Structure and IR Spectra of 3(5)-Aminopyrazoles and UV-Induced Tautomerization in Argon Matrix

The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol⁻¹; Gibbs free energy difference: 9.8 kJ mol⁻¹). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.     

Tricyanomethane and Its Ketenimine Tautomer: Generation from Different Precursors and Analysis in Solution,Argon Matrix,and as a Single Crystal

Solutions of azidomethylidenemalononitrile were photolyzed at low temperatures to produce the corresponding 2H‐azirine and tricyanomethane, which were analyzed by low‐temperature NMR spectroscopy. The latter product was also observed after short thermolysis of the azide precursor in solution whereas irradiation of the azide isolated in an argon matrix did not lead to tricyanomethane, but to unequivocal detection of the tautomeric ketenimine by IR spectroscopy for the first time. When the long‐known “aquoethereal” greenish phase generated from potassium tricyanomethanide, dilute sulfuric acid, and diethyl ether was rapidly evaporated and sublimed, a mixture of hydronium tricyanomethanide and tricyanomethane was formed instead of the previously claimed ketenimine tautomer. Under special conditions of sublimation, single crystals of tricyanomethane could be isolated, which enabled the analysis of the molecular structure by X‐ray diffraction.     

ChemInform Abstract: Matrix Reactions of Sulfur Atoms and Fluorine. IR Spectra of SF,SF2, and SF3 in Solid Argon.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: IR Spectrum and Structure of the GaCO3 Radical: A Matrix Isolation Study.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

The Threshold Photoelectron Spectrum of Fulvenone: A Reactive Ketene Derivative in Lignin Valorization

Unveiling reaction mechanisms by isomer-selective detection of reactive intermediates requires advanced spectroscopic knowledge. We study the photoionization of fulvenone (c-C₅H₄=C=O), a reactive ketene species relevant in catalytic pyrolysis of lignin, which was generated by pyrolysis of 2-methoxy acetophenone. The high-resolution threshold photoelectron spectrum (TPES) with vacuum ultraviolet synchrotron radiation revealed well-resolved vibrational transitions, assigned to ring deformation modes of the cyclopentadiene moiety. The adiabatic ionization energy was determined to be 8.25±0.01 eV and is assigned to the ²A₂← ¹A₁ transition. A broad and featureless band arising at 9 eV is associated with the ²B₁← ¹A₁ excitation. A conical intersection is responsible for the ultrafast relaxation of the fulvenone cation from the into the state resulting in a featureless and lifetime broadened band. These insights will increase the detection capabilities for fulvenone and thereby help to elucidate reaction mechanisms in lignin catalytic pyrolysis.     

IR125和HDITCP在不同烷基链长阳离子离子液体中的光异构化动力学

利用稳态吸收和荧光光谱以及时间相关单光子计数实验,分别测得近红外花菁分子IR125和HDITCP在不同烷基链长阳离子离子液体中的荧光量子产率和荧光寿命,并通过计算获得了它们各自在相应离子液体中的光异构化速率.发现IR125和HDITCP在不同离子液体中的光异构化速率没有随着离子液体粘度的增大而产生明显变化.与IR125和HDITCP在与离子液体具有相同粘度的甘油水溶液中的光异构化速率对比,发现IR125和HDITCP在离子液体中的光异构化能垒比它们在甘油水溶液中的光异构化能垒增大约2 kJ?mol-1,这表明在高粘度的离子液体中IR125或HDITCP与离子液体之间特殊的相互作用会阻碍它们各自的光异构化过程.     

Regio‐ and Stereoselective Generation of Alkenylindium Compounds from Indium Tribromide,Alkynes, and Ketene Silyl Acetals

InBr ₃ promotes the addition of ketene silyl acetals to monosubstituted alkynes to afford 2,2‐disubstituted alkenylindium compounds in high regio‐ and stereoselectivity (see scheme). In addition, the alkenylindium derivatives have been subsequently coupled with iodobenzene in the presence of a palladium catalyst.

