See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# D-Glucose Nomenclature The D/L designation in carbohydrates is determined by the stereochemistry of the **chiral carbon furthest from the carbonyl group** (the penultimate carbon), not by other carbons. ## Step-by-step reasoning: **1) Identify the reference carbon:** In glucose, the carbonyl carbon is C1. The furthest chiral carbon from it is C5 (the penultimate carbon). **2) Apply Fischer projection rules:** In Fischer projection, when the carbon chain is written vertically with the aldehyde group at the top: - If the $OH$ group on C5 is on the **right side** → D-sugar - If the $OH$ group on C5 is on the **left side** → L-sugar **3) Natural glucose structure:** In D-glucose, the $OH$ on the fifth carbon (penultimate carbon) is positioned on the right in Fischer projection. ## Why option (C) is correct: Option (C) correctly identifies that the $OH$ on the **fifth carbon** determines the D/L nomenclature. **Why others are wrong:** - **(A)** — C2 stereochemistry doesn't determine D/L; it determines epimers (glucose vs mannose) - **(B)** — C6 is not chiral (it's $CH_2OH$) - **(D)** — Dextratory refers to optical rotation direction, not D/L nomenclature