Search results
Results from the WOW.Com Content Network
The twist boat has a lower energy than the boat. In order to go from the chair conformation to a twist-boat conformation or the other chair conformation, bond angles have to be changed, leading to a high-energy half-chair conformation. So the relative stabilities are: chair > twist boat > boat > half-chair. All relative conformational energies ...
The molecular motions involved in a chair flip are detailed in the figure on the right: The half-chair conformation (D, 10.8 kcal/mol, C 2 symmetry) is the energy maximum when proceeding from the chair conformer (A, 0 kcal/mol reference, D 3d symmetry) to the higher energy twist-boat conformer (B, 5.5 kcal/mol, D 2 symmetry).
A-values help predict the conformation of cyclohexane rings. The most stable conformation will be the one which has the substituent or substituents equatorial. When multiple substituents are taken into consideration, the conformation where the substituent with the largest A-value is equatorial is favored.
The chair conformation is the favored configuration, ... In organic chemistry, the term aromaticity is used to describe a cyclic (ring-shaped), planar (flat) molecule ...
The anti conformation is more stable by 0.9 kcal mol −1. [1] We would expect that butane is roughly 82% anti and 18% gauche at room temperature. However, there are two possible gauche conformations and only one anti conformation. Therefore, entropy makes a contribution of 0.4 kcal in favor of the gauche conformation. [2]
The aza-Cope/Mannich reaction, when participating in ring-expanding annulations, follows the stereochemistry dictated by the most favorable chair conformation, which generally places bulky substituents quasi-equatorially. The vinyl and amine components can have either syn or anti relationships when installed on a ring.
Haworth projection approximate the shapes of the actual molecules better for furanoses—which are in reality nearly planar—than for pyranoses that exist in solution in the chair conformation. [1] Organic chemistry and especially biochemistry are the areas of chemistry that use the Haworth projection the most.
The chair and twist-boat are energy minima and are therefore conformers, while the half-chair and the boat are transition states and represent energy maxima. The idea that the chair conformation is the most stable structure for cyclohexane was first proposed as early as 1890 by Hermann Sachse, but only gained widespread acceptance much later.