     

Conformational interconversions in supersonic jets: Matrix IR spectroscopy and model calculations

Terminal conformer populations in supersonic molecular beams have been measured by use of matrix IR spectroscopy. the experimental technique is based on trapping of the beam molecules in to a cryogenic matrix. The ratio of conformational isomers is determined by comparing intensity ratios of infrared absorption bands with those found in analogous experiments with thermal effusive molecular beams. supersonic beams of pure 1,2-difluoroethane a considerable depopulation fo the less stable trans conformer is found, the lowest terminal conformational temperature reached being T_c^t8 = 207 (3) K. In seeded argon beams the cooling of the conformational distribution was found to be weaker. In supersonic beams of 1,2-dichloroethane and of methyl nitrite no significant conformational cooling was found. The experimental results are discussed in terms of a kinetic model of conformational interconversion in the flow field of a continuum free jet. The calculation indicate that conformational cooling by supersonic expansion may be expected only for molecules with a low energy barrier to internal rotation.     

The Photochemical Isomerization Kinetics of Urocanic Acid and Their Effects upon the in vitro and in vivo Photoisomerization Action Spectra

Abstract— The kinetic rate equation for the photoreversible photoisomerization between trans -urocanic acid (UA) and cis-UA following absorption of UV radiation has been solved and used to show that the maximum of the trans -UA photoisomerization action spectrum depends upon both the initial trans -UA concentration irradiated in an experiment and upon the irradiation dose used to determine the amount of cis -UA generated. This kinetic model can be used to explain current discrepancies between in vitro and in vivo photoisomerization action spectra reported in the literature.     

ChemInform Abstract: IR Spectra of As4-Ozone Reaction and Photolysis Products in Solid Argon.

The codeposition of As4 and O3 with excess argon at 14-17 K produces new IR bands at 921.7, 590.3 and 565.4 cm^-1, whose intensities are increased by red-light photolysis.     

ChemInform Abstract: Infrared Spectrum of a Symmetrical Phosphine-Ozone Complex in Solid Argon.

Cocondensation of Ar/PH₃ and Ar/O₃ samples at 12-18 K produces sharp satellite absorption bands.     

Carbonyl Diazide, OC(N(3))(2): Synthesis, Purification, and IR Spectrum

Carbonyl diazide (1), OC(N(3))(2), is prepared by reaction of triphosgene and tetra-n-butylammonium azide in a solution of diethyl ether or dimethyl ether. The advantage of this synthetic method, relative to other procedures, is that the use of triphosgene, OC(OCCl(3))(2), mitigates the need to use highly poisonous reagents such as phosgene, OCCl(2), or chlorofluorocarbonyl, OC(Cl)F. The identity and purity of OC(N(3))(2) are established by gas-phase IR spectroscopy, which reveals the presence of both syn-syn and anti-syn conformers. Computed anharmonic vibrational frequencies and infrared intensities of carbonyl diazide (1) display excellent agreement with experiment, and reveal the presence of strong Fermi resonances.     

ChemInform Abstract: IR Spectra of Molecular B(OH)3 and HOBO in Solid Argon.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Brute Force Orientation of Matrix‐Isolated Molecules: Reversible Reorientation of Formaldehyde in an Argon Matrix toward Perfect Alignment

Brute force orientation by an electric field is a promising way of controlling the orientation of polar molecules in the gas phase, but its application to condensed‐phase molecules has been very limited. We studied the reorientation of formaldehyde molecules in a solid Ar matrix under the influence of a strong electric field using reflection absorption infrared spectroscopy. Asymptotically perfect alignment of the formaldehyde molecules along the field was achieved at field strengths exceeding 1×10⁸ V m⁻¹. The vibrational bands of the aligned molecules exhibited a unidirectional Stark shift proportional to the field strength. The reorientation of the molecules was reversible despite the cryogenic solid environment of the system.     

ChemInform Abstract: IR Spectra of P4S10, P4S9, and P4S7 in Solid Argon.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.