Louis Pasteur observed that crystals of certain compounds exist in the form of mirror images, and solutions of these crystals showed equal-magnitude but opposite-direction optical rotation, leading to the concept of molecular asymmetry.

The phenomenon of having (+) and (–) isomers in optical isomerism is termed as optical isomerism, where compounds exhibit different rotations of plane-polarized light, leading to dextrorotatory and laevo-rotatory isomers.

Dextrorotatory isomers are denoted by placing a positive (+) sign before the degree of rotation, indicating a clockwise rotation. Laevo-rotatory isomers are denoted by a negative (–) sign before the degree of rotation, indicating a counterclockwise rotation.

Optical activity refers to the ability of certain compounds to rotate the plane of plane-polarized light. It is measured using a polarimeter, with a clockwise rotation (+) indicating dextrorotatory and a counterclockwise rotation (–) indicating laevo-rotatory.

Tertiary alkyl halides undergo SN₁ reactions more rapidly due to the higher stability of the resulting tertiary carbocations, making their formation easier and the reaction faster.