What is the smallest number of carbon atoms needed in a molecule containing only carbon, hydrogen and a single oxygen atom for it to be both chiral and a ketone
The Correct Answer and Explanation is:
To determine the smallest number of carbon atoms needed in a molecule containing only carbon, hydrogen, and a single oxygen atom for it to be both chiral and a ketone, let’s break down the requirements.
Chiral Molecule:
A molecule is chiral if it has no plane of symmetry and cannot be superimposed on its mirror image. This often occurs when the molecule contains a carbon atom with four different substituents, making it a chiral center or stereocenter.
Ketone:
A ketone is a type of organic compound in which the carbonyl group (C=O) is bonded to two carbon atoms. The general structure of a ketone is R-CO-R’, where both R and R’ are alkyl or aryl groups.
Step-by-Step Breakdown:
- Ketone Functional Group:
The presence of a ketone means the molecule must have a carbonyl group (C=O) bonded to two carbon atoms. This means there must be at least two carbon atoms attached to the carbonyl group. - Chirality Requirement:
For the molecule to be chiral, one of these carbon atoms must have four different substituents. This requires at least one of the carbons in the ketone to be attached to a different group besides hydrogen and another carbon. In simplest terms, it needs to be bonded to a different group, such as an alkyl or aryl group, which would make it a stereocenter. - Smallest Structure:
The simplest ketone that could be chiral is acetone (CH3-CO-CH3), but acetone is not chiral because the two methyl groups (CH3) are identical. We need a structure where the two groups attached to the carbonyl are different. A possible example is 2-propanone or acetone derivatives where the molecule has two different alkyl groups attached to the carbonyl. This requires at least three carbon atoms: one for the carbonyl group, one for each alkyl group, and one for the chiral center.
Conclusion:
Thus, the smallest number of carbon atoms needed in a molecule containing only carbon, hydrogen, and a single oxygen atom for it to be both chiral and a ketone is 3 carbon atoms. The molecule would be a ketone with two different alkyl groups, one of which would be chiral. An example is acetone derivatives, where the structure would meet both the ketone and chirality conditions.
