CHEMISTRY 2430
Survey of Organic Chemistry
KEY - Exam III - 100 points - KEY
March 9, 2001 - Dr. Howard Black

1. (12 pts) Provide an acceptable name for each of the following molecules, being sure to address stereochemistry where appropriate.
 

2. (14 pts) For each of the following four molecules, list the properties from the list on the right which best describe it. Each item on the list can be used as often as necessary, or not at all. You are penalized for both missing and incorrect answers, so DON'T GUESS!!
 

a. capable of an elimination reaction to form an alkene
b. most acidic of the four molecules shown
c. contains no sp2 carbon atoms
d. easily undergoes E1 reaction
e. gives different products when treated with PCC vs. H2CrO4
f. forms an ether when treated with NaH followed by CH3I
g. possesses a chiral center
h. reacts with H2CrO4

3. (30 pts) Complete the following reactions.
 


 

4. (16 pts) Choose two (2) of the following transformations, and then, on the following page, outline a synthetic scheme to prepare the target molecule from the indicated starting material(s). DO NOT use a starting material which hasn't been provided. Please write the letter of the synthesis you are outlining on the line provided..



5. (16 pts) Please carry out the following instructions.

a. The pKa for p-nitrophenol is 7.1, while that for phenol is 9.9, making the nitro derivative approximately 1000 times more acidic. Using resonance structures, explain this.

The conjugate base of phenol (A) has several resonance structures, including B and C.  Nitrophenol's conjugate base has the same resonance, except that the structure in which the anionic charge is para (D) allows the nitro group to afford additional stabilizaion by spreading out the charge even more, via an additional resonance form, E.  As you know, the more resonance forms, the more stable the entity, and the more stable the conjugate base, the more acidic the acid.


b. Explain the difference in regioselectivity between the addition of methanol to the epoxide depicted in the box under basic versus acidic conditions.
Under basic conditions, the nucleophile seeks out the d+ carbon that is more sterically accessible, as shown in the first equation below.  However, under acidic conditions, protonation of the epoxide oxygen atom enables the C-O bond to break (exactly like the first step in an SN1 reaction), resulting in the formation of a carbocation.  The neutral nucleophile then attacks the cation and loses a proton, resulting in the product shown, with the opposite regiochemistry than that in the first.
 

6. (12 pts) Circle the aromatic species from the following molecules/ions.
 

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Bonus (5 pts, no partial credit possible)
 

The reaction in the box is a variant on the Friedel-Crafts reaction. Outline its mechanism, including the para substitution.