有机反应Chapter 1

Mechanism involved: (a) Stable, reasonable species (b) Protonation and Removal of Protons (c) Intramolecular proton transfer
How do we know whether they are stable or not under a particular reaction condition?
O O C CD3 H H
BrMg O O C CH3 D
O O C CH3 D H
BrMg O O C CD3 H O D2 O C CD3 D H O C CD3 C CD3
CH3 MgBr
C CH3
C CH3
+
CH3 MgBr
C CD3
CH3D
+
CH4
Isotope Effect
O O
H2O
C CH3
O C CH3
pKa: pKa: 26.5
Why doesn’t the hydrogen abstraction happen at methyl group?
The protons of CH2 are more acidic than those of CH3
Mechanisms of Organic Reaction
H
(2) MeO
O
O
Cl
NaI Acetone
MeO
O
O
+
HI
+
Cl
-
Examples and Problems, You Will Start to Develop a Feel for This as Well.
Dual Functions of a Lewis Base as: Base: abstract a proton Nucleophile: Nucleophile: react with a positively charged atom
OTg COOMe
Na2CO3
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
Mechanism
I NaI Acetone MeO O O I
Tip
Cl
I
(1) MeO
O
O
+
Cl
-
Predicting the Course of a Reaction Can Be a More Difficult Task. However, As You Work Through a Number of
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
O
2.2 ElectronElectron-Rich Species: Bases or Nucleophiles? Nucleophiles?
O C CH2 CH3 CH3 O C CH O C CH3

CH3 MgBr
H CH H
C
+
C
CH4
CH3
pKa: pKa: 9.0
O C CH3 CH3 CH2
O CH3 MgBr O C CH2 CH3 CH2 BrMg O C CH2 O D2O CH2D C CH2 O C CH3 O C CH3
HO O2N
Mechanism
SOCl2
+
H CH2
C
+ CH4
MeO
O
O
OH
MeO
O
O
Cl
NaI Acetone
MeO
O
O
I
OH COOMe
TgO O2N
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
1.9 Nucleophiles / Electrophiles Definition: Nucleophiles / Electrophiles 亲核剂 / 亲电剂
C8H17 O H3C O Cl N
O C CH3 O: Esterification
H O C H O H O C H CH3 O HOCH3 H
O
CH3
O
CH3 O
CH3
CH3
C OH
C O H OCH3
+
CH3
CH3OH
+
O H
O C CH3 O OH2 CH3
O CH3 H C O H OH2 O
Mechanisms of Organic Reaction
2.2 ElectronElectron-Rich Species: Bases or Nucleophiles? Nucleophiles?
O O C CH3 D D
2.2 ElectronElectron-Rich Species: Bases or Nucleophiles? Nucleophiles?
PhSO3H 5%HCl
NH2
- 2.8 0
PhSO3Cl NH2
H2O
H2 N NH2
13.4
HN NH2
Dual functions of electronelectron-rich species MediaMedia-dependant mechanism: solvent, pH Structural Conformity between starting materials and products
Basic expression: balancing equations (atoms, charge), arrow direction (electron flow) Driving force: leaving groups/stable species Stability of intermediates: octet rule,structure, solvent
O O C CH3 H H
BrMg O O C CH3 H
O H2O C CH3 H H O C CH3
BrMg O O C CH3 H
O H2O C CH3 H H O C CH3
CH3 MgBr

C CH3
C CH3
+
CH4
CH3 MgBr

C CH3
C CH3
+
CH4
What’s the side product after workup?
What species are stable in strong acid like HCl ?

H

O H
H
O
H
?
H
O
H
?
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
Example 1: Hydrolysis of Methyl Acetate in NaOH
pKa values
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
Typical Acidities of Common Organic and Inorganic Substances
Conjugate Acid
HCl
Principles for writing mechanisms (game rule)
OMgBr
c. CH3 MgBr +
Cl
d.
+ H Cl
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
Prolegomena

2.1 Mechanisms in Acidic and Basic Media
In writing a reaction mechanism, ……, ……, These mechanisms do not have any objective existence; they are merely our attempt to represent what is going on in a reaction…… reaction…… we are free to write whatever mechanism we choose, subject only to the constraint that we conform to generally accepted mechanistic patterns.
CH3
O CH3 C O H O
CH3
+
H 3O
O CH3 C O CH3
Incorrect !
+
H3O
+
H2O
1
Mechanisms of Organic Reaction
Mechanisms of Organic Reaction
Example 2: Esterification
2.1 Mechanisms in Acidic and Basic Media
1
2
C H
3
H
C CH3
CH3
H 1 CH H
2
O C
O
D O O C CD3 H CD3
3
CH2