A study of the electron capture induced decompositions and charge separation reactions of the doubly charged isomeric ions of the methylpyridines and aniline

The doubly charged isomeric ions [C₆H₇N]²⁺ formed from 2-, 3- and 4-methylpyridine and aniline were investigated via their unimolecular charge separation reactions and by electron capture induced decompositions (ECID). The ECID spectra were compared with the collision induced decomposition (CID) spectra of the singly charged ions in an attempt to investigate the structure of the doubly charged ions. The four isomers could be unambiguously identified by their unimolecular charge separations. These differences were greater than in the mass spectra, ECID spectra or CID spectra of singly charged ions.     

Reassignment of the electronic states of the trans dimer of acenaphthylene

The fluorescence and excitation spectra of trans dimer of acenaphthylene in a shpol'skii matrix at 4K are reported. The spectra at 4k are compared with the fluorescence and excitation spectra at 77K, previously reported by us. A reassignment of the origin of the two electronic states is required by such a comparison. The comparison once again establishes the point that the g state is below the u state, as was originally found from the comparison of two-photon and one-photon spectra. However, the splitting, which was originally described as “exciton splitting” should actually be ascribed to “site splitting”. The “exciton splitting”, as given in the present study, is about 130 cm⁻¹.     

A new theoretical prediction of the infrared spectra of cytosine tautomers

The infrared spectra of the cytosine amino-oxo and amino-hydroxy tautomers predicted theoretically at the ab initio Hartree—Fock level with a 6-31G** basis set are reported. These are compared with the experimental spectra obtained in an argon low-temperature matrix. The IR spectra computed at this level reproduce the experimental spectra closer than the previous predictions.     

A study of the electronic spectra of 9-fluorenone

The absorption and MCD spectra of 9-fluorenone are measured. The CD spectra of the β-cyclodextrin complex with 9-fluorenone are also measured. The assignment for the first (≈26.0 × 10³ cm^?1) and fourth (≈48.0 × ³ cm^?1) absorption band has been determined from the sign of the CD spectra by reference to the observed MCD spectra.     

The mass spectra and ionization potentials of the neutral fragments produced during the electron bombardment of aromatic compounds

A mass spectrometer equipped with a dual ionization chamber ion source has been used to characterize directly the neutral species produced in the dissociative ionization of gases by electron impact. Neutral fragment mass spectra have been obtained for the electron ionization and fragmentation of benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene and isotopically labeled toluene. The neutral fragment mass spectra correlate well with the structures of the molecules. The abundant species in the neutral fragment mass spectra also correlate reasonably well with the abundant complementary positive ions of the normal mass spectra. Ionization potentials have been determined for the abundant neutral species produced. Where comparisons with values reported elsewhere are possible, the agreement is usually within ±0.2 eV or less.     

The role of structured water in the calibration and interpretation of theoretical IR spectra

The purpose of this study was to simulate theoretical infrared (IR) spectra of halogenated acetate salts using density functional theory (DFT), and to calibrate those results with high-resolution ATR-FTIR spectra. Two types of spectra were calculated: one of the solutes solvated in water droplets ranging in size from 15 to approximately 28 H(2)O molecules, and the other of a solvent molecule in equivalently sized (16-29 H(2)O molecules) droplets. The background-subtracted spectra, composed of solvated (halo)acetate spectra minus calculated solvent spectra, were compared with their experimental counterparts. Changes in the calculated IR spectra were used to determine the effects of dissolved salts on the structure of water. Calibrations of model dissolved salt spectra with observation were good; correlations of >0.90 were observed for all haloacetate species.     

NMR identification of the terminal groups of the telomers of tetrafluoroethylene with tetrahydrofuran

¹H, ¹³C, and ¹⁹F high-resolution NMR spectra with heteronuclear spin-spin decoupling and without it were recorded for identification of the terminal groups of oligomers obtained by radical polymerization of tetrafluroethylene (TFE) in tetrahydrofuran (THF) solutions. The analysis of the spectra and their comparison with the quantum-chemically calculated spectra of possible polymerization products led to the conclusion that the terminal groups of oligomers are the α radical of THF and the hydrogen atom. The structure of oligomers found in this study opens up an opportunity of synthesizing from them polymers consisting of a flexible main chain with substituents in the form of rigid perfluorinated rods.     

