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

Can Supported Reduced Vanadium Oxides form H2 from CH3OH? A Computational Gas-Phase Mechanistic Study

A detailed density functional theory study is presented to clarify the mechanistic aspects of the methanol (CH₃OH) dehydrogenation process to yield hydrogen (H₂) and formaldehyde (CH₂O). A gas-phase vanadium oxide cluster is used as a model system to represent reduced V(III) oxides supported on TiO₂ catalyst. The theoretical results provide a complete scenario, involving several reaction pathways in which different methanol adsorption sites are considered, with presence of hydride and methoxide intermediates. Methanol dissociative adsorption process is both kinetically and thermodynamically feasible on V-O-Ti and V═O sites, and it might lead to form hydride species with interesting catalytic reactivity. The formation of H₂ and CH₂O on reduced vanadium sites, V(III), is found to be more favorable than for oxidized vanadium species, V(V), taking place along energy barriers of 29.9 and 41.0 kcal/mol, respectively.

Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene

This paper reports on UV-stimulated synthesis of methylcyanotriacetylene carried out in cryogenic rare gas matrixes via coupling of smaller precursors: propyne and cyanodiacetylene. The detection was possible due to the strong visible ã ³A' → X̃ ¹A₁ phosphorescence of CH₃C₇N, discovered in the course of this work. The ensuing measurements of electronic spectroscopy revealed the formally forbidden B̃ ¹E-X̃ ¹A₁ system, as well as the allowed one Ẽ ¹A₁-X̃ ¹A₁, with origins at approximately 3.32 and 5.4 eV, respectively. It was also possible to revisit the spectroscopic characterization of cyanotriacetylene, HC₇N, formed in parallel to the title photoproduct. Spectral assignments were assisted with a density functional theory study.

Electronic Spectroscopy of Methylcyanodiacetylene (CH3 C5 N)

The results of a study devoted to the electronic spectroscopy of gaseous, solid, and cryogenic matrix-isolated methylcyanodiacetylene (CH₃ C₅ N) are reported. UV absorption and optical phosphorescence spectra of the compound are described here for the first time, and the corresponding vibronic assignments are proposed. UV absorption, studied directly or through the excitation of phosphorescence, revealed the B˜  ¹ E--X˜  ¹ A₁ system, very weak A˜  ¹ A₂ -X˜  ¹ A₁ bands, and a strong, broad absorption feature, tentatively identified as D˜  ¹ E-X˜  ¹ A₁ . Spectral measurements were assisted by quantum chemical calculations at the DFT and ab initio (coupled cluster) levels of theory.

Infrared and Raman Spectroscopy of Methylcyanodiacetylene (CH3 C5 N)

A spectroscopic study combining IR absorption and Raman scattering is presented for methylcyanodiacetylene (CH₃ C₅ N). Gas-phase, cryogenic matrix-isolated, and pure solid-phase substance was analyzed. Out of 16 normal vibrational modes, 14 were directly observed. The analysis of the spectra was assisted by quantum chemical calculations of vibrational frequencies, IR absorption intensities, and Raman scattering activities at density functional theory and ab initio levels. Previous assignments of gas-phase IR absorption bands were revisited and extended.