scholarly journals Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluene Derivatives. VI. Rotational Barrier and Conformational Energy Differences in α,α,2,3,6-Pentachlorotoluene

1971 ◽  
Vol 49 (7) ◽  
pp. 1085-1091 ◽  
Author(s):  
M. A. H. Stewart ◽  
T. Schaefer ◽  
H. M. Hutton ◽  
C. M. Wong
Keyword(s):  
Free Energy ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Energy Difference ◽  
Rotational Isomerism ◽  
Free Energy Difference ◽  
Magnetic Resonance Studies ◽  
Shape Fitting ◽  
Carbon Carbon Bond ◽  
Entropy Of Activation

Rotation by π radians about the sp2–sp3 carbon–carbon bond of the dichloromethyl group in α,α,2,3,6-pentachlorotoluene interconverts the two conformations which are characterized by coplanarity of the aromatic ring with the C—H bond of the sidechain. The ring protons undergo effective nonmutual exchange during this rotation. The rate of rotation as a function of temperature is extracted by line-shape fitting of the ring p.m.r. spectra. The rotation is characterized by a negative entropy of activation. The free energy difference between the two conformations is 50 ± 20 cal/mol at 240 °K.

Conformational analysis of 1,4-disubstituted cyclohexanes. III. trans-1,4-Di(trifluoroacetoxy)cyclohexane

1969 ◽  
Vol 47 (3) ◽  
pp. 429-431 ◽  
Author(s):  
Gordon Wood ◽  
E. P. Woo ◽  
M. H. Miskow
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Conformational Analysis ◽  
Integration Method ◽  
Standard Free Energy ◽  
Energy Difference ◽  
Free Energy Difference ◽  
Conformational Free Energy

By the low temperature nuclear magnetic resonance integration method the standard free energy difference between the diequatorial and the diaxial forms of 1-H,4-H-trans-1,4-di(trifluoroacetoxy)-cyclohexane-d8 was found to be 77 ± 5 cal/mole. The conformational free energy (−ΔG0) of the trifluoroacetoxy group in the monosubstituted cyclohexane was 485 ± 4 cal/mole at the same temperature. The non-additivity of the −ΔG0 values is discussed in terms of transannular electrostatic interaction.

Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluene Derivatives. IX. Rotational Barriers and Conformational Energy Differences in α,α,α′,α′,α″,α″, 2,4,6-Nonachloromesitylene

1973 ◽  
Vol 51 (13) ◽  
pp. 2110-2117 ◽  
Author(s):  
J. Peeling ◽  
B. W. Goodwin ◽  
T. Schaefer ◽  
J. B. Rowbotham
Keyword(s):  
Magnetic Resonance ◽  
Carbon Disulfide ◽  
Proton Magnetic Resonance ◽  
Methylene Chloride ◽  
Activation Parameters ◽  
Rotational Isomerism ◽  
Conformational Energy ◽  
The Other ◽  
Free Energies ◽  
Magnetic Resonance Studies

The activation parameters for the rotation of the dichloromethyl groups in the two conformations of α,α,α′,α′,α″,α″,2,4,6-nonachloromesitylene are reported for solutions in toluene-d8 and in methylene chloride. In addition, free energies of activation are given for solutions in bromochloromethane, tri-chloroethylene, and in carbon disulfide. The free energies of activation are lower in the toluene solution than in the other solutions. The entropies of activation are near zero, perhaps slightly negative. The symmetrical conformation is more stable than the unsymmetrical one in all the solvents.

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