Stereochemistry Problem 8

Description:

Problem

Molecules which have non-superimposable mirror images are chiral. Which of the following molecules is chiral?

1. 2 − Bromobutane

2. 1 − Bromobutane

3. 2 − Bromopropane

4. 2 − Bromobutan − 2 − ol

Solution

Chiral compounds have asymmetric carbon atom or the carbon atom that has 4 different substituents attached to it.

1. 2 − Bromobutane: CH₃ − CH₂ − CH(Br) − CH₃ … Chiral

The substituents are all different (−C₂H₅,−CH₃,−Br,−H)

2. 1 − Bromobutane: CH₃ − CH₂ − CH₂ − CH₂Br … Achiral

Two identical hydrogen atoms, thus not asymmetric carbon.

3. 2 − Bromopropane: CH₃ − CH(Br) − CH₃ … Achiral

Two identical methyl groups, thus all 4 substituents are not different.

4. 2 − Bromobutan − 2 − ol: CH₃ − C(Br)(OH) − C₂H₅ … Chiral

Four different substituents (−CH₃,−C₂H₅,−Br,−OH), thus, asymmetric carbon atom and the molecule is chiral.