On the vibrational spectra and conformational stability of 1,1-dimethylhydrazine from temperature dependent FT-IR spectra of krypton solutions and ab initio calculations

Variable temperature (−105 to −150 °C) studies of the infrared spectra (3500–400 cm⁻¹) of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, in liquid krypton have been carried out. No convincing spectral evidence could be found for the trans conformer which is expected to be at least 600 cm⁻¹ less stable than the gauche form. The structural parameters, dipole moments, conformational stability, vibrational frequencies, and infrared and Raman intensities have been predicted from MP2/6-31G(d) ab initio calculations. The predicted infrared and Raman spectra are compared to the experimental ones. The adjusted r₀ parameters from MP2/6-311+G(d,p) calculations are compared to those reported from an electron diffraction study. The energy differences between the gauche and trans conformers have been obtained from MP2 ab initio calculations as well as from density functional theory by the B3LYP method calculations from a variety of basis sets. All of these calculations indicate an energy difference of 650–900 cm⁻¹ with the B3LYP calculations predicted the larger values. The potential function governing the conformational interchange has been predicting from both types of calculations and comparisons have been made. The barrier to internal rotation by the independent rotor model of the inner methyl group is predicted to have a value of 1812 cm⁻¹ and that of the outer one of 1662 cm⁻¹ from ab initio MP2/6-31G(d) calculations. These values agree well with the experimentally determined values of 1852±16 and 1558±12 cm⁻¹, respectively, from a fit of the torsional transitions with the coupled rotor model. For the coupled rotor model the predicted V′₃₃ (sin 3τ₀ sin 3τ₁ term) value which ranged from 190 to 232 cm⁻¹ is in reasonable agreement with the experimental value of 268±3 cm⁻¹ but the predicted V₃₃ (cos 3τ₀ cos 3τ₁ term) value of −73 to −139 cm⁻¹ is 25% smaller and of the opposite sign of the experimental value of 333±22 cm⁻¹. These theoretical and spectroscopy results are compared to similar quantities of some corresponding molecules.     

Transients and cooperative action of β-carotene, vitamin E and C in biological systems in vitro under irradiation

Using N^•₃ species as specific electron acceptor a defined ascorbate radical: AH^•↔A^•−+H⁺ (λ_max=360 nm, =3400 dm³ mol⁻¹ cm⁻¹) is observed. The attack of DMSO^•+ on vit.E results in a vit.E^• radical (k=1×10⁹ dm³ mol⁻¹ s⁻¹; λ_max=425 nm, =2400 dm³ mol⁻¹ cm⁻¹; 2k=4.7×10⁸ dm³ mol⁻¹ s⁻¹). Vit.E-acetate leads to the formation of a radical cation (vit.E-ac^•+). β-carotene reacts also with DMSO^•+ forming a radical cation, β-car^•+ (k=1.75×10⁸ dm³ mol⁻¹ s⁻¹; λ_max=942 nm, =14 600 dm³ mol⁻¹ cm⁻¹), which probably leads to the formation of a dimer radical cation, (β-car)^•+₂ (k=2.5×10⁷ dm³ mol⁻¹ s⁻¹).

Using E.coli bacteria (AB1157) as a model system in vitro it was found that all three vitamins are rather efficient radiation protecting agents. They can also increase the activity of cytostatica, e.g., mitomycin C (MMC), by electron transfer process. The mixture of vit.E-ac and β-car acts contradictory, but adding vit.C to it a strong cooperative enhancement of the MMC activity is observed once again. A relationship between the pulse radiolysis and the radiation biological data is found and discussed. A possible explanation of the previously reported trials concerning the role of vit.E and β-car on the increased occurence of lung and other types of cancer in smokers and drinkers is presented.     

The rovibrational analysis of the high-resolution IR spectrum of CD2HF below 1200 cm: an interacting tetrad of vibrational levels

The spectrum of CD₂HF was measured by high-resolution interferometric Fourier-transform IR (FTIR) spectroscopy (apodised instrumental band with:0.004 cm⁻¹ fwhm) between 800 and 1200 cm⁻¹ covering the four lowest fundamentals. A complete rotational analysis using a semi-automatic assignment procedure yields accurate band centres (ν₉: 912.2028 cm⁻¹, ν₆:964.4994 cm⁻¹, ν₅: 1050.5104 cm⁻¹, ν₄: 1093.8632 cm⁻¹) and a complete set of first-order Coriolis coupling constants. The most important couplings occur between ν₉ and ν₆ (ξ_a= 1.069 cm⁻¹, ξ_c= −0.3535 cm⁻¹) and between ν₅ and ν₄ (ξ_b= −0.80606 cm⁻¹). The analysis was guided by and compared with results from our ab initio calculations for Coriolis constants and transition moments using CADPAC at TZP/MP2 level.     

