According to the CIP multiple bond expansion rules, how is an aldehyde group () correctly prioritize — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

CIP rules mandate that multiple bonds are mathematically expanded. An aldehyde's $C=O$ double bond means the carbon is treated as if it is bonded to (O, O, H). The primary alcohol's carbon is bonded only to (O, H, H). Since the second atom comparison pits Oxygen against Hydrogen, $-CHO$ receives higher priority.