SAMPLE QUESTIONS FOR CHAPTER 3 NOTE: This sample is not representative of ALL the questions that can be asked in the test. It is meant only as an illustration of how questions can be asked. It is also meant to serve as a starting point to study for the test. To be well prepared you should study the class notes and work the assigned problems. 1) The structures below are: A. not isomers. B. cis-trans isomers. C. conformational isomers. D. structural isomers. E. both B and D 2) Among the butane conformers, which occur at energy minima on a graph of potential energy versus dihedral angle? A. gauche only B. eclipsed only C. eclipsed and totally eclipsed D. anti only E. gauche and anti 3) Give the IUPAC name for the cycloalkane shown below. 4) Which of the following cycloalkanes exhibits the greatest molar heat of combustion? A. cyclohexane B. cyclobutane C. cyclopropane D. cyclooctane E. cycloheptane 5) Which of the following correctly ranks the cycloalkanes in order of increasing ring strain per methylene? A. cyclopropane < cyclopentane < cyclobutane < cyclohexane B. cyclopropane < cyclobutane < cyclohexane < cyclopentane C. cyclohexane < cyclobutane < cyclopentane < cyclopropane D. cyclopentane < cyclopropane < cyclobutane < cyclohexane E. cyclohexane < cyclopentane < cyclobutane < cyclopropane 6) Describe the source of angle strain and torsional strain present in cyclopropane. 7) In the most stable conformation of trans-1,2-dimethylcyclohexane, the methyl groups are: A. both axial B. one axial and one equatorial C. both equatorial D. none of the above 8) Which of the following correctly lists the conformations of cyclohexane in order of increasing energy? A. chair < boat < twist < half-chair B. half-chair < boat < twist < chair C. chair < twist < half-chair < boat D. half-chair < twist < boat < chair E. chair < twist < boat < half-chair 9) Draw the most stable conformation of cis-1-ethyl-3-methylcyclohexane. 10) From the perspective of viewing down the C2-C3 bond, draw the Newman projection of the least stable conformation of 2,3-dimethylbutane. 11) Provide an acceptable name for the following compound. 12) Which of the following statements concerning the conformers of butane is true? A. The eclipsed and totally eclipsed conformers have the same amount of strain. B. Unlike ethane, all butane conformers are classified as eclipsed. C. The lowest energy conformer of butane is the gauche conformer. D. There is more torsional strain in the anti conformer than in the totally eclipsed conformer. E. The gauche and anti conformers differ primarily in the amount of strain present. 13) Provide an acceptable name for (CH3CH2CH2)3CH. 14) Give structures for the three isomers with molecular formula C5H12 and provide the common name of each. 15) Provide an acceptable name for the alkane shown below. 16) Draw an acceptable structure for 1-ethyl-2-(2,2-dimethylpentyl)cyclopentane. 17) Draw an acceptable structure for 6-ethyl-2,6,7-trimethyl-5-propylnonane. ANSWERS 1) D 2) E 3) trans-1-ethyl-2-methylcyclopentane 4) D 5) E 6) The angle strain arises from the compression of the ideal tetrahedral bond angle of 109.5o to 60 o. The large torsional strain occurs since all C-H bonds on adjacent carbons are eclipsed. 7) C H CH3 CH3 H 8) E 9) CH2CH3 H3C 10) H H3C H H3C All methyl groups are eclipsed CH3 CH3 11) You should rewrite the structure in nonabbreviated form to clearly see the connectivity. isobutylcyclopentane or (2-methylpropyl)cyclopentane 12) E 13) Once again, redraw the structure to clearly see the connectivity. 4-propylheptanet 14) Try to visualize all the possible connectivity combinations for the condensed formula. If you come up with more than three, give them IUPAC names. Those with identical names are the same structure and should not be counted more than once. pentane, or isopentane neopentane n-pentane 15) 5-sec-butyl-2,2-dimethylnonane or 2,2-dimethyl-5-(1-methylpropyl)nonane 16) 17) .