Haloalkanes and Haloarenes - Optical rotation

Optical Activity: The property of certain organic substances to rotate the plane of polarized light. Substances that rotate light to the right (clockwise) are called dextrorotatory ($+$ or $d$), and those rotating it to the left (counter-clockwise) are laevorotatory ($-$ or $l$).

Chirality: A molecule is said to be chiral if it is non-superimposable on its mirror image. This usually occurs when a carbon atom is bonded to four different atoms or groups, known as an asymmetric carbon or chiral center ($C^*$).

Enantiomers: Stereoisomers that are non-superimposable mirror images of each other. They have identical physical properties (like boiling point and solubility) but rotate plane-polarized light in opposite directions by equal magnitudes.

Racemic Mixture: An equimolar mixture of a pair of enantiomers. It is optically inactive because the rotation caused by one isomer is exactly cancelled by the rotation caused by the other. This is known as external compensation and is denoted by the prefix $(\pm)$ or $dl$.

Racemization: The process of conversion of an enantiomer into a racemic mixture. This frequently occurs during $S_N1$ reactions due to the formation of a planar carbocation intermediate.

Inversion of Configuration: In $S_N2$ reactions, the nucleophile attacks from the side opposite to the leaving group, resulting in a product with a spatial arrangement opposite to the reactant, known as Walden Inversion.