Biphenyls & Optical Isomerism: When Planes Matter

The video tutorial explains the structure and properties of biphenyls, highlighting their lack of chiral centers and optical inactivity due to free rotation. It discusses how biphenyls can become chiral and optically active when bulky groups are substituted at ortho positions, preventing free rotation. This leads to the formation of ananchomers, a phenomenon known as heteroisomerism.

What is the reason biphenyls are generally optically inactive?

• They have chiral centers.

• They have a plane of symmetry.

• They contain bulky groups at ortho positions.

• The phenyl groups are in constant motion due to free rotation.

Under what condition do biphenyl compounds become optically active?

• When they are in constant motion.

• When they have no substituents.

• When they have identical substituents on one benzene ring.

• When bulky groups are substituted at ortho positions with different substituents.

What effect do bulky groups at ortho positions have on biphenyls?

• They make the molecule planar.

• They increase the free rotation of the molecule.

• They create a plane of symmetry.

• They restrict the rotation, leading to optical activity.

What is the term used to describe the formation of isomers due to restricted rotation in biphenyls?

• Heteroisomerism

• Stereoisomerism

• Optical isomerism

• Geometric isomerism

What is the bond angle difference between the benzene nuclei in a biphenyl molecule with restricted rotation?

• 60°

• 180°

• 120°

• 90°