Chapter 7 - Instructor Supplemental Solutions to Problems...

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Unformatted text preview: Instructor Supplemental Solutions to Problems 2010 Roberts and Company Publishers Chapter 7 Cyclic Compounds. Stereochemistry of Reactions Solutions to In-Text Problems 7.3 Following the procedure in the solution to Problem 7.2 (in the Study Guide and Solutions Manual), we first calculate the K eq for tert-butylcyclohexane: K eq = 10 G /2.30 RT = 10 20/5.71 = 10 3.5 = 3.1 10 4 From this we calculate, in a total concentration of mol L 1 , [ A ] = (3.1 10 4 )[ E ] 0.00031. There is about 0.051/0.00031 = 168 times more axial conformation of methylcyclohexane than there is axial conformation of tert- butylcyclohexane per mole. 7.6 (a) The two chair conformations of cis- 1,3-dimethylcyclohexane: 7.7 (a) A boat conformation of cis- 1,3-dimethylcyclohexane: 7.9 The more stable conformations of the two 1,4-dimethylcyclohexanes: The cis isomer has the same number of 1,4 methylhydrogen interactionstwoas the axial conformation of methylcyclohexane itself, and thus has a destabilizing contribution of 7.4 kJ mol 1 . There are no destabilizing interactions in the trans isomer. INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS CHAPTER 7 2 7.10 (b) (d) 7.11 (b) The most stable conformation is the one that has the greater number of groups in the equatorial position: 7.12 (b) 1,1-Dimethylcyclohexane is achiral, and therefore cannot be optically active. (d) Cis- 1-ethyl-3-methylcyclohexane can be isolated in optically active form. 7.14 (b) The two structures differ in configuration at both asymmetric carbons. They are enantiomers. (Show that they are noncongruent mirror images.) 7.15 (b) Cyclobutane undergoes an interconversion of puckered forms analogous to the chair interconversion of cyclohexane. This interchanges axial and equatorial groups. Therefore, one conformation of trans-1,2- dimethylcyclobutanethe more stable conformationhas diequatorial substituents, and the otherthe less stable conformationhas diaxial substituents. 7.16 (b) Trans- 1,2-dimethylcyclopropane is chiral. INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS CHAPTER 7 3 7.17 (b) Bicyclo[3.2.0]heptane 7.20 (b) The model of trans- bicyclo[5.3.0]decane is easier to build. The larger is a ring, the easier it is to compress the dihedral angle of the trans bonds at the ring junction without introducing significant strain in the ring. This angle must be very close to 0 in order to accommodate a fused cyclopropane, that is, to bridge the ends of trans bonds with only one carbon. 7.21 (b) Although both molecules have bridgehead double bonds, the double bond in compound B is more twisted, and a model of this molecule is more difficult to build. Consequently, compound B is less stable and therefore would have the greater (more positive or less negative) heat of formation....
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This note was uploaded on 12/30/2011 for the course CHEM CHEM231 taught by Professor Dixon during the Fall '09 term at Maryland.

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Chapter 7 - Instructor Supplemental Solutions to Problems...

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