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
