Acidic proton
The carboxyl O–H is the ordinary acidic proton.
Removing it gives lactate; the alcohol –OH is a different functional group.
Molecular compound · hydroxycarboxylic acid
Lactic acid
C₃H₆O₃
Lactic acid is C₃H₆O₃ with the connectivity CH₃–CH(OH)–COOH. It contains one alcohol group and one carboxylic acid group, and its middle carbon is stereogenic.
Stereochemistry rule: the generic master “lactic acid” does not silently choose one enantiomer. L- and D-lactic acid are stereochemically specified forms of the same connectivity.
Essentials
One –OH group and one –COOH group share the same three-carbon molecule.
The condensed structure shows why lactic acid is both a hydroxy compound and a carboxylic acid.
Detail
The middle carbon is a stereogenic center.
It is attached to four different groups: H, OH, CH₃ and COOH. Therefore two mirror-image configurations are possible.
Names matter
“Lactic acid” and a specific enantiomer are different levels of identity.
A stereochemical descriptor is required when the handedness matters.
Understand
Deprotonation gives lactate.
The carboxylic acid group transfers a proton in acid–base chemistry, giving a lactate anion while preserving the carbon skeleton and stereogenic center.
Biological context
Biological systems often distinguish enantiomers.
The stereochemical identity of lactate matters in enzyme recognition even though both enantiomers share formula and connectivity.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | C₃H₆O₃ / CH₃CHOHCOOH |
|---|---|
| CAS Registry Number | 50-21-5 |
| PubChem CID | 612 |
| Stereochemistry | generic master: unspecified |
Advanced
Push past the first model without losing the simple picture.
Is lactic acid always one enantiomer?
No. The generic name can be used without specifying configuration; stereospecific names are needed when handedness matters.
Why is lactate negatively charged?
Deprotonation of the carboxyl group leaves a carboxylate whose negative charge is resonance-delocalized over two oxygens.
Is lactic acid the same as lactate?
No. They are a conjugate acid–base pair differing by one proton and one unit of charge.
Constituent elements