Addition Reactions of Carbon-Carbon Pi Bonds – Part 3 Ni H 2 O 3 CH 2 O C O (CH 2 ) 14 CH 3 CO H C O (CH 2 ) 7 CH=CH(CH 2 ) 7 CH 3 CH 2 O P O O OCH 2 CH 2 N(CH 3 ) 3 Miscellaneous Pi Bond Addition Reactions Do all carbon-carbon pi bond addition reactions... ...involve electrophiles and carbocations? ...follow Markovnikov's rule? •Anti-Markovnikov addition of H 2 O •No electrophile •Markovnikov's rule irrelevant •Catalytic Hydrogenation Examples •Hydroboration-Oxidation CH 3 1. BH 3 2. NaOH, HOOH H CH 3 H OH H } CH 3 CH 3 H 2 Pt CH 3 H H CH 3 Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 1
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Addition Reactions of Carbon-Carbon Pi Bonds – Part 3
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Addition Reactions of Carbon-CarbonPi Bonds – Part 3
Ni
H2
O3
CH2O C
O
(CH2)14CH3
COH C
O
(CH2)7CH=CH(CH2)7CH3
CH2O P
O
O
OCH2CH2N(CH3)3
Miscellaneous Pi Bond Addition Reactions
Do all carbon-carbon pi bond addition reactions...
...involve electrophiles and carbocations?
...follow Markovnikov's rule?
•Anti-Markovnikov addition of H2O
•No electrophile
•Markovnikov's rule irrelevant
•Catalytic Hydrogenation
Examples•Hydroboration-Oxidation
CH31. BH3
2. NaOH, HOOH
H
CH3
H
OHH
}
CH3
CH3
H2
Pt
CH3
H
H
CH3
Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 1
Catalytic Hydrogenation
Catalytic hydrogenation: Addition of H2 in the presence of a catalyst.
Example:
Catalyst usually = Pt, Pd, Ni
Why catalyst needed?
•Bonds lost: C-C pi and H-H sigma Bonds gained: 2 x C-H sigma
•Bonds strengths: Sigma > pi
•Therefore ΔG < 0 (Keq > 1) ... but ΔG‡ (one or more mechanism steps) too high
•Catalyst alters mechanism but not Keq
CH3
CH3Pt
CH3
H
H
CH3
H H
Catalytic Hydrogenation
CH3
CH3
H2
Pt
CH3
H
H
CH3Syn addition
Why syn addition? You are not responsible for this mechanism.
•H2 is not an electrophile
•H2 symmetrical so Markovnikov's rule irrelevant
New bonds on same alkene face
Pt surface
H
R
RR
R
H
Pt surface
H H
RR R
R
Pt surfacePt surface
H2
Pt surface
H2
Pt surface
H H
Pt surface
H2
Pt surface
H HC C
R
R R
R
Pt surface
H2
Pt surface
H HC C
R
R R
R
Pt surface
H H
R
R R
R
Pt surface
H
R
RR
R
H
Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 2
Catalytic Hydrogenation - ApplicationPartially Hydrogenated Vegetable Oil and Margarine
Polyunsaturated fat•Lower melting point (oil)•Susceptible to air oxidation
Monounsaturated fat•Higher melting point (margarine)•Less susceptible to air oxidation
Trans fatHealth concerns
Saturated fatHealth concerns
H2, Ni
and/or
H2, Ni
Addition of Br2 and Cl2
Example: Anti addition
New bonds on opposite alkene faceCH3
CH3Br Br
Br
Br
CH3
CH3
•Br2 has no H so Markovnikov's Rule does not apply
•Mechanism: You are not responsible for this mechanism
Br2 polarized bypi electrons
•Similar reaction for Cl2
Backside attack
CH3
CH3
δ+ δ−Br Br Br
CH3
CH3BrBr
Br
CH3
CH3
Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 3
Hydroboration-Oxidation
Example:
Hydroboration Oxidation
Same as:
•Syn, anti-Markovnikov addition of water
•Compare with H3O+, which gives Markovnikov addition
•Electrophile = BH3 Open octet on boron
CH3BH3
BH2
HCH3
HOOH
HO-
OH
HCH3
CH3
OH
HCH3
1. BH3
2. HOOH, HO-
CH3BH3
BH2
HCH3
Hydroboration-Oxidation
•Hydroboration-oxidation used broadly in laboratory, industrial synthesis
Example:
Artemisinin (anti-malarial)
CH3
CH3
HO
1. BH3
2. HOOH, HO-
H
CH3
CH3
HO
1. BH3
2. HOOH, HO-
CH3
CH3
HO
HOHH H
CH3
CH3
HO
1. BH3
2. HOOH, HO-
CH3
CH3
HO
HO
Additional steps
O
O
O
CH3
CH3H
O
O
H3C
HH H
H H
Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 4
H
CH3
H3C
FAQ: Addition Reaction StereochemistrySyn or anti or mixture?
•Catalytic hydrogenation – syn anti
•Br2 or Cl2 – syn anti
•Hydroboration/oxidation – syn anti
•HBr, H3O+, etc. – syn anti ???
Syn addition
Anti addition
Addition reaction stereochemistry:
Conclusion: H-Br + alkene gives... Anti addition Syn addition A mixture is formed
H
CH3
Br
CH3CH3
CH3
H Br
H
CH3
H3C
Br
CH3
CH3
H Br
Br
H
CH3
CH3
Br
Explore via mechanism...
Ozonolysisozone destruction
Cleavage of C=C or by reaction with ozone (O3).
Example:
Addition stereochemistry: Syn Anti But none at the end
Orientation: Markovnikov addition Anti-Markovnikov addition Both Neither
Electrophile: Alkene O3 Both Neither
Mechanism: You are not responsible for this mechanism
C C
Ph
H
CC
H
CH3
OO O
Ph
H
CC
H
CH3
OO O
C C
OO
O
H
Ph H
CH3Ph
H
CC
H
CH3
OO O
C C
OO
O
H
Ph H
CH3
OO
CO
CH
Ph H
CH3Ph
H
CC
H
CH3
OO O
C C
OO
O
H
Ph H
CH3
(CH3)2SOO
CO
CH
Ph H
CH3Ph
H
CC
H
CH3
OO O
C C
OO
O
H
Ph H
CH3
(CH3)2S
CPh O
H O
H
CCH3
+
OO
CO
CH
Ph H
CH3
Ph
H
CC
H
CH3C
Ph O
H O
H
CCH3
+1. O3
2. (CH3)2S
Chem 14D Lecture Supplement: Addition Reactions of Carbon-Carbon Pi Bonds Part 3 -- Page 5
FAQ: What Must I Know About These Reactions?
You should know...
•Reactants and products
•Stereochemistry: Syn addition, anti addition, mixture, etc.
•Orientation: Markovnikov versus anti-Markovnikov addition
You are not responsible for mechanisms of...
•Catalytic hydrogenation
•Addition of Br2/Cl2
•Hydroboration-oxidation
•Ozonolysis
Familiarity with mechanisms = easier to remember stereochemistry, etc.