Confirmation of the cation radicals of hexamethylethane and hexamethyldisilane by ESR and other spectroscopy

Unambiguous ESR spectra of cation radicals of hexamethylethane and hexamethyldisilane were obtained for γ-irradiated solutions in CCl₃F at 77 and 140 K. INDO calculations, optical measurements, and comparison with photoelectron spectra are consistent with the observed ESR spectra.     

Comparison of the relative intensities of penning electron spectrum and photoelectron spectrum. Unsaturaated hydrocarbons

The Ne* (³P₂) Penning electron spectra and the Ne I photoelectron spectra of ethylene, benzene, 1,3-butadiene, and styrene were compared. The π bands in the Penning spectra showed enhancement relative to the σ bands in comparison with the corresponding photoelectron spectra, suggesting that Penning electron spectroscopy has potential value for the assignment of photoelectron bands.     

Ultrasoft X-ray emission and the electronic structure of the acetaldehyde molecule

The electronic structure of the acetaldehyde molecule was studied by the ultrasoft X-ray emission method with the use of quantum-chemical calculations. The OK _?? and CK _?? spectra of the compound in the gas phase were obtained. Quantum-chemical calculations were performed at the RHF/6-311++G** level. The calculation results were used to construct theoretical X-ray spectra. The experimental spectra are interpreted.     

盐对甲醇微观结构的影响

利用拉曼光谱研究盐对甲醇微观结构的影响.比较了不同盐/甲醇体系的O—H伸缩谱段和C—O伸缩谱段的超额拉曼光谱,对比给出了阴、阳离子与甲醇的相互作用.O—H伸缩谱段的超额拉曼光谱明显地显示了阴离子与甲醇形成弱氢键,氢键强度排序为CH3OH-CH3OHCl--CH3OHNO3--CH3OHClO4--CH3OH,在这个波段内,基本观察不到阳离子与甲醇的相互作用.在C—O伸缩谱段内,阴阳离子均有显著的体现,且与它们作用的甲醇C—O伸缩振动频率有如下的关系:CH3—OH(阴离子)CH3—OH(体相)CH3—OH(阳离子).根据C—O伸缩谱段的超额拉曼光谱,拟合了该谱段的拉曼光谱,由分解的谱峰强度得到阴、阳离子第一溶剂化层中甲醇分子的数目,结果显示在该浓度(～0.005)下离子对第一溶剂化层以外的甲醇氢键网络结构没有明显影响.     

The vibrational spectra of the elementoorganic starburst dendrimers

The main features of vibrational spectra of starburst dendrimers have been analyzed for the first time. Their spectral pattern, in general, is determined by the ratio of a number of terminal groups to a number of repeating units. This ratio tends to m_r−1 (m_r — branching functionality of repeating unit), and becomes constant, when the generation number of the starburst dendrimer increases higher than 3-5. IR and Raman spectra of twelve generations of the phosphorus-containing dendrimers are represented and interpreted on the basis of the calculation of frequencies of the normal vibrations and band intensities in the IR spectra of ‘molecules’ terminated by dangling methyl groups, which are the fragments of the dendrimer molecule. Tailored spectra of these fragments are then compared with experimental spectra and satisfactory similarity has been obtained. Experimental spectra of generations higher than 4 are very similar, according to the theoretical approach. The results can be used for the analysis of the chemical and physical transformations in starburst dendrimers.     

Fluorescence of the diterpenoid alkaloids lappaconitine andN-deacetyllappaconitine in acetonitrile

The absorption, excitation, and fluorescence spectra of the diterpenoid alkaloids, lappaconitine andN-deacetyllappaconitine, in acetonitrile were studied. On the basis of the coincidence of the spectra with the analogous spectra of model compounds, methyl esters of anthranilic andN-acetylanthranilic acids, the conclusion was drawn that the—OOC(Ph)NRH groups are fluorochromes in the alkaloids studied. The high quantum yield of fluorescence and the bathofluoric shift in the luminescence and absorption spectra ofN-deacetyllappaconitine were explained by an increase in the electron-releasing ability of the —NRH group in the deacetylation of lappaconitine.     

Classification of IR spectra of organic compounds by the methods of multidimensional statistics

In order to clarify the possibilities of classifying the IR spectra of organic compounds by methods of multidimensional statistics, with the object of casting further light on the relationship between the structure of a compound and noncharacteristic spectral criteria, an experiment was carried out, in which methods of factor analysis were applied to the entire set of spectra. A clusterization was obtained of the original spectra conforming with the chemical classification of the compounds studied and universal vectors for transition into a low-dimensionality space, where the spectra studied are described by 11 factors instead of the initial 65. The concept of spatial identification of the spectra is discussed.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 94–100, January–February, 1993.     

