Homework Chapter 9 w

Chapter 9—HOMEWORK
SHORT ANSWER
Drawing Instructions: Draw structures corresponding to each of the given names.
1.
Draw: ethynylcyclopropane
ANS:
2.
Draw: 3,10-dimethyl-6-sec-butylcyclodecyne
ANS:
3.
Draw: 4-bromo-3,3-dimethyl-1-hexen-5-yne
ANS:
4.
Draw: acetylene
ANS:
IUPAC Naming Instructions: Provide proper IUPAC names.
5.
Name:
ANS:
4-methyl-2-heptyne
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Alkynes: An Introduction to Organic Synthesis
6.
Name:
ANS:
1-ethynyl-2-methylcyclopentane
Exhibit 9-1
The compound below has been isolated from the safflower plant. Consider its structure to answer
the following question(s).
7.
Refer to Exhibit 9-1. What is the molecular formula for this natural product?
ANS:
C13H10
8.
Refer to Exhibit 9-1. What is the degree of unsaturation for this compound?
ANS:
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.
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Chapter 9
9.
Refer to Exhibit 9-1. Assign E or Z configuration to each of the double bonds in the
compound.
ANS:
10.
Refer to Exhibit 9-1. Provide the name for this unusual natural product.
ANS:
(3E, 11E)-1,3,11-tridecatrien-5,7,9-triyne or (3E,11E)-trideca-1,3,11-trien-5,7,9-triyne
Exhibit 9-2
To answer the following question(s), consider the information below:
The heat of hydrogenation of 1,4-pentadiene is 254.4 kJ/mol. The heat of hydrogenation of 1pentyne is approximately 292.9 kJ/mol.
11.
Refer to Exhibit 9-2. Which structure is more stable, 1,4-pentadiene or 1-pentyne? Briefly
explain your answer.
ANS:
1,4-pentadiene
The heat of hydration is the amount of energy released when hydrogen adds to the multiple
carbon-to-carbon bonds in a compound and converts it to the corresponding saturated compound.
The larger the value, the more energy that is released during the hydrogenation. Both of these
substances, end up as pentane upon complete hydrogenation. That is, they end up at the same final
energy level. Less energy is released by 1,4-pentadiene, therefore, this reactant has less energy to
start with or is more stable than 1-pentyne.
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Alkynes: An Introduction to Organic Synthesis
12.
Refer to Exhibit 9-2. Show the energy differences between the hydrogenation of 1,4pentadiene and 1-pentyne on a reaction energy diagram.
ANS:
Exhibit 9-3
Consider an unknown with the molecular formula C4H6.
13.
Refer to Exhibit 9-3. How many degrees of unsaturation are present?
ANS:
A saturated four carbon compound has the formula C4H10. Therefore this compound has (10 − 6) ÷
2 = 2 degrees of unsaturation.
14.
ANS:
4
Refer to Exhibit 9-3. Draw six of the nine possible structures with this formula.
Chapter 9
Exhibit 9-4
Predict the product of each reaction below. Be sure to indicate stereochemistry when appropriate.
15.
ANS:
16.
ANS:
17.
ANS:
18.
ANS:
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Alkynes: An Introduction to Organic Synthesis
19.
ANS:
20.
ANS:
21.
ANS:
Exhibit 9-5
To answer the following question(s) consider this reaction:
22.
6
Refer to Exhibit 8-5. On the structures provided, draw arrows showing the electron flow for
the reaction mechanism for the electrophilic addition of hydrogen bromide to 1-hexyne.
Chapter 9
ANS:
23.
a.
b.
c.
d.
Refer to Exhibit 8-5. The key intermediate in the electrophilic addition reaction shown
above is called:
an acetylenic carbocation
a vinylic bromide
a secondary carbocation
a vinylic carbocation
ANS:
d
Exhibit 9-6
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.
d.
H2SO4, H2O, HgSO4
H2, Lindlar
1. BH3, THF
2. H2O2
1. NaNH2, NH3
2. CH3CH2I
24.
e.
f.
g.
h.
1. Br2, CCl4
2. 2 NaNH2, NH3
1. HCl
2. NaNH2, NH3
Li/NH3
1. NaNH2, NH3
2. CH3CH2CH2I
_____
ANS:
g
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Alkynes: An Introduction to Organic Synthesis
25.
_____
ANS:
a
26.
_____
ANS:
h
27.
_____
ANS:
e
Exhibit 9-7
Show all reagents and intermediates necessary to carry out the following conversions.
28.
ANS:
8
Chapter 9
29.
ANS:
Exhibit 9-8
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.
30.
ANS:
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Alkynes: An Introduction to Organic Synthesis
31.
ANS:
32.
ANS:
33.
ANS:
10
Chapter 9
34.
ANS:
11

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