See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: In a Fischer projection, the molecule is oriented with the most oxidized carbon (highest priority in amino acids = COOH) at the top and the carbon chain running vertically. Horizontal bonds project toward the viewer (wedge) and vertical bonds project away (dash). Step 2 - Standard orientation for amino acids: The COOH group is placed at the top and the R-group (CH2OH for serine) at the bottom. The stereocenter (alpha carbon) has NH2 and H as the horizontal substituents. Step 3 - For L-serine (the naturally occurring form): In a Fischer projection with COOH on top and CH2OH on bottom, the NH2 group is on the LEFT side (analogous to L-alanine configuration). H is on the right. Step 4 - Evaluating option (d): COOH is on top (vertical, going away), CH2OH is on bottom (vertical, going away), H2N (NH2) is on the left (horizontal, coming toward viewer), H is on the right (horizontal, coming toward viewer). This matches the correct L-serine Fischer projection with the standard amino acid convention. Step 5 - Why other options fail: - Option (a): NH2 is on top instead of COOH; the vertical axis is not the carbon chain in standard orientation. - Option (b): H is on top, which is not the standard orientation for Fischer projections of amino acids. - Option (c): CH2OH is on top and NH2 is on the bottom, which inverts the standard amino acid Fischer projection convention. Option (d) correctly places COOH at top, NH2 on left, H on right, and CH2OH at bottom, representing L-serine in standard Fischer projection format. Therefore, the correct answer is D.