CHEM 241 ALKANES AND CYCLOALKANES CHAP 3 ASSIGN H H

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1 CEM 241 ALKANES AND CYCLOALKANES CAP 3 ASSIGN COMFORMATIONS AND cis-trans STEREOISOMERS 1. trans-1,2-dibromocyclohexane is represented by structure(s): D. II and III E. I and II 2. cis-1,3-dibromocyclohexane is represented by structure(s): D. II and III E. I and II 3. Which isomer of C 5 10 would you expect to have the smallest heat of combustion? A. cyclopentane B. methylcyclobutane C. 1,1-dimethylcyclopropane D. cis-1,2-dimethylcyclopropane E. trans-1,2-dimethylcyclopropane 4. The preferred conformation of cis-3-tert-butyl-1-methylcyclohexane is the one in which: A. the tert-butyl group is axial and the methyl group is equatorial. B. the methyl group is axial and the tert-butyl group is equatorial. C. both groups are axial. D. both groups are equatorial. E. the molecule exists in a boat conformation. 5. The least stable conformation of butane is: 3 C 3 C C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3 6. The most stable conformation of cis-1-tert-butyl-2-methylcyclohexane is the one in which: A. the tert-butyl group is axial and the methyl group is equatorial. B. the methyl group is axial and the tert-butyl group is equatorial. C. both groups are axial. D. both groups are equatorial. E. the twist boat conformation is adopted. 1 P a g e

2 7. What structure represents the most stable conformation of cis-1,3-dimethylcyclohexane? 3 C C 3 3 C C 3 C 3 C 3 3 C C 3 3 C C 3 8. The most stable conformation of trans-1-tert-butyl-3-methylcyclohexane is the one in which: A. the tert-butyl group is axial and the methyl group is equatorial. B. the methyl group is axial and the tert-butyl group is equatorial. C. both groups are axial. D. both groups are equatorial. E. the twist boat conformation is adopted. 9. The most stable conformation of 3-bromo-2-methylpentane, viewed through the C-3 C-4 bond (i.e., C-3 in the front, C-4 in the back): C 3 C(C 3 ) 2 I II C(C 3 ) 2 C 3 C(C 3 ) 2 C 3 C 3 C(C 3 ) 2 III C 3 C 3 C 2 C Consider the graph below, which is a plot of the relative energies of the various conformations of hexane, viewed through the C2-C3 bond. The conformations corresponding to the 60 o and 300 o are: A. Eclipsed B. Staggered, and gauche C. Staggered and anti D. More stable than the conformation at 180 o E. None of the above Relative energy 0 o 60 o 120 o 180 o 240 o 300 o 360 o Angle of rotation 2 P a g e

3 11. Which conformation of trans-1-isopropyl-3-methylcyclohexane would be present in greatest amount at equilibrium? A. The conformation with the methyl group equatorial and the isopropyl group axial B. The conformation with the methyl group axial and the isopropyl group equatorial C. The conformation with both groups axial D. The conformation with both groups equatorial E. The twist boat conformation. 12. Which conformation represents the most stable conformation of trans-1-bromo-4-methylcyclohexane? 3 C C 3 C 3 C 3 C Which of the following can be described as cis isomers?,, D. I, III and E. None of the above are cis isomers. O Cl C 3 F C C 3 3 O C 2 C Which of the following will have the same energy after undergoing ring flip? O O Cl C 3 F O C 3 C 2 C 3 C 2 C Which of the structures has two gauche interactions? 3 P a g e

4 16. Which of the following isomers of the formula C 8 14 would you expect to give the highest heat of combustion? A. B. C. D. E. 17. Which of these C isomers is predicted to be the most stable? 18. Which of the structures represents the most stable conformation of 2-methylbutane? MATC the Newman projection for the conformation of 2-methylbutane to the indicated position on the potential energy diagram, and place the letter corresponding to the correct projection in the blank. 19. Conformation A is represented by the Roman numeral in the diagram. 20. Conformation D is represented by the Roman numeral in the diagram. 21. Label each pair of compounds below as: A. identical B. stereoisomers C. constitutional isomers D. identical, but differing in conformation 4 P a g e

5 22. Which of the following Newman projections does not represent 2-methylhexane? C 3 C(C 3 ) 2 C 2 C 3 3 C C 2 C 2 C 2 C 3 C 3 C 2 C 3 C 2 C 2 C 3 C 2 C 3 C What is the correct IUPAC name for the following molecule? A. trans-3-methyl-5-ethylcyclohexane B. cis-3-methyl-5-ethylcyclohexane C. trans-1-ethyl-3-methylcyclohexane D. cis-1-ethyl-3-methylcyclohexane E. trans-1-methyl-3-ethylcyclohexane 24. Consider the graph below, which is a plot of the relative energies of the various conformations of 2,3-dimethylbutane, viewed through the C2-C3 bond. The conformations corresponding to the 120 o and 240 o are: A. Eclipsed, more stable than the conformation at 0 o B. Eclipsed, more stable than the conformation at 180 o C. Staggered, more stable than the conformation at 0 o D. Staggered, less stable than the conformation at 180 o E. Two of the above are true Relative energy 0 o 60 o 120 o 180 o 240 o 300 o 360 o Angle of rotation 25. The least stable conformation of cyclohexane is the: A. boat. B. twist boat. C. chair. D. half-chair. E. twist chair. 26. The most stable conformation of 2,3-dibromobutane, viewed through the C-2 C-3 bond : C 3 3 C 3 C C 3 3 C 3 C C 3 3 C 3 C C 3 5 P a g e

6 27. Which compound is a bicycloheptane? 28. Which is the correct name for the compound shown below? A. Bicyclo[2.2.0]hexane B. Bicyclo[2.2.0]butane C. Bicyclo[2.2.2]hexane D. Bicyclo[2.2.1]hexane E. Disquarane 29. A correct name for the following compound is: A. 4-bromo-3,8-dimethylbicyclo[5.2.2]nonane B. 3,8-dimethyl-4-bromo-bicyclo[5.2.0]nonane C. 4-bromo-3,8-dimethylbicyclo[5.2.1]decane D. 7-bromo-2,6-dimethylbicyclo[5.2.0]nonane E. 4-bromo-3,8-dimethylbicyclo[5.2.0]nonane NAME DATE ANSWER SEET CEM 241 CAP 3 ASSIGN FALL P a g e