Question

Which one of the following represent identical molecules?

• A. P and Q
• B. Q and S
• C. Q and R
• D. R and S

Answer 1

The correct option is C

Q and R

The correct option is option C

The explanation for the correct option:

1. A representation of the conformation(different 3D forms of a molecule) of a molecule known as a "Newman projection" shows the front carbon as a point and the back carbon as a circle, with the viewer's eye, thought to be sighting down a carbon-carbon bond.
2. For naming a conformation we must draw its skeletal structure. The longest chain consisting a maximum number of carbon is considered as the parent chain.
3. After drawing the skeletal structure draw the side groups present on each carbon.
4. In the Q structure, the front alkane chain has an ethyl group present at the third carbon and an alcohol group along with the methyl group present on the second carbon.
5. And also in the R structure, the front alkane chain has an ethyl group present at the third carbon and an alcohol group along with the methyl group present on the second carbon.

The explanation for the incorrect option:

Option (A): P and Q

1. In the given P structure the front alkane chain has three methyl groups present on the second and third carbon.
2. Whereas in the Q structure In the Q structure, the front alkane chain has an ethyl group present at the third carbon and an alcohol group along with the methyl group present on the second carbon.
3. Hence, it is an incorrect option.

Option (B): Q and S

1. In the Q structure In the Q structure, the front alkane chain has an ethyl group present at the third carbon and an alcohol group along with the methyl group present on the second carbon.
2. Whereas in the S structure, the alcohol group is present on the third carbon.
3. Hence, it is an incorrect option.

Option (D): R and S

1. In the R structure, the front alkane chain has an ethyl group present at the third carbon and an alcohol group along with the methyl group present on the second carbon.
2. whereas in the S structure, the alcohol group is present on the third carbon.
3. Hence, it is an incorrect option.

Final answer: The structures R and S represent identical molecules.