---
title: "Enantiomers and diastereomers of 3-bromo-2-butanol"
subject: "Engineering Chemistry"
chapter: 9
key: "semester_2/engineering_chemistry:enantiomers-diastereomers-bromobutanol"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/enantiomers-diastereomers-bromobutanol
site: BCT Engineering
---

# Enantiomers and diastereomers of 3-bromo-2-butanol

Engineering Chemistry · Chapter 9: Stereochemistry

- Asked in: 2071 Bhadra, 2+3 marks
- Video: [Diastereomers](https://www.youtube.com/watch?v=23-dfkwKCcg) — 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/enantiomers-diastereomers-bromobutanol
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-9

## Question

Distinguish between enantiomers and diastereomers. Show these isomers in 3-bromo-2-butanol.

## Short answer

Enantiomers are non-superimposable mirror images with identical physical properties; diastereomers are stereoisomers that are not mirror images and have different physical properties. 3-Bromo-2-butanol has four stereoisomers: two enantiomeric pairs, (2S,3R)/(2R,3S) and (2S,3S)/(2R,3R), with diastereomers between these pairs.

## Answer

#### Difference
| Basis | Enantiomers | Diastereomers |
|---|---|---|
| Relationship | Stereoisomers that are non-superimposable mirror images | Stereoisomers that are not mirror images |
| Number of chiral centres | One or more (all centres inverted) | Usually two or more (only some inverted); cis–trans isomers are also diastereomers |
| Physical properties | Identical (m.p., b.p., solubility) | Different |
| Chemical properties | Same with achiral reagents | Different |
| Optical rotation | Equal in magnitude, opposite in sign | Different, unrelated values |
| Separation | Difficult (needs resolution) | Easy (crystallisation, distillation) |
| Example | (+)- and (−)-lactic acid; (2R,3R)- and (2S,3S)-tartaric acid | (2R,3R)-tartaric acid and meso-tartaric acid |

#### In 3-bromo-2-butanol
```text
 (2S,3R)        (2R,3S)        (2S,3S)        (2R,3R)
   CH₃            CH₃            CH₃            CH₃
H—C—OH         HO—C—H         H—C—OH         HO—C—H
H—C—Br         Br—C—H         Br—C—H         H—C—Br
   CH₃            CH₃            CH₃            CH₃
```
3-Bromo-2-butanol, CH₃–CH(OH)–CH(Br)–CH₃, has two different chiral carbons (C2 and C3), so it has 2² = 4 stereoisomers (there is no meso form, since the two centres are different).
- **Enantiomers:** (2S,3R) and (2R,3S) form one pair; (2S,3S) and (2R,3R) form another pair. The two members of each pair are mirror images.
- **Diastereomers:** any member of one pair relative to a member of the other, e.g. (2S,3R) and (2S,3S); they are not mirror images and have different physical properties.

## Check yourself

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

1. How many stereoisomers does 3-bromo-2-butanol have?
   A. 2
   B. 3 including a meso
   C. 4, since it has two different chiral centres
   D. 8
   Answer: C. 2^2 = 4; no meso as the centres differ. (Key point: Number)

2. Which pair are enantiomers?
   A. (2S,3R) and (2R,3S)
   B. (2S,3R) and (2S,3S)
   C. (2R,3R) and (2S,3R)
   D. (2S,3S) and (2R,3S)
   Answer: A. Both centres are inverted in mirror images. (Key point: Enantiomer pair)

3. Which pair are diastereomers?
   A. (2S,3S) and (2R,3R)
   B. (2S,3R) and (2R,3S)
   C. (2S,3R) and (2S,3S)
   D. None exist
   Answer: C. Only one centre is inverted. (Key point: Diastereomers)

4. How do enantiomers differ from diastereomers in separation?
   A. Enantiomers are difficult to separate; diastereomers are easy
   B. Enantiomers are easy; diastereomers difficult
   C. Both are easy by distillation
   D. Both impossible
   Answer: A. Diastereomers have different physical properties. (Key point: Properties)

## Related in Engineering Chemistry

- [Isomers of 3-bromo-2-butanol; racemization, resolution](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Abromobutanol-isomers-resolution) — Engineering Chemistry, chapter 9
- [Enantiomers vs diastereomers](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aenantiomers-diastereomers) — Engineering Chemistry, chapter 9, asked 6×