CHE 31: Organic Chemistry
Name
Test 1
March 16, 1998

1. Multiple choice (2 points each)
Which of the following species is aromatic?

When an organic molecule is irradiated with ultraviolet light, the energy absorbed by the molecule corresponds to:
(a) the amount necessary to increase molecular motions in functional groups.
(b) the amount necessary to excite electrons from one molecular orbital to another.
(c) the amount necessary to "flip" the spin of atomic nuclei.
(d) the amount necessary to strip a molecule of one electron to generate a cation radical.

Which of the following is the best method to accomplish the transformation shown?

(a) (1) 2 CH3MgBr, ether; (2) H3O+
(b) (1) (CH3)3SiCl, Et3N; (2) CH3MgBr, ether; (3) H3O+
(c) (1) LiAlH4, ether; (2) H3O+
(d) (1) NaBH4, ethanol; (2) H3O+

Which of the following is the best method to accomplish the transformation shown?


(a) (1) HOCH2CH2OH, H+; (2) LiAlH4; (3) H3O+
(b) (1) LiAlH4; (2) H3O+
(c) (1) (CH3)3SiCl, Et3N; (2) LiAlH4; (3) H3O+
(d) (1) HOCH2CH2OH, H+; (2) NaBH4; (3) H3O+

Which of the following statements is generally true about aromatic compounds?
(a) They have pleasant odors.
(b) Their reactivity is similar to alkenes and other unsaturated compounds.
(c) They are very stable.
(d) They are colored.

 

2. (5 points each)
(a) A student was instructed to recrystallize her crude product from a mixture of ethanol and water. She dissolved her compound in hot ethanol and water and then isolated the product by evaporating off the remaining solvent. Will she obtain a high recovery of pure sample? Explain.

(b) A student was preparing a carboxylic acid by the reaction of a Grignard with dry ice. He noticed that his glassware was dirty, so he quickly washed it with water before putting the reagents in the flask. How will his technique influence his reaction?

 

3. Propose a mechanism to account for the formation of a cyclic acetal from 4-hydroxypentanal and one equivalent of methanol, shown below. If the carbonyl oxygen of the aldehyde is enriched with oxygen-18, do you predict that the oxygen label appears in the cyclic acetal or in the water. Your mechanism should show each step, and should use arrows to show the flow of electrons. (20 points)

 

4. Provide the major products for the following reactions, indicating stereochemistry where relevant. (4 points each)

 

5 The following syntheses contain one or more flaws. What is wrong in each case? How would you correct the overall synthesis (and obtain the desired product shown)? (10 points each)

(a)

(b)

 

6. Choose two of the following synthesis problems to work. (10 points each)