The Structure of a Non-Symmetric Disordered Tetramer: A Crystallographic and Solid State Multinuclear NMR Study of the Properties of 3(5)-Ethyl-5(3)-Phenyl-1H-Pyrazole

The X-ray structure and the solid-state NMR measurements, mainly ¹⁵N CPMAS of the labelled compound, allow to determine the static and dynamic properties of 3(5)-ethyl-5(3)-phenyl-1H-pyrazole. The compound is a tetramer formed by three 5-ethyl-3-phenyl-1H-pyrazole and one 3-ethyl-5-phenyl-1H-pyrazole tautomers in dynamic equilibrium with the complementary situation.     

The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study

The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H...pi interaction, present in solution.     

A study of the tautomerism of β-dicarbonyl compounds with special emphasis on curcuminoids

Six β-diketones related to curcumin and curcumin itself have been studied by ¹³C NMR spectroscopy in chloroform in order to determine the equilibrium constant between the two keto/enol tautomers. In order to do this GIAO/B3LYP/6-31G^∗∗ calculations of absolute shieldings (σ, ppm) were carried out. To establish relationships between σ and experimental chemical shifts (δ, ppm), three simple β-diketones (acetylacetone, dibenzoylmethane and benzoylacetone) have been studied. The preference for different groups to be conjugated with the CO has been determined.     

The structure of β-diketones related to curcumin determined by X-ray crystallography,NMR (solution and solid state) and theoretical calculations

Structural Chemistry - Structural data are reported on sixteen ketoenols of β-diketones: solution NMR, solid-state NMR (CPMAS and MAS) and X-ray crystallography (four compounds, where three...     

A molecular balance to measure the strength of N-H?π hydrogen bonds based on the tautomeric equilibria of C-benzylphenyl substituted NH-pyrazoles

A theoretical (B3LYP/6-31G^∗∗) study of 30 pyrazoles, most of them existing in two tautomeric forms, has been carried out. 3(5)-(2-Benzylphenyl)-5(3)-methyl-1H-pyrazole (11) and 3(5)-(2-benzylbenzylphenyl)-5(3)-phenyl-1H-pyrazole (20) were synthesized from 2-benzoylacetophenone, and their annular tautomeric equilibrium determined. The substituent effects were statistically analyzed and discussed with the help of Hammett substituent constants. In the case of the 5-(2-benzylphenyl) groups, the strength of the N-H?π hydrogen bond depends on the electronic effect of the substituent at position 3.     

Design,optimization and fabrication of 2D photonic crystals for solar cells

This paper presents the optimization of 2D photonic crystals (PCs) onto Si wafers to improve the performance of c-Si PV cells. The objective is to find a structure capable of minimizing the reflectance of the Si wafer in the spectral range between 400 nm and 1000 nm. The study has been limited to PCs that can be fabricated and characterized with the tools and technology available and to dimensions in the same order as the visible light wavelength. PCs with different shapes and dimensions have been simulated and finally the optimum structure has been fabricated by a process based on laser interference lithography (LIL) and reactive ion etching (RIE). This optimized PC presents an average reflectance of 3.6% in the selected wavelength range, without any other material used as antireflective coating. This result means a drastic reduction in comparison with reflectance obtained out of the standard wet etch texturization used in current solar cell manufacturing lines.