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 →H2C (c) An alkyl substituent is more stable in the equatorial position. An equatorial substituent at C-3 C 3.6 A tert-butyl group is much larger than a methyl group and has a greater preference for the equator- rial position. The most stable conformation of l-tert-butyl-1-methylcyclohexane has an axial methyl group and an equatorial tert-butyl group CH3 C(CHi) I-ferr-Butyl-1-methylcyclohexane 3.7 Ethylcyclopropane and methylcyclobutane are isomers(both are CsHo) 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 CHCH Less stable More stable Heat of combustion: 3384 kI/m (808.8 kcal/mol) (801.2 kcal/mol) 3. 8 The four constitutional isomers of cis and trans-1, 2-dimethylcyclopropane that do not contain double bond CH,CH3 I, l-Dimethylcyclopropane Ethy cyclopropane CH Methylcyclobutane Cyclopentane 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. H3C H3 H,C cis-1, 3. 5-Trimethy lcycloher Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website48 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 C5H10). 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 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 H3C CH3 CH3 CH3 CH3 H H3C H H CH3 CH3 1,1-Dimethylcyclopropane CH3 Methylcyclobutane Ethylcyclopropane CH2CH3 Cyclopentane CH2CH3 CH3 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 CH3 C(CH3)3 H H3C Up Down H CH3 Up Down H H3C Up Down 4 5 6 3 2 1 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website