CHE 24, Fall 1998
Test 3
December 2, 1998

1. Multiple choiceŚchoose the one BEST answer for each of the following: (2 points each)

Grignard reagents are prepared by reacting

Which is the best method for carrying out the transformation shown?

(a) PBr3 (b) HBr (c) NBS (d) Br2

Which is the best method for carrying out the transformation shown?

Which is the best method for carrying out the transformation shown?

Which of the following isomers would undergo the most rapid SN2 reaction with cyanide anion?

How many signals would the following compound display in its 13C NMR spectrum?

(a) 2 (b) 3 (c) 4 (d) 5 (e) 9

2. Provide the major products for the following reactions, showing stereochemistry where appropriate. (4 points each reaction)

 

 

 

 

3. A student carried out the dehydration of 1-butanol in the presence of acid. She used 2.00 grams of alcohol starting material. (Note that the instructor has calculators available for people who need to borrow them. Useful atomic masses: C, 12.01; H, 1.008, O, 16.00)

(a) What is the theoretical yield (in grams) for her reaction? (3 points)

(b) If she obtained 1.00 grams of product, what is her percent yield? (2 points)

(c) What features should she look for in the spectra of her product to determine how well the reaction worked? (Your answer here should be detailed.) (5 points)

4. (a) Treatment of 1,3-dichloropropane with potassium cyanide results in formation of 1,3-dicyanopropane, with the reaction shown below. The rate of this reaction is about 1000 times greater in DMSO than it is in ethanol. Propose a mechanistic explanation to account for this rate difference. (8 points)

(b) 3-Chloro-1-butene reacts with sodium ethoxide in ethanol to produce 3-ethoxy-1-butene. The rate of this reaction is second order (first order in 3-chloro-1-butene and first order in sodium ethoxide). In the absence of sodium ethoxide, 3-chloro-1-butene reacts with ethanol to produce both 3-ethoxy-1-butene and 1-ethoxy-2-butene. Propose an explanation to explain these results. (10 points)

5. (a) Propose a mechanism for the formation of these products in the reaction shown below. Use arrows to show the flow of electrons in your mechanism, and show every step. (10 points)

(b) Consider the diastereomers A and B of 3-bromo-3,4-dimethylhexane. On treatment with sodium ethoxide in ethanol, each gives 3,4-dimethyl-3-hexene as the major product. One diastereomer gives the E alkene and the other gives the Z alkene. Which diastereomer gives which alkene? Account for the stereoselectivity of each of these elimination reactions. (10 points)

6. Interpret the spectra on the following page, and propose a structure consistent with these spectra. Please note that this compound contains carbon, hydrogen, and oxygen. (20 points)