Chapter 8 - Alkynes: An Introduction to Organic Synthesis
Draw structures corresponding to each of the following names.
1.
ethynylcyclopropane
Answer:
2.
C
C
H
3,10-dimethyl-6-sec-butylcyclodecyne
Answer:
3.
4-bromo-3,3-dimethyl-1-hexen-5-yne
CH3 Br
Answer: H2C
CH
C
CH
C
C
H
CH3
4.
acetylene
Answer:
H
C
C
H
Provide names for each compound below.
5.
CH3
CH3C
Answer:
CCHCH2CH2CH3
4-methyl-2-heptyne
CH3
6.
C
Answer:
CH
1-ethynyl-2-methylcyclopentane
Test Items for McMurry’s Organic Chemistry, Seventh Edition
59
The compound below has been isolated from the safflower plant. Consider its structure to answer the following
questions.
H
H
C
H3C
C
C
C
C
C
C
H
C
C
C
C
H
H
C
H
H
7.
What is the molecular formula for this natural product?
Answer:
8.
C13H10
What is the degree of unsaturation for this compound?
Answer:
We can arrive at the degree of unsaturation for a structure in two ways. Since we know that the
degree of unsaturation is the number of rings and/or multiple bonds in a compound, we can
simply count them. There are three double bonds (3 degrees) and three triple bonds (six
degrees), so the degree of unsaturation is 9.
We can verify this by using the molecular formula, C13H10, to calculate a degree of unsaturation.
The saturated 13-carbon compound should have the base formula C13H28, so (28 - 10) ÷ 2 = 18 ÷
2 = 9.
9.
Assign E or Z configuration to each of the double bonds in the compound.
Answer:
H
H
E C
H3C C
C
C
H
C
C
C
C
H
C E
C C
H
C
H
H
10. Provide the name for this unusual natural product.
Answer:
(3E, 11E)-1,3,11-tridecatrien-5,7,9-triyne or (3E,11E)-trideca-1,3,11-trien-5,7,9-triyne
To answer the following questions, consider the information below:
The heat of hydrogenation of 1,4-pentadiene is 254.4 kJ/mol. The heat of hydrogenation of 1-pentyne is
approximately 292.9 kJ/mol.
11. Which structure is more stable, 1,4-pentadiene or 1-pentyne?
Answer:
60
1,4-pentadiene
Chapter 8: Alkynes: An Introduction to Organic Synthesis
12. Show the energy differences between the hydrogenation of 1,4-pentadiene and 1-pentyne on a reaction
energy diagram.
Answer:
A = 1-pentyne
B = 1,4-pendatiene
C = 1-pentene
D = pentane
A
Energy
B
C
292.9 kJ/mol
254.4 kJ/mol
D
Reaction Progress
Consider an unknown with the molecular formula C4 H 6 .
13. How many degrees of unsaturation are present?
Answer:
A saturated four carbon compound has the formula C4 H10 . Therefore this compound has
(10 − 6) ÷ 2 = 2 degrees of unsaturation.
14. Draw six of the nine possible structures with this formula.
Answer:
H
H2C
C
CCH2CH3
C
CH3C
CCH3
H2C
CHCH
CH2
CHCH3
CH3
CH3
CH2
Predict the product of each reaction below. Be sure to indicate stereochemistry when appropriate.
Br
15.
2 KOH
ethanol
Br
Test Items for McMurry’s Organic Chemistry, Seventh Edition
61
Answer:
Br
2 KOH
ethanol
Br
16.
CH3CH2
C
C
D2
CH3
Lindlar catalyst
Answer:
CH3CH2
C
C
D2
CH3
CH3CH2
CH3
C
Lindlar catalyst
D
17.
C
C
H
1. BH3, THF
2. H2O2, NaOH, H2O
C
D
Answer:
O
18.
C
C
H
1. BH3, THF
2. H2O2, NaOH, H2O
C
C
H
1. NaNH2, NH3
2. CH3CH2I
C
C
H
1. NaNH2, NH3
2. CH3CH2I
CH2
C
H
Answer:
C
C
CH2CH3
KMnO4
19.
H3O+
Answer:
KMnO4
+
H3O
62
COOH
COOH
Chapter 8: Alkynes: An Introduction to Organic Synthesis
20.
CH3CH2C
CH
HgSO4, H2SO4
H2O
Answer:
O
CH3CH2C
CH
HgSO4, H2SO4
H2O
CH3CH2CCH3
CH
CH
C
C
H
CH
CH
C
C
H
excess H2
Pd/C
21.
