Question

Choose the incorrect statement from the following.

• A. The energy difference between the staggered and eclipsed conformation of ethane is \( 12.55 \, kJ/mol \)
• B. Staggered conformation of ethane is more stable than the eclipsed conformation.
• C. The distance between non-bonded H-atoms of ethane in eclipsed conformation is \( 2.29 \, \AA \)
• D. A \( 90^\circ \) rotation converts staggered conformation of ethane into eclipsed conformation.

Hint:

In ethane, every \( 60^\circ \) rotation alternates between staggered and eclipsed conformations.

Answer 1

The Correct Option is D

Step 1: Understand ethane conformations.
Ethane shows conformational isomerism due to rotation about the \( C-C \) single bond.
The two extreme conformations are staggered (most stable) and eclipsed (least stable).

Step 2: Analyze statement (A).
The energy difference between staggered and eclipsed conformations is approximately \( 12.5 \, kJ/mol \).
Thus, statement (A) is correct.

Step 3: Analyze statement (B).
Staggered conformation has minimum torsional strain and is therefore more stable than eclipsed conformation.
Thus, statement (B) is correct.

Step 4: Analyze statement (C).
In eclipsed conformation, the distance between non-bonded hydrogen atoms is minimum, around \( 2.29 \, \AA \).
Thus, statement (C) is correct.

Step 5: Analyze statement (D).
Rotation of \( 60^\circ \) converts staggered conformation into eclipsed conformation.
A \( 90^\circ \) rotation does not give an eclipsed conformation.
Thus, statement (D) is incorrect.

Step 6: Conclusion.
Hence, the incorrect statement is:
\[ \boxed{\text{A } 90^\circ \text{ rotation converts staggered conformation into eclipsed conformation}} \]