Chapter 8 - Alkynes: Alkynes: An Introduction to Organic Synthesis Synthesis Draw structures corresponding to each of the following names. 1.
ethynylcyclopropane
Answer:
2.
C
C
H
3,10-dimethyl-6- sec-butylcyclodecyne 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.
CH3 5.
CH CH3C
CCHCH2CH2CH3
Answer: 4-methyl-2-heptyne
CH3 6.
C
CH
Answer: 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 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 is the degree of unsaturation for this this compound? compound? Answer:
We can arrive at the degree of of unsaturation unsaturation for a structure a structure in 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. them. There are three double bonds (3 degrees) and three triple bonds (six (six degrees), so the degree of unsaturation is 9. We can verify this by using the molecular formula, C13H10, to calculate a 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 Assign E or Z Z configuration configuration to each of the double bonds in the compound. Answer:
H E C H3C C
H C
C
H
C
C
C
C
H
C E C H
C C
H
H 10.
Provide the name name for this unusual natural product. Answer:
(3 E , 11 E )-1,3,11-tridecatrien-5,7,9-triyne )-1,3,11-tridecatrien-5,7,9-triyne or (3 E ,11 ,11 E )-trideca-1,3,11-trien-5,7,9-triyne )-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 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: 1,4-pentadiene
60
Chapter 8: Alkynes: An Introduction to Organic Synthesis
12.
Show the energy differences between the hydrogenation hydrogenation of 1,4-pentadiene and 1-pentyne on a reaction energy diagram. Answer:
A =
1-pentyne 1,4-pendatiene C = 1-pentene D = pentane B =
A
Energy B
C
292.9 kJ/mol
254.4 kJ/mol D
Reaction Progress
Consider Consider an unknown unknown with with the molecular molecular formu formula la C4 H6 . 13.
How many degrees of unsaturation are are present? Answer:
A saturated saturated four carbon carbon compound compound has the formula formula C4 H10 . Therefore this compound compound has (10 − 6) ÷ 2 = 2 degrees of unsaturation.
14.
Draw six 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 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.
CH CH3CH2
C
C
D2
CH3
Lindlar Lindlar catalyst catalyst
Answer:
CH CH3CH2
C
C
D2
CH3
CH3CH2
CH3 C
Lindlar catalyst catalyst
D
17.
C
C
H
C D
1. BH3, THF 2. H2O2, NaOH, H2O
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:
62
KMnO4
COOH
H3O+
COOH Chapter 8: Alkynes: An Introduction to Organic Synthesis
20.
CH CH3CH2C
CH
HgSO4, H2SO4 H2O
Answer:
O CH3CH2C
CH
CH
HgSO4, H2SO4
CH3CH2CCH CCH3
H2O
CH
C
C
H
excess excess H2
21.
Pd/C
Answer:
CH
CH
C
C
H
CH2CH2CH2CH3
excess excess H2 Pd/C
To answer the following questions consider this reaction: Br CH CH3CH2CH2CH2 22.
C
C
HBr HBr CH3COOH
H
CH3CH2CH2CH2
C
CH2
On the structures provided, draw arrows showing the electron flow for the reaction mechanism for the electrophilic addition of hydrogen bromide to 1-hexyne
CH CH3CH2CH2CH2
C
C
H
H
Br
+ C
CH3CH2CH2CH2
CH2
+
_ Br
Br CH3CH2CH2CH2
C
CH2
Answer: CH 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 the electrophilic addition addition reaction shown above is called: called: a. b. c. d.
an acetylenic carbocation a vinylic bromide 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 transformation below. Place the letter corresponding corresponding to the reagent(s) in the blank to the left of each reaction. 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. Br 2, 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
C
CH2
CH
C
CH3
25.
Answer: 26.
H
Answer:
a C
H
CH3 CH2 CH2 C
CH
Answer:
C
H
h
27.
64
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.
(CH (CH3)2CHCH2C
CH
CH2CH3 C
C
(CH (CH3)2CHCH2
H
Answer:
(CH (CH3)2CHCH2C
CH
1. NaNH2, NH3 2. CH3CH2Br H (CH (CH3)2CHCH2C
CCH2CH3
Li/NH3
CH2CH3 C
C
(CH (CH3)2CHCH2
H
OH 29.
CH3CH2C
C
H
H
1. NaNH2, NH3
CH3CH2CHCH2CH2CH3
Answer: CH3CH2C
C
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, materials, synthesize the following following compounds. More than one step may be required. Show all reagents and all intermediate compounds compounds in your synthetic scheme. O CH3CCH CCH2CH2CH2CH2CH3
30.
2-heptanone (responsible for the odor of cheddar cheese) Answer:
HC HC
1. NaNH2, NH3
CH
2. CH3CH2CH2CH2CH2I
HC
CCH2CH2CH2CH2CH3 HgSO4, H2SO4 H2O O
CH3CCH CCH2CH2CH2CH2CH3
31.
Answer:
HC
1. NaNH2, NH3
CH
CH2C
2. C6H5CH2I
CH2C
CCH2
CH
1. NaNH2, NH3 2. C6H5CH2I
Li/NH3
Cl 32.
1,2-dichloropropane Cl Cl
(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 CCl CCl4 Cl
Cl 66
Chapter 8: Alkynes: An Introduction to Organic Synthesis
O 33.
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 CH
1. NaNH2, NH3 2. CH3CH2CH2I
HC
CC CCH2CH2CH3
H2 Lindlar catalyst
H2C
CHCH2CH2CH3 HBr HBr ether Br
CH3CHCH2CH2CH3
Test Items for McMurry’s Organic Chemistry, Seventh Edition
67
