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Unformatted text preview: Organic Chemistry - Ch 3 143 Daley & Daley Half chair Half chair '()*&
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12%345$36 +,%)- +,%)Figure 3.10. The energy diagram for the ring inversion of cyclohexane. 3.8 Conformational Analysis of Monosubstituted
The ring inversion, or ring flipping, that occurs in a molecule of
cyclohexane takes place between two equivalent conformations. Thus,
when a cyclohexane molecule flips between chair forms, the energy
level for both forms is the same. However, if there is a substituent on
the ring, the number of molecules in each conformation is different
because the conformations are no longer equivalent. For example, if a
hydrogen of cyclohexane is replaced with a methyl group to form
methylcyclohexane, the two chair forms are different. In one the
methyl group is equatorial, and in the other, it is axial.
The arrows between the
indicate that the two
conformations are not
present in equal
conformation on the
right is the more
common conformation. +89
Methylcyclohexane 8 The two chair forms are not present in equal amounts. Experimental
evidence shows that at room temperature approximately 95% of the
methyl groups are equatorial. This preponderance is due to the www.ochem4free.com 5 July 2005 ...
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- Fall '11
- Organic chemistry