第三章不饱和碳氢化合物
Unsaturated Hydrocarbons
第三章重点内容一、不饱和碳氢化合物的命名二、不饱和碳氢化合物的稳定性三、共振理论和分子轨道理论简介四、芳香性与Hückel’s规则一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（1）母体——含有双键的最长碳链
?（2）编号——给双键以尽可能小的编号
CH
3
CH
2
CH
2
CH
2
CCH
2
CH
3
CH
2
1
23456
正确的母体名为：
而不是：
1-
己烯
1-hexene
庚烷
10'
9'
8'
7'
6'
5'
4'
7
3'
8
2'
1'
6
5
4
3
2
1
9
10正确的名称是 3,6-二甲基-5-癸烯
3,6-dimethyl-5-decene
一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（2）编号——环的1位可以省略
H
3
C
CH
3
CH
3
CH
2
CH
3
1,6-
二甲基环己烯
1,6-dimethylcyclohexene
1-
甲基
-5-
乙基环己烯
5-ethyl-1-methylcyclohexene
一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（3）构型——使用“Z”，“E”表示
CC
B
D
A
C
若
A>C
B>D
为
"Z"
型若
A>C
B<D
为
"E"
型
10'
9'
8'
7'
6'
5'
4'
7
3'
8
2'
1'
6
5
4
3
2
1
9
10正确的名称是 (E)-3,6-二甲基-5-癸烯
(E)-3,6-dimethyl-5-decene
(E)-3-
甲基
-6-
乙基
-4-
辛烯
(E)-3-ethyl-6-methyl-4-octene
一、Nomenclature of Unsatuated Hydrocarbons
? 2、多烯烃的命名
?母体——含有尽可能多双键的最长碳链
CH
3
CH CH CH
2
CH
2
C
CH
2
CH
2
CH
2
CH
3
2-
丙基
-1,5-
庚二烯
2-propyl-1,5-heptadiene
(5E,9E)-2,6,10-
三甲基
-2,5,9-
十二碳三烯
(5E,9E)-2,6,10-trimethyl-2,5,9-dodecatriene
一、Nomenclature of Unsatuated Hydrocarbons
? 3、炔烃的命名
?（1）母体——含有叁键的最长碳链
?（2）编号——给叁键以尽可能小的编号
CH
3
CHCHC
CH
3
CH
3
CCH
2
CHCH
2
CH
3
CH
3
2,3,7-
三甲基
-4-
壬炔
2,3,7-trimethyl-4-nonyne
CH
3
CHCHC
CH
3
CH
3
CCH
2
CHC
CH
3
CH
3,7,8-
三甲基
-1,5-
壬二炔
3,7,8-trimethyl-1,5-nonadiyne
一、Nomenclature of Unsatuated Hydrocarbons
? 4、多烯多炔的命名
?,某几烯几炔”，英文词尾为“enyne”
?双键和叁键的数目使用“di”、“tri”等表示。
CH
3
CCH
2
CH
2
CHC
CH
2
CH
3
CH
2,5-
二甲基
-1-
庚烯
-6-
炔
2,5-dimethyl-1-hepten-6-yne
CH
3
C CCHCH
2
CH
CH CH
2
CH
2
HC CCHCH
CH CH
2
CHCH
2
CH
3
4-
乙烯基
-1-
庚烯
-5-
炔
4-ethenyl-1-hepten-5-yne
3-
乙炔基
-1,4-
庚二烯
3-aceylenyl-1,4-heptadiene
一、Nomenclature of Unsatuated Hydrocarbons
? 5、苯环衍生物的命名
? ——取代基碳链不太长或不复杂的情况下，多采用以苯或带官能团的苯环为母体；
? ——侧链很长或很复杂时，以苯作取代基，要提醒同学们的是英文名中苯为benzene，但苯基为phenyl，而代表的却是苯甲基(常称为苄基，C
6
H
5
CH
2
-)。
CH
3
CH
2
CH
3
1-甲基-2-乙基-4-异丙基苯
2-ethyl-4-isopropyl-1-methylbenzene
(Z)-2,4-二甲基-3-苯基-3-庚烯
(Z)-2,4-dimethyl-3-phenyl-3-heptene
一、Nomenclature of Unsatuated Hydrocarbons
? 5、苯环衍生物的命名
?苯环含有官能团部分的命名请与第四章的能团化合物命名结合起来自学不饱和烃基的名称一览表
C
6
H
5
CH
2
-
苯甲基（苄基）
benzyl
C
6
H
5
-
苯基
phenyl
CH≡CCH
2
-
炔丙基
propargyl
CH
3
CH=CH-
丙烯基
1-propenyl
CH
2
=CHCH
2
-
烯丙基
2-propenyl
(allyl)
CH≡C-
乙炔基
ethynyl
CH
2
=CH-
乙烯基
Ethenyl
结构中文名称英文名称二、Stability of Unsaturated Hydrocarbons
?化合物的稳定性
——越稳定，越不容易发生化学反应；反过来，反应中更容易形成。
——不稳定，表示化合物处在高能量状态，
容易发生化学变化。
?燃烧热（ΔH
c
）
—— CO
2
+ H
2
O
——燃烧热越高，化合物越不稳定二、Stability of Unsaturated Hydrocarbons
?生成热（ΔH
f
）
——
——生成热越高，化合物越稳定
nC + (n+1)H
2
C
n
H
2n+2
+ H
f
?氢化热（ΔH
h
)
——双键+ nH2饱和烃
——判断双键的稳定性
——氢化热越高，化合物越不稳定二、Stability of Unsaturated Hydrocarbons
? Class of dienes
CH
3
CH CH CH
2
CH CH
2
CH
3
CH C CHCH
2
CH
3
CH
3
CH CH CH CHCH
3
孤立二烯烃累积二烯烃共轭二烯烃
an isolated diene a cumulated diene
a conjugated diene
二、Stability of Unsaturated Hydrocarbons
? Stability of dienes
C
-70.5 kcal/mole
-60.8 kcal/mole
-54.1 kcal/mole
+ 2H
2
+ 2H
2
+ 2H
2
The difference between the heats reflects the
differnce in stability between the nonconjugated
and conjugated dienes
conjugated > isolated > cumulated dienes
二、Stability of Unsaturated Hydrocarbons
? Structure and Stability of Benzene
1,All the carbon are sp
2
hybridized (ring plane)
2,The p orbital on each carbon can overlap with two
adjacent p orbitals.
3,Particularly stable
二、Stability of Unsaturated Hydrocarbons
? Structure and Stability of Benzene
An unusually large resonance energy (151kJ/mole)
3 H
2
H
0
- 49.8 kacl/mol (208 kJ/mol)
benzene
experimental
Questions
1,Why is a conjugated diene more
stable than an isolated diene?
2,Why is benzene a particularly
stable compound?
Explanation 1——价键理论
Single bond between C-C formed by sp
2
-sp
2
overlap,the length of the bond is shorter,
therefore the bond is stronger.
CH
3
—CH
3
Csp
3
-Csp
3
154 pm
CH
2
=CH—CH
3
Csp
2
-Csp
3
150 pm
CH2=CH—CH=CH
2
Csp
2
-Csp
2
146 pm
C
6
H
6
Csp
2
-Csp
2
139 pm
Explanation 2 ——共轭与共振理论电子离域与共振
Electron Delocalization and Resonance
? p-electrons in conjugated dienes and benzene are
delocalized
?定域电子：被限制在两个原子核区域内运动的电子
?离域电子：不局限于两个原子核区域内运动的电子
?这种电子的离域作用我们也称之为共轭作用
H
2
C
H
C
H
C
CH
2
?上述非经典结构式较好地表示了电子的离域，但是却无法告诉我们该结构中含有多少双键。因此化学常用共振结构（共振极限结构）来表示。
Explanation 2 ---共振理论
Some basic concepts
? A compound with delocalized electrons is said to
have resonance（共振）
? The approximate structure using localized
electrons is called a resonance contributor,a
resonance structure,or a contributing
resonance structure（共振结构或共振极限式）
? The actual structure,drawn using delocalized
eletrons,is called a resonance hybrid（共振杂化体）
How to drow resonance contributors
In order to draw contributors,the electrons in
one resonance contributor are moved to
generate the next contributor.
Rules for Drawing Resonance Contributors
1,Only electrons move,The nuclei of the
atoms never move
2,The only electrons that can move are π
electrons and nonbonding electrons
3,The total number of electrons in the
molecule does not change,neither do the
numbers of paired and unpaired electrons
The electrons can be moved
in one of the following ways
1,Move πelectrons toward a positive charge
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
δ
+
δ
+
δ
+
δ
+
The electrons can be moved
in one of the following ways
2,Move πelectrons toward a πbond
The electrons can be moved
in one of the following ways
3,Move a nonbonding pair of electrons toward a πbond
The electrons can be moved
in one of the following ways
4,Move a single nonbonding electron toward a
πbond
CH
2
CH
2
CH
2
CH
2
CH
2
1
23
4
5
CH
2
δ
δ
δ
δ
Explanation 2 ——共振理论
1.共振杂化体比它的任何一个共振式都要稳定
2.共价键数目越多的共振式越稳定
3.共振式中的电荷越分散就越稳定
4.越稳定的共振式对共振杂化体的贡献越大
CHH
2
CCHCH
2 CH
2
CH CH CH
2
CH
2
CH CH CH
2
CH
2
CH CH CH
2
CHH
2
CCHCH
2
CHH
2
CCHCH
2
CH
2
CH
2
CH CH
1,3-butadiene
Explanation 2 ——共振理论
5.相对稳定的共振式的数目越多，共振杂化体越稳
Explanation 2 ——共振理论
6.共振式越接近等价，共振杂化体越稳定
Expanation 3 ——分子轨道理论
? Introduction of Molecular Theory
? Orbitals are conserved ---- the number
of atomic orbitals combined must equal
the number of molecular orbitals formed
=
H
H
H,H
1s atomic
orbital
1s atomic
orbital
bonding molecular orbital
.
.
Introduction of Molecular Theory
? The 1s atomic orbitals can combine in
one of two ways
+
+
+
wave reinforce
each other,
resulting in
bonding
+
+
node
wave cancel
each other
and no bond
forms
Introduction of Molecular Theory
? —— The 1s atomic orbitals combine in a
way that enhance each other,similar to two
light waves or two sound waves that
reinforce each other,It is a sigma bonding
molecular orbitalσ键
? —— The 1s atomic orbitals can also combine
in a way that cancel each other,producing a
node between the nuclei,It is a sigma
antibonding molecular orbitalσ* 键
Introduction of Molecular Theory
? There are two electrons in the bonding
molecular orbital,but the antibonding
molecular orbital contains no electron
H
H
H,H
1s atomic
orbital
1s atomic
orbital
bonding molecular orbital
.
.
antibonding molecular orbital
Introduction of Molecular Theory
? Similar as p-orbital combines to σbond
and σ*bond
Introduction of Molecular Theory
? Side-to-side overlapping of in-phase p
orbitals produces a bonding pi-
molecular orbitalπ键
? Side-to-side overlapping of out-of-
phase p orbitals producing an
antibonding pi- molecular orbitalπ* 键
2p atomic
orbital
2p atomic
orbital
bonding pi-molecular orbital
Expanation 3 ——分子轨道理论
?丁二烯分子轨道能级图分子轨道理论阐述1，3-丁二烯的结构分子轨道理论阐述苯的结构
?苯分子轨道能级图
? 6个电子分布在
?成键的分子轨道上
IV.Aromaticity and Hückel’s Rule
? Benzene ------ particularly stable because of
the resonance energy
? But cyclobutadiene and cyclooctatetraene
containscyclic two or four Pi-bond,they are
not stable,
IV,Aromaticity and Hückel’s Rule
?In 1938,a German chemist Erich Huckel
recognized the difference between them and
generalized this observation into Huckel’s
Rule
?---any plannar,cyclic,conjugated system
containing (4n+2) Pi electrons (n=1,2,3,….)
experiences unusual aromatic stabilization
It is also called 4n + 2 rule
IV,Aromaticity and Hückel’s Rule
芳香化合物的结构特点:
1.有一个环状的共轭体系，共轭体系中的原子均在一个平面内
2.环平面上下两侧存在由p轨道电子相互重叠而形成的环状离域p电子云（大p键）
3.组成大p键的p轨道电子数必须符合Huckel’s
Rule:
a,有4n + 2个p电子的环烯烃具有芳香性
b,有4n 个p电子的环烯烃具有反芳香性和非芳香性
IV,Aromaticity and Hückel’s Rule
芳香性>>开链烯烃
4 + 2
芳香性>>开链烯烃
4 + 2
非芳香性接近开链烯烃
4 + 4
芳香性>>开链烯烃
4 + 2
反芳香性<< 开链烯烃
4
是否具芳香性稳定性
P电子数环烯烃
IV,Aromaticity and Hückel’s Rule
? Molecular Orbital theory
? ------- in benzene
6
IV,Aromaticity and Hückel’s Rule
? Molecular Orbital theory
? ------- in cyclooctatetraene
?从分子轨道处理的情况看：环辛四烯应具有反芳香性，但实际上不是平面分子分子内单双键交替，
属于非芳香分子
8
IV,Aromaticity and Hückel’s Rule
? Other member rings
0
-1
-2
1
2
0.618
-1.618
1.247
-.445
-1.802
1.414
-1.414
IV,Aromaticity and Hückel’s Rule
? Other aromatic molecular
IV,Aromaticity and Hückel’s Rule
请思考：
1、为什么[10]-轮烯没有芳香性？而1，6-桥连[10]-轮烯具有芳香性？
2、[14]-轮烯，[18]-轮烯，[22]-轮烯又如何？
第三章重点内容一、不饱和碳氢化合物的命名二、不饱和碳氢化合物的稳定性三、共振理论和分子轨道理论简介四、芳香性与Hückel’s规则
Unsaturated Hydrocarbons
第三章重点内容一、不饱和碳氢化合物的命名二、不饱和碳氢化合物的稳定性三、共振理论和分子轨道理论简介四、芳香性与Hückel’s规则一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（1）母体——含有双键的最长碳链
?（2）编号——给双键以尽可能小的编号
CH
3
CH
2
CH
2
CH
2
CCH
2
CH
3
CH
2
1
23456
正确的母体名为：
而不是：
1-
己烯
1-hexene
庚烷
10'
9'
8'
7'
6'
5'
4'
7
3'
8
2'
1'
6
5
4
3
2
1
9
10正确的名称是 3,6-二甲基-5-癸烯
3,6-dimethyl-5-decene
一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（2）编号——环的1位可以省略
H
3
C
CH
3
CH
3
CH
2
CH
3
1,6-
二甲基环己烯
1,6-dimethylcyclohexene
1-
甲基
-5-
乙基环己烯
5-ethyl-1-methylcyclohexene
一、Nomenclature of Unsatuated Hydrocarbons
? 1、单烯烃的命名
?（3）构型——使用“Z”，“E”表示
CC
B
D
A
C
若
A>C
B>D
为
"Z"
型若
A>C
B<D
为
"E"
型
10'
9'
8'
7'
6'
5'
4'
7
3'
8
2'
1'
6
5
4
3
2
1
9
10正确的名称是 (E)-3,6-二甲基-5-癸烯
(E)-3,6-dimethyl-5-decene
(E)-3-
甲基
-6-
乙基
-4-
辛烯
(E)-3-ethyl-6-methyl-4-octene
一、Nomenclature of Unsatuated Hydrocarbons
? 2、多烯烃的命名
?母体——含有尽可能多双键的最长碳链
CH
3
CH CH CH
2
CH
2
