In stereochemistry of amino acids: D-alanine and L-alanine are technically classified as which type of stereoisomers (considering the mirror-image relationship of their chiral centers)?

Introduction / Context:
Understanding the stereochemistry of amino acids is fundamental in biochemistry because enzyme recognition, peptide folding, and receptor binding depend on precise 3-D arrangements. Naturally occurring proteins overwhelmingly use L-amino acids, while the D-forms are their mirror images and can display very different biological behavior.

Given Data / Assumptions:

• Alanine has one chiral center at the alpha carbon (Cα).
• D-alanine and L-alanine differ only in the spatial arrangement around this single stereocenter.
• No ring closures or cyclic sugar contexts are involved.

Concept / Approach:
Stereoisomers that are non-superimposable mirror images are called enantiomers. Epimers differ at one stereocenter but are not mirror images. Anomers are a special case of epimers formed upon cyclization of sugars (α/β at the anomeric carbon), not relevant to amino acids. Polymers refer to macromolecules composed of repeating units and are not a stereochemical class.

Step-by-Step Solution:
Identify the chiral center in alanine → the alpha carbon attached to H, CH3, NH2, and COOH. Recognize D vs L as mirror-image configurations around the same stereocenter. Classify mirror-image, non-superimposable pairs → enantiomers. Exclude epimer/anomer/polymer definitions as inapplicable here.

Verification / Alternative check:
Enantiomers rotate plane-polarized light equally and oppositely and interconvert only by bond breaking at the stereocenter. D- and L-alanine meet this criterion.

Why Other Options Are Wrong:
Anomers apply to cyclic sugars; epimers are not mirror images; polymers describe chain length, not stereochemistry; diastereomers are stereoisomers that are not mirror images (need ≥2 stereocenters), which alanine lacks.

Common Pitfalls:
Confusing epimer with enantiomer; extending sugar terminology (anomer) to amino acids.

Final Answer:
Enantiomers.