Types of Conformations of Butane

1. Anti Conformation (Most Stable)

• Dihedral angle = 180°
• Two CH₃ groups are opposite
• Minimum steric hindrance

Stability: Highest

✔ No torsional strain
✔ No steric crowding

2. Gauche Conformation

• Dihedral angle = 60°
• CH₃ groups are close but not eclipsed

Stability: Moderate

✔ Some steric hindrance
✔ Still relatively stable

3. Eclipsed Conformations (Unstable)

(a) CH₃–H Eclipsed

• Dihedral angle = 120° or 240°
• CH₃ eclipses H

Stability: Low

✔ Torsional strain present

(b) Fully Eclipsed (CH₃–CH₃)

• Dihedral angle = 0°
• CH₃ groups directly overlap

Stability: Lowest

❌ Maximum torsional strain
❌ Maximum steric repulsion

Energy Order (Important for Exams)

$$\text{Anti} < \text{Gauche} < \text{Eclipsed (CH₃–H)} < \text{Fully Eclipsed (CH₃–CH₃)}$$