Carbon tetrachloride as solvent in proton magnetic resonance. Importance of size and charge effects of proximate substituents

1968 ◽  
Vol 46 (17) ◽  
pp. 2775-2781 ◽  
Author(s):  
T. Schaefer ◽  
B. Richardson ◽  
R. Schwenk
Keyword(s):  
Carbon Tetrachloride ◽  
Magnetic Resonance ◽  
Bond Length ◽  
Steric Hindrance ◽  
Proton Magnetic Resonance ◽  
Shape Effect ◽  
Proton Resonance ◽  
Charge Effects ◽  
Low Field

A model (not a theory), based on steric and charge removal characteristics of the substituents, is used to rationalize the low-field shifts caused by carbon tetrachloride (compared to cyclohexane) in the proton resonance spectra of 22 polyhalosubstituted benzenes. The low-field shifts are as large as 0.16 p.p.m. and these are found for protons situated between two ortho fluorine substituents. Larger halogens present a steric hindrance to the approach of the polarizable C—Cl bonds of the solvent and lead to smaller shifts. The charge removed from the region of the C—H bonds by the substituents is estimated by means of a function of the bond dipole divided by the bond length. A shape effect, arising when two hydrogens are ortho to each other, also appears to be present if there are bulky distant groups.

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.

Benzene solvent induced shifts of the proton magnetic resonance spectra of some benzene derivatives. Importance of charge effects

1970 ◽  
Vol 48 (18) ◽  
pp. 2885-2895 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaefer ◽  
R. Schwenk
Keyword(s):  
Magnetic Resonance ◽  
Linear Correlation ◽  
Proton Magnetic Resonance ◽  
Steric Effects ◽  
Benzene Derivatives ◽  
Charge Effects ◽  
Solvent Shift ◽  
Solvent Shifts ◽  
Substituent Constants ◽  
Magnetic Resonance Spectra

The benzene solvent shifts of the proton magnetic resonance spectra of numerous polysubstituted benzene derivatives are measured with respect to cyclohexane as reference solvent. For many of these compounds, an additive scheme can be devised in which the effect of a substituent, X, on the solvent shift, Δ, of a proton is given by Δix so that Δ = Σx, Σi Δix where i = ortho, meta, or para. There is a linear correlation of Δmx or Δpx with Taft's substituent constants σm0 and σp0. It is suggested that charge effects are much more important than steric effects in determining both the magnitude and sign of Δ.

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.

Complexes of uranyl β-diketonates with sulphoxides

1973 ◽  
Vol 26 (1) ◽  
pp. 85 ◽  
Author(s):  
MS Subramanian ◽  
SA Pai ◽  
VK Manchanda
Keyword(s):  
Magnetic Resonance ◽  
Steric Hindrance ◽  
Proton Magnetic Resonance ◽  
Free Rotation ◽  
Sulphur Atom ◽  
Neutral Donor ◽  
Restricted Rotation ◽  
Metal Bond ◽  
Methylene Group ◽  
Magnetic Resonance Spectra

The proton magnetic resonance spectra of the synergistic complexes of uranyl β-diketonates with dihexyl sulphoxide as the neutral donor give a multiplet consisting of eight lines for the terminal methylene group protons adjacent to the sulphur atom of the sulphoxide and a triplet for the β-methylene protons. This conforms to an ABX2 pattern arising as a result of nonequivalence of the two protons of the terminal methylene group as a result of steric hindrance to free rotation about the C-S bond. The presence of such restricted rotation has been adduced as evidence for a direct donor-metal bond.

Aromatic amides. VII. Steric hindrance to hydrogen bonding in ortho-substituted acetanilides

1972 ◽  
Vol 25 (3) ◽  
pp. 639 ◽  
Author(s):  
BD Andrews ◽  
AJ Poynton ◽  
ID Rae
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Steric Hindrance ◽  
Proton Magnetic Resonance ◽  
Intramolecular Hydrogen Bonding ◽  
Intramolecular Hydrogen ◽  
Magnetic Resonance Spectra

A series of 2-substituted 3,5-dimethylanilines and their N-acetyl derivatives have been synthesized, and their proton magnetic resonance spectra recorded. Intramolecular hydrogen bonding between the amide N-H and the 2-substituent is disturbed by steric hindrance of the 2-substituent only in the case of the 2-nitro, 2-acetyl, and 2-methoxycarbonyl substituents.

THE PROTON MAGNETIC RESONANCE SPECTRUM OF 1-FLUORO-2,4-DINITROBENZENE

1962 ◽  
Vol 40 (3) ◽  
pp. 431-433 ◽  
Author(s):  
T. Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Solvent Effects ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Previous Analysis ◽  
Proton Magnetic Resonance Spectrum ◽  
Proton Resonance ◽  
Reliable Analysis ◽  
Source Of Error

A reliable analysis of the proton resonance spectrum of 1-fluoro-2,4-dinitrobenzene is described. Solvent effects were used to obtain this analysis and a possible source of error in a previous analysis is indicated. Spectra parameters are also derived for 1,5-difluoro-2,4-dinitrobenzene. The spectrum of the latter compound confirms the assignment of peaks in the spectrum of the former.

The analysis of the proton magnetic resonance spectra of heteroaromatic systems. V. Diazanaphthalenes

1965 ◽  
Vol 18 (5) ◽  
pp. 707 ◽  
Author(s):  
PJ Black ◽  
ML Heffernan
Keyword(s):  
Carbon Tetrachloride ◽  
Magnetic Resonance ◽  
Long Range ◽  
Iterative Procedure ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Direct Calculation ◽  
Coupling Constants ◽  
Dilute Solutions ◽  
Magnetic Resonance Spectra

The proton magnetic resonance spectra of the four isomeric diazanaphthalenes, quinoxaline, phthalazine, quinazoline, and cinnoline, all as dilute solutions in carbon tetrachloride and acetone, have been investigated at 100 Mc/s. The chemical shifts and coupling constants have been obtained by direct calculation or, where appropriate, by an iterative procedure. Long-range coupling constants between protons separated by five and six bonds have been observed.

A PROTON MAGNETIC RESONANCE INVESTIGATION OF ROTATIONAL ISOMERISM IN 1,1,2,2-TETRACHLORO-1-FLUOROETHANE

1961 ◽  
Vol 39 (1) ◽  
pp. 39-41 ◽  
Author(s):  
R. J. Abraham ◽  
H. J. Bernstein
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Rotational Isomerism ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Resonance Investigation ◽  
Magnetic Resonance Investigation

The doublet separation in the proton resonance spectrum of the liquid was measured from −53 to 100 °C. From the variation of the separation with temperature approximate values of the trans and gauche HF coupling constants were obtained. The values of ΔH ≈ 400 cal/mole and ΔS ≈ 0 are also consistent with the data.

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