Which of the following molecules has a pro-chiral centre?

Options

A. `CH_(3)CH_(2)COOH`
B. `HOOC CH_(2)COOH`
C. `(CH_(3))_(2)CHCOOH`
D. `CH_(3)CHOHCOOH`

Answer

A

Explanation

An atom linked to two identical ligands amd to two other differ ligands `[Caabc]` is said to be prochiral. If one of the a ligands is replaced by another ligand different from any of the other then a new chiral centre is produced `[Cabcd]`. For example, both ethanol and propanoic acid contain prochiral centre.

This is an important feature of many biological reactions becasue enzymes (themselves chiral) can somtiomes distinguish between the two identi9cal ligands and replace only one of them. The identi9cal ligands (most commonly `H`)can be designated as pro `-(R)` and pro-`(S)` depending on whether the `(R )` or `(S)` enantiomer results when the ligand is replaced by one of higher precendence without changing the precendence of the remianing ligands.
The two identical ligands attached to a prochiral centre are said to be enantiotopic of their separate replacement by a group different from any attacjed to the prochiral centre gives rise to a pair of enantiomers and to be diastereotopic if diastereoisomers are obtained on replacement.
Enantiotopic ligands at a prochiral centre

Diastereotopic ligands at a prochiral centre