MECHANISMS For Final Exam Electrophilic Aromatic Substitution Br H
H
Br
Br
Electron Donating Groups alkyl
OR
H
Br
Br
Br
-HBr
Electron Withdrawing Groups
NR2
acyl
NO2
CN
SO3H
meta directors
SR
X ortho-para director
ortho-para directors
Nucleophilic Aromatic Substitution Cl O2N
NO2
NaOH
O2 N
Cl
OH
NO2
O2N
Cl
NO2
NO2
OH
NO2
O2N
NO2
Cl
OH
NO2
NO2
Carbonyl Addition Reactions Acid Catalyzed Hydration acid activates the carbonyl making it more reactive (more electrophilic) so water can add
HA
O
H
H2O
O
HO
H O H
A
HO
OH
more electrophilic
Base Catalyzed Hydration hydroxide is a more reactive nucleophile than water and can add more readily to the carbonyl
O
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OH
O
OH
H2O
page
HO
OH
Chem Exam Mecahnisms
Mechanism for Imine Formation
O
H2N R
H O
HA
H H N R
H O
H O
A
H N
Up to here this is identical to a hydration with amine as nucleophile instead of water
R
Hemiaminal HA
N
R
A
H N
H N R
imine
-H2O R
H
H O
H N
R
resonance structures
Mechanism for Enamine Formation
O
HN R R
H O
HA
H O
R H N R
H O
A
R N
R
Hemiaminal HA
R
N
R
R N R
A
R N
H enamine
-H2O R
H
H O
R N
R
resonance structures
The only difference is this last step. There is no proton on the nitrogen to come off, so a proton is taken off of the alpha carbon
© Gregory R Cook North Dakota State University
page
Chem Exam Mecahnisms
Mechanism for Acetal Formation
H O
HA
O
H O
H O R
H O
A
O
Up to here this is identical to a hydration with alcohol as nucleophile instead of water
R
Hemiacetal HA
R
H O
R OH O
R
O
-H2O
O
R
R
H
H O
O
R
resonance structures A
R
O
O
R
Acyl Substitution Reactions
Fischer Esterification O
OH
HA OH
R
R
R'OH
OH
H HO OR' R
OH
A
HO OR' R
OH
HA
A
O R
OR'
© Gregory R Cook North Dakota State University
OH R
OR'
page
HO OR'
HO OR'
R
R
OH H
Chem Exam Mecahnisms
Acid Catalyzed Hydrolysis O
HA
H
H
O
OCH3
H2O
O
OCH3
H O H OCH3
H O
OCH3
H O
A
O H OCH3 HA
O
H
A
H
O
OH
O
OH
H O
O H OCH3 H
+
HOCH3
OH
Base Catalyzed Hydrolysis (Saponification) O
OH
O
O
OH
OCH3
O + OH
OCH3
OCH3
O
Acid Catalyzed Hydrolysis of Amides O
HA
H
H
O
NH2
O
NH2
H2 O
H O
NH2
H O H NH2
A
H O
O H NH2 HA
O
A
H
OH
© Gregory R Cook North Dakota State University
H
O OH
page
H O
O OH
O H NH2 H
Chem Exam Mecahnisms