Newman Projections Explained
How to draw and read Newman projections, tell staggered from eclipsed conformations, and rank the conformations of butane by energy.
What Is a Newman Projection?
A Newman projection lets you look directly down a carbon–carbon bond axis to see how substituents are arranged in space. This arrangement is called a conformation. Because single bonds rotate freely, a molecule can adopt infinite conformations, but some are far more stable than others.
You're the camera. The C–C bond is the road. The front carbon (center dot) is close to you. The back carbon (large circle) is further away. The angle between front and back bonds is the dihedral angle, and it controls energy.
How to Read the Diagram
Front Carbon ●
The center dot. Its three bonds radiate outward like clock hands. This is the carbon closer to you.
Back Carbon ○
The large circle. Its three bonds stick out from the ring edge. This carbon is farther from you.
Most common mistake: drawing back bonds from the center instead of from the circle edge. Front bonds come from the dot. Back bonds come from the ring perimeter. Always.
Interactive Diagram: Drag the Slider
Interactive Newman Projection
Staggered
Dihedral Angle: 60°Drag to rotate
0°90°180°270°360°
Relative EnergyMinimum (most stable)
✓ Back bonds (grey) are 60° offset from front bonds (green). Electron clouds are far apart → minimum repulsion → lowest energy. This is the most stable conformation.
Drag the slider to rotate the back carbon and watch the energy change in real time.
Torsional Strain
When bonds are eclipsed, the bonding electron clouds of C–H bonds on adjacent carbons come as close as possible. Their mutual repulsion costs energy: this is torsional (Pitzer) strain. In ethane, the energy difference between staggered and eclipsed is ~3 kcal/mol. Small, but molecules "feel" it.
Torsional strain = electron cloud repulsion in eclipsed bonds (quantum origin). Steric strain = van der Waals repulsion between bulky groups that are too close physically. Both raise energy, for different reasons. Newman projections reveal both.
All Conformations: Complete Reference
Conformation | Dihedral | Energy | Notes
Anti | 180° | Lowest | Largest groups furthest apart. Most stable in butane.
Staggered | 60° | Low | All bonds offset 60°. Most stable for ethane.
Gauche | 60°* | Moderate | Methyl groups 60° apart in butane. Gauche strain present.
Eclipsed (Me–H) | 120° | High | Methyl eclipses H. ~3.4 kcal/mol above anti.
Eclipsed (Me–Me) | 0° | Highest | Max steric + torsional strain. ~4.5–5 kcal/mol above anti.
Butane: Why Size Matters
Replace two H's in ethane with CH₃ groups (butane, looking down C2–C3) and the energy differences become large. The bulky methyl groups introduce steric strain on top of torsional strain.
Relative Energy: Butane C2–C3 Rotation
Most stable
Anti
180°
+0.9 kcal/mol
Gauche
60°
+3.4 kcal/mol
Eclipsed
120°
~+4.5 kcal/mol
Eclipsed Me–Me
Anti (180°)
Most stable
Methyls on opposite sides. Zero steric interaction. Lowest energy in butane.
Gauche (60°)
+0.9 kcal/mol
Methyls 60° apart. Some van der Waals repulsion, 'gauche strain'.
Eclipsed Me–H (120°)
+3.4 kcal/mol
Methyl eclipses a hydrogen. Torsional + some steric strain.
Eclipsed Me–Me (0°)
Least stable
Both methyls fully eclipsed. Maximum steric + torsional strain. Avoid.
Practice Problems
Q1.Draw the Newman projection of butane (C2–C3 bond) in the anti conformation. Which groups are on the front carbon? Which on the back?
Q2.Rank these butane conformations from most to least stable: gauche, anti, eclipsed (Me–Me), eclipsed (Me–H).
Q3.In ethane, how many kcal/mol does the molecule gain going from staggered to eclipsed?
Quick Reference
Stability Order
Anti > Gauche > Eclipsed (Me–H) > Eclipsed (Me–Me)
Key Angles
0° = eclipsed · 60° = staggered/gauche · 180° = anti
Diagram Rule
Front bonds from center dot. Back bonds from circle edge. Never mix them up.
Think of a steering wheel: you're the driver. Front carbon = your dashboard. Back carbon = the road ahead. Staggered = smooth ride (no bumps). Eclipsed = potholes every 120°.
Practice questions with answers
- In a Newman projection, the front carbon is represented by: Answer: A center dot
- In a staggered ethane conformation, the dihedral angle is: Answer: 60°
- Which conformation of ethane has the LOWEST energy? Answer: Staggered
- Torsional strain arises from: Answer: Electron cloud repulsion in eclipsed bonds
- In butane (C2–C3 bond), the MOST stable conformation is: Answer: Anti (180°)
- The energy difference between staggered and eclipsed ethane is approximately: Answer: ~3 kcal/mol
- Gauche strain (in butane) is caused by: Answer: Van der Waals repulsion between methyl groups 60° apart