Question

will the compound show any optical activity if there is restricted rotation along the central bond?atropisomers are stereoisomers that occur when rotation restriction around a central bond is to allow isolation of individual conformers. the two atropisomers shown in (a) a plane of symmetry, so pure samples of each rotate the plane of plane polarized light.(c)what will happen to the optical activity at elevated temperatures as the rotation becomes less restricted?at higher temperature, as rotation becomes less restricted, the molecule becomes a meso compound because the chiral centers marked a and b have substituents on them and possess and chirality, respectively. therefore, as rotation of the central bond becomes less restricted, the optical rotation of either isolated conformer will be until it reaches a when full rotation is observed.

Answer 1

At elevated temperatures where the rotation around the central bond becomes unrestricted, the optical activity of atropisomers will decrease and eventually become zero if the fully rotating molecule is a meso compound.

What occurs in this system?

The compound will show optical activity if there is restricted rotation along the central bond. This is because the two conformers of the atropisomer are no longer able to interconvert freely, so they are effectively separate molecules. Each conformer has a chiral center, so it can rotate the plane of polarized light.

The optical activity of the compound will decrease as the temperature increases, and it will eventually reach zero when the rotation around the central bond becomes unrestricted. This is because the two conformers will be able to interconvert freely at high temperatures, so they will exist as a racemic mixture. A racemic mixture is a mixture of equal amounts of two enantiomers, so it does not have any optical activity.