Gas‐Phase Infrared Spectroscopy of Substituted Cyanobutadiynes: Roles of the Bromine Atom and Methyl Group as Substituents

The IR spectra of 5‐bromo‐2,4‐pentadiynenitrile (Br?C≡C?C≡C?CN) and 2,4‐hexadiynenitrile (CH₃?C≡C?C≡C?CN), a compound of interstellar interest, have been recorded within the 4000–500 cm^?1 spectral region and calculated by means of high‐level ab initio and density functional calculations. Although the calculated structures of both compounds are rather similar, there are very subtle differences, mainly in the strength of the C≡C bond not directly bound to the substituent. These subtle bonding differences are reflected in small, but not negligible, differences in the electron density at the corresponding bond critical points, and, more importantly, are reflected in the IR spectra. Indeed, the IR spectrum for the bromine derivative presents two well‐differentiated strong bands around 2250 cm^?1, whereas for the methyl derivative both absorptions coalesce in a single band. These bands correspond in both cases to the coupling between C≡C and C≡N stretching displacements. A third, very weak, band also associated with C≡C and C≡N coupled stretches is observed for the bromine derivative, but not for the methyl one, owing to its extremely low intensity.     

EGB-promoted electrochemical synthesis of 6-thioxo-[1,3,5]-triazinane-2,4 dione derivatives

A simple method for the synthesis of 6-thioxo-[1,3,5]-triazinane-2,4-dione derivatives was reported. The electrogenerated cyanomethyl base obtained from electroreduction of neat acetonitrile assisted the reaction between thiourea derivatives and alkyl or aryl isocyanate. This protocol had the advantage of giving good yields using mild conditions. The obtained products have been identified by spectroscopic data, mass spectrometry, and high-resolution mass spectra or elemental analysis.     

Tetrahydroxy-p-benzoquinone as a source of polydentate O-donor ligands. Synthesis, crystal structure, and magnetic properties of the [Cu(bpy)(dhmal)]2 dimer and the two-dimensional [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2].16H2O inorganic-metalorganic hybrid

The use of tetrahydroxy-p-benzoquinone as a slow source of dihydroxymalonato and oxalato ligands led to the isolation under open-air mild reaction conditions of five different compounds, two of them prepared for the first time: [Cu(bpy)(dhmal)]2 (1) and [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2].16H2O (5) (bpy, 2,2'-bipyridine; dhmal, dihydroxymalonate; ox, oxalate). A possible mechanism for the oxidation of the benzoquinone to give the croconate dianion, which undergoes further ring-opening oxidation to decompose into dihydroxymalonate and oxalate, is proposed. All compounds have been characterized by elemental analysis, thermogravimetry, infrared spectroscopy, and powder X-ray diffraction. Single-crystal X-ray diffraction, electron paramagnetic resonance, and magnetic susceptibility measurements have been performed for compounds 1 and 5. A complete band assignment of the experimental FT-IR spectra is given through comparison with the ones calculated using density functional theory (DFT). The neutral dimer 1 constitutes the first structurally characterized example of a transition metal-dhmal complex, and it contains two copper atoms bridged by two dihydroxymalonato ligands acting in a mu2-kappa3O,O',O":kappa1O coordination fashion, so that an equatorial-axial Cu2(mu2-O)2 rhomboid core is formed. On the other hand, the inorganic-metalorganic hybrid compound 5 shows a two-dimensional arrangement of Keggin polyanions linked by one of the Cu atoms of the oxalate cationic dimers to give layers parallel to the (10) plane, the remaining ox-Cu-bpy fragments acting as interlamellar separators. In both cases, magnetic and EPR results are discussed with respect to the crystal structure of the compounds and, for compound 1, also with respect to DFT calculations of the exchange coupling constant.     

Synthesis and Crystal Structure of Peptide‐2,2′‐Biphenyl Hybrids

1,1′‐Biphenyl derivatives with amino acid/peptide substitution at C(2) and C(2′) (‘peptide‐biphenyl hybrids', 6 – 8 ) have been prepared by direct N‐acylation of amino acid/peptide derivatives with 1,1′‐biphenyl‐2,2′‐dicarbonyl dichloride ( 5 ). Both conformers, which arise from the rotation around the aryl aryl bond, have been detected by ¹H‐NMR spectroscopy. Single atropisomers of each 6 ((R)‐configuration at the stereogenic axis) and 7 ((S)‐configuration at the stereogenic axis) have been obtained in quantitative yield by slow evaporation of methanolic solutions. The procedures are dynamic atropselective resolutions (asymmetric transformations of the second kind). The crystal structures of the peptide‐biphenyl hybrids 6 and 7 show highly ordered molecular and supramolecular structures with extensive intramolecular and intermolecular H‐bonding.     

Experiments on small (H2)N clusters

The nucleation process of small hydrogen clusters has been studied in detail with space, time, and number size resolution on the basis of supersonic expansions of the gas through a cryogenic nozzle operating in the thermal range 24 < T <110 K. The diagnostic of the jet medium is based on high sensitivity (few photons/sec) Raman spectroscopy with very high spatial resolution ( $\approx 2~\mu$ m), enabling for quantitative measurements with time resolution in the domain of nanoseconds. Temperatures down to 0.1 K have been attained in the jet at a collisional rate low enough to avoid sudden freezing of the gas. Clusters between two and eight molecular units are observed size-resolved. Features of the ortho-ortho and ortho-para hydrogen dimers, and the role of three-body collisions for nascent dimers and trimers are reported.     

Analytical performance of some methods for the determination of trace elements in lichens used as air quality assessment

In this study, the validity of the effective (virtual) point-detector concept for the CdZnTe (CZT) detector for disc-shaped radioisotope sources has been investigated in the photon energy range of 50–662 keV. It has been found that the virtual point-detector model is valid for conventional CZT detectors. The photon energy dependence of the virtual interaction depth (VID) in the CZT detector does not seem to fit to a good trend. However, in general, the measured VID values are increasing with increasing γ-ray energy in the range of 50–662 keV, but the VID values always remain within the physical thickness of the CZT detector. For instance, the VID value was measured to be about 4.4±0.5 mm in the 5 mm thick CZT detector at 662 keV γ-ray energy. In application, the VID values for photons can be used for efficiency calculation models by scaling the measured detection efficiency as a function of energy and source-to-detector distance.