Application of proton magnetic resonance to rotational isomerism in halotoluene derivatives. III. α,α-Dichloro-2,4,6-tribromotoluene

1970 ◽  
Vol 48 (18) ◽  
pp. 2839-2842 ◽  
Author(s):  
J. Peeling ◽  
T. Schaefer ◽  
C. M. Wong
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Room Temperature ◽  
Proton Magnetic Resonance Spectrum ◽  
Methine Proton ◽  
Proton Spectrum ◽  
Kcal Mole ◽  
Ring Proton ◽  
Line Shapes ◽  
Carbon Carbon Bond

At room temperature the proton magnetic resonance spectrum of α,α-dichloro-2,4,6-tribromotoluene is ABX where the methine proton in the sidechain is X and is lying in the plane of the aromatic ring. At higher temperatures the ring proton spectrum, AB, broadens and eventually collapses to yield an A2X spectrum. From an analysis of the ring proton line shapes the barrier to rotation of the dichloromethyl group about the sp2–sp3 carbon–carbon bond is obtained; ΔG* = 17.5 ± 0.1 kcal/mole at 304°K, ΔH* = 15.67 ± 0.08 kcal/mole, ΔS* = −7 e.u., Ea = 16.38 ± 0.08 kcal/mole, log A = 11.78 ± 0.23 where the least squares errors given should probably be multiplied by a factor of from 3 to 5 to take possible systematic errors into account. The barrier is about 2 kcal/mole higher than in α,α,2,4,6-pentachlorotoluene. The barrier to rotation arises from the conformation in which chlorine and bromine atoms are eclipsed.

Proton magnetic resonance spectrum of 2,6-dichlorobenzaldoxime. Signs and magnitudes of long-range spin–spin couplings. Degree of nonplanarity

1969 ◽  
Vol 47 (19) ◽  
pp. 3707-3709
Author(s):  
T. Schaefer ◽  
R. Wasylishen
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constant ◽  
Hydroxyl Proton ◽  
Ring Proton ◽  
Proton Shift

From the sign and magnitude of the coupling constant between the C—H proton in the sidechain and the para ring proton in 2,6-dichlorobenzaldoxime it is estimated that the deviation from coplanarity of the sidechain is at least 40°. The hydroxyl proton shift in dimethylsulfoxide solution of −11.7 p.p.m., relative to internal tetramethylsilane, indicates a cis arrangement of the hydroxyl and aromatic groups.

The proton magnetic resonance spectrum of triptycene. The effect of magnetic anisotropy on the proton shifts

1967 ◽  
Vol 45 (19) ◽  
pp. 2155-2162 ◽  
Author(s):  
K. G. Kidd ◽  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Current Model ◽  
Small Strain ◽  
Proton Magnetic Resonance Spectrum ◽  
Methine Proton ◽  
Coupling Constants ◽  
Proton Spectrum ◽  
Proton Proton ◽  
Ring Proton ◽  
Proton Shift ◽  
Proton Coupling

The ring proton spectrum of triptycene (2.2 mole % in CS2) was analyzed after the methine proton was decoupled. The modified ring current model accounts for most of the internal shift. Bond anisotropies and electron density contributions are also present. The latter account for the mean proton shift. The agreement between the predicted and calculated shifts is excellent for the proton meta to the methine substituent, but a discrepancy of 0.1 p.p.m. is found for the ortho proton. Correction for the ring anisotropy effects produces excellent agreement of the methine proton shift with the empirical correlation between the C—H proton shifts and the 13C–H coupling constants. The ring proton–proton coupling constants are little different from those in benzene, but a small strain in the bonds near the methine carbons is implied.

The nuclear magnetic resonance spectra of pyrrole and [N-D]pyrrole

1969 ◽  
Vol 22 (6) ◽  
pp. 1199 ◽  
Author(s):  
GF Katekar ◽  
AG Moritz
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
High Resolution ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Proton Spin ◽  
Proton Spectrum ◽  
Proton Proton ◽  
Nuclear Magnetic Resonance Spectra

The proton magnetic resonance spectrum at 60 MHz of pyrrole, spin- decoupled from 14N, has been studied under high resolution. Similar studies have been made on [N-D]pyrrole in which the proton spectrum was obtained simultaneously spin-decoupled from both the 14K and 2H nuclei. Analysis of the 13C-H spectra of pyrrole and [N-D]pyrrole, observed in natural abundance, gave values for all six proton-proton spin-spin couplings. Values for some of the couplings have been obtained directly and unambiguously from the spectra of samples of [S-H]pyrrole and [N- D]pyrrole in which the C-H protons have been predominantly exchanged for deuterium. The values for the couplings derived are J1,2 2.60, J1,3 2.45, J2,3 2.69, J2,4 1.44, J2,5 1.87, and J3,4 3.34 Hz.

Application of proton magnetic resonance to rotational isomerism in halotoluene derivatives. II. α,α,2,4,6-Pentachlorotoluene

1970 ◽  
Vol 48 (10) ◽  
pp. 1558-1565 ◽  
Author(s):  
B. J. Fuhr ◽  
B. W. Goodwin ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Energy Transition ◽  
High Energy ◽  
Methine Proton ◽  
Mirror Image ◽  
Proton Spectrum ◽  
Free Energy Barrier ◽  
Matrix Formalism ◽  
High Energy Transition

At temperatures below −40 °C the proton magnetic resonance of α,α,2,4,6-pentachlorotoluene in toluene-d8 or methylcyclohexane is an ABX spectrum where X is the methine proton. The C—H bond of the dichloromethyl group lies in the plane of the ring and its proton couples to one ring proton only. As the temperature increases the mean lifetime before interconversion of the "mirror image" isomers decreases and at 70 °C the proton spectrum is A2X. A density matrix formalism is used to calculate the line shape as a function of the lifetime before exchange. The free energy barrier to rotation of the dichloromethyl group is 15.0 ± 0.1 kcal/mole in both solvents. In toluene-d8 the entropy of activation is near zero. The high energy transition state is very likely one in which the C—Cl bonds of the ring and the dichloromethyl groups are eclipsed.

Proton magnetic resonance investigation of the system zinc perchlorate–methanol: evidence for the association of zinc and perchlorate ions

1969 ◽  
Vol 47 (8) ◽  
pp. 1417-1421 ◽  
Author(s):  
S. A. Al-Baldawi ◽  
T. E. Gough
Keyword(s):  
Magnetic Resonance ◽  
Temperature Dependence ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Solvation Shell ◽  
Proton Magnetic Resonance Spectrum ◽  
Kcal Mole ◽  
Resonance Investigation ◽  
Line Widths ◽  
Magnetic Resonance Investigation

The proton magnetic resonance spectrum of the system zinc perchlorate–methanol is reported for a range of sample concentrations and temperatures. The results are interpreted in terms of association between the zinc and perchlorate ions, and the various features of the spectrum discussed in terms of this interaction. From the temperature-dependence of line-widths, Ea = 14 ± 2 kcal mole−1 and log10A = 16 ± 3 are estimated for the molecular exchange of methanol from the solvation shell of zinc into the bulk solvent.

Proton magnetic resonance spectrum of 4-pyrone, chromone and xanthone

1966 ◽  
Vol 22 (7) ◽  
pp. 1391
Author(s):  
Caroline T. Mathis ◽  
J.H. Goldstein
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum

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.

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