Hydrogen bonding in chloroform and ether mixtures

1971 ◽  
Vol 24 (10) ◽  
pp. 2047 ◽  
Author(s):  
JR Baker ◽  
ID Watson ◽  
AG Williamson
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Mole Fraction ◽  
Proton Magnetic Resonance ◽  
Equilibrium Constants ◽  
Association Constants ◽  
Enthalpies Of Formation ◽  
Temperature Coefficients ◽  
Alkyl Ethers

The hydrogen bonding between chloroform and di-n-alkyl ethers has been studied over the temperature range -50�C to + 50�C using proton magnetic resonance. The measurements of chemical shift have been interpreted in terms of the formation of a 1 : 1 complex between the chloroform and the ether. Mole fraction association constants in the range 1-5 were found. The enthalpies of formation of the complexes deduced from the temperature coefficients of the equilibrium constants varied from -8 kJ mol-1 to -11.7 kJ mol-1.

A STUDY OF TAUTOMERISM IN CYCLIC β-DIKETONES BY PROTON MAGNETIC RESONANCE

1965 ◽  
Vol 43 (11) ◽  
pp. 3057-3062 ◽  
Author(s):  
Natsuko Cyr ◽  
Leonard W. Reeves
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shift ◽  
Proton Magnetic Resonance ◽  
Enthalpy Change ◽  
Enol Form ◽  
Proton Resonance ◽  
Kcal Mole ◽  
Intensity Measurements ◽  
Acetonitrile Solutions ◽  
Monomer Form

The keto–enol equilibrium of cyclohexane-1,3-dione in chloroform is best interpreted from proton resonance measurements as[Formula: see text]K1 and K2 may be separately determined from chemical shift measurements of the enol-OH proton and intensity measurements of peaks assigned to keto and enol forms. K1 and K2 are satisfactorily independent of concentrations except in very dilute solutions where intensity measurements become unreliable. The overall equilibrium constant K = K1 × K22 can be obtained for the same molecule in acetonitrile solutions where the enol monomer form is in very low concentration. 5,5′-Dimethylcyclohexane-1,3-dione in chloroform has less enol form than the unsubstituted molecule. The enthalpy change associated with 'K' for cyclohexane-1,3-dione in chloroform is 2.05 ± 0.5 kcal mole−1.

scholarly journals ORYX-MRSI: A Fully-Automated Open-Source Software for Three-Dimensional Proton Magnetic Resonance Spectroscopic Imaging Data Analysis

2021 ◽  
Author(s):  
Sevim Cengiz ◽  
Muhammed Yildirim ◽  
Abdullah Bas ◽  
Esin Ozturk-Isik
Keyword(s):  
Data Analysis ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Open Source ◽  
Proton Magnetic Resonance ◽  
Spectroscopic Imaging ◽  
Brain Atlas ◽  
Magnetic Resonance Spectroscopic Imaging ◽  
Spectral Quality ◽  
Chemical Shift Artifact

Proton magnetic resonance spectroscopic imaging (1H-MRSI) provides noninvasive evaluation of brain metabolism. However, there are some limitations of 1H-MRSI preventing its wider use in the clinics, including the spectral quality issues, partial volume effect and chemical shift artifact. Additionally, it is necessary to create metabolite maps for analyzing spectral data along with other MRI modalities. In this study, a MATLAB-based open-source data analysis software for 3D 1H-MRSI, called Oryx-MRSI, which includes modules for visualization of raw 1H-MRSI data and LCModel outputs, chemical shift correction, tissue fraction calculation, metabolite map production, and registration onto standard MNI152 brain atlas while providing automatic spectral quality control, is presented. Oryx-MRSI implements region of interest analysis at brain parcellations defined on MNI152 brain atlas. All generated metabolite maps are stored in NIfTI format. Oryx-MRSI is publicly available at https://github.com/sevimcengiz/Oryx-MRSI along with six example datasets.

Effects of pH on the C-13 Magnetic Resonance Spectrum of Phenol

1972 ◽  
Vol 26 (2) ◽  
pp. 220-223 ◽  
Author(s):  
Thomas T. Nakashima ◽  
Gary E. Maciel
Keyword(s):  
Hydrogen Bonding ◽  
Fourier Transform ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Resonance Spectrum ◽  
Effects Of Ph ◽  
The Fourier Transform ◽  
Solvent Properties

The C-13 chemical shift dependences of phenol on pH have been investigated and the shifts interpreted in terms of the phenol-phenoxide equilibrium and hydrogen bonding. In the low and high ranges of pH the carbon shifts have been related to subtle changes in the characteristics of solvent properties. The spectra were obtained using the Fourier transform technique.

