Nuclear magnetic resonance studies. XIV. Conformational equilibria of α-halocyclohexanones

1967 ◽  
Vol 45 (23) ◽  
pp. 2943-2953 ◽  
Author(s):  
Yuh-Hsu Pan ◽  
J. B. Stothers
Keyword(s):  
Equilibrium Constants ◽  
Dipolar Interactions ◽  
Proton Spectroscopy ◽  
Solvent Interactions ◽  
Reaction Field ◽  
Conformational Equilibria ◽  
Classical Models ◽  
Acetonitrile Solutions ◽  
Cis And Trans ◽  
Good Agreement

The conformational equilibria of α-fluoro-, α-chloro-, and α-bromo-cyclohexanone have been examined by proton spectroscopy in cyclohexane, carbon tetrachloride, benzene, chloroform, p-dioxane, and acetonitrile solutions over a range of concentrations. The cis- and trans-4-t-butyl derivatives were used as reference compounds for the two chair conformations. Equilibrium constants were estimated from the α-proton spectral data in two ways and compared with the results obtained by a variety of methods. Consistently good agreement was found between our results and those available from dipole moment measurements. This study is the most extensive investigation of the α-halocyclohexanone equilibria to date. Calculations using simple classical models for steric, electrostatic, and induced dipolar interactions were found to predict the observed trends. The solvent effects on the axial and equatorial α-proton shieldings in the "fixed" systems are discussed in terms of solute–solute and (or) solute–solvent interactions, and evidence for reaction field contributions is presented.

Solvent effect on the conformational behavior of substituted spiro[4.5]decanes and spiro[5.5]undecanes

1995 ◽  
Vol 73 (5) ◽  
pp. 703-709 ◽  
Author(s):  
S. Sağ Erdem ◽  
T. Varnali ◽  
V. Aviyente ◽  
M.F. Ruiz-Lopez
Keyword(s):  
Solvent Effect ◽  
Electrostatic Interactions ◽  
Multipole Moment ◽  
Semiempirical Methods ◽  
Main Role ◽  
Solvent Interactions ◽  
Reaction Field ◽  
Solvent Models ◽  
Conformational Equilibria

We studied the relatively complex polar systems 6-substituted-1,4-dioxospiro[4.5]decanes and 7-substituted-1,5-dioxospiro[5.5]undecanes with substituents X = CH3, F, Cl, CN, OH, OCH3, and NO2. Solvent effects on the equilibrium have been analysed by means of a Self-Consistent-Reaction-Field model and the PM3 method. Complete geometry optimizations have been carried out for all the structures in the gas phase and in solution. For some substituents, a set of rotamers have been separately optimized. The discussion of the results is focussed on the effects arising from structural aspects and from steric and electrostatic interactions on the axial/equatorial relative stability. The role played by multipole moment is considered. In general, good agreement with available experimental data and with previous theoretical studies has been obtained. Though the use of semiempirical methods and simple solvent models prevents us from reaching definitive conclusions, this approach seems to be very useful in predicting the main role of solute–solvent interactions in conformational equilibria of complex systems for which ab initio calculations cannot be performed. Keywords: conformational equilibria, spiro decanes and undecanes, cavity model, SCRF, solvent effect, PM3 calculations.

Transfer Thermodynamic Functions ∆Gt0, ∆Ht0 and T∆St0 of cis- and trans-[CoCl2(en)2]+ Isomers in Aqueous Mixtures of Methanol, tert-Butyl Alcohol and Acetonitrile

2000 ◽  
Vol 65 (9) ◽  
pp. 1455-1463
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Enthalpy Of Solution ◽  
Transfer Functions ◽  
Partial Molar Volumes ◽  
Butyl Alcohol ◽  
Aqueous Mixtures ◽  
Aqueous Methanol ◽  
Solvent Interactions ◽  
Tert Butyl Alcohol ◽  
Surface Charge Distribution ◽  
Cis And Trans

The solubility, partial molar volume and standard integral molar enthalpy of solution of cis- and trans-[CoCl2(en)2]Cl in water, aqueous methanol, aqueous tert-butyl alcohol and aqueous acetonitrile are reported. The transfer functions ∆Gt0, ∆Ht0 and T∆St0 as well as partial molar volumes are used to obtain information on the solute-solvent interactions. Results obtained are discussed in terms of differences in the surface charge distribution in isomeric coordination species.

