Portmess Homework Q&S 62

Portmess Homework Q&S 62 - tert-butyl groups anti...

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( c ) These hydrocarbons all have different molecular formulas. Their heats of combustion de- crease with decreasing number of carbons, and comparisons of relative stability cannot be made. ( d ) Bicyclo[3.3.0]octane and bicyclo[5.1.0]octane are isomers, and their heats of combustion can be compared on the basis of their relative stabilities. The three-membered ring in bicy- clo[5.1.0]octane imparts a signi f cant amount of angle strain to this isomer, making it less stable than bicyclo[3.3.0]octane. The third hydrocarbon, bicyclo[4.3.0]nonane, has a greater number of carbons than either of the others and has the largest heat of combustion. 3.28 ( a ) The structural formula of 2,2,5,5-tetramethylhexane is (CH 3 ) 3 CCH 2 CH 2 C(CH 3 ) 3 . The sub- stituents at C-3 are two hydrogens and a tert -butyl group. The substituents at C-4 are the same as those at C-3. The most stable conformation has the large
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Unformatted text preview: tert-butyl groups anti to each other. ( b ) The zigzag conformation of 2,2,5,5-tetramethylhexane is an alternative way of expressing the same conformation implied in the Newman projection of part ( a ). It is more complete, Anti conformation of 2,2,5,5-tetramethylhexane C(CH 3 ) 3 C(CH 3 ) 3 H H H H H H H H H H Bicyclo[4.3.0]nonane (C 9 H 16 ) Bicyclo[5.1.0]octane (C 8 H 14 ) Bicyclo[3.3.0]octane (C 8 H 14 ) Heat of combustion 5652 kJ/mol (1350.9 kcal/mol) Heat of combustion 5089 kJ/mol (1216.3 kcal/mol) Heat of combustion 5016 kJ/mol (1198.9 kcal/mol) Cyclopropylcyclopropane (C 6 H 10 ) Heat of combustion 3886 kJ/mol (928.8 kcal/mol) Spiropentane (C 5 H 8 ) Heat of combustion 3296 kJ/mol (787.8 kcal/mol) Bicyclo[1.1.0]butane (C 4 H 6 ) Heat of combustion 2648 kJ/mol (633.0 kcal/mol) 56 CONFORMATIONS OF ALKANES AND CYCLOALKANES...
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