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Tutorial topics:


Viewing Basics

Molecular Shapes



Substituted Cyclohexane


SN2 Reaction

SN1 Reaction



Conformations of Butane

Butane has a molecular formula of C4H10. The four carbons are connected by C-C single bonds. Its line-angle structure is shown below on the left, with its "live" structure showing to the right. The two "live" structures are viewed from the top and the left side of the line-angle structure respectively.

butane molecule
butane with rotation around

viewed from the top

viewed from the left side, with your eyes looking down C2-C3

Again the rotation around C2-C3 creates an infinite number of conformations. The most interesting ones are shown below:

Now rotate each conformation so that you are looking along the C2-C3 (i.e. you will only see C2 carbon since C3 is directly behind C2). Note that all three conformations are derived from C2-C3 rotation of the "live" molecule displayed above on the right side. After you examine these conformations, test yourself on the following questions:

a) What are the terminologies given to each of the above three conformations? (gauche, total eclipse, anti?)

b) Rank order the relative energy level of the three conformers. For the two conformers with higher energy, what factor(s) is(are) responsible for the extra energy? (torsional strain, steric hindrance?)

c) One of above three has the lowest energy of all butane conformations. Can you provide a reason why this is true?

d) Draw on a piece of paper the structure of each of the above conformations, using solid line for , wedged-line and dashed-lines.

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This page was last updated on September 4, 2001 by Dr. Linfeng Xie.
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