Question

In the following structures, which one is having staggered conformation with maximum dihedral angle?

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is C

To determine which structure has a staggered conformation with the maximum dihedral angle, we need to understand the concept of dihedral angles in organic chemistry. A dihedral angle is the angle between two planes, and in the context of molecular conformations, particularly for alkanes, it refers to the angle between substituents on adjacent carbon atoms.

In staggered conformation, the dihedral angle between the front carbon's substituents and the back carbon's substituents is typically 60° for ethane. However, when we seek the maximum dihedral angle in staggered conformations with other groups, it should ideally be 180° in the anti conformation to minimize steric repulsions, especially in larger alkanes.

Let's analyze each option and see their dihedral angles:

• The first image shows a typical staggered but not maximized dihedral angle of 60°.
• The second image also represents a staggered conformation but with less than 180° dihedral angle.
• The third image () displays staggered conformation with a 180° dihedral angle, known as the anti conformation, minimizing steric hindrance.
• The fourth image also shows staggered conformation but, again, not with maximum dihedral angle.

Therefore, the correct answer is the third structure, as it represents the staggered conformation with the maximum dihedral angle of 180°

It is essential to choose the staggered anti conformation when assessing maximum dihedral angles amongst different structural possibilities. This conformation prevents steric clashes between large groups, making it energetically more favorable.