Molecules
Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
Published: August 2020
A computational study of the structures and energetics of amine N-oxides, including pyridine N-oxides, trimethylamine N-oxide, bridgehead bicyclic amine N-oxides, and lactam N-oxides, allowed comparisons with published experimental data. Most of the computations employed the B3LYP/6-31G* and M06/6-311G+(d,p) models and comparisons were also made between the results of the HF 6-31G*, B3LYP/6-31G**, B3PW91/6-31G*, B3PW91/6-31G**, and the B3PW91/6-311G+(d,p) models. The range of calculated N-O bond dissociation energies (BDE) (actually enthalpies) was about 40 kcal/mol. Of particular interest was the BDE difference between pyridine N-oxide (PNO) and trimethylamine N-oxide (TMAO). Published thermochemical and computational (HF 6-31G*) data suggest that the BDE of PNO was only about 2 kcal/mol greater than that of TMAO. The higher IR frequency for N-O stretch in PNO and its shorter N-O bond length suggest a greater difference in BDE values, predicted at 10-14 kcal/mol in the present work. Determination of the enthalpy of sublimation of TMAO, or at least the enthalpy of fusion and estimation of the enthalpy of vaporization might solve this dichotomy. The "extra" resonance stabilization in pyridine N-oxide relative to pyridine was consistent with the 10-14 kcal/mol increase in BDE, relative to TMAO, and was about half the "extra" stabilization in phenoxide, relative to phenol or benzene. Comparison of pyridine N-oxide with its acyclic model nitrone ("Dewar-Breslow model") indicated aromaticity slightly less than that of pyridine.
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http://dx.doi.org/10.3390/molecules25163703 | DOI Listing |
Org Biomol Chem
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Department of Applied Chemistry, Waseda University, 513 Wasedatsurumakicho, Shinjuku, Tokyo 162-0041, Japan.
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Institute of Chemistry CAS: Institute of Chemistry Chinese Academy of Sciences, Beijing National Laboratory for Molecular Sciences, Zhongguancun North First St, 100190, Beijing, CHINA.
The photoelectrochemical (PEC) urea oxidation reaction (UOR) presents a promising half-reaction for green hydrogen production, but the stable resonance structure of the urea molecule results in sluggish kinetics for breaking the C-N bond. Herein, we realize the record PEC UOR performance on a NiO-modified n-Si photoanode (NiO@Ni/n-Si) by harnessing the adsorbate-adsorbate interaction. We quantificationally unveil a dependence of the UOR activation barrier on the coverage of photogenerated surface high-valent Ni-oxo species (NiIV=O) by employing operando PEC spectroscopic measurements and theoretical simulations.
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Division of Theoretical Chemistry, IFM, Linköping University, 58183 Linköping, Sweden.
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Department of Chemistry, University of Turku, Henrikinkatu 2, 20500 Turku, Finland.
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MOE Key Laboratory of Advanced Micro-Structured Materials, Institute of Precision Optical Engineering (IPOE), School of Physics Science and Engineering, Tongji University, Shanghai 200092, China.
Considering the application of titanium nitride (TiN) films as a release layer in producing Wolter-I X-ray telescope mirror shells by the electroformed nickel replication (ENR) technique, this research pays attention to the influence of nanometer-scale thickness variation in the microstructure and physical properties of TiN films deposited by the pulsed direct current (DC) magnetron sputtering method. This topic has received limited attention in the existing literature. TiN films (9.
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