Ques. 1NEET 2013 (Karnataka)
Given: [figure] I and II are
- identical
- a pair of conformers
- a pair of geometrical isomers
- a pair of optical isomers
Answer
(2) a pair of conformers
Solution
Both I and II are sawhorse projections of 2,3-dibromobutane, CH3-CHBr-CHBr-CH3.
Front carbon: going clockwise, the order CH3 H Br is the same in I and II.
Rear carbon: going clockwise, the order Br CH3 H is the same in I and II.
∴ Both carbons have the same configuration in I and II; the two drawings differ only in the relative position of the groups on the front and rear carbons.
⇒ II is obtained from I by rotation about the C2–C3 single bond.
∴ As per NCERT, such spatial arrangements obtained by rotation about a C–C single bond are conformations ⇒ I and II are a pair of conformers.
Answer: (2)