Spectra and structure of phosphorus-boron compounds : IV. Vibrational spectra of solid trifluorophosphineborane

The Raman spectra of F₃PBH₃ and F₃PBD₃ have been recorded (2500-10 cm⁻¹) of the liquids (−80°C) and solids (−196°C) as well as the infrared spectra (4000-33 cm⁻¹) of the solids. In the spectrum of the solid state many of the ¹⁰B and ¹¹B fundamentals were clearly defined and it was also possible to assign the BH₃ torsional frequency from the infrared and Raman spectra of the solids. A complete vibrational assignment is proposed and a normal coordinate calculation carried out. The force constant of 2.46 mdyn Å⁻¹ for the P-B stretching mode is consistent with the short P-B bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. All of the E modes for the “free” molecule are shown to be split by the site symmetry which indicates that the molecules occupy C_s or C₁ sites. The large number of observed lattice modes is consistent with two or more molecules per primitive cell. The torsional frequency was observed at 224 cm⁻¹ and 167 cm⁻¹ in hydrogen and deuterium compounds in the solid, respectively. These frequencies gave a periodic barrier of 4.15 kcal mole⁻¹ for F₃PBH₃ and 4.31 kcal mole⁻¹ for F₃PBD₃. CNDO/2 calculations have been carried out for F₃PBH₃ and the isoelectronic F₃SiCH₃ molecule in both the staggered and eclipsed forms and the dipole and barrier origins are discussed.     

The vibrational spectra and conformational properties of liquid dimethyl oxalate

The infrared spectra of dimethyl oxalate and dimethyl oxalate-d₆ have been recorded in the liquid phase. These spectra are compared with both the infrared and Raman spectra recorded in solid phase. It is shown that dimethyl oxalate exists as a conformational equilibrium mixture in the liquid phase. The most stable conformer is that present exclusively in the crystal, the planar, cis-ester C_2h structure. The second conformer is probably one formed by rotation about the carbonyl carbon-oxygen bonds of the molecule.     

Vibrational spectra of ethyl iodedes

The infrared spectra of CH₃CH₂I, CD₃CH₂I, and CH₃CD₂I of the vapors and the solids at 170°C have been recorded from 4000-200 cm^?1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH₃CH₂X molecules is presented.     

Vibrational spectra and structure of trinitromethane

The vibrational spectrum of trinitromethane was interpreted in terms of the additive interatomic interaction model on the basis of experimental infrared and Raman spectra of HC(NO₂)₃, DC(NO₂)₃, HC(¹⁵NO₂)₃ and normal coordinate analysis. The frequency assignment results were used in discussing its structure. It was shown that the symmetry of trinitromethane is below C₃ in the liquid state.     

The vibrational spectra and structure of sodium bromoacetate and sodium bromoacetate-d2

The complete vibrational spectra of crystalline sodium bromoacetate and sodium bromoacetate-d₂ have been recorded and a vibrational assignmem proposed. The intermolecular coupling of these compounds is quite strong and the data are consistent with a centrosymmetric unit cell containing at least four molecules.The product rule calculations support a structure m which the bromine atom is rotated out of the plane of the remaining heavy atoms, but the frequency of the carbon-bromine stretching mode indicates that the degree of rotation is not large.     

A study of adsorption characteristics of traces of chromium(III) and (VI) on selected surfaces

The adsorption losses of chromium(III) or (VI) on the walls of Pyrex, flint glass and polyethylene beakers have been investigated. Chromium(III) or (VI) solutions were stored in beakers at different hydrogen ion concentrations, and losses due to adsorption were measured at various contact times by counting the γ-ray activity from chromium-51 radiotracer. At pH 6.95, chromium(III) solutions showed the greatest instability, particularly in polyethylene beakers, where losses up to 25% were observed at the end of the 15-day contact period. Chromium(VI) showed a completely different pattern; losses less than 1% were observed at the end of 15 days on all the three types of containers.     

Microwave spectrum and substitutional structure of CH2DF

Forty-two transitions of the microwave spectrum of CH₂DF have been observed in the region between 75 and 450 GHz. The measurement of both a-type and b-type transitions makes possible the analysis of the spectrum and the accurate calculation of the rotational constants (in MHz): = 119 675.0535 ± 0.074, = 24 043.4415 ± 0.072, ? = 22959.3732 °0.072, °j = 0.049371 ±0.00011, °_jk = 0.34268 ±0.0006, 2_k = 3,3774 ± 0.0035, δ _j = 0.002329 ± 0.000045, δ_k = 0.0687 ± 0.036. These constants, in combination with the results of earlier work on the symmetric speci r_s structure calculation based entirely on high-accuracy microwave data. The structural parameters are r_CH = 1.100 Å, r_CF = 1.383 Å, and ∠HCH = 110° 37'.     

