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• The following three slides leads students to realize that free rotation around C=C bonds does not occur at room temperature.
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Characteristics of s and p Bonds s bonds p bonds s bonds formed from end to end p bonds formed from side
interaction to side interaction
______ orbital overlap ______ orbital overlap
a. more, less b. less, more c. same
______ bond ______ bond______ reactive ______ reactive
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s bonds p bonds s bonds formed from end to end p bonds formed from
side interaction to side interaction
______ orbital overlap ______ orbital overlap
a. more, less b. less, more c. same
stronger__ bond 80 – 90 kcal/mole weaker_ bond 66 kcal/moleless__ reactive more__ reactive
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Characteristics of s and p Bonds
cylindrically symmetrical not cylindrically symmetrical
~ > 3-5 kcal/mole p orbitals must be in same required for rotation plane for bond. What
happens to the bond if the orbitals don't overlap?
a. Nothing b. bond becomes stronger c. bond breaks
“Free" rotation How much energy is requiredoccurs at room temp. for rotation?
Will free rotation occur at room temperature?
a. no b. yes c. can’t predict
66
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Alkynes
• Which has the greatest overall bond strength in the 3 structures?
a. C-C bond of ethaneb. C=C of ethylene
c. CC of acetylene d. no difference
H3C CH3 H2C CH2 HC CH
1.54 A 1.33 A 1.20 A
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Which compound will form preferentially? A or B
OHH3PO4
+
A B
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Acid-Base Reactions
When an alkene reacts wit H-X, this is also a Lewis Acid-Base reaction.
Which is the Lewis acid and which is the Lewis base?
a. alkene = Lewis acid, H-X Lewis base
b. alkene = Lewis base, H-X = Lewis acid
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• The next two slides explains the exothermicity of additions across p bonds.
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Overall Reaction: Favorable or Not
• In this reaction, 1 s bond and 1 p bond is being replaced with 2 s bonds.
C C
R R
R R
+ H X C
H
R
R
C
X
R
R
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Overall Reaction: Favorable or Not
What would you expect to be stronger 1 s bond and 1 p bond or 2 s bonds? Would you expect the reaction to be favorable or unfavorable then?
a. 1 s bond and 1 p bond and the reaction would be favorable
b. 1 s bond and 1 p bond and the reaction would be unfavorable
c. 2 s bonds and the reaction would be favorable
d. 2 s bonds and the reaction would be unfavorable
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• Forward Reaction : elimination of H-Br from bromoalkane to give alkene
• Reverse Reaction : What is happening in the reverse reaction?
a. SN2 reaction
b. SN1 reaction
c. E1 reaction
d. E2 reaction
e. Addition reaction
CH3C
CH3
CH3
Br H3C C
CH3
CH
H
H
+ BrH3C
C
CH3
CH2
+ H+
or HBr
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Electron density is easily donated. Why?
a. p bond weaker than s bondb. p electrons more accessiblec. Both a and bd. Electrons on atom with high
electronegativity
CC
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Which of the following could initiate the cationic polymerization of styrene?
Ph ? H2C C
Ph
H nstyrene
C
Ph
Ph Ph
SbCl5-
B
F
F F
F
Al
Cl
Cl Cl
Cl
H-Br
a. b. c. d. e
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Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from 1-methylcyclohexene
SOCl2 N1 D2O 2 Raney Ni, EtOH 3 Mg, Et2O(Li, THF)
4 Cl2 5
6 H2O 7 -OD 8 HCl 9 NaNH2, NH3 10 CH3CH2O-, CH3CH2OH,
11 H2SO4, H2O 12 Na 13 CH3CH2Br 14 PBr3
OHH2SO4,H2O
11
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Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from (bromomethyl)cyclohexane
SOCl2 N1 D2O 2 Raney Ni, EtOH 3 Mg, Et2O(Li, THF)
4 Cl2 5
6 H2O 7 -OD 8 HCl 9 NaNH2, NH3 10 CH3CH2O-, CH3CH2OH,
11 H2SO4, H2O 12 Na 13 CH3CH2Br 14 PBr3
OHH2SO4,H2O
Br
CH3CH2O-
CH3CH2OH,
10,11
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• The next 3 slides compares the mechanism in a biological hydration to the recently covered acid catalyzed hydration.
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Citric Acid Cycle
• aconitase : enzyme (m.w. 89000)
OHO
OOO
O
O
O
OOO
O
O
O
OOO
O
O
OH
aconitase aconitase
elimination hydration
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Hydration of cis-Aconitate to Isocitrate
H
C
-O2C
C
CO2-
-O2C
H
O
H
His 101
101 His H
OH
CH
CO2-
C
-O2C
CO2-
OH
CH
CO2-
C
-O2C
CO2-
H O Ser 642OH
CH
CO2-
C
-O2C
CO2-
HO Ser642
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Hydration of cis-Aconitate to Isocitrate After 180 Flip
Is this the same mechanism as that shown for the addition of water to 2-methypropene using sulfuric acid as a catalyst?
a. Yes b. Noc. Can’t be distinguished
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• The next 2 slides are part of one question.
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An Example of a Biological Electrophilic Addition
• Biosynthesis of a-Terpineol (found in pine oil) PPO
OH
PHO
O
OH
O P
O
O
OH
P
O
OH
O = -OPP a good L
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Which of the following in not a step in the mechanism of the reaction?
OHO H
H
a.
H2O
O H
H
b.
c.
H2O
O H
H
d.
PPO
e.
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Hydroboration
• Which way would the B-H bond prefer to add if steric hindrance wasn’t a factor?