Metal – Aminopolycarboxylic Acid Complexes. II. Studies of Triethylenetetraaminehexaacetic Acid and its Lead(II) Complexes in Aqueous Solution by Proton Magnetic Resonance Spectroscopy

1971 ◽  
Vol 49 (12) ◽  
pp. 2086-2095 ◽  
Author(s):  
P. Letkeman ◽  
J. B. Westmore
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Equilibrium Constants ◽  
The Other ◽  
Resonance Spectroscopy ◽  
Carboxylate Groups ◽  
Triethylenetetraaminehexaacetic Acid ◽  
Nitrogen Bonds ◽  
Aminopolycarboxylic Acid

Nuclear magnetic resonance (n.m.r.) spectroscopy was used to determine the preferred protonation sites in TTHA. For its 1:1 complex with Pb(II) the following equilibrium constants for protonation were obtained (triethylenetetraaminehexaacetic acid ≡ H6A)[Formula: see text]The non-protonated complex is considered to have four coplanar (or nearly coplanar) metal–nitrogen bonds with the center carboxylate groups coordinated above and below this plane, and with the terminal carboxylate groups playing only a small part in the coordinate bonding. The first and second protonations of the complex occur preferentially at the terminal and center nitrogen atoms, respectively, on the same side of the complex, accompanied by breaking of the respective metal–nitrogen bonds. This causes partial unwrapping of the complex from one side. Rapid interconversion between configurations in which unwrapping and rewrapping occurs first from one side of the molecule and then from the other leads to simplified n.m.r. spectra.

Solvent effects in ultraviolet spectral studies of hydrogen bonding between phenol and N,N-dimethylacetamide

1967 ◽  
Vol 45 (18) ◽  
pp. 2033-2038 ◽  
Author(s):  
F. Takahashi ◽  
W. J. Karoly ◽  
J. B. Greenshields ◽  
N. C. Li
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Complex Formation ◽  
Equilibrium Constant ◽  
Proton Magnetic Resonance ◽  
Mixed Solvent ◽  
Resonance Method ◽  
Spectral Studies ◽  
Magnetic Resonance Method ◽  
Hydrogen Bonded

Ultraviolet spectral studies of hydrogen bonding between phenol and N,N-dimethylacetamide (DMA) in several media are reported. The equilibrium constant for the formation of the phenol–DMA complex is strongly solvent dependent, varying from 295 1/mole in cyclohexane to 130 in CCl4 and 16 in CHCl3, all at 28°. The greatly reduced value in CHCl3 indicates that the measured equilibrium constant is only an apparent one which does not take into account the decrease in free DMA concentration resulting from hydrogen-bonded complex formation with the solvent acting as hydrogen donor. In CCl4/CHCl3 mixed solvent, in the range of [chloroform] = 0 to 1.227 M, the measured equilibrium constant, K′, varies linearly with K′ [chloroform]. The slope of the line corresponds to the equilibrium constant for the formation of the hydrogen-bonded complex between CHCl3 and DMA in CCl4. The value, 0.9 1/mole, agrees with that obtained from a proton magnetic resonance method. The agreement is particularly noteworthy when we consider that the concentrations of phenol used in the proton magnetic resonance and ultraviolet spectral methods differ by a factor of 200, which leads definitely to the conclusion that the hydrogen-bonded CHCl3–DMA complex formed is 1:1. In cyclohexane/CHCl3 mixed solvent, similar results are obtained.

Selective deshielding of aromatic protons in some ortho-substituted acetanilides

1968 ◽  
Vol 46 (15) ◽  
pp. 2593-2600 ◽  
Author(s):  
James R. Bartels-Keith ◽  
Ronald F. W. Cieciuch
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Solvent Effects ◽  
Proton Magnetic Resonance ◽  
Aromatic Proton ◽  
Intramolecular Hydrogen Bonding ◽  
Low Field ◽  
Intramolecular Hydrogen

Certain ortho-substituted acetanilides exhibit proton magnetic resonance signals at unusually low field for the amido proton and the aromatic proton adjacent to the acetamido group. This effect, explicable in terms of intramolecular hydrogen-bonding, has been observed for nitro, carbonyl, sulfamoyl, and sulfonyl substituents. Solvent effects are discussed.

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