ALKENES AND ALKYNES – REACTIONS
A STUDENT WHO HAS MASTERED THE MATERIAL IN THIS SECTION SHOULD BE
ABLE TO:
1.
Given the starting materials and reaction conditions, predict the products of the following
reactions of alkenes and alkynes.
Markovnikov addition of acids to alkenes and alkynes, including the acid-catalyzed addition
of water (hydration). Rearrangement is possible in the additions to alkenes;
tautomerization occurs in the hydration of alkynes.
Anti-Markovnikov addition of HBr.
Addition of halogens (and halohydrin formation). These reactions are anti additions. In
halohydrin formation, the OH goes to the more substituted carbon.
Epoxidation, and the hydrolysis of the resulting epoxides to glycols (overall anti addition).
Glycol formation using either KMnO4 (cold) or OsO4 (these are syn additions).
Degradation of alkenes and alkynes using either ozonolysis or KMnO4 (hot)
Addition of carbenes to alkenes
2.
Using any of the above reactions, propose syntheses of compounds that can be made using
alkenes as starting materials or intermediates. As always, synthesis problems may require
any reaction that you have studied in the course so far.
3.
Propose mechanisms, and predict and explain experimental results using your knowledge of
mechanism. Important reactions include:
Markovnikov additions (which proceed by protonation of the alkene to give a carbocation).
Addition of bromine and bromohydrin formation (by formation of the bromonium ion).
Hydrolysis of epoxides (under acid conditions the oxygen is protonated first).
4.
Identify unknown alkenes and alkynes when given either the products of ozonolysis or of
KMnO 4 degradation. You will not be called on to distinguish between cis and trans
isomers; these methods do not give that information. (Further information can be obtained
from the index of hydrogen deficiency).
5.
Use the results of simple chemical tests in identifying unknown compounds. Data from IR
spectra may also be used. Important tests include:
Solubility in concentrated sulfuric acid (compounds containing only alkanes, halogens, and
aromatic rings do not dissolve)
Bromine in carbon tetrachloride (alkenes and alkynes give an immediate reaction,
decolorizing the reddish-brown bromine solution)
Potassium permanganate (cold, dilute) (alkenes and alkynes give an immediate brown
precipitate; other compounds leave the permanganate solution purple)
Silver nitrate in alcohol solution (gives a white precipitate with alkyl chlorides, a tan ppt.
with alkyl bromides, a brown ppt. with alkyl iodides, no reaction when the halogen is
attached to an sp2 carbon, and no reaction with other materials)
Silver nitrate in ammonia (gives a white ppt. with terminal alkynes)
96
A STUDENT WHO HAS MASTERED THE OBJECTIVES ON THE PREVIOUS PAGE
SHOULD BE ABLE TO SOLVE THE FOLLOWING PROBLEMS AND RELATED ONES:
1.1
Predict the major organic product or products of each of the following reactions.
a) (CH3 )2 CHCH=CH2 + HCl ----->
no peroxides
b) CH3 CH2 CH2 CH=CH 2 + HBr ------------------>
peroxides
c) CH3 CH2 CH2 CH=CH 2 + HBr --------------->
d)
(cold, dilute)
+ KMnO4 ----------------->
e)
KOC(CH 3 )3
---------------->
CHCl3
f)
CCl4
+ Br2 -------->
g)
+ Cl 2 + H2 O ----->
OH , H2 O, heat H3 O
+ KMnO4 --------------------> --------->
h)
COOH
HOOC
i)
C
H
j)
C
CCl4
+ Br2 -------->
H
CH2 I2 /Zn(Cu)
------------------>
ether
97
1.2
For each of the following compounds, compare the reaction products from the addition of
HBr in the presence of peroxides with the addition of HBr in the absence of peroxides.
CH3
|
a) CH3 —CH—CH=CH2
H
b)
CH=CH 2
2.
Propose a synthesis of each of these compounds, from the given starting material and any
needed inorganic reagent and/or solvent.
CH3
a)
CH3
from
Br
b) CH3 CH2 CHBr2 from CH3 C≡CH
OH
c)
from
OH
OH
d)
Br
from
OH
98
2.2
Propose a synthesis of each of these compounds from the given starting materials(s) and
any needed inorganic reagents or solvents.
CH3
CH3
a)
from
Br
b) CH3 CH2 CH2 CH2 Br from HC≡CH and CH3 CH2 I
c) (CH3 )3 CBr from (CH3 )2 CHCH 2 OH
OH
d)
from
OH
CH3
e)
C
H
H
CH3
from
C
CH3
C
H
CH3
C
H
f) (CH3 )2 CHCH 2 CH2 CH3 from (CH3 )2 C=CH 2 and H-C≡CNa
99
3.