H
B
B
H
H
B
B
H
+
A B C
H
B
A
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Which structures appears to have less electron repulsion between the atoms?
HB
H
H
BH
H
H
A B
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What would be the structure of the polymer formed from cationic polymerization of 2-methylpropene?
a. b. c.
d. e.
CH2 C
CH3
CH3 n
CH C
CH3
n
CH2 C
CH3
H n
CH2
H2C
n
C
CH3
CH3 n
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Which of the following is a step in the mechanism
for the following reaction if it is acid catalyzed?
a. b. c.
d. e.
+ H2O
OH
+ H+
O
+ H2O
H H
+ -OH
OH
+ -OH
OH
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Which of the following is a major product of the following reaction used in carbohydrate synthesis?
a. b. c.
d. e.
O
OH
HOHO
H2SO4+ CH3OH
O
OHHO
HOOH
O
OHHO
HO
HO
O
OHHO
HO
HO
OH
O
OHHO
HO
H3CO
O
OHHO
HOOCH3
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Predict the major stable product of the following reaction.
1. B2H6
2. NaOH, H2O2
OH
HO
BH2 OH OH
A B C D E
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• The next 5 slides asks students to explain experimental results after they have already learned something about electrophilic addition.
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• Bottle contains bromine in water• Left test tube contains cyclohexane• Right test tube contains cyclohexene
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Bromine/H2O is added to each test tube
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After Shaking
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A Chemical Reaction Occurred
• Which compound reacted?
a. Cyclohexane b. Cyclohexene
• What type of bond most likely was involved in the reaction?
a. C-H s bond b. C-C s bond c. p bond
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What might be a product of the reaction?(H2O is a complicating factor covered later)
Br Br
Br
Br
Br
Br
a b c d
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Mechanism of X2
Addition to Alkenes
• In the first step, what is the reactive intermediate formed called?
a. cyclic halide ion
b. cyclic halidium ion
c. cyclic carbocation
d. cyclic halonium ion
e. cyclic halocarbocation
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Mechanism of X2
Addition to Alkenes
• What reaction does the second step look like?
a. E2
b. Addition of HX
c. SN2
d. SN1
e. E1
(reaction of bromide anion with cyclic halonium ion)
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Mechanism of X2
Addition to Alkenes
• Why does only the trans product form?
a. The reactive intermediate is resonance stabilized.
b. The reactive intermediate is stabilized by the alkyl groups.
c. SN2 reactions require backside displacement.
d. The trans product is more stable.
e. The bromide ion is too unreactive.
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Br2, CH3OH
CH3
OHBr
H
CH3
OCH3Br
H
OCH3
CH3Br
H
OH
CH3Br
H
Br
CH3H
Br
a. b. c. d. e.
Predict the major product of the following reaction.
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Catalytic Hydrogenation of Alkenes
Does this appear to be a syn or anti addition? a. syn b. anti c. neither
CH3
CH3
H
HCH3
CH3
H2, "Pt",
high pressure
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Carbenes
• Based on this structure, would you expect a carbene to be an electrophile or nucleophile?
a. nucleophile b. electrophile c. neither d. both
R
C
R
- only 2 bonds
- 6 valence e -
C
R
R
p
"sp2 hybridized C"
"sp2 hybrid orbital"
(
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O
H H
O
+
1. O3
2. Zn, H2Oalkene ?
a. b.
c. d.
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Oxidation of Alkenes to Diols
• How could the trans diol be synthesized from cyclohexene?
OH
OH
1. MCPBA 2. (1. OsO4 2. Na2SO3, H2O) 3. PtO2
4. KMnO4, H2O, OH- 5. Cl2, H2O 6. excess NaOH, H2O
7. H2SO4, H2O 8. BH3 9. H2O2, NaOH
16 or 56
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Predict the major stable product(s) of the following reaction.
H3C
C C
CH2CH3
H
H
Br2, CCl4
Br
C C
Br
H3C CH2CH3
HH
Br
C C
Br
H HCH2CH3H3C
Br
C C
Br
H CH2CH3
HH3C
Br
C C
Br
H3C HCH2CH3H
Br
C C
CCl3
H3C CH2CH3
HH
Br
C C
CCl3
H HCH2CH3H3C
Cl3C
C C
Br
H CH2CH3
HH3C
Br
C C
CCl3
H3C HCH2CH3H
Br
C C
Br
H3C CH3
HH
++
a. b.
c.
+ +
d.
e.
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Predict the major stable product(s) of the following reaction.
O O O
C C
HO OH
H H
C C
HO OH
HH
C C
HO OH
HH
C C
O3Os OH
HH
C C
HO OsO3
HH
a. b.
c. d.
e.
1. OsO4
2. Na2SO3, H2O
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How could the oxirane be synthesized from but-2-yne?
H3C C C CH3
O?
1. MCPBA 2. (1. OsO4 2. Na2SO3, H2O) 3. H2, PtO2
4. H2, Pd/CaCO3, PbO 5. CH2O h 6. (1. BH3 2. H2O2, NaOH )
7. H2SO4, H2O 8. (1. Hg(OAc)2, H2SO4, H2O 2. NaBH4, NaOH )
9. (1. Na, NH3 2. NH4OH)
41
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• In the biosynthesis of fatty acids, the crotonyl ACP is converted to butyryl ACP. What type of reaction does it formally appear to be?
a. dehydration b. hydration
c. alkyl shift d. hydrogenation
e. hydride shift
H3C CH
CH
C
O
SACP H3CH2C
H2C C
O
SACP
NADPHmultienzymecomplex