I Promise to Uphold the University's Honor Code

Chem 233 Davis Organic Chemistry I Hour Exam 2 Friday Oct. 27, 2000

Print Name______

I promise to uphold the University's Honor Code

Signature______

Circle Lab TA's Name: Noble Jarrell, Mike Shi, Frank Kotch, Matt Thompson,

Lisa Koterwas, Kevin Catalano, Andrew Kung, Jason Lagona, Bill McElroy, Emily Payne

There are 6 questions on 5 pages. Read each question carefully.

Write all answers and draw all structures clearly.

QuestionPointsScore

1. Structure and Stability(15) ______

2. Cyclohexane Conformation(15) ______

3. Oxymercuration(10) ______

4. Electrophilic Addition(20) ______

5. Energy Diagrams(20) ______

6. Carbenes(20) ______

TOTAL______
1. Circle the lowest energy (most stable) species in the following sets (15 pts).

2. Draw the two chair conformations of trans-1,2-dimethyl-cyclohexane. It is not necessary to draw all the hydrogen atoms. But, you must draw the hydrogen atoms at the carbons bearing methyl substituents. Identify each methyl substitutent as either axial or equatorial. Indicate the lowest-energy conformation with an asterisk *. (15 pts).

3. There is something wrong with the following figure. Briefly explain the problem and draw a more accurate figure (10 pts).

4. Hydrobromination of indene 1 occurs at the double bond in the 5-membered ring to give 2. The reaction is regiospecific, as no compound 3 is
formed. Note that the double bonds in the 6-membered ring of 1 are unreactive.

a) Draw a stepwise mechanism for the formation of compound 2 from indene 1 and HBr. Use arrows to indicate electron flow and show intermediates. (10 pts).

b)Briefly explain and illustrate why this reaction is regiospecific. (5 pts)

c) Based on the above information draw the structure of the major product formed upon hydroboration/oxidation of indene 1. (5 pts).

5. Below, is a mechanism for addition of HCl to 3-methyl-1-butene 1 to give

2-chloro-2-methyl butane 2. A few facts:

1) Go for the reaction is negative.

2) the first step, protonation of 1 to give A is the reaction's rate-determining step.

3) the hydride shift step (conversion ofA to B) has a higher activation energy barrier than does the addition of chloride anion to carbocation B.

Question: Draw a free energy vs. reaction coordinate diagram that is consistent with the above information. Clearly label the positions for 1, 2, A and B. Also, clearly indicate

Go for the reaction and G+ for the reaction's rate-determining step. (20 pts).

6. Nitrenes are the nitrogen analogs of carbenes

a) Provide a mechanism for reaction of methyl nitrene 1 with cis-2-butene 2 to give the cis-substituted ring 3. You may draw the mechanism as stepwise or concerted, but it must make sense. (10 pts)

b) Briefly explain why the retention of stereochemistry in product 3 either supports or disfavors a step-wise mechanism? (5 pts).

c) Assume the following bond dissociation energies: N-C sigma bond is 51 kcal/mol, while a C-C pi bond is 55 kcal/mol. What is Ho for the reaction of 1 and 2 to give 3? (5 pts).

H = ______

This page is for scratch work. Nothing on this page will be graded.