---
title: "Stereoisomers of tartaric acid; meso form"
subject: "Engineering Chemistry"
chapter: 9
key: "semester_2/engineering_chemistry:tartaric-acid"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tartaric-acid
site: BCT Engineering
---

# Stereoisomers of tartaric acid; meso form

Engineering Chemistry · Chapter 9: Stereochemistry

- Asked in: 2073 Magh, 2+1 marks
- Video: [Meso Compounds](https://www.youtube.com/watch?v=cK5lbHf1Rlg) — The Organic Chemistry Tutor
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tartaric-acid
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-9

## Question

Write all the possible stereoisomers of tartaric acid. Does tartaric acid has meso form? Explain with reason.

## Short answer

Tartaric acid has three stereoisomers: (2R,3R), (2S,3S), and meso (2R,3S). The meso form exists because the two chiral carbons have the same four groups, and the (2R,3S) configuration creates an internal plane of symmetry, making it optically inactive by internal compensation.

## Answer

Tartaric acid HOOC–CH(OH)–CH(OH)–COOH has two chiral carbons with the same four groups, so it has **three** stereoisomers (not four).
```text
   COOH         COOH         COOH
H—C—OH       HO—C—H       H—C—OH
HO—C—H       H—C—OH       H—C—OH
   COOH         COOH         COOH
 (2R,3R)      (2S,3S)      meso (2R,3S)
 L-(+)        D-(−)        inactive
```
- (2R,3R) and (2S,3S) are enantiomers (optically active, equal and opposite rotation).
- The meso form has a plane of symmetry (internal mirror) between C2 and C3, so it is optically inactive by internal compensation. It is a diastereomer of both active forms.
- An equimolar mixture of the (+) and (−) forms is the racemic (±) acid.

**Does tartaric acid have a meso form? Yes.** Both chiral carbons carry the same four groups (H, OH, COOH, CH(OH)COOH). In the (2R,3S) form the configuration at C2 is the mirror of C3, so a plane of symmetry runs through the middle of the C2–C3 bond. The rotation of the upper half is cancelled by the lower half (internal compensation), so this form is optically inactive and not resolvable.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How many stereoisomers does tartaric acid have?
   A. Three: (2R,3R), (2S,3S) and meso
   B. Four
   C. Two
   D. Six
   Answer: A. Two chiral centres would give 4, but identical groups make meso a duplicate. (Key point: Number)

2. Why is the meso form optically inactive?
   A. It is a racemic mixture
   B. It has no chiral carbons
   C. An internal plane of symmetry cancels rotation of the two halves
   D. It is the mirror image of the active form
   Answer: C. This is internal compensation. (Key point: Meso reason)

3. Which configuration is meso-tartaric acid?
   A. (2R,3S)
   B. (2R,3R)
   C. (2S,3S)
   D. (2R,2S)
   Answer: A. C2 is the mirror of C3. (Key point: Meso config)

4. How is meso-tartaric acid related to the active forms?
   A. It is an enantiomer of each
   B. It is identical to one
   C. It is a diastereomer of each
   D. It is a structural isomer
   Answer: C. It is not a mirror image of either. (Key point: Relationship)

## Related in Engineering Chemistry

- [Optical activity; tartaric acid stereoisomers](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aoptical-activity-tartaric) — Engineering Chemistry, chapter 9
- [Optical isomerism; tartaric acid; maleic/fumaric Z,E](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aoptical-isomerism-tartaric-maleic) — Engineering Chemistry, chapter 9