Chemistry / organic chemistry 1
Newman projection explorer
Rotate a carbon–carbon bond to compare its 3D structure, Newman projection, and conformational energy.
Bond rotation model
Butane CH₃–CH₂–CH₂–CH₃
The molecule in 3D
C2 → C3The Newman projection
Front → backThe dot represents the front carbon and the circle represents the back, with colors matching the 3D model.
Clockwise rear rotation as viewed front → back. Playback is illustrative, not a molecular timescale.
Conformation names and the energy curve are hidden until you check your answer.
Go to the question ↓Follow the energy landscape
Relative energy · kcal/molClick the curve to set the angle. Use the angle slider for keyboard control.
Teaching approximation with smooth interpolation between 60° reference points. Model notes and sources ↓
Viewing direction
The labeled front carbon sits closest to you. Use “Look along bond” to align the 3D model with the projection.
Front and back carbons
Amber bonds meet at the central dot. Mint bonds emerge from the circle’s edge. At an eclipse, paired labels separate radially so both stay readable.
Bond rotation
The slider changes conformation. Dragging the 3D model changes your viewing angle while the projection keeps its fixed viewing direction.
Try it yourself
Conformation practice
Load a challenge to hide the energy and conformation names. Use the linked views to work out your answer.
Load this question to begin.
The chemistry
How bond rotation affects energy
A carbon–carbon single bond allows rotation without breaking the molecule’s connections. The different arrangements are conformations. A Newman projection makes their relative bond directions easier to compare.
In a staggered arrangement, rear bonds fall between front bonds. In an eclipsed arrangement, they line up. The preference for staggered geometry involves electronic interactions; a drawing of overlapping bonds is not a literal picture of atoms colliding.
Explore the cyclohexane chair flip →Why isn’t every staggered butane equally stable?
Butane adds a methyl group to each end of the viewed bond. Their separation distinguishes anti (180°) from gauche (60° by the smaller angle). The closer methyl groups make gauche higher in energy. Both remain staggered.
The angle needs a reference
For butane, θ follows CH₃–C2–C3–CH₃. It is shown clockwise from 0° to 360°. The smaller angle between the two methyl groups is at most 180°.
Model assumptions, energy values, and sources
Central carbons have ideal tetrahedral angles with a 1.54 Å bond. C–H bonds use 1.09 Å. Each CH₃ marker represents an entire methyl group, with its internal hydrogens omitted. Changing the style changes rendering, not geometry. The selected bond is always viewed from the same labeled front carbon toward the back.
Energy is relative to the lowest reference conformation for each molecule. The approximate reference values in kcal/mol are: ethane, 0 staggered and 2.9 eclipsed; propane, 0 staggered and 3.4 eclipsed; butane, 0 anti, 0.9 gauche, 3.8 eclipsed with methyl–hydrogen alignments, and 4.5 with the methyl groups eclipsing each other.
Between each neighboring pair of 60° reference points, the curve uses a half-cosine interpolation with zero slope at each endpoint. It is an educational potential-energy sketch, not a force-field calculation, free-energy surface, population prediction, or simulation of rotation rates. Molecular geometry does not relax with angle. Small environmental and experimental differences in these values are omitted.
Background and reference values: John McMurry, Organic Chemistry, OpenStax, conformations of ethane and conformations of other alkanes.