Explain when optical isomerism occurs and how it differs from structural isomerism.

Optical isomerism occurs in molecules that contain one or more chiral carbon atoms, resulting in two enantiomers that rotate plane-polarised light in opposite directions. In contrast, structural isomerism occurs when compounds have the same molecular formula but differ in the arrangement of atoms. Optical isomerism applies specifically to chiral molecules, while structural isomerism can occur in a broader range of compounds.

This question assesses the student's ability to apply knowledge of isomerism types. The answer effectively explains the conditions for optical isomerism and distinguishes it from structural isomerism, showcasing a deeper understanding of organic chemistry concepts.