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Unformatted text preview: 60 CONFORMATIONS OF ALKANES AND CYCLOALKANES (e) The ﬁrst stereoisomer of 1,2,4-trimethylcyclohexane is the more stable one here, as it was in
part (d ). All its methyl groups are equatorial, but one of the methyl groups is axial in the most
stable conformation of the second stereoisomer.
4 2 CH3 1 More stable stereoisomer H3C CH3 1 4 All methyl groups equatorial in
most stable conformation CH3
1 H3C CH3 2 CH3 Less stable stereoisomer (f) H3C 2 4 CH3 2 H3C 1 4 One axial methyl group in
most stable conformation Each stereoisomer of 2,3-dimethylbicyclo[3.2.1]octane has one axial and one equatorial
methyl group. The ﬁrst one, however, has a close contact between its axial methyl group and
both methylene groups of the two-carbon bridge. The second stereoisomer has repulsions with
only one axial methylene group; it is more stable.
CH3 H H3C
H Less stable stereoisomer
(more van der Waals strain) 3.30 More stable stereoisomer
(less van der Waals strain) First write structural formulas showing the relative stereochemistries and the preferred conformations of the two stereoisomers of 1,1,3,5-tetramethylcyclohexane. H3C H3C CH3 CH3 CH3 written in its most stable
conformation as H3C CH3
CH3 cis-1,1,3,5-Tetramethylcyclohexane H3 C CH3 CH3
written in its most stable
conformation as H3C CH3 CH3
CH3 CH3 trans-1,1,3,5-Tetramethylcyclohexane The cis stereoisomer is more stable than the trans. It exists in a conformation with only one axial
methyl group, while the trans stereoisomer has two axial methyl groups in close contact with each
other. The trans stereoisomer is destabilized by van der Waals strain. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website ...
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This note was uploaded on 09/20/2011 for the course CHM 2210 taught by Professor Reynolds during the Spring '01 term at University of Florida.
- Spring '01
- Organic chemistry