C HAPTER 12 HW: R EDOX R EACTIONS
OXIDATION STATES AND GENERAL CONCEPTS
1. Are the following statements true or false?
a. When a carbon atom changes its oxidation state from -2 to 0 it is reduced.
b. The oxidation state of carbon in methane is -4.
c. When a carbon atom “gains hydrogen,” (is connected to more hydrogen atoms than before), it is reduced.
d. The SN2 reaction CH3Br + OH– à CH3OH + Br– is not a redox reaction.
2. Calculate the oxidation state for each atom in the transformations below. Then identify whether the organic
compound in each process is oxidized, reduced or not undergoing a redox reaction.
OH
O
a.
H
C
H
H
C
OH
H
OH
b.
H
c.
OH
Br
3. Identify if each process below is a reduction, oxidation or neither (not a redox reaction).
OH
Process
O
Rxn Type
O
Br
Pair
HO
HO
Rxn Type
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HYDROGENATION
4. Draw the two enantiomeric products formed in this reaction, then briefly explain why a racemic mixture is
produced.
H2
Pd cat.
5. Explain why reactions A + C make only or mainly one product, while reaction B makes two products.
A
B
D2
C
Pd cat.
D2
Pd cat.
D2
Pd cat.
6. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic
mixture is expected.
a.
b.
c.
d.
excess H2
Pd (cat.)
H2
Pt (cat.)
D2
Pt (cat.)
D2
Pd (cat.)
e.
f.
g.
h.
excess H2
Pd (cat.)
excess H2
Pd (cat.)
D2
Pt (cat.)
D2
Pd (cat.)
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7. Structures A-C are constitutional isomers of C8H14. Propose a possible structure for A-C that fits each of the
observations below.
Structure A reacts with 2 moles
of H2 (w/ Pd catalyst).
Structure B reacts with 1 mole of
H2 (w/ Pd catalyst).
Structure C does not react with
H2 /Pd.
8. (Multiple choice) Which statement is false about the platinum used in a hydrogenation reaction?
1. 2. 3. 4. The platinum is regenerated after the reaction.
The platinum changes oxidation state during the course of the reaction.
The platinum lowers the activation barrier for the reaction between alkene and H2.
One mole of platinum must be used for every mole of alkene to fully hydrogenate an alkene.
mCPBA OXIDATION
9. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic
mixture is expected.
a. mCPBA
a.
mCPBA
c.
b. H C CNa
c. H+, H2O
a. mCPBA
b.
a. mCPBA
d.
b. NaOH
c. H+, H2O
b. H+, CH3OH
10. (Multiple choice) Which substance is most likely to react in a similar way to mCPBA? (Hint: what is the
reactive part of the mCPBA reagent?)
O
O
OH
O
A
O
H
B
Cl
C
HOO
D
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OsO 4 OXIDATION
11. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic
mixture is expected.
a. OsO4, NMO, H2O
cat. OsO4
a.
c.
NMO, H2O
cat. OsO4
b.
d.
NMO, H2O
b. excess NaH
c. CH3CH2Br
a. OsO4, NMO, H2O
b. excess PBr3
12. (Multiple choice) The function of NMO in the reaction between an alkene and osmium tetroxide is to:
1. 2. 3. 4. Block one face of the alkene so the oxygen atoms add to the same face.
Oxidize the osmium intermediate to regenerate the OsO4.
Lower the activation barrier between the alkene and the OsO4.
To prepare the osmium surface for the alkene.
OZONOLYSIS
13. Give all organic products of these reactions.
a.
b.
a. O3
b. CH3SCH3
a. O3
b. Zn, H2O
c.
d.
a. O3
b. Zn, H2O
a. O3
b. S(CH3)2
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14. For each problem, propose a structure that upon ozonolysis would yield only the products shown.
O
a. O3
a.
O
+
b. Zn, H2O
H
H
a. O3
b.
b. Zn, H2O
O
O
a. O3
c.
b. Zn, H2O
H
O
a. O3
d.
O
+
O
b. Zn, H2O
15. Propose structures for A-D in the scheme below.
Unknown A (with molecular formula C10H18O) reacts with concentrated H2SO4 to form two compounds (B +C,
both with a molecular formula of C10H16). B + C both react with H2 in the presence of a Pd catalyst to form
decalin. Ozonolysis of B produces E and ozonolysis of C produces diketone D with a molecular formula of
C10H16O2.
B
A
C
con. H2SO4
+
heat
C10H18O
C10H16
C10H16
a. O3
H2
H2
Pd cat.
Pd cat.
a. O3
b. Zn
b. Zn
decalin
O
decalin
D
O
E
H
diketone, C10H16O2
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CHROMIUM OXIDATIONS
16. Give the major organic product of each reaction. Assume sufficient chromium reagent (excess) for complete
reaction of the organic substance.
OH
a.
CrO3
H2SO 4 (aq)
OH
Na2Cr2O7
b.
H2SO 4 (aq)
O
CrO3
c.
HO
H
OH
d.
CH2Cl2
OH PCC
CH2Cl2
g. HO
Na2Cr2O7
h.
H2SO 4 (aq)
H2SO 4 (aq)
OH
O
K2Cr2O7
H2SO 4 (aq)
H
OH
O
PCC
j.
CH2Cl2
PCC
i.
OH
e. HO
PCC
OH
f.
H
O
CH2Cl2
CrO3
H2SO 4 (aq)
17. For each problem, draw a structure that matches each set of criteria.
Criteria
Possible Structure
• Has a molecular formula of C5H10O
• Reacts with CrO3/H2SO4 to produce a blue-green precipitate
• Reacts with H2 in the presence of a Pd catalyst
• Has a molecular formula of C5H10O
• Reacts with CrO3/H2SO4 to produce a blue-green precipitate
• Does not react with H2 in the presence of a Pd catalyst
• Has a molecular formula of C6H12O
• When CrO3/H2SO4 is added, an orange solution is observed
• When Br2 is added, the solution turns colorless
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18. (Multiple choice) The reason a primary alcohol is oxidized to a carboxylic acid with CrO3/H2SO4, but to an
aldehyde with PCC/CH2Cl2 is:
1. 2. 3. 4. There are not enough oxygen atoms in the PCC reagent.
PCC is not a strong enough oxidizing agent to react with alcohols.
The CrO3 reagent is in an aqueous solvent while the PCC reagent is not.
The CrO3 reagent is acidic, which helps the OH to leave.
SUMMARY OF REDOX REACTIONS
19. For each reaction, decide whether the organic compound is undergoing a reduction, oxidation or neither (is not
undergoing a redox reaction).
Reaction
RCl rxn with NaOH
ROH rxn with HBr
ROH rxn with CrO3 /
H2SO4
Alkene rxn with
mCPBA
Alkene rxn with H2 /
Pd
Alkene rxn with HCl
Alkene rxn with
OsO4 / NMO, H2O
Red, Ox
or neither
Reaction
Red, Ox
or neither
20. Give the major organic product of each reaction. Indicate if a racemic mixture is produced.
OH
a.
b.
c.
CrO3
OCH3
H2SO 4 (aq)
a. O3
b. Zn, H2O
OsO4 cat.
D2
d.
CH3
Pt cat.
a. mCPBA
e.
b. H+, CH3OH
PCC
f.
CH2Cl2
NMO, H2O
OH
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