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The existence of specific conformations is due to hindered rotation around sigma bonds, although a role for hyperconjugation is proposed by a competing theory. The importance of energy minima and energy maxima is seen by extension of these concepts to more complex molecules for which stable conformations may be predicted as minimum-energy forms.
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]
The chair conformation is the most stable conformer. At 298 K (25 °C), 99.99% of all molecules in a cyclohexane solution adopt this conformation. The C–C ring of the chair conformation has the same shape as the 6-membered rings in the diamond cubic lattice. [7]: 16 This can be modeled as follows.
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.
Any disorder in hydrogenation conformation tends to contract the lattice constant by about 2.0%. [8] Graphane is an insulator. Chemical functionalization of graphene with hydrogen may be a suitable method to open a band gap in graphene. [1] P-doped graphane is proposed to be a high-temperature BCS theory superconductor with a T c above 90 K. [9]
Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.
A major application of Walsh diagrams is to explain the regularity in structure observed for related molecules having identical numbers of valence electrons (e.g. why H 2 O and H 2 S look similar), and to account for how molecules alter their geometries as their number of electrons or spin state changes.
Such a conformation can exist in any open chain, single chemical bond connecting two sp 3-hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance , but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms).