按卤素所连接的烃基的结构分类
Saturated halohydrocarbons (饱和卤代烃) Unsaturated halohydrocarbons (不饱和卤代烃) Aromatic halohydrocarbons (芳香卤代烃)
Allylic halides (烯丙型卤代烃, 烯丙基卤) Propgarpyl halides (炔丙型卤代烃) Benzylic halides (苄型卤代烃, 苄基卤)
Stereochemistry
Nu C back side attΒιβλιοθήκη ckNu-C+
Nu-
front side attack
C
Nu
H3CH2CH2C H3C H3CH2C C
H2O H3CH2CH2C Br C H3C acetone H3CH2C
O H
+ H
O
CH2CH2CH3 + HBr C CH3 CH2CH3
Polarizability (可极化度): the ease with which the electron distribution around an atom is distorted by a nearby electric field(核外电子分布受外界电场影响而 发生扭曲变形)
Larger atoms are more polarizable. I > Br > Cl > F S>O
O H C N CH3 CH3
O CH3 S CH3
DMF
DMSO “Naked” anions are highly reactive both as bases and nucleophiles (裸露的负离子具有很强的亲核 性和碱性).
在偶极溶剂中亲核性顺序: F- > Cl- > Br- > I(与碱性顺序一致)
60% S (inversion)
Ion-pair Mechanism(离子对机理)
RL
R+LClose ion-pair (紧密离子对)
R+‖ Lloose ion-pair (松散离子对)
R+ + Lfree ions (自由离子)
Energy Diagram
R3CX
Side Reaction
O ROH H3C OSOCH3 碱 O
CH3OR
硫酸二甲酯是个很好的甲基化试剂， 常用于和醇反应得到甲基醚
O R OS O
CNCH3 RCN
OSO2
G C2H5OH
OC2H5
SN1
G = OCH3 CH3 H Cl NO2 速率 1.0 1.6 3.1 8.4 55
8.2.1.2.3 The nucleophile
v= k[CH3Br][OH-] second order
bimolecular nucleophilic substitution (双分子亲核取代)
Mechanism
≠ Nu: + C L

Nu C L

Nu C
+
:L
Stereochemistry
single-step reaction(一步反应)
8.2.1.2.1 The structures of alkyl groups
SN2 Substituent Methyl 1° 2° Neopentyl 3° Steric effect Compound CH3X CH3CH2X (CH3)2CHX (CH3)3CCH2X (CH3)3CX Relative Rate 30 1 0.02 0.00001 ~0
RX
Formation of Organomatelic Compounds (形成金属有机化合物)
8.2.1 Nucleophilic Substitution (亲核取代)
8.2.1.1 SN1 and SN2
SN2
CH3Br + OH-
80%C2H5OH 55℃
CH3OH + Br-
Kinetics
NuNu
+ CH3Br
HS– CN–
NuCH3 + BrI– CH3O–
SN2 HO– 16,000 Cl– 1,000 NH3 700 H2 O 1
Relative 125,000 125,000 100,000 25,000 reactivity In aqueous ethanol
Polar aprotic solvents(偶极溶剂, 极性非质子溶剂)
The nucleophile attacks the carbon bearing the leaving group from the BACK SIDE.
Inversion of configuration(构型翻转): Walden inversion
Energy Diagram
Side Reaction
Rearrangement and E1
8.2.1.2 Factors affecting SN1 and SN2 • The structures of alkyl groups (烃基的结构)
• Leaving groups (离去基团)
• The nucleophile (亲核试剂) • The solvent (溶剂)
Racemization
H3C C2H5 Cl H3C C2H5 OH 40% R (retention) + HO C2H5 CH3
H2O
C2H5OH (CH2)3CH(CH3)2 (R)-6-Chloro2,6-dimethyloctane
(CH2)3CH(CH3)2
+ HCl (CH2)3CH(CH3)2
8.2 Reactions
Nucleophilic Substitution (亲核取代)：SN1/SN2)
Nu -+ R X
Nu R + X-
Elimination Reactions (消除反应): E1/E2
B- +
Reduction (还原)
H C C X
[H] RH
C C + HB + X-
Vinylic halides (乙烯型卤代烃, 乙烯基卤)
Aryl halides (芳型卤代烃, 芳基卤)
按与卤素相连的碳原子的级数分类
伯(1º )卤代烃 仲(2º )卤代烃 叔(3º )卤代烃
RCH2X
R2CHX
R3CX
按分子中卤素的数目分类
一卤代烷 多卤代烷（邻二卤代烷 偕二卤代烷）
CH2Cl2 二氯甲烷
8.2.1.2.2 Leaving groups
离去基团对SN2和SN1具有类似的影响，但对SN1影响程度更大
Good L (好的离去基团)
Stable (稳定) Weakly basic (碱性弱)
HL Strong acid (强酸)
离去能力
-I > -Br > -Cl >> -F
其它常见的离去基团
-OTs -OMs -ONs -OSO2OR
N N
O OS O O OSCH3 O O OS O
O O S O O R
CH3
对甲基苯磺酸酯基 -OSO2C6H4CH3-p
甲基磺酸酯基
NO2
对硝基苯磺酸酯基 -OSO2C6H4NO2-p 烷基硫酸酯基
NR3
OH2
OR2
Leaving group Relative reactivity
TsO– 60,000 ×
I– 30,000
Br– 10,000
Cl– 200 √
F– 1
HO–, H2N–, RO– ~0
离去基团的离去顺序： -N+≡N > -O+R2 > -OSO2C6H4NO2-p > -OSO2Ph > -OSO2C6H4CH3-p > -OSO2CH3 > -I > -O+H2 > -Br > -Cl
对SN2反应，偶极溶剂比质子溶剂有利
N3 + CH3CH2CH2CH2Br
Solvent Relative reactivity HMPA
Solvent
CH3CN
CH3CH2CH2CH2N3 +
DMF 2,800 DMSO 1,300 H2O 6.6
Br
200,000 5,000
3) Sterically hindered nucleophiles are poor ones (位阻大的试剂亲核性差) 亲核性顺序：CH3O- > CH3CH2O- > (CH3)2CHO- > (CH3)3CO(与碱性顺序相反) SN2
(CH3)2CHOH 12
SN2反应速度: PhCH2X, CH2=CHCH2X > CH3X > 1º RX > 2º RX > 3º RX >> CH2=CHX, PhX
SN1反应速度: PhCH2X , CH2=CHCH2X > 3º RX > 2º RX > 1º RX > CH3X >> CH2=CHX, PhX
对于苄基卤、烯丙基卤， SN1和SN2均容易发生；对于乙烯型卤、芳基卤，SN1 和SN2均难以发生；使用非常强的碱，如NaNH2，将使其发生消除反应，分别 得到炔烃、苯炔(会进一步发生加成) (CH3)3CCH2Cl为何既难以发生SN2又难以发生SN1?
Br + CH3ONa
×
OCH3
?
SN2 ONa + CH3Br