Question:
Which of the following amino acid is optically inactive?
Which of the following amino acid is optically inactive?
Show Hint
Glycine is the only proteinogenic amino acid that is not chiral.
Updated On: May 10, 2026
- Glycine
- Alanine
- Valine
- Leucine
- Isoleucine
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Optical activity in amino acids arises from the presence of a chiral carbon atom (the \(\alpha\)-carbon).
Step 2: Detailed Explanation:
For an \(\alpha\)-amino acid, the general structure is H\(_2\)N-CH(R)-COOH. The \(\alpha\)-carbon is bonded to -NH\(_2\), -COOH, -H, and the side chain R.
• Glycine: The side chain is just a hydrogen atom (-H). Therefore, the \(\alpha\)-carbon is bonded to two hydrogen atoms, making it achiral (not a stereocenter). Glycine is optically inactive.
• Alanine (R = -CH\(_3\)), Valine (R = -CH(CH\(_3\))\(_2\)), Leucine (R = -CH\(_2\)CH(CH\(_3\))\(_2\)), Isoleucine (R = -CH(CH\(_3\))CH\(_2\)CH\(_3\)): All have different side chains, so their \(\alpha\)-carbon is chiral and they are optically active.
Step 3: Final Answer:
Glycine is the optically inactive amino acid.
Optical activity in amino acids arises from the presence of a chiral carbon atom (the \(\alpha\)-carbon).
Step 2: Detailed Explanation:
For an \(\alpha\)-amino acid, the general structure is H\(_2\)N-CH(R)-COOH. The \(\alpha\)-carbon is bonded to -NH\(_2\), -COOH, -H, and the side chain R.
• Glycine: The side chain is just a hydrogen atom (-H). Therefore, the \(\alpha\)-carbon is bonded to two hydrogen atoms, making it achiral (not a stereocenter). Glycine is optically inactive.
• Alanine (R = -CH\(_3\)), Valine (R = -CH(CH\(_3\))\(_2\)), Leucine (R = -CH\(_2\)CH(CH\(_3\))\(_2\)), Isoleucine (R = -CH(CH\(_3\))CH\(_2\)CH\(_3\)): All have different side chains, so their \(\alpha\)-carbon is chiral and they are optically active.
Step 3: Final Answer:
Glycine is the optically inactive amino acid.
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