EPR lineshape studies of low-temperature vanadium 3d polaron dynamics in the 70V2O5-30P2O5 binary glass

In a specimen of 70V₂O₅-30P₂O₅glass, EPR lineshapes of the vanadium 3d¹ polaron have been studied between 4 and 77 K. At the lowest temperature the unpaired electron is localized at a single ⁵¹V site, and values of g=1.959, g= 1.989, A = 156.6 × 10⁻⁴ cm⁻¹ and A=53.8 × 10⁻⁴ cm⁻¹ have been measured. A Markovian small-step rotational diffusion model consistent with the random structure of the glass network is proposed for the polaron dynamics at the higher temperatures up to 77 K. This motion has a small activation energy barrier of 114 μeV.     

A valence force field for phenylalkynes Part II. Fundamental frequencies of phenylacetylene and tolane and molecular conformation of tolane in solution

The Raman and infrared spectra of tolane solutions and solid were recorded in the range 3200—30 cm⁻¹. An overlay calculation of valence force field for a group of molecules (benzene, phenylacetylene, tolane and diphenyldiacetylene) was undertaken to assign the tolane and diphenyldiacetylene fundamentals. A 46-parameter force field was derived from 371 observed wavenumbers. Reasonably good fits were obtained with an average error of 7 cm⁻¹ for in-plane and 6 cm⁻¹ for out-of-plane frequencies.

The tolane conformation in solution is discussed and evidence that the most probable geometry is planar is presented. Some experimental results inexplicable in terms of the planar model were obtained, and were ascribed to the fraction of non-planar molecules present.     

A theoretical investigation of C5

Large-scale CEPA-1 calculations have been carried out for linear C₅, a molecule of substantial interest to combustion processes and astrochemistry. The equilibrium bond lengths are predicted to be 1.289 Å (outer CC bond) and 1.283 Å (inner CC bond), with an accuracy of 0.002 Å. The calculated ν₃ band origins of 2161 cm⁻¹ (105 CGTO basis) and 2137 cm⁻¹ (150 CGTO basis) are in good agreement with the experimental value of 2169 cm⁻¹. This band has an extremely large transition moment of 0.74 D. The less intense stretching fundamental ν₄ (μ=0.18 D) is predicted to occur at 1478 ± 10 cm⁻¹. Predictions for the totally symmetric stretching and the bending vibrational frequencies (in cm⁻¹) are 2008 (1σ_g⁺), 792 (2σ_g⁺), 570 (1π_u), 209 (1π_g) and 119 (2π_u).     

Vibrational overtone activation of methylcyclopropene

The vibrational overtone spectrum of methylcyclopropene in the region of the 6-0 and 5-0 C---H stretching transitions is reported. Transitions corresponding to the methyl, methylenic and vinyl C---H stretches are assigned. From the Birge-Sponer plots the anharmonicities and mechanical frequencies for the methyl in-plane and out-of-plane C---H stretches are −67.0 and 3118.0 cm⁻¹ and −64.0 and 3071.0 cm⁻¹, respectively. The corresponding values for the methylenic C---H stretches are −60.5 and 3030.7 cm⁻¹. Photolysis at 17093 cm⁻¹ (585 nm) yields two stable products which were identified by gas chromatography. Approximately 60% of the total yield was 2-butyne. A specific rate constant of 1.66×10⁸ s⁻¹ results from the Stern-Volmer analysis of the product yield of 2-butyne.     

An ab initio study on the equilibrium structure and torsional potential energy function of dinitrogen tetroxide

The molecular parameters of dinitrogen tetroxide, N₂O₄, have been determined in large-scale ab initio calculations using the multiconfigurational second-order perturbation method, CASSCF/CASPT2, and basis sets of double- to quadruple-zeta quality. With the largest basis set employed, cc-pVQZ for nitrogen and cc-pVTZ for oxygen, the structural equilibrium parameters are determined to be r(NN) = 1.7940 Å, r(NO) = 1.1906 Å and (NNO) = 112.55°. The potential energy barrier at the staggered conformation of the molecule is found to be 2313 cm⁻¹, and the binding energy of the NN bond is calculated to be 4616 cm⁻¹ (13.2 kcal/mol).     

Vibrational spectra and structure of chlorine substituted cyclopropanes : Part I. cis-1,2,3-Trichlorocyclopropane

The synthesis of cis-1,2,3-trichlorocyclopropane is reported. The infrared spectra have been recorded between 4000 and 400 cm⁻¹ in the polycrystalline solid phase, and between 4000 and 200 cm⁻¹ in the gas phase. The spectrum of a solution in carbon disulphide was measured from 1400 to 400 cm⁻¹. The Raman spectrum has been obtained between 4000 and 100 cm⁻¹ in the solid phase. An assignment of the fundamentals of the title compound is proposed and compared with similar molecules. The spectrum unequivocally proves the C_JV structure of the molecule.     

