Question

1. Draw all the staggered and eclipsed conformers that result from rotation about the C-2^_ C-3bond of pentane.
2. Draw a potential-energy diagram for rotation about the C-2^_C-3bond of pentane through 360⁰, starting with the least stable conformer.

Short answer

Eclipsed forms are those where the same groups are in the syn-position with a 0⁰dihedral angle.

Staggered forms are those where the same groups are in anti-position having a dihedral angle 180⁰.

Step-by-step solution

Definition of eclipsed and staggered form.

Eclipsed forms are those where the same groups are in the syn-position with a 0⁰dihedral angle.

Staggered forms are those where the same groups are in anti-position having a dihedral angle 180⁰.

Pictorial representation of all Eclipsed and Staggered forms.

The pictorial representation of Eclipsed and Staggered form is given below,

 Step 2: Structures of the staggered and eclipsed conformers that result from rotation about the C-2_C-3 bond of pentane.

All the staggered and eclipsed forms are drawn below, rotating around their dihedral angle from 0⁰ to 360⁰.

There are 3 eclipsed forms and 3 staggered forms and D is having the least energy and this anti-form is the most stable one.

Subpart (b)Step 1: Potential energy diagram for rotation about the C-2_C-3 bond of pentane through 3600, starting with the least stable conformer.

The potential energy diagram is drawn below. Anti-conformer is the most stable one due to the least steric repulsion between bulky groups.