ANSWERS TO EXAM 2 - CHEM 227 - HARDING - SPRING 1997

Kenn Harding, Texas A&M University

1. (3 pts) Draw the structure corresponding to the IUPAC name below.

(E)-3-bromo-4-methyl-2-pentene

2. (6 pts) Label the following structures as (E) or (Z). Hint: Make sure you understand the bonding in each structure. Mark the highest priority group on each end of the double bond.

a)

b)

Draw out line bond structures for any condensed structure functional groups to be sure you see the correct bonding.

3. (4 pts) Calculate the number of rings plus double bonds (degrees of unsaturation) in Clorprenaline, C₁₁H₁₆ClNO, a drug used as a bronchodilator. Show your calculations.

4. (18pts) Predict the major products for the following reactions. If more than one product is expected in significant amounts, draw all of them. Show stereochemistry where relevant.

a)

b)

c)

d)

f)

g)

5. (4 pts) Write the structure of another diene that would give the products shown for problem 4f.

6. (12 pts) Choose the best reagents or sequence of reagents for carrying out each of the transformations shown below. Place the letter corresponding to the correct answer to the left of the reaction.

A. 1) OsO₄; 2) NaHSO₃, H₂O

B. HgSO₄, H₂O, H₂SO₄

C. Li, NH_3(liq.)

D. 1) Hg(OAc)₂, H₂O; 2) NaBH₄

E. 1) BH₃, THF; 2) H₂O₂, NaOH

F. H₂, Lindlar's catalyst

G. CHCl₃, NaOH

H. CH₂I₂, Zn(Cu)

I. NaNH₂, NH_3(liq.)

a) D

Markovnikov hydration

b) E

anti-Markovnikov hydration

c) C

trans reduction of alkyne

d) H

cyclopropanation with Simmons-Smith reaction

7. (4 pts) Draw the structure of the starting material that would produce the products shown for each reaction.

8. (8 pts) Complete the chain propogation steps below for the radical chain reaction of HBr and with alkene A.

9. (8 pts) Draw the structure of the carbocation that would be generated from protonation by HBr for each of the following alkenes

Circle the least stable of the three carbocations.

10. (3 pts) Draw the cationic intermediate that would be expected in the first step of the reaction shown below.

11. a) (3 pts) The carbocation II can be generated from reaction of an alkene I with an acid, H-Y. Draw the structure for I and show a mechanism (curved arrows) for formation of II.

b) (3 pts)The carbocation II undergoes a fast reaction to become carbocation III. Draw the structure expected for III and write a mechanism showing the conversion of II to III.

c) (6 pts) Draw a reaction coordinate diagram that would represent the conversion of the beginning alkene to II and then to III. Label all transition states and indicate the DG^o between II and III.

12. (10 pts) Draw the five isomers of formula C₅H₆ that contain one double bond and one triple bond

13. (8 pts) Consider the reaction coordinate diagram below.

1. Is the reaction endothermic or exothermic?

endothermic

1. Is the K_eq > or < 1?

<1

1. Are starting materials or products expected to predominate at equilibrium?

Starting materials

1. If the activation for the reaction was not known, what minimum value could we place on the activation energy?