High-order torsional couplings in the infrared spectrum of 3,3,3-trifluoropropene

A 2 MHz resolution electric-resonance optothermal spectrometer and a microwave-sideband CO₂ laser have been used with microwave-infrared double resonance to investigate high-order torsional couplings in the 10 μm infrared spectrum of 3,3,3-trifluoropropene. Three normal mode vibrations are studied with band origins at 963.4, 980.2 and 1025.2 cm⁻¹. The 963.4 cm⁻¹ band is well characterized by an asymmetric-top Hamiltonian, except for the presence of a weak perturbation for J′ = 7, K_a′ = 2 affecting only the A-symmetry internal-rotor state. Microwave-infrared double resonance is used to study the microwave spectrum of the perturbing or ‘dark’ state. The observed dark-state K-doublet asymmetry splittings and rotational-state selection rules indicate that the perturbing state has five quanta of excitation in the torsional mode (ν₂₁) built upon the A″ ν₁₉ fundamental. The precise frequency determined for 5 β₂₁ of 421(2) cm⁻¹ leads to the first accurate determination of the barrier to CF₃ internal rotation as 641(5) cm⁻¹. In contrast to the 963.4 cm⁻¹ vibration, the 980.2 and 1025.2 cm⁻¹ modes show a large number of J′ and K_a′ perturbations which differentially affect the A and E symmetry internal-rotor states. The magnitude of the perturbation-induced A/E splittings indicate that the perturbing states must have at least four quanta of torsional excitation. The present results suggest that high-order vibrational interactions are important in the vibrational dynamics of molecules at low levels of overall vibrational excitation.     

Application of transform theory to the resonance Raman spectra of the 1:1 hexamethylbenzene: TCNE electron donor—acceptor complex

The resonance Raman excitation profiles of the 1:1 electron donor—acceptor complex between hexamethylbenzene and tetra-cyanoethylene (TCNE) have been gathered and analyzed using transform theory. Scaling factors and non-Condon factors have been obtained for the excitation profiles of the donor—acceptor stretch at 168 cm⁻¹, the C=C stretch at 1550 cm⁻¹, and the CN stretch at 2223 cm⁻¹, and used to estimate the change in donor—acceptor distance and in TCNE bond lengths in the charge trasfer excited state.     

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.     

Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

Evidence for Pdx(CO)y compound formation on an alumina substrate

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 × 10¹³ atoms s⁻¹ cm⁻² onto an alumina substrate (90 K) at a pressure of 2 × 10⁻⁶ mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 × 10¹⁴ Pd atoms cm⁻² and 1.4 × 10¹⁶ Pd atoms cm⁻². The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.     

Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine

Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pK_a = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm⁻¹ and a band at 811 cm⁻¹ due to the ν_s(C₃N) mode of the perturbed amine. The strongest phenol, CNP (pK_a = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH⁺---O⁻) absorption between 3000−1800 cm⁻¹, by the ν_as(C₃N⁺) and ν_s(C₃N⁺) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pK_a = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm⁻¹ and 950–400 cm⁻¹ regions due to the ν(NH⁺O⁻) and ν(OHN) modes, respectively.     

Infrared matrix isolation studies of complexes formed between dimethylsulfide, dimethyldisulfide and nitrous acid

The complexes formed by dimethylsulphide (DMS) and dimethyldisulphide (DMDS) with two isomers of nitrous acid have been observed, and characterised in argon and nitrogen matrices. The ν₁ OH stretching vibration of the perturbed trans-HONO monomer is 425 and 294 cm⁻¹ red shifted, respectively, for the DMS and DMDS complex in solid argon, and 441 and 301 cm⁻¹ in solid nitrogen. A large blue shift is also observed for the ν₃ NOH in-plane deformation mode: 101 and 80 cm⁻¹ for DMS–HONO-trans in argon and nitrogen matrices and 46 cm⁻¹ for DMDS–HONO-trans in nitrogen matrix. The results indicate formation of strong hydrogen bonds in the studied DMS–HONO and DMDS–HONO systems. The origin of the complicated shape of the ν₁ OH absorption is discussed. Similarities and differences between argon and nitrogen matrices are considered.     

