNA.     

Micro and two-dimensional NIR FT raman spectroscopy

The former major problem in conventional Raman spectroscopy in the visible range, the disturbing fluorescence of impurities, has now been eliminated: Raman spectra can be excited by light quanta in the near-infrared range, the energy of which is too low to excite fluorescence spectra. An inherent disadvantage of this technique, the v ⁴-dependence of the intensity of the Raman radiation, is compensated for by using interferometers, which are more powerful, by a factor of several hundred, than grating spectrometers. Raman spectroscopy can now be applied to analyses of real world samples bio materials, food, paintings, micro electronics and new materials, as well as to quality control of raw materials, to production and product control without special sample preparation. By using fiber bundles, Raman spectra can be recorded on line at the sample site, in containers and in real time. For successful recording of NIR FT Raman spectra of small samples a compromise between large lateral resolution and a large signal/noise ratio has to be found. Its theoretical base and practical approach is discussed. Confocal microscopes allow recording of NIR FT Raman spectra of small particles or inclusions. They can be coupled to the spectrometer by fiber optics, so that they may be placed at some distance from the spectrometer. By using computer-driven x-y stages, systematic mapping of the distribution of specific compounds on the surface of different samples is possible with the FT Raman microscope, as well as with the ordinary sample arrangement.     

Tetrazole derivatives. 25. Investigation of the synthesis of 1-(5-tetrazolyl)-3,5-diphenylleucoverdazyl. Structure and some properties of the accompanying product — 1,3,7,9-tetraphenyl-5-oxo-5H-1,2,4-triazolo[3′,4′:5,1]imidazo[4,3-c] -1,2,4-triazole

In the reaction of 1,3-diphenyl-5-(5-tetrazolyl)formazan with formaldehyde, in addition to a leucoverdazyl, one can obtain 1,3-diphenyl-1,2,4-triazole and 1,3,7,9-tetraphenyl-5-oxo-5H-1,2,4-triazolo[3,45,1]imidazo[4,3-c]-1,2,4-triazole. The structure of the latter was established from data from the mass spectrum and the ¹H and ¹³C NMR, UV, and IR spectra, as well as from the products of alcoholysis of this compound, which leads to 1,3-diphenyl-1,2,4-triazole and 1,3-diphenyl-5-carbethoxy-1,2,4-triazole. According to the data from the PMR spectra, the leucoverdazyl displays prototropic tautomerism due to the NH proton of the tetrazine ring.See [1] for Communication 24.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 694–700, May, 1981.The author thank V. I. Svergun ans M. B. Smirnov for recording the ¹³C NMR spectra and their assistance in their interpretation.     

Selective 1H-13C correlation by low power single frequency off-resonance decoupling assisted by exhaustive simulation techniques

Selectivity in the ¹H-¹³C correlation for assignments of ¹³C spectra is enhanced by recording single frequency off-resonance ¹³C NMR spectra with low decoupling field strength (? 2J_o), distortion of signal patterns is avoided by submitting the spin system to a previous noise broad band decoupling. Correlation is obtained by comparison of observed and simulated 2-D spectra (π ¹³C vs decoupler frequency) joined to fitting of the curve J_R = f (decoupler frequency) with the equation of Freeman and Anderson.₁     

Novel synthesis of 2,2-bis(2-methoxy-1-oxidodiazenyl)ethylnitramines via the relative ethyl trifluoroacetate

Russian Chemical Bulletin - A novel synthesis of 2,2-bis(2-methoxy-1-oxidodiazenyl)ethyl derivatives of methylnitramine and ethylenedinitramine consists in the treatment of...