Portmess Homework Q&S 66

Portmess Homework - 60 CONFORMATIONS OF ALKANES AND CYCLOALKANES(e The first stereoisomer of 1,2,4- is the more stable one here as it was in

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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. H3C CH3 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. H CH3 CH3 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.

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