C
CH
2
CH
2
CH
2
CH
3
2-
丙基
-1,5-
庚二烯
2-propyl-1,5-heptadiene
(5E,9E)-2,6,10-
三甲基
-2,5,9-
十二碳三烯
(5E,9E)-2,6,10-trimethyl-2,5,9-dodecatriene
一、Nomenclature of Unsatuated Hydrocarbons
? 3、炔烃的命名
?（1）母体——含有叁键的最长碳链
?（2）编号——给叁键以尽可能小的编号
CH
3
CHCHC
CH
3
CH
3
CCH
2
CHCH
2
CH
3
CH
3
2,3,7-
三甲基
-4-
壬炔
2,3,7-trimethyl-4-nonyne
CH
3
CHCHC
CH
3
CH
3
CCH
2
CHC
CH
3
CH
3,7,8-
三甲基
-1,5-
壬二炔
3,7,8-trimethyl-1,5-nonadiyne
一、Nomenclature of Unsatuated Hydrocarbons
? 4、多烯多炔的命名
?,某几烯几炔”，英文词尾为“enyne”
?双键和叁键的数目使用“di”、“tri”等表示。
CH
3
CCH
2
CH
2
CHC
CH
2
CH
3
CH
2,5-
二甲基
-1-
庚烯
-6-
炔
2,5-dimethyl-1-hepten-6-yne
CH
3
C CCHCH
2
CH
CH CH
2
CH
2
HC CCHCH
CH CH
2
CHCH
2
CH
3
4-
乙烯基
-1-
庚烯
-5-
炔
4-ethenyl-1-hepten-5-yne
3-
乙炔基
-1,4-
庚二烯
3-aceylenyl-1,4-heptadiene
一、Nomenclature of Unsatuated Hydrocarbons
? 5、苯环衍生物的命名
? ——取代基碳链不太长或不复杂的情况下，多采用以苯或带官能团的苯环为母体；
? ——侧链很长或很复杂时，以苯作取代基，要提醒同学们的是英文名中苯为benzene，但苯基为phenyl，而代表的却是苯甲基(常称为苄基，C
6
H
5
CH
2
-)。
CH
3
CH
2
CH
3
1-甲基-2-乙基-4-异丙基苯
2-ethyl-4-isopropyl-1-methylbenzene
(Z)-2,4-二甲基-3-苯基-3-庚烯
(Z)-2,4-dimethyl-3-phenyl-3-heptene
一、Nomenclature of Unsatuated Hydrocarbons
? 5、苯环衍生物的命名
?苯环含有官能团部分的命名请与第四章的能团化合物命名结合起来自学不饱和烃基的名称一览表
C
6
H
5
CH
2
-
苯甲基（苄基）
benzyl
C
6
H
5
-
苯基
phenyl
CH≡CCH
2
-
炔丙基
propargyl
CH
3
CH=CH-
丙烯基
1-propenyl
CH
2
=CHCH
2
-
烯丙基
2-propenyl
(allyl)
CH≡C-
乙炔基
ethynyl
CH
2
=CH-
乙烯基
Ethenyl
结构中文名称英文名称二、Stability of Unsaturated Hydrocarbons
?化合物的稳定性
——越稳定，越不容易发生化学反应；反过来，反应中更容易形成。
——不稳定，表示化合物处在高能量状态，
容易发生化学变化。
?燃烧热（ΔH
c
）
—— CO
2
+ H
2
O
——燃烧热越高，化合物越不稳定二、Stability of Unsaturated Hydrocarbons
?生成热（ΔH
f
）
——
——生成热越高，化合物越稳定
nC + (n+1)H
2
C
n
H
2n+2
+ H
f
?氢化热（ΔH
h
)
——双键+ nH2饱和烃
——判断双键的稳定性
——氢化热越高，化合物越不稳定二、Stability of Unsaturated Hydrocarbons
? Class of dienes
CH
3
CH CH CH
2
CH CH
2
CH
3
CH C CHCH
2
CH
3
CH
3
CH CH CH CHCH
3
孤立二烯烃累积二烯烃共轭二烯烃
an isolated diene a cumulated diene
a conjugated diene
二、Stability of Unsaturated Hydrocarbons
