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The two have equal free energy; neither is more stable, so neither predominates compared to the other. A negative difference in free energy means that a conformer interconverts to a thermodynamically more stable conformation, thus the equilibrium constant will always be greater than 1.
The gauche effect is very sensitive to solvent effects, due to the large difference in polarity between the two conformers.For example, 2,3-dinitro-2,3-dimethylbutane, which in the solid state exists only in the gauche conformation, prefers the gauche conformer in benzene solution by a ratio of 79:21, but in carbon tetrachloride, it prefers the anti conformer by a ratio of 58:42. [9]
One category of reactions under Curtin–Hammett control includes transformations in which the more stable conformer reacts more quickly. This occurs when the transition state from the major intermediate to its respective product is lower in energy than the transition state from the minor intermediate to the other possible product.
When two fluorine atoms are in vicinal (i.e., adjacent) carbons, as in 1,2-difluoroethane (H 2 FCCFH 2), the gauche conformer is more stable than the anti conformer—this is the opposite of what would normally be expected and to what is observed for most 1,2-disubstituted ethanes; this phenomenon is known as the gauche effect. [9]
Cyclohexane is the most stable of the cycloalkanes, due to the stability of adapting to its chair conformer. [4] This conformer stability allows cyclohexane to be used as a standard in lab analyses. More specifically, cyclohexane is used as a standard for pharmaceutical reference in solvent analysis of pharmaceutical compounds and raw materials.
More complex molecules, such as butane, have more than one possible staggered conformation. The anti conformation of butane is approximately 0.9 kcal mol −1 (3.8 kJ mol −1) more stable than the gauche conformation. [1] Both of these staggered conformations are much more stable than the eclipsed conformations.
The cis conformer is 3.13 kJ mol −1, more stable than the trans form, with an energy barrier to rotation of 45.3 kJ mol −1. [3] The cis and trans structure have also been determined by microwave spectroscopy (see external links).
Chemical substances or states can persist indefinitely even though they are not in their lowest energy state if they experience metastability - a state which is stable only if not disturbed too much. A substance (or state) might also be termed "kinetically persistent" if it is changing relatively slowly (and thus is not at thermodynamic ...