Propose a mechanism for each of the reactions shown.
OH
H3 O
a)
O + H 2 O ---------->
OH
b) (CH3 )2 CHCH=CH2 + HCl -----> (CH 3 )2 CClCH2 CH3
CH2 CH3
CH=CH 2
c)
H3 O
+ H 2 O ---------->
OH
d) CH3 CH2 CH=CH 2 + Br2 + I– -----> CH3 CH2 CH—CH 2 + Br–
|
|
I
Br
HO
CH2
H3 O
+ H 2 O ---------->
e)
CH3
CH2
f)
CH3
H3 O (trace)
------------------->
100
4.1
Identify each of these unknowns from the information given.
O
O
O3
Zn
||
||
a) C6 H12 ----> ------> CH3 C-CH3 + CH3 CH2 C-H
H2 O
O
||
CH3 CH2 C-H
b) C9 H16
O3
Zn
----> ------>
H2 O
c) C6 H10
O
O
KMnO 4 , OH
H3 O
||
||
-------------------> ---------> HO-C-CH2 CH2 CH2 C-CH3
heat
O +
O
KMnO 4 , OH
H3 O
d) C10 H16 -------------------> --------->
heat
4.2
Predict the products of the following reactions.
O3
Zn
a)
----> ------>
H2 O
CH2
b)
CH=CHCH3
5.1
CH2 CH2 CH2 COOH
H3 O
KMnO 4 , OH
--------->
------------------->
heat
Match each set of test results with one of the compounds shown.
OH
CH3 CH2 CH2 CH2 Br
A
B
C
D
a) Decolorizes Br2 in CCl4
Soluble in H2 SO 4
No reaction with AgNO3 in ammonia
b) No reaction with cold dilute KMnO4
No reaction with AgNO3 in alcohol
Soluble in conc. H2 SO 4
101
CH3 CH2 CH2 C
E
C-H
5.1
Unknowns, continued. The possibilities are:
OH
CH3 CH2 CH2 CH2 Br
A
B
C
D
c) Gives a brown precipitate with cold dilute KMnO4
Gives a white precipitate with AgNO3 in ammonia
Soluble in conc. H2 SO 4
d) No reaction with cold dilute KMnO4
No reaction with alcoholic AgNO3
Insoluble in conc. H2 SO 4
5.2
Describe simple chemical tests that can distinguish between:
a)
b)
c)
d)
e)
cyclohexene and cyclohexyl bromide
1-hexene and 1-hexyne
tert-butyl alcohol and tert-butyl bromide
pentane and 1-pentene
ethanol and 2-pentyne
102
CH3 CH2 CH2 C
E
C-H
ANSWERS TO THE PROBLEMS:
1.1
Predict the major organic product or products of each of the following reactions.
a) (CH3 )2 CHCH=CH2 + HCl -----> (CH 3 )2 CClCH2 CH3
no peroxides
b) CH3 CH2 CH2 CH=CH 2 + HBr ------------------> CH3 CH2 CH2 CHBrCH 3
peroxides
c) CH3 CH2 CH2 CH=CH 2 + HBr ---------------> CH3 CH2 CH2 CH2 CH2 Br
(cold, dilute)
+ KMnO4 ----------------->
d)
OH
OH
KOC(CH 3 )3
---------------->
CHCl3
e)
f)
+ Br2
Cl
Cl
Br
CCl4
-------->
+ enantiomer
Br
Cl
g)
+ Cl 2 + H2 O ----->
+ enantiomer + HCl
OH
COOH
OH , H2 O, heat H3 O
+ KMnO4 --------------------> --------->
h)
COOH
COOH
HOOC
i)
C
H
j)
C
+ Br2
CCl4
-------->
H
COOH
HOOC
C
Br H
CH2 I2 /Zn(Cu)
------------------>
ether
103
C
Br H
+ enantiomer
1.2
Compare the addition of HBr in the presence and in the absence of peroxides to each of the
following compounds. (Hint: Predict the products.)
CH3
|
a) CH3 —CH—CH=CH2
HBr, no peroxides
HBr, peroxides
(CH3 )2 CBr—CH2 CH3
(CH3 )2 CH—CH 2 CH2 Br
Note that both of these problems involve rearrangements in the absence of peroxides.
Br
HBr, no peroxides
H
CH2 CH3
b)
CH=CH 2
H
HBr, peroxides
CH2 CH2 Br
2.1
Synthesis problems. These answers are in shorthand (not balanced equation) form.
a)
CH3
CH3
HBr, peroxides
-------------------->
Br
2 HBr, peroxides
b) CH3 C≡CH -----------------------> CH3 CH2 CHBr2
c)
C6 H5 CO3 H
---------------->
H2 O, H3 O
O ----------------->
OH
OH
d)
Br KOH, heat
--------------->
C6 H5 CO3 H
H2 O, H3 O
----------------> ----------------->
OH
OH
(Last two steps as in c) above)
2.2
More synthesis:
Br
a)
CH3 Br2 , light
------------->
KOH
HBr
CH3 --------> ------------->
peroxides
heat
104
CH3
Br
NaNH 2
CH3 CH2 I
b) HC≡CH -----------> HC≡CNa --------------> HC≡CCH2 CH3 and then
H2 , Ni2 B
HBr
HC≡CCH2 CH3 ------------> H2 C=CHCH 2 CH3 ------------> CH3 CH2 CH2 CH2 Br
peroxides
H2 SO 4 , heat
HBr, no peroxides
c) (CH3 )2 CHCH 2 OH ----------------> (CH3 )2 CH=CH 2 ----------------------> (CH3 )3 CBr
Br2
------>
light
d)
CH3
e)
C
H
CH3
C
H
Br KOH
------>
heat
C6 H5 CO3 H H3 O
---------------> --------->
H2 O
Br2
NaNH 2
-------> CH3 CHBrCHBrCH 3 ---------> CH3 C
CCl4
CH3 C
CCH3
CH3
Li, NH3
----------->
C
H
H
C
CH3
HBr, peroxides
f) (CH3 )2 C=CH 2 ---------------------> (CH3 )2 CHCH 2 Br, then:
H-C≡CNa
(CH3 )2 CHCH 2 Br ---------------> (CH3 )2 CHCH 2 C≡CH, then:
2H2 , Pt
(CH3 )2 CHCH 2 C≡CH ----------> (CH3 )2 CHCH 2 CH2 CH3
105
CCH3
OH
OH
then
3)
Mechanisms. Note that balanced equations are used throughout.
OH
H3 O
a)
O + H 2 O ---------->
OH
O + H3O
----->
O
H + H2 O
OH
O H + H2 O ----->
OH 2
OH
OH
+ H2 O ----->
+ H3O
OH 2
OH
b) (CH3 )2 CHCH=CH2 + HCl -----> (CH 3 )2 CClCH2 CH3
(CH3 )2 CHCH=CH2 + HCl -----> (CH 3 )2 CHCHCH 3 + Cl
H
|
(CH3 )2 C—CHCH 3 -----> (CH3 )2 C—CH2 CH3
(CH3 )2 C—CH2 CH3 + Cl -----> (CH 3 )2 CClCH2 CH3
CH=CH 2
c)
CH2 CH3
H3 O
+ H 2 O ---------->
OH
CHCH 3
CH=CH 2
+ H3 O
+ H2O
----->
CHCH 3
CH2 CH3
----->
H
CH2 CH3
+ H 2 O ----->
CH2 CH3
OH 2
CH2 CH3
OH 2
CH2 CH3
+ H 2 O ----->
106
OH
+ H3 O
3)
Mechanisms, continued. Note again that balanced equations are used throughout.
d) CH3 CH2 CH=CH 2 + Br2 + I– -----> CH3 CH2 CH—CH 2 + Br–
|
|
I
Br
CH3 CH2 CH=CH 2 + Br—Br -----> CH 3 CH2 CH—CH 2
Br
CH3 CH2 CH—CH 2 + I
-----> CH3 CH2 CH—CH 2
I
Br
HO
CH2
CH3
H3 O
+ H 2 O ---------->
e)
CH2
CH3
+ H3 O
---------->
+ H2O
H3 C OH 2
CH3
+ H 2 O ------>
OH 2
H3 C
HO CH3
+ H3 O
+ H 2 O ------>
CH3
CH2
f)
H3 O (trace)
------------------->
CH3
CH2
+ H3 O
----->
CH3
+ H2 O
CH3
H
+ H2 O ----->
+ H3 O
107
Br
+ Br
4.1
The unknowns are:
a) CH3 CH2 CH=C(CH 3 )2
CH3
CHCH 2 CH3
d)
c)
4.2
b)
The products are:
O3
Zn
----> ------>
H2 O
a)
O
CHO
H3 O
KMnO 4 , OH
-------------------> --------->
heat
CH=CHCH3
CH2
b)
O
O
||
||
+ HCCH2 CH
O
+ CH3 COOH
COOH
+ CO2
5.1
The unknowns are: a) B; b) A; c) E; d) C
5.2
Descriptions of simple chemical tests that can distinguish between the pairs. (Only one
answer is required.)
a) Cyclohexene gives no reaction with alcoholic AgNO3 , while cyclohexyl bromide gives a
white precipitate. Cyclohexene reacts with bromine in carbon tetrachloride and with
cold dilute potassium permanganate, and dissolves in concentrated sulfuric acid;
cyclohexyl bromide does none of these things.
b) 1-Hexene gives no reaction with AgNO3 in ammonia, while 1-hexyne gives a white
precipitate.
c) tert-Butyl alcohol dissolves in concentrated sulfuric acid, while tert-butyl bromide does
not. The bromide gives a white precipitate with AgNO3 in alcohol, while the tert-butyl
alcohol does not react.
d) 1-Pentene decolorizes bromine in carbon tetrachloride, gives a brown precipitate with
cold dilute potassium permanganate, and dissolves in conc. sulfuric acid. Pentane does
not react with any of these reagents.
e) 2-Pentyne reacts with bromine in carbon tetrachloride and with cold dilute potassium
permanganate; ethanol does neither of these things.
108
Name ___________________________________________________ Eighth Drill Test (Sample)
Organic Chemistry 2210 DR
Answer All Questions
1)
Predict the major organic product or products the following reaction.
CH3 CH2 CH2 CH=CH 2 + C6 H5 CO3 H ------>
2)
Propose a synthesis of each of the following compounds from the given starting material
and any needed inorganic reagents or solvents.
OH
a)
from
OH
b)
Br
Br
from
c) (CH3 )3 COH from (CH 3 )2 CHCH 2 OH
3)
Propose a mechanism for each of the reactions shown.
H3 O+
a) CH3 CH2 CH=CH 2 + H2 O -------> CH3 CH2 CHOHCH3
Br
b)
+ Br2 + Cl ----> Br +
Cl
4)
Give the structures of these unknowns from the information given.
O
O3 Zn, H2 O
||
a) C8 H16 ----> -----------> 2 CH3 CH2 CH2 C-H
KMnO 4 , base, heat acid
b) C8 H14 ------------------------> ------>
5)
O + CH3 CO2 H
Which of these compounds gives a peak in the IR spectrum near 1640 cm-1 , is soluble in
conc. H2 SO 4 , reacts with cold alkaline KMnO4 , and gives no reaction with either silver
nitrate in ethanol or Ag(NH3 )2 +?
A. CH3 CH=CH 2
B. CH3 C≡C-H
C. CH 3 CH2 CH3
109
D. CH 3 CH2 OH
E. CH 3 CH2 Cl
Name _________________________________________________ Eighth Drill Test (Sample B)
Organic Chemistry 2210 DR
Answer All Questions
1)
Predict the major organic product of each of the following reactions.
H2 SO 4
a) CH3 CH=CH 2 + H2 O ---------->
b)
2)
peroxides
CH3 + HBr ------------->
Propose a synthesis of each. You may use any needed inorganic reagents and solvents.
a) (CH3 )3 CCl from (CH3 )3 COH
b) bicyclo[3.1.0]hexane from cyclopentene
c) trans-1,2-cyclohexanediol from bromocyclohexane
3)
Propose a mechanism for each of the reactions shown. For problem a), first complete the
equation by predicting the product.
H3 O
a)
O + H 2 O ---------->
b) CH3 CH=CH 2 + Br2 + Cl
4)
Which of the compounds shown is soluble in conc. H2 SO 4 , reacts with cold alkaline
KMnO 4 , and gives no reaction with either AgNO3 in alcohol or Ag(NH3 )2 +?
A. CH3 CH2 Br
5)
------> CH3 CHClCH2 Br + Br
B. CH3 CH2 OH
C. CH 3 CH=CH 2
D. CH 3 C≡C-H
Give the structures of the unknowns from the information given.
O
KMnO 4 , base, heat acid
||
a) C7 H12 ------------------------> ------> HO
O
O
|
|
||
O3 Zn, H2 O
b) C7 H14 ----> -----------> H
+
110
E. CH3 CH2 CH3
O
||
OH