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#1 2010-09-17 08:12:20

orgopete
Administrator

Rank conformations of butane

Yahoo!Answers in chemistry wrote:

Organic chem, rank steric energy?
I want to rank theres 5 conformations of butane in decreasing steric energy.

You need to examine the eclipsed conformations. In the diagram in your book, you would find that staggered is the most stable and eclipsed the least stable conformation. There are two different kinds of eclipsed conformations. If the hydrogens are eclipsed, they are of lesser importance than if the CH3-groups are eclipsed. If you look at the conformations, B, D, and E, have carbons eclipsed, green. This brings the hydrogens of the 1- and 4-carbons close together, green. From the diagrams, you can see the hydrogens of conformation E, nearly touch. That is the highest energy conformation.

In A and C, the central atoms are staggered, but the hydrogen are eclipsed, yellow. An eclipsing occurs in B and E as well, yellow.   

         http://www.curvedarrow.com/chem/ZZ1800F42B.jpg

My predictions is as follows: E>B>D>A>C.

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