Interactions gauches et chemins réactionnels. Etudes conformationnelles d'hydroxyalkyl-4 cyclohexènes contraints

1981 ◽  
Vol 59 (5) ◽  
pp. 859-864
Author(s):  
Jeanine Bouteiller-Prati ◽  
Jean-Claude Bouteiller ◽  
Jean-Pierre Aycard
Keyword(s):  
Free Energy ◽  
Reaction Path ◽  
High Energy ◽  
Nmr Study ◽  
Conformational Equilibria ◽  
The Stability ◽  
Cis And Trans ◽  
Conformational Free Energy

From J and δ values determined by the nmr study of alcohols obtained by addition of CH3Li and LiAlH4 to the exocyclic carbonyl of cis and trans 3-alkyl 4-carbomethoxy (or acetyl) cyclohexenes (alkyl = H, CH3, C(CH3)3), we have deduced the conformational free energy values (ΔG0X) of the CH(CH3)OH and C(CH3)2OH substituents (0.62 and 2.08 kcal mol−1 respectively) as well as the values for some related conformational equilibria. For transtert-butyl derivatives the stability of the diaxial conformer agrees with a reaction path involving high energy conformers.

SOLVENT EFFECTS ON THE PROTON RESONANCE SPECTRA OF THE DICHLORO- AND DIBROMO-ETHYLENES: REACTION FIELD EFFECTS IN ALIPHATIC SOLVENTS AND SPECIFIC INTERACTIONS IN AROMATIC SOLVENTS

1963 ◽  
Vol 41 (12) ◽  
pp. 3034-3041 ◽  
Author(s):  
F. Hruska ◽  
E. Bock ◽  
T. Schaefer
Keyword(s):  
Field Effect ◽  
Dielectric Constants ◽  
Specific Interactions ◽  
Proton Resonance ◽  
Water Solutions ◽  
Reaction Field ◽  
Aromatic Solvents ◽  
Triple Bonds ◽  
Induced Dipole ◽  
Cis And Trans

The proton resonance shifts relative to internal cyclohexane and tetramethylsilane of cis and trans dichloro- and dibromo-ethylenes were measured in dioxane–water solutions, aliphatic solvents, and aromatic solvents. The dielectric constants of the dioxane–water solutions could be smoothly varied between 2 and 10 and, by taking Δ = cis–trans shifts as containing only the dipolar reaction field effect, the data for these solutions were treated as a test of the Buckingham reaction field equation. Linear plots were obtained and reasonable values of the coefficients of the E term confirmed the usefulness of this equation. An equation based on a nonspherical cavity was also used. It was also shown that quadrupolar reaction fields affected the proton shifts. Sizeable deviations from the dioxane–water standards were found for halogenated aliphatic solvents and those containing double or triple bonds. These deviations are interpreted in terms of the shape of the solute molecules and dispersion and anisotropic interactions. The much larger deviations found for aromatic solvents are harder to rationalize but specific interactions were found for both cis and trans forms, indicating an inadequacy in a simple dipole-induced dipole model.

Ligand Redistribution Equilibria in Aqueous Fluoroberyllate Solutions

1998 ◽  
Vol 53 (11) ◽  
pp. 1294-1300 ◽  
Author(s):  
Michael Schmidt ◽  
Hubert Schmidbaur
Keyword(s):  
Experimental Data ◽  
Ligand Exchange ◽  
Room Temperature ◽  
Chemical Shifts ◽  
Equilibrium Constants ◽  
Individual Species ◽  
Ph Values ◽  
Exchange Processes ◽  
The Individual ◽  
Good Agreement

The composition of aqueous fluoroberyllate solutions has been studied by 9Be and 19F NMR spectroscopy for various ratios of the beryllium and fluorine concentrations, and at different pH values. The equilibrium constants have been determined for the ligand exchange processes, which involve the species [Be(OH2)4]2+, [BeF(OH2)3]+, [BeF2(OH2)2], [BeF3(OH2)]- , and [BeF4]2-. These equilibria are shifted towards [BeF4]2- at high pH. No polynuclear fluoroberyllates have been detected. The fluoride exchange between the individual species is slow on the NMR time scale at room temperature, and separate sharp signals with the expected multiplicity are therefore recorded. Calculated 9Be chemical shifts are in good agreement with experimental data.

Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz

1992 ◽  
Vol 65 (2) ◽  
pp. 427-443 ◽  
Author(s):  
M. R. Krejsa ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chain Scission ◽  
Sulfur Concentration ◽  
Nmr Studies ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Equilibrium Swelling ◽  
Cis And Trans ◽  
Good Agreement

Abstract Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.

EXCITATION FUNCTIONS OF ALPHA INDUCED REACTIONS ON NATURAL NICKEL UP TO 50 MeV

2005 ◽  
Vol 14 (04) ◽  
pp. 611-629 ◽  
Author(s):  
N. L. SINGH ◽  
S. MUKHERJEE ◽  
M. S. GADKARI
Keyword(s):  
Angular Momentum ◽  
Alpha Particle ◽  
Gamma Ray ◽  
Level Density ◽  
The Other ◽  
Gamma Ray Spectrometry ◽  
Excitation Functions ◽  
Classical Models ◽  
Nucleon Emission ◽  
Good Agreement

Excitation functions have been measured for alpha-particle induced reactions on natural nickel leading to the production of 62 Zn , 61 Cu , 56,57 Ni and 56,58 Co radioisotopes up to 50 MeV by the activation method and gamma-ray spectrometry. Most of these radioisotopes are produced by one or two alpha-particle emissions and a few nucleon emissions. The excitation functions were compared with semi-classical models codes, like ALICE/90, which includes a shell corrected level density formulation and the COMPLET, which takes into account angular momentum removal effects. In the case of multi-nucleon emission channels, ALICE/90 gives fairly good agreement. The COMPLET code on the other hand, explains the α-particle emission channels in a more convincing manner.

The Interaction of Sulfite Ion with 2,4,6-Trinitrobenzaldehyde: Kinetic, Equilibrium, and Proton Magnetic Resonance Studies

1973 ◽  
Vol 51 (23) ◽  
pp. 3927-3935 ◽  
Author(s):  
Neven Marendic ◽  
Albert Richard Norris
Keyword(s):  
Proton Magnetic Resonance ◽  
Equilibrium Constants ◽  
Visible Absorption ◽  
Rapid Formation ◽  
Aqueous Dimethylsulfoxide ◽  
Cis And Trans ◽  
In Cis ◽  
Kinetics Of ◽  
Sulfite Ion ◽  
Kinetic Equilibrium

Sulfite ion reacts with 2,4,6-trinitrobenzaldehyde in aqueous solution of ionic strength 0.14 M to yield a 1:1 σ-complex at low sulfite concentrations and a 2:1 σ-complex at high sulfite concentrations. The visible absorption characteristics of these two σ-complexes as well as equilibrium constants and relevant thermodynamic parameters for their formation have been determined. P.m.r. studies demonstrate that two isomeric forms of the 1:1 σ-complex occur in aqueous dimethylsulfoxide solution and two isomeric forms of the 2:1 σ-complex occur in water. In both the 1:1 and the 2:1 complexes isomers are found which contain sulfite ion attached to the C-1 carbon and one of the isomeric 2:1 σ-complexes is postulated to exist in cis and trans forms. Observations are presented concerning the kinetics of the very rapid formation of the 1:1 σ-complex in water.

Role of Interfacial Surfactant Layers in the Thermal Conductivity of Nanofluids

2012 ◽  
Vol 531-532 ◽  
pp. 535-538
Author(s):  
Liu Yang ◽  
Kai Du ◽  
Yun Long Wu ◽  
Shuai Yang Bao
Keyword(s):  
Thermal Conductivity ◽  
Interfacial Layer ◽  
Langmuir Adsorption ◽  
Adsorption Theory ◽  
Proposed Model ◽  
Classical Models ◽  
Interfacial Surfactant ◽  
S Model ◽  
Good Agreement

Various mechanisms and correlations have been developed for prediction of thermal conductivity of nano-suspensions. However, seldom theoretical researches on thermal conductivity of nanofluids containing surfactant are found. In this work, a thermal conductivity prediction-model of nanofluid containing surfactants is proposed based on Leong et al.’s model and Langmuir adsorption theory by considering the interfacial surfactant layers. The thickness of the interfacial layer is defined by Langmuir adsorption theory. Compared with the experimental data available in the literature on thermal conductivity of nanofluid containing surfactants, the calculated values on the proposed model have been verified that the proposed models show reasonably good agreement with the experimental results and give better predictions for the effective thermal conductivity of nanofluids compared to existing classical models.

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