Search results for "Hydrogen atom"

Hyperfine measurements in a storage ring

1995

Starting with a look at the outstanding role of the hydrogen atom in modern physics, this work reviews aspects of an extension of precision spectroscopy to the ground-state hyperfine structure of highly charged hydrogenic ions. In this connection, the preferences of heavy-ion storage rings are outlined and illuminated by the laser-spectroscopic measurement (the first of that kind) of the 1s hyperfine splitting of 209Bi82+, stored in the heavy-ion storage ring at GSI. The experimental results, including the mean lifetime of the upper 1s substate, are compared with the presently available theoretical calculations. The relevance of studying further hydrogenicc ions in the vicinity of the doubl…

Effects of the Surface and Finite Temperature on the Electronic Structure of Metal Clusters

1996

The most fascinating feature of simple metal clusters is the existence of the electronic shell structure. This was observed first in alkali[1] and noble metals[2] and later also in some other nontransition metals[3,4,5]. The shell structure is a consequence of nearly free valence electrons confined to a finite volume. A spherical potential will always lead to a shell structure, the origin of which is the orbital angular momentum l and the large degeneracy (2l+1) associated with it. However, this primitive shell structure is strengthened by ’accidental’ degeneracies between states having different principal quantum numbers. Thus the shell structure of a hydrogen atom is different from that o…

The ins and outs of proton complexation

2009

Proton complexation differs from simple protonation by the fact that the coordinated hydrogen atom is bound intramolecularly to more than one donor atom. This is usually achieved by covalent bonding supplemented by hydrogen bonding. In a few cases, however, the complexed proton is hydrogen-bound to all donor atoms, which gives rise to single well (SWHB) and low barrier (LBHB) hydrogen bonds. This tutorial review highlights a full range of proton complexes formed with chelating and "proton-sponge"-type ligands, cryptand-like macropolycycles, and molecules of topological relevance, such as rotaxanes and catenanes. The concept of proton complexation can explain how the smallest cation possible…

ChemInform Abstract: The Ins and Outs of Proton Complexation

2009

Proton complexation differs from simple protonation by the fact that the coordinated hydrogen atom is bound intramolecularly to more than one donor atom. This is usually achieved by covalent bonding supplemented by hydrogen bonding. In a few cases, however, the complexed proton is hydrogen-bound to all donor atoms, which gives rise to single well (SWHB) and low barrier (LBHB) hydrogen bonds. This tutorial review highlights a full range of proton complexes formed with chelating and “proton-sponge”-type ligands, cryptand-like macropolycycles, and molecules of topological relevance, such as rotaxanes and catenanes. The concept of proton complexation can explain how the smallest cation possible…

Ab initio study on the mechanism of the HCO+O2→HO2+CO reaction

2003

Abstract The gas-phase reaction HCO+O 2 →CO+HO 2 has been investigated by means of ab initio calculations. The mechanism can proceed through either a direct hydrogen abstraction or addition of O 2 to the formyl radical. The energy barriers calculated at the QCISD(T)/6-311G(2df,2p) level of theory upon QCISD/6-311G(d,p) optimized structures are, respectively, of 2.98 kcal mol −1 for the direct abstraction and of 2.26 kcal mol −1 for the addition. Thus, the results obtained show that there is not a dominant pathway in the HCO+O 2 reaction under atmospheric conditions of temperature and pressure.

Calculation of the rate constants for hydrogen abstraction reactions by Hydroperoxyl radical from Methanol, and the investigation of stability of CH3…

2020

Abstract Master equation (ME) with Lennard-Jones potential utilized to simulate the collision between CH3OH and HO2 radical in the presence of bath gas. The reaction mechanism explored through the lowest doublet potential energy surface at CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory that is barrierless and forms shallow energized intermediate at the entrance channel. The investigation of the fractional population showed that lifetime of CH3OH.HO2 intermediate (INT*) is fairly short due to its shallow depth, and at the low temperature, most reaction takes place by re-dissociation back to reactants and also when the pressure is high enough, the INT* is thermalized and comes into eq…

Non-Classical Transformation of Benzendiazonium Hydrogen Sulfates. Access to 1,3-Dimethylisochromeno[4,3-c]pyrazol-5(1H)-one, a Potential Benzodiazep…

2013

The compound 2-((1,3-dimethyl-1H-pyrazol-5-yl)(methyl)carbamoyl)benzene-diazonium hydrogen sulfate (10) was reacted with copper sulfate and sodium chloride, in the presence of ascorbic acid as reducing agent, to afford a mixture of the chlorinated epimers 4′-chloro-2,2′,5′-trimethyl-2′,4′-dihydrospiro[isoindoline-1,3′-pyrazol]-3-one (18) and (19), the epimers 4′-hydroxy-2,2′,5′-trimethyl-2′,4′-dihydrospiro[isoindoline-1,3′-pyrazol]-3-one (20) and (21), and N-(1,3-dimethyl-1H-pyrazol-5-yl)benzamide (22). Under the foregoing conditions, diazonium salt 10 affords neither the 2-chloro-N-(1,3-dimethyl-1H-pyrazol-5-yl)-N-methylbenzamide (23) nor the tricyclic derivative 24, the classical products…

Intramolecular proton transfer of serine in aqueous solution. Mechanism and energetics

2000

Serine amino acid in aqueous solution is theoretically studied at the B3PW91/6-31+G** level using a dielectric continuum solvent model. Neutral and zwitterionic structures in the gas phase and in solution are described and the proton-transfer mechanism is discussed. A neutral conformation in which the carboxyl hydrogen atom is already oriented toward the amino group seems to be the absolute energy minimum in the gas phase and the most stable neutral form in solution. The absolute energy minimum in solution is a zwitterionic form. The energy barrier for proton transfer is predicted to be very small, in particular when zero-point-energy contributions are added. Our calculations allow the dyna…

1976

tert-Butoxy radicals were generated by decomposing di-tert-butyl hyponitrite. The relative reactivities of substrates were measured from the ratio of tert-butanol and acetone formed. Polystyrene was found to be less reactive than model compounds. Activation parameters for the hydrogen abstraction reaction for cumene, 3-phenylpentane, and 2,4-diphenylpentane are reported and show small differences for the enthalpy of activation; large negative values for the entropy of activation demonstrate the importance of steric hindrance in the hydrogen abstracting step. 2,3-Diphenylbutane as model compound for head to head links in polystyrene exhibits low reactivity, whereas 2,5-diphenylhexane, a mode…

Preparation of 2-amino-5-methyl-7H-1,3,4-thiadiazolo[3,2-α]pyrimidin-7-ones

2005

2-Amino substituted 7H-1,3,4-thiadiazolo[3,2-α]pyrimidin-7-ones 11a-e were prepared by the reaction of 2-bromo-5-amino-1,3,4-thiadiazole (1b) and diketene (8), subsequent cyclocondensation (9b 3b) and displacement of the bromo substituents by the reaction with primary or secondary amines (3b 11a-e). The hydrogen atom 6-H in the heterobicycle 3b is replaced by a Cl or Br atom in the transformation of 3b 14a,b. The 2-bromo-6-chloro compound 14a reacts chemoselectively in the 2-position with dimethylamine (14a 15). The structure elucidations are based on one- and two-dimensional NMR techniques including a heteronuclear NOE measurement.