Infrared and Raman multi-phonon spectra and structure of PbWO4

Improved Raman spectra of PbWO₄ show previously reported spectra contain large polarization and/or orientation errors. New spectroscopic information, obtained from polarized IR reflection and Raman spectra, allowed us to assign the IR and the previously unreported Raman multi-phonon bands. It was also used to show that it determines uniquely the C_4h factor group of PbWO₄. The use of IR reflection vs. infrared transmission spectra in the vibrational determination of crystal structures is also discussed.     

Structure,hydrogen bonding and vibrational spectra of pyruvic acid

The complete vibrational spectra of liquid pyruvic acid and the infrared spectrum of crystalline pyruvic acid at about 20 K have been recorded and analyzed. A vibrational assignment is proposed based on these spectra and comparison with spectra of derivatives of pyruvic acid.The spectra of pyruvic acid can best be interpreted in terms of a cyclic hydrogen-bonded dimer structure in which the two carbonyl groups are in a trans configuration in the pure liquid phase. A similar structure has been reported for crystalline pyruvic acid by X-ray diffraction. In dilute solution the structure appears to be monomeric with an internal hydrogen bond, in essential agreement with the structures of the monomer reported from microwave spectroscopic measurements.     

Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

Vibrational spectra and molecular configuration of hexafluoroazomethane

Twenty-one of the 24 fundamental frequencies of CF₃N=NCF₃ have been identified from the infrared and Raman spectra of the vapor and condensed states. The spectra reveal a total lack of infrared-Raman coincidence, i.e., the rule of mutual exclusion is obeyed. This evidence strongly supports the existence of hexafluoroazomethane in the trans configuration and negates the results of a recent electron diffraction study which favor the cis form.     

Synthesis of 1,1′-di-t-butylstannocene and its reaction with trifluoroborane. The crystal and molecular structure of η5-(CH3)3CC5H4Sn+BF4−

The reaction of Li(CH₃)₃CC₅H₄ with SnCl₂ in THF affords 1,1′-di-t-butylstannocene in 78% yield as an air-sensitive oil. ¹H and ¹³C NMR spectra are consistent with a pentahapto-structure. Mössbauer parameters of the stannocene and its trimethylsilyl counterpart match closely those of known stannocenes and neither compound appears to undergo oligomerization. The reaction of 1,1′-di-t-butylstannocene with BF₃ in CH₂Cl₂ affords η⁵-(CH₃)₃CC₅H₄Sn⁺ BF₄^? and other uncharacterized product(s) thought to involve tetracoordinate tin. The structure of η⁵-(CH₃)₃CC₅H₄Sn⁺ BF₄^? was determined by single crystal X-ray diffraction (orthorhombic,Pbcn, (T 25°C), a 18.423(3), b 11.723(1), c 11.044(2) Å, Z Å, m.p. 95–96°C, colorless, Mo-K_α, R = 0.043).     

The molecular structure and conformation of gaseous bis(chloromethyl)dimethyl silane as determined by electron diffraction

The molecular structure of bis(chloromethyl) dimethyl silane has been investigated in the gas phase at a nozzle temperature of 60° C. The molecules exist mainly in the GG form with the presence of 30% (+10%, ?20%) AG form. The values of the principal distances (r_a) and angles with estimated error limits of 2σ are r(C-H) = 1.093 (0.009) Å, r(C-Cl) = 1.801 (0.019) Å, r(Si-C) (the average Si-C bond) = 1.875 (0.009) Å, ∠(CSiC) = 109.5°, ∠(SiCCl) = 110.5° (0.4), ∠(CCH) = 112.5° (1.8) and φ (the gauche torsion angle relative to 0° for the anti form) = 117.4° (3.8).     

