Question

Choose the correct statement(s) among the following regarding conformers:

• A. Ethane has infinite number of conformers
• B. Dihedral angle for staggered conformation of ethane is $60°$
• C. Dihedral angle for skew conformation of ethane is $120°$
• D. Torsional angle for eclipsed conformation of ethane is $0°$

Answer 1

Answer: (A), (B), (D)

Torsional angle for eclipsed conformation of ethane is $0°$

Conformational isomers are isomers that are interconvertible by free rotation about the single bonds.
Energy difference between conformational isomers is less and they are rapidly interconvertible and non separable. Thus, alkanes have infinite number of conformers.
Dihedral angle is the angle between the two intersecting planes of Sawhorse or Newman projection. It is also known as torsional angle.
For Staggered conformation, atoms/substituents attached to adjacent carbons are as far as possible. Thus, for ethane its dihedral angle of staggered conformation is $60°$.
For Eclipsed conformation, atoms/substituents attached on the adjacent carbons are at a minimum distance or in closest proximity. Thus, for ethane dihedral angle of eclipsed conformation is $0°$.
Skew conformation is the intermediate conformer between Eclipsed and Staggered. Hence, for ethane the dihedral angle of skew conformers will be between $0°$ and $60°$.