Portmess Homework Q&S 64

Portmess Homework Q&S 64 - located too close together...

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Place the larger substituent (the tert -butyl group) at the equatorial site and the smaller sub- stituent (the ethyl group) at the axial one. ( f ) First write a chair conformation of cyclohexane, then add two methyl groups at C-1, and draw in the axial and equatorial bonds at C-3 and C-4. Next, add methyl groups to C-3 and C-4 so that they are cis to each other. There are two different ways that this can be accomplished: either the C-3 and C-4 methyl groups are both up or they are both down. ( g ) Draw the projection formula as a chair conformation. Check to see if this is the most stable conformation by writing its ring- f ipped form. The ring- f ipped form, with two equatorial methyl groups and one axial methyl group, is more stable than the originally drawn conformation, with two axial ethyl groups and one equatorial methyl group. 3.29 Begin by writing each of the compounds in its most stable conformation. Compare them by exam- ining their conformations for sources of strain, particularly van der Waals strain arising from groups
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Unformatted text preview: located too close together in space. ( a ) Its axial methyl group makes the cis stereoisomer of 1-isopropyl-2-methylcyclohexane less stable than the trans. cis-1-Isopropyl-2-methylcyclohexane (less stable stereoisomer) trans-1-Isopropyl-2-methylcyclohexane (more stable stereoisomer) H H CH 3 CH(CH 3 ) 2 4 6 1 2 CH 3 CH(CH 3 ) 2 H H H H 3 C CH 3 CH 3 1 2 4 Less stable conformation: two axial methyl groups More stable conformation: one axial methyl group 2 4 H H CH 3 H 3 C 1 H CH 3 H H H CH 3 H 3 C CH 3 1 2 4 H H 3 C H H CH 3 CH 3 1 2 4 More stable chair conformation: C-3 methyl group is equatorial; no van der Waals strain between axial C-1 methyl group and C-3 methyl Less stable chair conformation: C-3 methyl group is axial; strong van der Waals strain between axial C-1 and C-3 methyl groups H H CH 3 CH 3 CH 3 CH 3 1 4 CH 3 H 3 C H H CH 3 CH 3 1 4 H H C(CH 3 ) 3 CH 2 CH 3 58 CONFORMATIONS OF ALKANES AND CYCLOALKANES...
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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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