Answer:
CH2CH2CH2CH3
excess H2
Pd/C
To answer the following questions consider this reaction:
Br
CH3CH2CH2CH2
C
C
HBr
CH3COOH
H
CH3CH2CH2CH2
C
CH2
22. On the structures provided, draw arrows showing the electron flow for the reaction mechanism for the
electrophilic addition of hydrogen bromide to 1-hexyne
CH3CH2CH2CH2
C
C
H
H
Br
+
C
CH3CH2CH2CH2
CH2
+
Br
_
Br
CH3CH2CH2CH2
C
CH2
Answer:
CH3CH2CH2CH2
C
C
H
H
Br
CH3CH2CH2CH2
+
C
CH2
+
Br
_
Br
CH3CH2CH2CH2
Test Items for McMurry’s Organic Chemistry, Seventh Edition
C
CH2
63
23. The key intermediate in the electrophilic addition reaction shown above is called:
a.
b.
c.
d.
an acetylenic carbocation
a vinylic bromide
a secondary carbocation
a vinylic carbocation
Answer:
d
Select the best reagent or sequence of reagents from the list provided which would best accomplish each
transformation below. Place the letter corresponding to the reagent(s) in the blank to the left of each reaction.
Each transformation requires only one answer.
a.
b.
c.
H2SO4, H2O, HgSO4
H2, Lindlar
1. BH3, THF
2. H2O2
1. NaNH2, NH3
2. CH3CH2I
d.
e. 1. Br2, CCl4
2. 2 NaNH2, NH3
f. 1. HCl
2. NaNH2, NH3
g. Li/NH3
h. 1. NaNH2, NH3
2. CH3CH2CH2I
H3C
24.
CH3C
C
CCH3
H
Answer:
H
C
CH3
g
O
CH2
25.
Answer:
26.
H
Answer:
64
CH2
CH
C
CH3
a
C
C
H
CH3 CH2 CH2 C
C
H
h
CH
27.
Answer:
C
CH
C
C
e
Chapter 8: Alkynes: An Introduction to Organic Synthesis
Show all reagents and intermediates necessary to carry out the following conversions.
H
28.
(CH3)2CHCH2C
CH
CH2CH3
C
C
H
(CH3)2CHCH2
Answer:
(CH3)2CHCH2C
CH
1. NaNH2, NH3
2. CH3CH2Br
(CH3)2CHCH2C
CCH2CH3
H
Li/NH3
CH2CH3
C
C
(CH3)2CHCH2
H
OH
29.
CH3CH2C
C
H
CH3CH2CHCH2CH2CH3
Answer:
CH3CH2C
C
H
1. NaNH2, NH3
2. CH3CH2Br
CH3CH2C
CCH2CH3
H2, Pd/C
or
Li/NH3
CH3CH2CH
CHCH2CH3
1. Hg(OAc)2, H2O,/THF
2. NaBH4
or
1. BH3, THF
2. H2O2, NaOH, H2O
OH
CH3CH2CHCH2CH2CH3
Test Items for McMurry’s Organic Chemistry, Seventh Edition
65
Using acetylene and any alkyl halides as starting materials, synthesize the following compounds. More than
one step may be required. Show all reagents and all intermediate compounds in your synthetic scheme.
O
CH3CCH2CH2CH2CH2CH3
30.
2-heptanone
(responsible for the odor of cheddar cheese)
Answer:
HC
1. NaNH2, NH3
CH
2. CH3CH2CH2CH2CH2I
HC
CCH2CH2CH2CH2CH3
HgSO4, H2SO4
H2O
O
CH3CCH2CH2CH2CH2CH3
31.
Answer:
HC
1. NaNH2, NH3
2. C6H5CH2I
CH
CH2C
Cl
32.
Cl
CCH2
CH2C
1. NaNH2, NH3
2. C6H5CH2I
CH
Li/NH3
1,2-dichloropropane
(a degreasing solvent used in dry cleaning)
Answer:
HC
CH
1. NaNH2, NH3
2. CH3I
HC
CCH3
H2/Lindlar
or
Li/NH3
H2C
CHCH3
Cl2
CCl4
Cl
Cl
66
Chapter 8: Alkynes: An Introduction to Organic Synthesis
33.
O
H3C
C
OH
acetic acid
(raw material for the vinyl acetate
polymer used in paints and adhesives)
Answer:
HC
CH
1. NaNH2, NH3
2. CH3I
CH3C
CH
1. NaNH2, NH3
2. CH3I
CH3C
CCH3
KMnO4
H3O+
O
2
H3C
C
OH
Br
34.
CH3CHCH2CH2CH3
Answer:
HC
CH
1. NaNH2, NH3
2. CH3CH2CH2I
HC
CCH2CH2CH3
H2
Lindlar catalyst
H2C
CHCH2CH2CH3
HBr
ether
Br
CH3CHCH2CH2CH3
Test Items for McMurry’s Organic Chemistry, Seventh Edition
67