Chapter 7 PP Part A

Chem 241 Fall 2008 Chapter 7 Practice Problems – Part 1 Question 1. A student had carefully prepared pure (R)-2-iodope...

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Chem 241

Fall 2008 Chapter 7 Practice Problems – Part 1

Question 1. A student had carefully prepared pure (R)-2-iodopentane, but in his/her haste had left the compound in solution overnight. When that student came back in the morning and took an optical rotation, the compound was racemic. It was also discovered that a small amount of sodium iodide was present in the solution. What happened?

1

Chem 241

Fall 2008

Question 2. For each reaction shown below, provide the mechanism (i.e. draw in the curved arrows showing the movement of electrons) and identify the expected major product.

S

Na

a)

b)

+

excess NaI

H3C

Br

Br

+ Br

Br

c)

+

KCN

H Br

d)

NaOH

+

Br HO

2

C4H8O

Chem 241

Fall 2008

LiOH e) I

O OH

f)

NaOH

C7H10O2

I

H3C O S O

g)

O Me

LiSEt

3

Chem 241

Fall 2008

Question 3. As mentioned in class, methyl tert-butyl ether (MBTE) is a common gasoline additive used to boost octane rating. Below are two reactions that are both attempts to form MBTE. Which reaction will be successful? Which reaction will fail to produce MBTE? Why will it fail?

(1)

(CH3)3COK

+

?

CH3Br

H3C H3C H3C

(2)

(CH3)3CBr

+

? CH3OK

4

O CH3

MBTE

Chem 241

Fall 2008

Question 4. Below are a series of reactions that fail to give the indicated SN2 products. Explain why each reaction fails.

CH3

a)

NaOH

OH

+

X

CN

Br

b)

KCN

+

X

I

Cl

c)

NaI

+

H3C

X

CH3

Me

d)

NMe3

+

H3C

CH3

Me Br

X

5

NMe3

Chem 241

Fall 2008

Question 5. Rank the following sets of carbocations from most to least stable. Careful, part (c) is tricky!

Me

Me

Me

a)

Me

b)

c)

The carbocation formed from ionization of the following iodides: Me

Me

Me

I

I

I

6

Chem 241

Fall 2008

Question 6. The reaction below does not proceed as written, but an SN2 reaction does take place. What is the major product formed?

H3C

S

H3C

CH3

CN

NaCN

+ H3C

CH3

CH3 B

A

7

SMe2

Chem 241

Fall 2008

Question 7. Explain the major difference in reactivity between the following pair of reactions: NH4OH NH2

I

NH4Br Br

I

8