---
title: "Optical isomerism; tartaric acid; maleic/fumaric Z,E"
subject: "Engineering Chemistry"
chapter: 9
key: "semester_2/engineering_chemistry:optical-isomerism-tartaric-maleic"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/optical-isomerism-tartaric-maleic
site: BCT Engineering
---

# Optical isomerism; tartaric acid; maleic/fumaric Z,E

Engineering Chemistry · Chapter 9: Stereochemistry

- Asked in: 2068 Magh, 1+3+1 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/optical-isomerism-tartaric-maleic
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-9

## Question

What is optical isomerism? Write the possible stereoisomers of tartaric acid. Specify Z and E configuration of maleic acid and fumaric acid.

## Short answer

Optical isomerism arises from chirality, giving enantiomers that rotate plane-polarised light differently. Tartaric acid stereoisomers: active (2R,3R) and (2S,3S) pair, and inactive meso form. Maleic acid is Z (COOH groups on same side), fumaric acid is E (COOH groups opposite).

## Answer

#### Optical isomerism
Optical isomerism is stereoisomerism in which isomers have identical constitution but differ in their effect on plane-polarised light. It occurs when a molecule is chiral (non-superimposable on its mirror image), most commonly due to a carbon with four different groups. Optical isomers are called enantiomers.

#### Stereoisomers of tartaric acid
```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.

#### Maleic and fumaric acid
```text
 HOOC   COOH            HOOC   H
    \  /                   \  /
     C=C                     C=C
    /  \                   /  \
   H    H                 H    COOH
 maleic acid           fumaric acid
```
On each carbon, COOH has higher priority than H. In maleic acid the COOH groups are on the same side, so it is **Z**. In fumaric acid they are on opposite sides, so it is **E**.

## Check yourself

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

1. What causes optical isomerism?
   A. Chirality, commonly a carbon with four different groups
   B. Restricted rotation about C=C
   C. Different functional groups
   D. Different chain length
   Answer: A. Optical isomers are enantiomers. (Key point: Cause)

2. Which tartaric acid form is optically inactive?
   A. (2R,3R)
   B. (2S,3S)
   C. Meso (2R,3S)
   D. None
   Answer: C. Internal plane of symmetry. (Key point: Tartaric)

3. What is the configuration of maleic acid?
   A. Z
   B. E
   C. R
   D. S
   Answer: A. Fumaric acid is E. (Key point: Maleic)

4. Why does Z/E assignment put COOH above H?
   A. COOH is larger in mass only
   B. H is not counted
   C. Carbon has higher atomic number than hydrogen
   D. Alphabetical order
   Answer: C. CIP rules. (Key point: Priority)

## 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
- [Stereoisomers of tartaric acid; meso form](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atartaric-acid) — Engineering Chemistry, chapter 9
- [Isomerism in 2-hydroxypropanoic acid](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alactic-acid-isomerism) — Engineering Chemistry, chapter 9
- [Optical isomerism; chiral centre and optical activity](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aoptical-isomerism-chiral) — Engineering Chemistry, chapter 9