Atomic and molecular absorption spectra of indium in air-acetylene flame

Absorption spectra of both atomic and molecular species in the air-acetylene flame, which are produced when the aqueous solutions of indium dissolved in HNO₃, HF, HCl, HBr and HI were aspirated into the flame, have been investigated in the u.v. region. Numerous atomic absorption lines of indium have been observed in the absorption spectra. Most of these lines were previously listed only as emission lines. Those atomic lines have been ascribed to the electronic transitions from the ground states of 5p ²P_1/2⁰ and 5p ²P_3/2⁰ to the excited states such as ls ²S_1/2, md ²D_3/2, nd ²D_5/2, 4p^{2 4}P_1/2, 4p^{2 4}P_3/2 and 4p^{2 4}P_5/2, respectively, where 13 l 6 and 14 m,n 5. The molecular absorption bands for InF, InCl and InBr in the airacetylene flame have been also observed near 234 nm, 267 nm and 282 nm, respectively, as the electronic transition of ¹Σ⁺ → ¹Π₁ Those absorption bands show fine structures due to the molecular vibrations. The spectral parameters for the molecular vibrations have been obtained from the simulations of the observed spectra. The molecular absorption band for InI was not observed because of the decomposition of the molecule in the flame. In addition, the molecular absorption band for InO has been observed near 273 nm and those for NO near 205 and 215 nm.     

Excitation temperature,degree of ionization of added iron species,and electron density in an exploding thin film plasma

Time and spacially resolved spectra of a cylindrically symmetric exploding thin film plasma were obtained with a rotating mirror camera and astigmatic imaging. These spectra were decouvolved to obtain relative spectral emissivity profiles for nine Fe(II) and two Fe(I) lines. The effective (electronic) excitation temperature at various positions in the plasma and at various times during the first current halfcycle was computed from the Fe(II) emissivity values using the Boltzmann graphical method. The Fe(II)/Fe(I) emissivity ratios together with the temperature were used to determine the degree of ionization of Fe. Finally, the electron density was estimated from the Saha equilibrium. Electronic excitation temperatures range from 10,000–15,000 K near the electrode surface at peak discharge current to 7000–10,000 K at 6–10 mm above the electrode surface at the first current zero. Corresponding electron densities range from 10¹⁷-10¹⁸ cm^?3 at peak current to 10¹⁵-10¹⁶cm^?3 near zero current. Error propagation and criteria for thermodynamic equilibrium are discussed.     

A spectral and polarographic study of the acid--base and complexing behaviour of bromazepam.

A method for the microdetermination of periodate in the presence of iodate is presented. It is based on reduction of periodate to iodate by leucothionine generated in situ by photochemical reaction between EDTA and blue thionine. Biamperometric curves are used for evaluation, representing reduction time for the periodate versus the current generated in the oxidation of the T_red in excess after the end-point. A polarographic study of the process is presented. An applied potential of 100 mV is suitable for the biamperometric measurements with Pt—Pt electrodes. The method is applicable for 0.4–45 ppm periodate. Iodate does not interfere up to IO^-₃ : IO^-₄ ratios of 100:1.     

S42+ and S42− : an ab initio study

The structures of S₄²⁺ and S₄^2? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S₄^2? was also investigated. The anti chain form of S₄²⁺ was found to be 78.3 kJ mol^? more stable than the square form, in contrast to previous experimental data. S₄^2?is predicted to adopt the chain structure with the anti conformation.     

Characteristics of the background emission spectrum from a miniature inductively-coupled plasma

The spectral characteristics of the background radiation emitted by a miniature inductively-coupled plasma (i.c.p.) are carefully examined and methods for reducing undesirable features discussed. The complex nature of the background emission spectrum for the mini-i.c.p. indicates that careful line selection criteria and background correction procedures should be employed. Extending the torch coolant tube to the bottom of the region being observed in the plasma proved to be the most effective method for reducing undesirable spectral band features. Acute changes in background emission levels with r.f. power and nebulizer gas flow rates emphasize the need for careful control of these parameters to achieve high precision. Comparison between mini-i.c.p. and conventional i.c.p. spectra reveals the basic similarity of the two sources.     

The rhodophytin and chondriol natural products; structures of several new acetylenes from laurencia, and a reassignment of structure for cis-rhodophytin

The structures of five new halogenated vinyl acetylenes are described which are natural products from various species of the red seaweed Laurencia. The structure of epoxyrhodophytin (1) was determined by spectral, chemical, and X-ray diffraction analyses. The structures of trans-rhodophytin (5) and trans-chondriol (8) are based on chemical and spectral comparisons with the previously reported compounds cis-rhodophytin (4) and cis-chondriol (7). The structures of cis-chondrin (14) and trans-chondrin (15) were secured by synthesis from cis- and trans-chondriol, respectively. The reactivity of these enol-ethers to various conditions of catalytic hydrogenation has been examined in detail. Hydrogenation yields an unexpected and facile incorporation of oxygen into the reaction products. Based upon these studies, and upon combustion analysis, the structure of rhodophytin has been revised as the vinyl ether rather than the vinyl peroxide originally proposed.