Chirality of Molecule
First and foremost, let’s recap on the meaning of chirality in an organic molecule.
We have learned that there must be at least one chiral centre in the molecule for it to be chiral and exhibits enantiomerism (optical isomerism). Chiral centre is a tetrahedral atom (usually carbon) that has four different substituent groups on it. This gives rise to enantiomers. Due to the chiral centre, there is an absence of a internal plane of symmetry in the molecule. A internal plane of symmetry is any plane cutting through the molecule such that one side is a perfect reflection of the other. For molecules with an internal plane of symmetry, we say that they are achiral and will not exhibit enantiomerism.
Three quick questions for you to think through before we move on:
- Must a molecule with chiral centre(s) be always chiral?
- Must a molecule without a plane of symmetry be always chiral?
- Must a molecule have a chiral centre in order to be chiral?
There are 3 special (unusual) cases of chirality and achirality which JC students taking A-Level H2 Chemistry syllabus should take note, namely:
- Meso compounds
- Some molecules without a plane of symmetry can