Portmess Homework Q&S 54

Portmess Homework Q&S 54 - cis and...

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48 CONFORMATIONS OF ALKANES AND CYCLOALKANES occupy equatorial rather than axial sites, a methyl group that is up at C-1 is less stable than one that is up at C-4. ( c ) An alkyl substituent is more stable in the equatorial position. An equatorial substituent at C-3 is down. 3.6 A tert -butyl group is much larger than a methyl group and has a greater preference for the equato- rial position. The most stable conformation of 1- tert -butyl-1-methylcyclohexane has an axial methyl group and an equatorial tert -butyl group. 3.7 Ethylcyclopropane and methylcyclobutane are isomers (both are C 5 H 10 ). The less stable isomer has the higher heat of combustion. Ethylcyclopropane has more angle strain and is less stable (has higher potential energy) than methylcyclobutane. 3.8 The four constitutional isomers of
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Unformatted text preview: cis and trans-1,2-dimethylcyclopropane that do not contain double bonds are 3.9 When comparing two stereoisomeric cyclohexane derivatives, the more stable stereoisomer is the one with the greater number of its substituents in equatorial orientations. Rewrite the structures as chair conformations to see which substituents are axial and which are equatorial. cis-1,3,5-Trimethylcyclohexane H H H H 3 C CH 3 CH 3 CH 3 CH 3 H H 3 C H H CH 3 CH 3 1,1-Dimethylcyclopropane CH 3 Methylcyclobutane Ethylcyclopropane CH 2 CH 3 Cyclopentane CH 2 CH 3 CH 3 More stable 3352 kJ/mol (801.2 kcal/mol) Less stable 3384 kJ/mol (808.8 kcal/mol) Heat of combustion: 1-tert-Butyl-1-methylcyclohexane CH 3 C(CH 3 ) 3 H H 3 C Up Down H CH 3 Up Down H H 3 C Up Down 4 5 6 3 2 1...
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