Search results for "Hydrogen"
showing 10 items of 4254 documents
Comparison of Water Adsorption Properties of Cellulose and Cellulose Nanocrystals Studied by Near-Infrared Spectroscopy and Gravimetry
2017
The adsorption properties of water molecules on cellulose and cellulose nanocrystals (CNCs), isolated from defatted rice bran (DRB) by 55% sulfuric acid hydrolysis under sonication were investigated. The powdered samples of cellulose and CNCs were analysed by using near infrared spectroscopy (NIR) and gravimetry at 38% and 55% humidities. Small amounts of samples were dried under vacuum at 120°C and the NIR spectra of the dry samples and their spectra during the adsorption water molecules were measured by using an NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The quantitative adsorption of water molecules by the samples was determined by gravimetry. Second a…
The role of potassium and hydrogen ions in the Prussian Blue ⇆ Everitt's Salt process
1998
Cyclic voltammetry experiments have proved very useful in the knowledge and understanding of the role of the potassium and hydrogen ions during the Prussian Blue ⇄ Everitt's Salt process. While potassium ions act as a stoichiometric reactant, the hydrogen ions play a very important role in the kinetics of the electron-hopping process. The entropy change for the reaction PB ⇄ ES has proved to be dependent on the degree of crystallinity of the film, indicating that this entropy change is related to the fixation of inner counterions on the crystal structure of the films.
Halo and Pseudohalo Cu(I)-Pyridinato Double Chains with Tunable Physical Properties
2015
The properties recently reported on the Cu(I)-iodide pyrimidine nonporous 1D-coordination polymer [CuI(ANP)] (ANP = 2-amino-5-nitropyridine) showing reversible physically and chemically driven electrical response have prompted us to carry a comparative study with the series of [CuX(ANP)] (X = Cl (1), X = Br (2), X = CN (4), and X = SCN (5)) in order to understand the potential influence of the halide and pseudohalide bridging ligands on the physical properties and their electrical response to vapors of these materials. The structural characterization of the series shows a common feature, the presence of -X-Cu(ANP)-X- (X = Cl, Br, I, SCN) double chain structure. Complex [Cu(ANP)(CN)] (4) pre…
7-Amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid as the dimethylformamide and water monosolvates at 293 K.
2010
The molecular structure of 7-amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid is reported in two crystal environments, viz. as the dimethylformamide (DMF) monosolvate, C(7)H(7)N(5)O(2)S·C(3)H(7)NO, (I), and as the monohydrate, C(7)H(7)N(5)O(2)S·H(2)O, (II), both at 293 (2) K. The triazolo[1,5-a]pyrimidine molecule is of interest with respect to the possible biological activity of its coordination compounds. While the DMF solvate exhibits a layered structural arrangement through N...O hydrogen-bonding interactions, the monohydrate displays a network of intermolecular O...O and N...O hydrogen bonds assisted by cocrystallized water molecules and weak π-π stacking intera…
Vibrational relaxation of matrix-isolated carboxylic acid dimers and monomers.
2009
Femtosecond mid-IR transient absorption spectroscopy was used to probe the vibrational dynamics of formic acid and acetic acid isolated in solid argon following excitation of the fundamental transition of the carbonyl stretching mode. Carboxylic acids form extremely stable H-bonded dimers, hindering the study of the monomeric species at equilibrium conditions. The low-temperature rare-gas matrix isolation technique allows for a unique control over aggregation enabling the study of the monomer vibrational dynamics, as well as the dynamics of two distinct dimer structures (cyclic and open chain). This study provides insight into the role of the methyl rotor and hydrogen bonding in the vibrati…
Zero-field NMR of urea : spin-topology engineering by chemical exchange
2021
Well-resolved and information-rich J-spectra are the foundation for chemical detection in zero-field NMR. However, even for relatively small molecules, spectra exhibit complexity, hindering the analysis. To address this problem, we investigate an example biomolecule with a complex J-coupling network─urea, a key metabolite in protein catabolism─and demonstrate ways of simplifying its zero-field spectra by modifying spin topology. This goal is achieved by controlling pH-dependent chemical exchange rates of 1H nuclei and varying the composition of the D2O/H2O mixture used as a solvent. Specifically, we demonstrate that by increasing the proton exchange rate in the [13C,15N2]-urea solution, the…
Association Equilibria Theory for Polymers in Mixed Solvents with Specific Interactions
2004
Hydrogen bonding plays an important role in determining the physical and thermodynamic properties of polar fluids. Theoretical and experimental aspects of polymers, in mixed solvents with hydrogen-bonding-specific interactions, are investigated using a simple association model based on the theory of association equilibria developed by Pouchly et al. The thermodynamic non-idealities are accounted for using a modified Flory-Huggins theory with effective g ij parameters. The entropic term of the above formalism has been formulated taking into account the pplymer segment-solvent as well as the solvent-solvent hydrogen-bond formation. Four equilibrium constants are introduced to make a realistic…
Allylammonium hydrogen oxalate hemihydrate
2014
In the title hydrated molecular salt, C3H8N+·C2HO4−·0.5H2O, the water O atom lies on a crystallographic twofold axis. The C=C—C—N torsion angle in the cation is 2.8 (3)° and the dihedral angle between the CO2and CO2H planes in the anion is 1.0 (4)°. In the crystal, the hydrogen oxalate ions are linked by O—H...O hydrogen bonds, generating [010] chains. The allylammonium cations bond to the chains through N—H...O and N—H...(O,O) hydrogen bonds. The water molecule accepts two N—H...O hydrogen bonds and makes two O—H...O hydrogen bonds. Together, the hydrogen bonds generate (100) sheets.
Enhancing reactivity of carbonyl compounds via hydrogen-bond formation. A DFT study of the hetero-Diels-Alder reaction between butadiene derivative a…
2003
To examine how hydrogen-bond (HB) formation involving chloroform solvent molecules influences the chemical reactivity of ketones, the hetero-Diels-Alder reaction of N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene and acetone has been studied by using density functional theory (DFT) at the B3LYP/6-31G level. The effects of the chloroform on the activation energies have been modeled by means of discrete-continuum models. In the gas phase, the formation of specific HB between acetone and one and two chloroform molecules decreases the activation barriers from 19.3 to 13.6 and 8.5 kcal/mol, respectively. Inclusion of solvent effects by means of combined discrete and polarizable continuum models yie…
Studien zum Vorgang der Wasserstoffübertragung, 68. Die reduktive Überführung aromatischer Säurechloride in Diarylacetylene mit Lithiumamalgam in ein…
1983
Endioldiester A, die durch “Acylierende reduktive Dimerisierung” mit Lithiumamalgam (Li/Hg) nach (1) zuganglich sind, werden mit zwei weiteren Reduktionsaquivalenten nach (2) durch “Reduktive Eliminierung” in Acetylenderivate ubergefuhrt. Hierbei hat sich praparativ das Eintopfverfahren in der Zweistufenarbeitsweise bewahrt. Auch mit Natriumamalgam (Na/Hg) und Kaliumamalgam (K/Hg) gelingt die reduktive Eliminierung nach (2) sowohl von cis- als auch von trans-Endiol-diestern zu Acetylenverbindungen mit guten Ausbeuten. Voraussetzung fur den erfolgreichen Ablauf der Reaktion (2) ist die direkte Verknupfung von zwei Aromaten mit der C C-Doppelbindung in den Endiol-diestern. Endiol-diester mit …