Answers to PF

Answers to CH241 Practice Final Exam Question 1 a) Circle the strongest base from the list below. O OCH3 F NH4 b) Ci...

0 downloads 19 Views 353KB Size
Answers to CH241 Practice Final Exam Question 1 a) Circle the strongest base from the list below. O

OCH3

F

NH4

b) Circle the strongest acid from the list below.

H

O

HF

O

NH4

H3C

H

H3C

OH

c) Circle the strongest nucleophile from the list below.

acetate

ammonia

methanol

fluoride

d) Circle the most stable carbocation from the list below.

OCH3

Addition of HCl to propyne gives which of the following dichlorides?

Cl

Cl

Cl

Cl Cl

Cl Cl

Cl

Question 2. a) Circle meso-2,3-dichlorobutane. Cl

Cl

Cl Cl Cl

Cl

Cl

Cl

b) Draw the compound that you circled in part (a) as a Newman projection (you may use the template if you wish). CH3 H

Cl

Cl

H CH3

c) Circle a diastereomer of E-2-chloro-2-butene.

Cl

Cl Cl Cl

d) Draw a structural isomer of E-2-chloro-2-butene that is chiral.

Cl

e) Circle the compound below that contains a bridged bicyclic ring system.

Question 3.. a) You have a sample of known chiral compound. If the optical rotation of the (+)-enantiomer is reported at +60.0° and your sample has an optical rotation of +30.0°, what percent of your sample is the (–)-enantiomer?. 25% (–)-enantiomer

b) Draw cis-1,3-dimethylcyclohexane in it's lowest-energy chair conformation. CH3 CH3 H H

c) Clearly explain why bromocyclopropane bromide does not undergo an SN1 reaction (if you wish, you can compare it to 2-bromopropane, which does undergo an SN1 reaction).

The resulting cyclopropyl cation would have severe angle strain since 60° bond angels are enforced in a 3-membered ring and a carbocation is most stable in the sp2hybridization state (120° bond angles). The isopropyl cation has no such angle strain.

Question 4. Provide clear structural drawings for the following compounds.

O H Cl

S

CH3

H B

O

H

borane

tosyl chloride

O

O H3C

NH2

H3C

O

an ester

an amide

CH3 H3C

O

CH3

H3C

OH CH3

diethyl ether

tert-butanol

CH3

Question 5. Provide the missing reagents and products to complete the reactions shown below.

H

1. BH3 2. H2O2, NaOH

O

a)

H

CH3

1. Na, NH3 2. mCPBA

H O CH3

H3C

b)

H

CH3

H2, Pd/C

c)

CH3 d)

1. H2, Pd/CaCO3/Pb 2. Br2, CCl4

Br CH3

H3C Br

Question 6. Provide the missing starting materials, reagents and products to complete the reactions shown below.

OH CH3

1. H2SO4 2. OSO4; Na2SO3

OH CH3

a)

H OH

CH3 b)

O

1. O3 2. SMe2

Br

H3C

H

H

excess NaSCH3

c) H

SCH3

Br

Br

1-butene, h! d)

H2C

N2

O

Question 7. Provide the missing reagents and products to complete the reactions shown below.

Me a)

Br

Me C

C

H

HBr

C H C5H9Br

MgBr

O

b) OH

Et N

O c)

1. excess conc. HBr 2. ethylamine C7H15N

Question 8. Epoxides can be synthesized by treating an alcohol containing a proximal halogen atom with strong base as shown below: HO

KOtBu

O

+

+

KBr

HOtBu

Br

a) Provide a mechanism for the reaction above. HO

KOtBu

O

OtBu

+

+

KBr

HOtBu

Br

SN2 O

Br

b) Explain why trans-2-chlorocyclohexanol will form an epoxide when treated with strong base, but cis-2-chlorocyclohexanol will not. Hint: Drawing the starting materials in their chair forms will aid your analysis. OH

KOtBu O

Cl

OH

KOtBu Not Formed

O Cl

OH

O O Cl

Cl Cl

unreactive conformation

reactive conformation (aligns the electrons on oxygen to donate into !* C–Cl)

OH

Cl

O

Cl Cl

O

neither conformation aligns the electrons on oxygen to donate into !* C–Cl)

Question 9. Provide a mechanism for the following reaction. OCH3 Br H3C

OCH3

Br

Ag

AgNO3

H3CO

MeOH

H3C

OCH3

OCH3

H3C

H3C

OCH3 H3C

CH3OH

CH3OH

H H3CO H3C

OCH3

H3CO H3C

OCH3