chair_inversion - Organic Chemistry Ch 3 143 Daley&...

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Unformatted text preview: Organic Chemistry - Ch 3 143 Daley & Daley Half chair Half chair '()*& #$%& ./"0 12%345$36 #$%& !"! 12%345$36 '()*& #$%& ."7 12%345$36 +,%)- +,%)Figure 3.10. The energy diagram for the ring inversion of cyclohexane. 3.8 Conformational Analysis of Monosubstituted Cyclohexanes 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 two methylcyclohexanes indicate that the two conformations are not present in equal quantities. The conformation on the right is the more common conformation. +89 8 +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 5 July 2005 ...
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