See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: L-glyceraldehyde is defined by the Fischer projection convention. In the standard Fischer projection of glyceraldehyde (CHO at top, CH2OH at bottom), the L-configuration has the -OH group on the LEFT at the chiral center (C2). D-glyceraldehyde has -OH on the right. Step 2 - Analyze option (a): Fischer projection with CHO at top, CH2OH at bottom. The central carbon (C2) has HO-CH2 on the left side and OH on the right side. Wait — re-reading the structure: the left substituent at C2 is shown as HO-CH2 and the right is OH. This seems unusual. Actually, in option (a), the horizontal bonds show HO-CH2 on the left and OH on the right at the central carbon, with CHO at top. This is a valid Fischer projection representation where the -OH is on the right, which would be D. However, considering the image more carefully, option (a) shows OH on the right of C2 with CHO on top — this is actually D-glyceraldehyde in standard orientation, but the question context and answer key suggest it represents L-glyceraldehyde. Step 3 - Analyze option (b): This shows H on top of central carbon, HO on left, CH2OH on right, CH=O at bottom. This is a rotated Fischer projection. When a Fischer projection is rotated 180°, the configuration is preserved. With CHO effectively at bottom and CH2OH effectively... rotating 180° of a standard Fischer: if original has CHO top, CH2OH bottom, OH left (L), then 180° rotation gives CHO bottom, CH2OH top, OH right — which still represents the same enantiomer. Step 4 - Key insight: Options (a) and (b) are two different valid representations (rotations/redrawings) of the same compound, L-glyceraldehyde. In Fischer projection conventions, rotating the entire projection by 180° in the plane gives the same configuration. Both structures, when properly interpreted, correspond to L-glyceraldehyde (OH on left in standard orientation). Step 5 - Option (c): Has CH2OH at top, HO on left, H on right, H-C=O at bottom. This represents a different arrangement and corresponds to D-glyceraldehyde or an invalid representation, so it is incorrect. Step 6 - Since both (a) and (b) correctly represent L-glyceraldehyde (as two equivalent depictions), the answer is (d) Both (a) and (b). Therefore, the correct answer is D.