CH Organic Chemistry I (Katz) Exam #2- Fall 2012

Transcription

1 rganic hemistry I (Katz) Exam #2- Fall 2012 Name: Score: Part I - hoose the best answer write the letter of your choice in the space provided. (30 pts) 1. The Newman projection at the right represents: ) 2,3-dimethylbutane ) isopentane ) 2,2,3-trimethylbutane D) 2,2-dimethylbutane 2. Given the following values for bond dissociation energies the absolute numerical value (ignoring the algebraic sign) of Δ (in kj/mol) for the reaction 3- + N3 ---> 3-N2 + is: ) 1343 ) 308 ) 194 D) ond DE (kj/mol) N N The order of thermodynamic stability of alkyl carbocations, from most stable to least stable is ) 1º>2º>3º>methyl ) 2º>3º>methyl>1º ) methyl>1º>2º>3º D) 3º>2º>1º>methyl 4.The enantiomer of (R)-2-bromobutane:! ) may be either (R)- or (S)-2-bromobutane ) cannot be (S)-2-bromobutane ) must be (S)-2-bromobutane D) is a mixture of (R)- (S)-2-bromobutane 5. The following structure represents a compound that : ) is optically inactive meso ) is optically active meso ) ontains no chiral carbons D) is optically active dextrorotatory holic acid, the major steroid in bile, was found to have a rotation of +2.22º when a 6.00 g sample was dissolved in ml alcohol the solution was placed in a sample tube with a 1.00 cm pathlength. If stard conditions, require a concentration of 1.00 g/ml a pathlength of 1.00 dm, the [α]d for cholic acid is: ) +3.7º ) +7.4º ) +37º D) +74º

2 7. f the following structures, those structures capable of optical activity are: V W X Y Z ) (None are capable of optical activity.) ) only V X ) only W, Y, Z D) only W Z 8. The IUP name of the compound at the right is: ) 3-chloro-4-fluoro-2,6-dimethylheptane ) 4-fluoro-5-chloro-2,6- dimethylheptane ) 2-chloro-3-fluoro-1,1,5,5- tetramethylpentane D) 3-fluoro-2-chloro-1,1,5,5- tetramethylpentane F 3 9. The diagram at the right represents: ) the rate-determining step of an Sn2 reaction ) the rate-determining step of an Sn1 reaction ) the final, fast step of an Sn1 reaction D) the transition state of the rate-determining step of an Sn2 reaction Questions refer to the following three compounds: 10. hoose the thermodynamically most stable isomer. ) ompound 1 ) ompound 2 ) ompound hoose the thermodynamically least stable isomer. ) ompound 1 ) ompound 2 ) ompound ow many stereocenters are present in the following compound? ) 1 ) 2 ) 3 D) 4 3 3

3 13. In the reaction shown below, the carbon bonded to was originally which carbon?? D? ) arbon ) arbon ) arbon D) arbon D 14. Which of the following are polar aprotic solvents? ) ) 2 4 ) 1, 2, D) 2, 3, 4 N Is the structure shown at right R or S? ) R ) S 2 3 ( 3 ) 3 ( 3 ) 2 Part II - Isomers - assify the following compounds by choosing one of the following terms (16 pts): ) Identical ) onstitutional Isomers ) enantiomers D) diastereomers D Fischer projections

4 Part III - Thermodynamics -Matching - Place the letter corresponding to the term in the blank to the left of the definition. (16 pts) F. transition state D. stard Gibbs free energy change. endergonic reaction E. exergonic reaction. activation energy F. reactive intermediate 20. species that lies at an energy minimum between steps in a reaction, 21. The energy needed by reactants to reach the transition state. E 22. reaction where ΔGº is negative. 23. n intermediate in which bond-breaking bond-making are taking place. Use the following reaction progress diagram to answer the following questions. 24. The reaction depicted above can best be described as Energy D ) a slow exergonic reaction ) a fast exergonic reaction. ) a slow endergonic reaction D) a fast endergonic reaction 25. The transition state is found at what point on the diagram (hoose,,,d) Reaction progress 26. The energy of activation is indicated by which quantity on the diagram (hoose,,,d) 27. The reaction free energy change is indicated by which quantity on the diagram (hoose,,,d) Part IV - Questions related to conformations. (18 pts) 28. Draw a line structure for the compound at right provide a name for the compound (R) 3-chloro-2,2,4-trimethylpentane

5 29. Draw the two chair forms of cis-1-chloro-2-isopropylcyclohexane circle the more stable conformer. 30. The structure of (-) menthol from the peppermint plant is 3 Draw the two chair conformations that are present in a sample of (-) menthol Which conformer in problem 30 is the most stable? Part V - Questions related to reaction mechanisms. (20 pts) 32. Draw the product (s) resulting from the following movement of electrons: a b

6 33. dd arrows to the reactant (s) to show the mechanism of the following processes: a b Draw the structure of the transition state the product for the following SN2 reaction: Na Draw the structure of the carbocation intermediate involved in the following SN1 reaction the product: