6 Chaoter - Alkenes:
Structure and Reactivitv
Calculate the degree of un saturation in each fonnula below. Show your calculations.
1.
pinene, ClOHl8
Answer:
2.
The saturated ten carbon compound would have 22 hydrogens so the number of degrees of
unsaturation is: (22 -18) -;-2 = 4 -;-2 = 2 .
eicosapentaenoic
Answer:
acid, C2oH3002, a constituent offish oil
Oxygen does not affect the base fonnula which in this case is C2oH3o. The saturated'20
compound would have 42 hydrogens so the number of degrees ofunsaturation for
eiscosapentaenoic acid is: (42 - 30) -;-2 = 12 -;-2 = 6.
carbon
3. diazepam (Valium), C16H13N2OCl
Answer:
Oxygen does not affect the base fonnula. A hydrogen is added to the base fonnula for each
halogen and subtracted for each nitrogen so the base fonnula for diazepam is C16H12' The
saturated 16 carbon compound would have 34 hydrogens so the number of degrees of
unsaturation for diazepam is: (34 - 12) -;-2 = 22 -;-2 = 11.
Dieldrin, C12HgCI6O, is a pentacyc1ic compound fonnerly used as an insecticide.
4. Calculate the degree ofunsaturation for Dieldrin. Show calculations for credit.
Answer:
Oxygen does not affect the base fonnula. A hydrogen is added to the base fonnula for each
halogen so the base fonnula for dieldrin is C12H14. The saturated 12 carbon compound would
have 26 hydrogens so the number of degrees of unsaturation for dieldrin is (26 - 14) -;-2 = 12 -;2=6.
5.
How many double bonds does dieldrin have?
Answer:
Dieldrin has 6 degrees of unsaturation and it is pentacyc1ic, meaning it has 5 rings. Therefore,
dieldrin must have one double bond.
Draw structures corresponding to each name below. Either condensed or line structures may be used.
6.
(3E)-3, 7 -dimethyl-l ,3,6-octatriene
Answer:
~
Test Items for McMurry's
or
(CH3hC= CHCH2
\
/
H
Organic Chemistry,
Seventh Edition
C=C
/
CH3
\
CH= CH2
37
7. 3,6-dimethyl-l,4-cyclohexadiene
CH3
Answer:
or
CH3
8.
cis-2-hexene
Answer:
~
9.
H3C
\
or
/
H
/
C=C
CH2CH2CH3
\
H
trans-4,4-dimethyl-2-pentene
Answer:
H3C
\
~
or
/
/
H
2- Pentene is an example of a disubstituted
C=C
H
\
C(CH3hCH3
alkene.
CH3CH= CHCH2CH3
10. Draw the cis and trans isomers of2-pentene and label them.
Answer:
H3C
\
/
H
/
C=C
\
H3C
\
CH2CH3
/
H
H
/
C=C
\
H
CH2CH3
trans
cis
11. Circle the isomer which is most stable.
Answer:
H3C
\
/
H
/
C=C
\
CH2CH3
H
cis
38
Chapter 6: Alkenes:
Structure and Reactivity
Provide names for each structure below. Be sure to include the cis, trans or E, Z designations where applicable.
~
12.
Answer:
0
13.
Answer:
14.
trans-2-methyl-3-hexene or (E)-2-methyl-3-hexene
3-methylcyclopentene
~
Answer:
(2E,4E)- 5-ethyl-6-methyl- 2,4-heptadiene
aI2aI2aI3
15.
H2C= aIC(aI3haI
I
\
/
H
Answer:
/
C=C
\
aI2aI3
H
cis-3,3-dimethyl-4-propyl-l,5-octadiene
or (Z)-3,3-dimethyl-4-propyl-l ,5-octadiene
Rank each set of substituents using the Cahn-Ingold-Prelog sequence rules by numbering the highest priority
substituent 1 and numbering the lowest priority substituent 4. Place the number in the blank below the
substituent.
0
16.
II
-C-H
-
aI= aIaI3
-
aI=NaI3
-C
C-CH3
Answer:
0
II
-C-H
Testltems
for McMurry's
-
aI= aIaI3
4
Organic Chemistry,
-
Seventh Edition
aI=
NaI3
2
-C
C-aI3
3
39
-- :>:
17.
II
-
CH3
CH3
0
NHCCH3
I
- CH- CH3
-C=C-H
I
-CH-OH
Answer:
II
-
CH3
CH3
0
-C=C-H
3
NHCCH3
1
I
CH- CH3
4
-
I
-CH-OH
2
0
II
18. -
-C==N-OH
CH2- I
-
C- OCR3
Answer:
-
-
CH== CHCH3
-
CH==CHCH3
4
0
-C==N-OH
CH2- I
II
C- OCR3
-
2
3
1
19.
-
-
-C=N
CH2- OH
-
CH2- C1
CH==CH2
Answer:
-
-C=N
3
CH2- OH
2
-
CH2- C1
1
-
CH==CH2
4
MATCH each alkene below with the appropriate heat of hydrogenation. Place the letter of the correct answer in
the blank to the left of the alkene.
a. 125.9 kJ/mol
b. 118.4 kJ/mol
c. 115.5 kJ/mol
H3C
20. -
>===<
H
Answer:
40
H
CH3
c
Chapter 6: Alkenes:
Structure and Reactivity
21.
H
H
>=< CH3
H
Answer:
a
H3C
22.
CHzCH3
>=< H
H
Answer:
b
23. Arrange the following bicyclic alkenes in order of increasing stability (least stable to most stable).
00 0)
I
a.
b.
c.
d.