? Stability of dienes
C
-70.5 kcal/mole
-60.8 kcal/mole
-54.1 kcal/mole
+ 2H
2
+ 2H
2
+ 2H
2
The difference between the heats reflects the
differnce in stability between the nonconjugated
and conjugated dienes
conjugated > isolated > cumulated dienes
二、Stability of Unsaturated Hydrocarbons
? Structure and Stability of Benzene
1,All the carbon are sp
2
hybridized (ring plane)
2,The p orbital on each carbon can overlap with two
adjacent p orbitals.
3,Particularly stable
二、Stability of Unsaturated Hydrocarbons
? Structure and Stability of Benzene
An unusually large resonance energy (151kJ/mole)
3 H
2
H
0
- 49.8 kacl/mol (208 kJ/mol)
benzene
experimental
Questions
1,Why is a conjugated diene more
stable than an isolated diene?
2,Why is benzene a particularly
stable compound?
Explanation 1——价键理论
Single bond between C-C formed by sp
2
-sp
2
overlap,the length of the bond is shorter,
therefore the bond is stronger.
CH
3
—CH
3
Csp
3
-Csp
3
154 pm
CH
2
=CH—CH
3
Csp
2
-Csp
3
150 pm
CH2=CH—CH=CH
2
Csp
2
-Csp
2
146 pm
C
6
H
6
Csp
2
-Csp
2
139 pm
Explanation 2 ——共轭与共振理论电子离域与共振
Electron Delocalization and Resonance
? p-electrons in conjugated dienes and benzene are
delocalized
?定域电子：被限制在两个原子核区域内运动的电子
?离域电子：不局限于两个原子核区域内运动的电子
?这种电子的离域作用我们也称之为共轭作用
H
2
C
H
C
H
C
CH
2
?上述非经典结构式较好地表示了电子的离域，但是却无法告诉我们该结构中含有多少双键。因此化学常用共振结构（共振极限结构）来表示。
Explanation 2 ---共振理论
Some basic concepts
? A compound with delocalized electrons is said to
have resonance（共振）
? The approximate structure using localized
electrons is called a resonance contributor,a
resonance structure,or a contributing
resonance structure（共振结构或共振极限式）
? The actual structure,drawn using delocalized
eletrons,is called a resonance hybrid（共振杂化体）
How to drow resonance contributors
In order to draw contributors,the electrons in
one resonance contributor are moved to
generate the next contributor.
