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In the study of conformational isomerism, the gauche effect is an atypical situation where a gauche conformation (groups separated by a torsion angle of approximately 60°) is more stable than the anti conformation (180°). [2] Relative conformation energy diagram of butane as a function of dihedral angle. [3]
Cis-1,4-Di-tert-butylcyclohexane has an axial tert-butyl group in the chair conformation and conversion to the twist-boat conformation places both groups in more favorable equatorial positions. As a result, the twist-boat conformation is more stable by 0.47 kJ/mol (0.11 kcal/mol) at 125 K (−148 °C) as measured by NMR spectroscopy. [9]
The structure was found, using a cluster expansion method, to be the most stable of all the possible hydrogenation ratios of graphene. [4] In 2007, researchers found that the compound is more stable than other compounds containing carbon and hydrogen, such as benzene, cyclohexane and polyethylene. [1]
Thus, B is the most stable conformation. With certain polar substituents, hydrogen bonding can occur in the allylic system between the substituents. Rather than the strain that would normally occur in the close group proximity, the hydrogen bond stabilizes the conformation and makes it energetically much more favorable.
The staggered conformation is more stable by 12.5 kJ/mol than the eclipsed conformation, which is the energy maximum for ethane. In the eclipsed conformation the torsional angle is minimised. staggered conformation left, eclipsed conformation right in Newman projection
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.
This conformation is more specifically referred to as the gauche conformation of butane. This is due to the fact that the methyl groups are staggered, but only 60° from one another. This conformation is more energetically favored than the eclipsed conformation, but it is not the most energetically favorable conformation.
For this orbital overlap to occur, the trans, trans conformation is preferred for most heteroatoms, however for the stabilization to occur in dimethoxymethane, the gauche, gauche conformation is about 3–5 kcal/mol lower in energy (more stable) than the trans,trans conformation—this is about two times as big as the effect in sugars because ...