II
CO
III
III<II<I
I<II<III
I<III<II
II<III<I
Answer:
d
Assign E or Z configurations
to each alkene below.
CII,
24.
H'C)==<
Br
CHzCH3
Answer: Z
CN
CHzCHzOH
25.
CH3
Answer:
E
Test Items for McMurry's
Organic Chemistry,
Seventh Edition
41
a
CH3
II
26.
I
H3COC
O=C
C= CHz
>=<
C=CH
I
OH
Answer:
E
MATCH definition each to the tenn it describes. Place the letter corresponding to the tenn in the blank to the
left of the definition.
a.
b.
c.
Hammond Postulate
Cahn-Ingold-Prelog Rules
Markovnikov's Rule
Predicts that the more stable carbocation intennediate is fonned in electrophilic additions to
27. alkenes.
Answer:
28. -
Predicts that the transition state of an exergonic reaction step structurally resembles the reactant.
Answer:
29. -
-
b
Predicts that the transition state of an endergonic reaction step structurally resembles the product.
Answer:
31.
a
Assigns priorities to the substituent groups on a carbon.
Answer:
30.
c
a
Predicts that in additions ofHX to alkenes, the H adds to the less substituted alkene carbon and the
X adds to the more substituted alkene carbon.
Answer:
c
32. Rank the carbocations below in order of increasing stability (least stable = 1; most stable = 3). Place the
number corresponding to the carbocation's relative stability in the blank below the structure.
()
()+()
Answer:
()
3
42
()+()
2
Chapter 6: Alkenes:
Structure and Reactivity
Consider the following reaction:
(YCH3
HCI
0+
~
0':
33. Write the complete stepwise mechanism for this reaction. Show all intermediate structures and show all
electron flow using the curved arrow convention.
Answer:
r
---.CH',.g:
~;-
(YCH3
~~vl
H
-0':
34. Draw a qualitative reaction energy diagram for this reaction. Label the positions of all reactants,
intenmediates and products.
Answer:
first TS
Energy
~Gf
~~~J[-~~-----
products
~
Reaction Progress
Test Items/or
McMurry's
Organic Chemistry,
Seventh Edition
43
Consider the following reaction:
CI
(CH3hCCH= CHz
+
I
.
HCI
(CH3)3CCHCH3
+
I
(CH3)zCCHCH3
I
CI
CH3
A
50%
B
50%
35. Below are all the chemical structures and intermediates involved in this reaction. On the structures
provided, show all electron flow using the arrow formalism for the complete stepwise mechanism fo~ this
reaction.
Pathway A
(CH3)3CCH= CHz
H- Cl
.. (CH3hCCH- CH3
+
:CI:
(CH3)3CCHCH3
I
CI
A
Pathway B
l
Cl
CH3
CH3
I
(CH3)2C- CH+
..
CH3
I
(CH3)2C- CH- CH3
+
I
.. :CI:
.
(CH3)2CCHCH3
I
CH3
B
Answer:
~
Vi
(CH3)3CCH
Pathway~
(CH3)3C~:CI:
+"
--.
(CH3)3CCHCH3
I
Cl
A
Pathway B
~
CH
(CH3hb~-
CI
I
CH3
+
CH3
..
I
(CH3hC- CH+~..
CH3
.. :CI:
..
(CH3hCCHCH3
I
CH3
B
36. Why does the rearrangement that results in the formation of product B occur?
Answer:
44
The 1,2-alkyl shift is the rearrangement of a secondary carbocation to a more stable tertiary
carbocation.
Chapter 6: Alkenes:
Structure and Reactivity
37. Write the complete stepwise mechanism for the following reaction. Show all intermediate structures and
all electron flow with arrows.
H30H3
H3aCH3
HBr
..
Answer:
CH3
II;O~
~I3q
\J
..
+ :Br:..
H
~
+
H3C
CH3..
:Br:
..
X/
Br
CH3
~
Predict the major organic product for each reaction below.
38.
c5
Hi ..
Answer:
H3X
c5
Hi
"U
HCI..
39)=l
ether
Answer:
HCl ..
ether
)=l
Test Itemsfor
McMurry's
Organic Chemistry,
~
Seventh Edition
45
40.
~HBr
~Answer:
Br
~HBr
~~41.
U
KI
~H3P04
I
Answer:
u
KI
~H3P04
if
Predict the structure of the alkene you would use to prepare each alkyl halide below.
42.
~
(only product)
Answer:
u
I
43.
I
I
I
CH3CHCH2CHCH3
Answer:
~
46
Chapter 6: Alkenes:
Structure and Reactivity
The reaction ofisobutene with HBr in ether gives one of the two products below as the major product. Answer
the following questions about this reaction.
A
HBr
~
ether
~Br
Product A
+
xr
Product B
44. Which product would be the major product?
Answer:
Product B
45. Which product would be formed via a primary carbocation?
Answer:
Product A
46. Which product would have a higher energy transition state for the formation of the intermediate leading to
it?
Answer:
Product A
47. Which product is the non-Markovnikov product?
Answer:
Product A
..
48. According to Hammond's Postulate, which product would have a transition state structure most closely
resembling the carbocation intermediate?
Answer:
Product A
49. Which product would be formed by a carbocation experiencing the greatest degree of hyper conjugative
stabilization?
Answer:
Product B
50. Increasing the temperature at which the reaction is run would lead to an increase in the percentage of which
product relative to the other product?
Answer:
Test Itemsfor
Product A
McMurry's
Organic Chemistry,
Seventh Edition
47