Understand the conformations of ethane

Ethane, $\mathrm{C_2H_6}$, can rotate about its $\mathrm{C-C}$ single bond. Due to this free rotation, different spatial arrangements of the hydrogen atoms are possible. These are called conformations.

Key facts about ethane conformations

• Staggered conformation: hydrogen atoms on the back carbon are placed exactly between the hydrogen atoms on the front carbon.
• Eclipsed conformation: hydrogen atoms on the back carbon lie directly behind those on the front carbon.
• The staggered conformation is most stable because torsional strain is minimum.
• The eclipsed conformation is least stable because torsional strain is maximum.
• Since rotation about the single bond is continuous, ethane has infinitely many conformations.
• These conformations are interconvertible by rotation about the $\mathrm{C-C}$ bond.

Check each option

Option A: The dihedral angle in staggered conformation is $60^\circ$.

• True. In staggered ethane, the dihedral angle between a $\mathrm{C-H}$ bond on the front carbon and the nearest $\mathrm{C-H}$ bond on the back carbon is $60^\circ$.

Option B: Ethane has infinite number of conformations.

• True. Because rotation about the $\mathrm{C-C}$ bond is continuous, infinitely many conformations exist.

Option C: Eclipsed conformation is the most stable conformation.

• False. Eclipsed conformation is actually the least stable, while staggered is the most stable.

Option D: The conformations of ethane are inter-convertible to one-another.

• True. They convert into one another by rotation around the single bond.

Conclusion

The incorrect statement is: $\boxed{\text{C}}$