Infrared studies of chromones—I Carbonyl and hydroxyl regions

Quantitative IR solution data in carbon tetrachloride and chloroform are recorded for the CO and OH regions of 31 chromones. In the 1580–1700 cm⁻¹ region, 5-hydroxychromones show three main maxima, the two of highest frequency, at 1663 ± 3 cm⁻¹ and 1630 ± 5 cm⁻¹ in CCl₄ (1661 ± 2 cm⁻¹ and 1627 ± 5 cm⁻¹ in CHCl₃), being sufficiently intense as to possess high CO character. Typically, 5-alkoxychromones exhibit two intense maxima in this region, 1663 ± 3 cm⁻¹ and 1613 ± 7 cm⁻¹ in CCl₄ (1657 ± 2 cm⁻¹ and 1608 ± 12 cm⁻¹ in CHCl₃). Diagnostically useful changes in contour and principal peak positions can be seen for substituted and annellated 5-hydroxychromones. In the 2500–3650 cm⁻¹ region, the stretching frequencies of OH groups at the most commonly encountered positions (C-5, C-7, and 2-CH₂OH) in natural chromones, are identified.     

Determination of trace amounts of beryllium using derivative spectrophotometry in non-ionic micellar medium

A rapid and sensitive method for the trace level determination of beryllium based on the formation of a 1:2 complex (λ_max 560 nm) with 1,4-dihydroxy-9,10-anthracenedione in an aqueous medium containing Triton X-100 is reported. Beer’s law is followed in the range 3.60–360 ng ml⁻¹ of Be(II). The molar absorptivity and Sandell’s sensitivity are 1.68×10⁴ l mol⁻¹cm⁻¹ and 0.54 ng cm⁻², respectively; detection limit is 0.23 ng ml⁻¹ of Be(II). Analysis of synthetic mixtures of composition similar to that of alloys and spiked samples of distilled water, gave results that are in agreement with their beryllium content.     

FT-Raman spectroscopic investigation of a pseudopolymorphic transition in caffeine hydrate

The FT-Raman spectra of caffeine hydrate and anhydrous β-caffeine have been recorded. The accelerated dehydration of the hydrate has been monitored at 30, 35 and 40°C using an environmental chamber. The spectra representing the individual pseudopolymorphic phases differed subtly throughout the entire spectral range. Gradual broadening of the =CH stretching vibration observed at 3121 cm⁻¹ and the progressive appearance of a C=O stretch at 1656 cm⁻¹ were ascribed to intermolecular bonding between CH and C=O in the anhydrous phase. Accompanying loss of resolution of CH deformations in the lower wavenumber region observed at 1475 and 1255 cm⁻¹ supports the suggestion of intermolecular association involving CH. Concurrent loss of resolution of the weak C=N stretch at 1454 cm⁻¹ and recession of the medium intensity H---C=N deformation at 1255 cm⁻¹ were also detected, acknowledging the loss of interaction between N9 of the imidazole ring and the water molecule. The concomitant disappearance of the weak H₂O libration at 890 cm⁻¹ is observed, which suggests the occurrence of molecular realignment associated with corresponding loss of water of crystallisation. On removal of the hydrate backbone of the caffeine hydrate crystal structure, the lattice collapses, resulting in reduction of the intermolecular distance between individual caffeine molecules. The subsequent formation of a less rigid structure is evident, whereby molecules are weakly associated by unconventional CH…O interactions.     

A Fourier transform infrared study of the lamellar liquid crystalline phase of dimethyldodecyl amineoxide-water and dimethyldodecyl amineoxide-gramicidin-D-water systems

The overall conformational order of the alkyl tail of the lyotropic lamellar phase of the dimethyldodecyl amineoxide, (CH₃)₂ON⁺(CH₂)₁₁CH₃ (DDAO)---H₂O system (75.7 wt.%) has been studied by using Fourier transform infrared spectroscopy. The spectral region 1000–1400 cm⁻¹, covering the CH₂ wagging modes and the methyl umbrella modes of DDAO, has been recorded in the temperature interval 3–60°C and at different mole fractions of gramicidin-D with respect to DDAO (X_g = 0.03, 0.05 and 0.1) for both DDAO-H₂O and DDAO-D₂O systems. It has been shown that the DDAO amphiphile molecules of the lamellar phase reorganise in a phase-like transition near 25–30°C. The DDAO-water system does not show any significant bands corresponding to a double gauche conformation at 1355 cm⁻¹ nor to a gauche-transgauche (kinked) conformation at 1367 cm⁻¹. These bands are probably present but hidden in the broad low-frequency side of the CH₃ umbrella band at 1377 cm⁻¹. Upon incorporation of gramicidin into the lamellar phase both head group and acyl chain spectra of the lipid change in such a way as to indicate a decreased “ordering” of the molecules, as judged by comparison with spectra of the same molecule in a micellar environment, and with increased fluidity of the acyl chains.