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.

Novel stereochemical equilibria in crown ethers. Detection of additional conformations of cis-syn-cis- and cis-anti-cis-dicyclohexano-18-crown-6 by 100.6-MHz 13C nuclear magnetic resonance at 173 K

1985 ◽  
Vol 63 (10) ◽  
pp. 2747-2751 ◽  
Author(s):  
G. W. Buchanan ◽  
K. Bourque ◽  
J. W. Bovenkamp ◽  
A. Rodrigue
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Crown Ethers ◽  
High Field ◽  
13C Nuclear Magnetic Resonance ◽  
Conformational Equilibria ◽  
Conformational Free Energy ◽  
C Nmr

High field, 13C nmr has been utilized for the analysis of new conformational equilibria in each of the title crown ethers at low temperature. Evidence indicates that these equilibria arise from restricted rotation in the macrocyclic portions of these molecules. The conformational free energy differences between the isomers are small (0.1–0.3 kcal/mol) while barriers to their interconversion are of the order of 8.5–9.0 kcal/mol. Comparisons are made with the degenerate equilibria involving inversion of the cyclohexane rings.

The conformational free energy difference for the trideuteromethyl substituent in cyclohexane

1980 ◽  
Vol 58 (23) ◽  
pp. 2714-2719 ◽  
Author(s):  
Harold Booth ◽  
Jeremy Ramsey Everett
Keyword(s):  
Free Energy ◽  
Room Temperature ◽  
Energy Difference ◽  
Axial Orientation ◽  
Free Energy Difference ◽  
Nmr Spectrum ◽  
Enthalpy Difference ◽  
Methyl Cyclohexane ◽  
Conformational Free Energy ◽  
C Nmr

Studies at 169 K to 194 K of the 13C nmr spectrum of cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane show that the conformational enthalpy difference −ΔH°(C2H3) is 1.82 ± 0.07 kcal mol−1 and the conformational entropy difference ΔS°(C2H3) is −0.28 ± 0.4 cal K−1 mol−1, values which do not differ significantly from the values for CH3. However, analysis of the room temperature 13C nmr spectrum of a mixture of cis-1-ethyl-4-methylcyclohexane and cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane showed that −ΔG°(C2H3) at 298 K is 11.89 ± 1.46 cal mol−1less than that for CH3, i.e. C2H3 has a slightly greater preference than CH3 for the axial orientation. The 13C nmr spectrum of a mixture of trans-1-ethyl-4-methylcyclohexane and trans-1-ethyl-[4-Me-2H3]-4-methyl-cyclohexane indicates that deuterium-induced 13C nmr isotope shifts, all upfield, occur across 1,2, 3, and 5 bonds.

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