DFT, ab initio and FT-IR studies of the structure of sulfonamide triazenes

We present an in-depth investigation of the structural, infrared spectra and visible spectra of various triazenes with a sulfonamide moiety. The preparation of 4-sulfonyl amide benzenediazonium chloride with cyclic amines of various ring sizes (pyrrolidine, piperidine, 4-methylpiperidine, N-methylpiperazine, morpholine and hexamethyleneimine) are theoretically investigated using the density functional theory (DFT) and Hartree-Fock (HF) levels of theory with the standard 6-31G* basis set. The calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid-phase FT-IR spectra are assigned modes based on the results of the theoretical calculations. The UV-Vis spectrum of each compound is measured in various solvents with a wide range of polarity to examine the role of solvent chemistry on observed spectral changes. The calculated spectra are in good agreement with the experimental spectra.     

Mass spectrometry of the triethylsilyl,tri-n-propylsilyl and tri-n-butylsilyl derivatives of some alcohols,steroids and cannabinoids

The 25 _eV mass spectra of the trialkylsilyl (R = Et, Pr, Bu) derivatives of several alcohols, steroids and cannabinoids are compared with those of the corresponding trimethylsilyl (TMS) derivatives. Abundant ions produced by elimination of one of the alkyl groups characterize most of the spectra. Although the presence of such ions is advantageous in certain cases, such as for single ion monitoring studies, the spectra usually contain fewer ions of diagnostic use than the spectra of corresponding TMS derivatives. Successive elimination of C_nH_2n fragments is also a feature of these spectra.     

Determining the time needed for the vortex method for preparing solvent-free MALDI samples of low molecular mass polymers

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is an important technique to characterize many different materials, including synthetic polymers. MALDI mass spectral data is used to determine the polymer average molecular weights, repeat units, and end groups. The development of the vortex method of solvent-free sample preparation showed that remarkably short mixing times could prepare samples that yielded high quality MALDI mass spectra. In this paper, we use microscopy images and MALDI mass spectra to evaluate the mixing time required by the vortex method to produce mass spectra for low molecular mass polymer samples. Our results show that mixing times of as little as 10 s can generate homogeneous thin films that produce high quality mass spectra with S/N ∼ 100. In addition, ultrashort mixing times of only 2 s still produce samples with mostly smooth morphology and mass spectra with S/N ∼ 10.     

A study of the practical limitations of principal components analysis and the labelling of unresolved HPLC peaks

Summary The method of iterative target transformation factor analysis (ITTFA) used in conjunction with second derivative peak finding has shown to be a practical method for the peak deconvolution and reconstruction of HPLC chromatograms and spectra. The second derivative method of peak finding is acceptable for resolutions above 0.5 for peaks of similar heights. Above 0.5 resolution the labelling gives correct results where the spectra are substantially different and also when reasonably similar. Below this value the peak labelling was still accurate where the spectra were different. Solvent effects on the spectra of the compounds studied are small and do not hinder the peak labelling process. Thus small “local” libraries are feasible. Presented at the 17th International Symposium on Chromatography, September 25–30, 1988. Vienna, Austria.     

Calculation of the information content of retrieval procedures applied to mass spectral data bases

A procedure has been developed for estimating the information content of retrieval systems with binary-coded mass spectra, as well as mass spectra coded by other methods, from the statistical properties of a reference file. For a reference file, binary-coded with a threshold of 1% of the intensity of the base peak, this results typically in an estimated information content of about 50 bits for 200 selected $\text{m}\text{z}$ values. It is shown that, because of errors occurring in the binary-coded spectra, the actual information content is only about 12 bits. This explains the poor performance observed for retrieval systems with binary-coded mass spectra.     

The electronic structure of heteroaromatic molecules; non-empirical calculations and photoelectron spectra for the isomeric-thiazoles and -thiadiazoles

The He(I) and MgKα photoelectron spectra are reported for the isomeric thiazoles, and He(I) spectra for the isomeric-thiadiazoles. Marked fine structure is apparent on some of the spectra. Comparison with the earlier spectra for thiophen and the azoles, and with ab initio calculations for the seven compounds, has led to assignment of the spectra. The calculations suggest that 1,3,4-thiadiazole is less aromatic than the other title compounds. As expected, the role of the 3d_s orbitals is found to be that of polarisation functions for all of the compounds, but inclusion of these orbitals leads to much better agreement with the observed dipole moments, both in magnitude and direction.