Chem 210 - Exam #5 Sample

Sample Exams are designed to give you an idea of the types of questions you can expect.  Questions on these sample exams may not exactly agree with currently assigned material, so you may need to view other sample exams to see questions that might be similar to the upcoming exam. Answers for Sample Exam #5 are available.

1. Describe simple chemical tests that would distinguish between the following. Tell exactly what you would do and see.

1,3-pentadiene and n-pentane

1,3-pentadiene and 1-pentene

cyclohexanol and 1-bromocyclohexane

2. When treated with 1 mole equivalent of HCl, 1,3-butadiene yields a mixture of 3-chloro-1-butene and 1-chloro-2-butene. Show why you get both of these two products.

3. Show the complete reaction for the dehydrohalogenation of 4-bromo-1-hexene and show only the major product.

4. Give structures of the chief product or products expected from addition of one mole of HCl to each of the following compounds.

3-cyclohexen-1-ol

3-methyl-1,3-butadiene

1,4-pentadiene

5. Describe how an experiment can be set up to show that E2 elimination occurs anti not syn using a cyclic compound as the starting point.

6. Starting with cyclohexanol, prepare:

cyclohexene

3-bromocyclohexene

1,3-cyclohexadiene

7. Starting with cyclopentanol, outline a synthesis protocol to produce stereochemically pure cis-1,2-cyclopentanediol or pure trans-1,2-cyclopentanediol.

8. Starting with ethene, show how you would produce the two-carbon epoxide (ethylene oxide). Show the product for reaction of this epoxide (H⁺ catalysis) with (a) water, (b) ethanol, and (c) HBr.

(a)

(b)

(c)

9. Show the complete reaction mechanism for the reaction of an epoxide with water.

10. Give the principal organic product for each of the following reactions:

cyclopentane + Cl₂ (300 ^oC)

cyclopentene + Br₂ (in CCl₄)

cyclopentene + Br₂ (300 ^oC)

cyclopentene + cold KMnO₄

11. Show the reaction products of propene with (a) HCl(aq), (b) HBr(aq) + peroxides, (c) Cl₂ (low temp, CCl₄), and (d) Cl₂ (500 ^oC, gas phase).

(a)

(b)

(c)

(d)

12. Explain why the allyllic free radical is much easier for form, and is more stable, than even the tertiary free radical. Conversely, why is the vinyl free radical so hard to form, even being harder to form than the methyl free radical.

13. NBS (n-bromosuccinimide) is a reagent used for the specific purpose of brominating alkenes at the allylic position via free radical substitution. NBS maintains a constant, low concentration of free Br₂.

Show the product(s) you would get by treating 1-octene with NBS.

Why do you get allylic rearrangement?

14. Draw resonance structures (if they exist) for (a) the allyl free radical, (b) allyl carbocation, and (c) 1,4-pentadiene.

(a)

(b)

(c)

EXTRA CREDIT (4 points): Do either part A or part B. If you do both, you will be graded on part A.

A. Starting with isoprene, show the mechanism for free radical polymerization. Then, show the structure of the polymer, which is latex, or natural rubber.

B. When 1,4-hexadien-3-ol is dissolved in H₂SO₄, it is converted completely into 3,5-hexadien-2-ol. How do you account for this?