Chiral carbon are carbons which are linked to 4 different atoms or groups simply. It is also called as asymmetrical carbon. Carbon forms 4 valence bond with other atoms. If all 4 atoms linked to that carbon atom are different, then it is said to be chiral or asymmetrical carbon. For a carbon to be chiral, all atoms linking to it must be different. If there are even 2 atoms similar, then it is not said to be chiral. It is denoted by an asteric symbol (C*)
How to find chiral carbon
Steps to find/identify chiral carbon.
- Examine the nature of atoms bonding to that particular carbon. If all the valence bond (4 bond) of carbon is attached to dissimilar atoms or groups then it is chiral carbon.
- To count the number of chiral carbon present in a compound, Look for each specific carbon and its bonded atoms.
- Leave the carbon that are involved in double bond formation as in carbon no. 1 in glucose (aldehyde) & carbon no. 2 (ketone group) in fructose because to be a chiral carbon, a carbon must be linked to 4 different atoms or groups i.e. SP3 hybridized.
- But some exception occurs in case of double bonds in compounds like CH3-CH2=C=CH3, CH3-CBr=C=CHCl. The carbon with double bond =C= is chiral due to formation of nonsuperimposable mirror image and different linking groups.
Counting number of chiral carbons
The nuber of chiral carbon present in compounds can be found by following the above mentioned steps. Let’s find the number of chiral carbon in following molecules.
Molecules 1: Glucose
Glucose has 4 chiral carbon both in ring and open structure marked with star(*).
Molecule 2: Fructose
Fructose has 3 chiral carbon in open structure and 4 in closed ring shaped structure.
Molecule 3
Chiral carbon = 2
Molecule 4
Chiral carbon = 0
Molecule 5
Chiral carbon = 0
Molecule 6
Chiral carbon = 1
Molecule 7
Chiral carbon = 2
