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.

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.

A comprehensive computational examination of transannular Diels–Alder reactions of unsubstituted C14 trienes — Barriers, template effects, and the Curtin–Hammett principle

2001 ◽  
Vol 79 (8) ◽  
pp. 1284-1292 ◽  
Author(s):  
Saul Wolfe ◽  
Anthony V Buckley ◽  
Noham Weinberg
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Diels Alder ◽  
Molecular Orbital Calculations ◽  
Free Energy Difference ◽  
Molecular Mechanics Calculations ◽  
Geometrical Isomers ◽  
Free Energy Of Activation ◽  
Transition Structures ◽  
Cyclic Compounds

A combination of MM3-level molecular mechanics calculations and PM3-level semiempirical molecular orbital calculations has been employed, in conjunction with an algorithm for the comprehensive conformational analysis of cyclic compounds, to obtain 1202 unique 1,3,9-cyclotetradecatriene conformations, distributed over the six possible geometrical isomers, and 70 unique transannular Diels–Alder transition structures leading to the six possible stereoisomeric tricyclic olefins. A kinetic analysis that takes into account all minima of a given geometrical isomer and all transition structures leading to the same tricyclic product leads to a free energy of activation that is almost the same as the free energy difference between the lowest minimum and the lowest transition structure (the Curtin–Hammett principle). A substantial template effect, mainly entropic in origin, is found when the transannular reactions are compared to the Diels–Alder reactions of the cognate 2,4-hexatrienes with the 2-butenes. Although the cyclization of the trans-cis-trans triene favours the cis-anti-cis over the trans-anti-trans product by more than 20 kcal mol–1, the situation is reversed in the acyclic reaction. A cyclic triene that can cyclize directly to a trans-anti-trans tricycle can therefore be proposed.Key words: molecular models, Deslongchamps, Takahashi, trans-anti-trans tricycle, MM3, PM3, transition states.

Applying Bi-directional Jarzynski Methods to Quasi-equilibrium States

2010 ◽  
Vol 63 (3) ◽  
pp. 357 ◽  
Author(s):  
James C. Reid ◽  
Stephen R. Williams ◽  
Debra J. Searles
Keyword(s):  
Free Energy ◽  
Recent Work ◽  
Glassy State ◽  
Energy Difference ◽  
Fundamental Importance ◽  
Energy Measurement ◽  
Quasi Equilibrium ◽  
Major Advance ◽  
Free Energy Difference ◽  
Jarzynski Equality

Measuring free energy differences between states is of fundamental importance to understanding and predicting the behaviour of thermodynamic systems. The Jarzynski equality provides a method for measuring free energy differences using non-equilibrium work paths and represents a major advance of modern thermodynamics. Recent work has extended the theory by using work paths in both directions between the states to improve the accuracy of the free energy measurement. It has also been shown that the Jarzynski equality can be adapted to measure the free energy of quasi-equilibrium systems such as glasses. Here we combine these advances to accurately measure the free energy difference between a glassy state and equilibrium using bi-directional methods. For this system however, the result is not as accurate as that achieved using the work evaluated in a single direction.

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