Rules for Drawing Resonance Contributors
1,Only electrons move,The nuclei of the
atoms never move
2,The only electrons that can move are π
electrons and nonbonding electrons
3,The total number of electrons in the
molecule does not change,neither do the
numbers of paired and unpaired electrons
The electrons can be moved
in one of the following ways
1,Move πelectrons toward a positive charge
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
δ
+
δ
+
δ
+
δ
+
The electrons can be moved
in one of the following ways
2,Move πelectrons toward a πbond
The electrons can be moved
in one of the following ways
3,Move a nonbonding pair of electrons toward a πbond
The electrons can be moved
in one of the following ways
4,Move a single nonbonding electron toward a
πbond
CH
2
CH
2
CH
2
CH
2
CH
2
1
23
4
5
CH
2
δ
δ
δ
δ
Explanation 2 ——共振理论
1.共振杂化体比它的任何一个共振式都要稳定
2.共价键数目越多的共振式越稳定
3.共振式中的电荷越分散就越稳定
4.越稳定的共振式对共振杂化体的贡献越大
CHH
2
CCHCH
2 CH
2
CH CH CH
2
CH
2
CH CH CH
2
CH
2
CH CH CH
2
CHH
2
CCHCH
2
CHH
2
CCHCH
2
CH
2
CH
2
CH CH
1,3-butadiene
Explanation 2 ——共振理论
5.相对稳定的共振式的数目越多，共振杂化体越稳
Explanation 2 ——共振理论
6.共振式越接近等价，共振杂化体越稳定
Expanation 3 ——分子轨道理论
? Introduction of Molecular Theory
? Orbitals are conserved ---- the number
of atomic orbitals combined must equal
the number of molecular orbitals formed
=
H
H
H,H
1s atomic
orbital
1s atomic
orbital
bonding molecular orbital
.
.
Introduction of Molecular Theory
? The 1s atomic orbitals can combine in
one of two ways
+
+
+
wave reinforce
each other,
resulting in
bonding
+
+
node
wave cancel
each other
and no bond
forms
Introduction of Molecular Theory
? —— The 1s atomic orbitals combine in a
way that enhance each other,similar to two
light waves or two sound waves that
reinforce each other,It is a sigma bonding
molecular orbitalσ键
? —— The 1s atomic orbitals can also combine
in a way that cancel each other,producing a
node between the nuclei,It is a sigma
antibonding molecular orbitalσ* 键
Introduction of Molecular Theory
? There are two electrons in the bonding
molecular orbital,but the antibonding
molecular orbital contains no electron
H
H
H,H
1s atomic
orbital
1s atomic
orbital
bonding molecular orbital
.
.
antibonding molecular orbital
Introduction of Molecular Theory
? Similar as p-orbital combines to σbond
and σ*bond
Introduction of Molecular Theory
? Side-to-side overlapping of in-phase p
orbitals produces a bonding pi-
molecular orbitalπ键
? Side-to-side overlapping of out-of-
phase p orbitals producing an
antibonding pi- molecular orbitalπ* 键
2p atomic
orbital
2p atomic
orbital
bonding pi-molecular orbital
Expanation 3 ——分子轨道理论
?丁二烯分子轨道能级图分子轨道理论阐述1，3-丁二烯的结构分子轨道理论阐述苯的结构
?苯分子轨道能级图
? 6个电子分布在
?成键的分子轨道上
IV.Aromaticity and Hückel’s Rule
? Benzene ------ particularly stable because of
the resonance energy
? But cyclobutadiene and cyclooctatetraene
containscyclic two or four Pi-bond,they are
not stable,
IV,Aromaticity and Hückel’s Rule
?In 1938,a German chemist Erich Huckel
recognized the difference between them and
generalized this observation into Huckel’s
Rule
?---any plannar,cyclic,conjugated system
containing (4n+2) Pi electrons (n=1,2,3,….)
experiences unusual aromatic stabilization
It is also called 4n + 2 rule
IV,Aromaticity and Hückel’s Rule
芳香化合物的结构特点:
1.有一个环状的共轭体系，共轭体系中的原子均在一个平面内
2.环平面上下两侧存在由p轨道电子相互重叠而形成的环状离域p电子云（大p键）
3.组成大p键的p轨道电子数必须符合Huckel’s
Rule:
a,有4n + 2个p电子的环烯烃具有芳香性
b,有4n 个p电子的环烯烃具有反芳香性和非芳香性
IV,Aromaticity and Hückel’s Rule
芳香性>>开链烯烃
4 + 2
芳香性>>开链烯烃
4 + 2
非芳香性接近开链烯烃
4 + 4
芳香性>>开链烯烃
4 + 2
反芳香性<< 开链烯烃
4
是否具芳香性稳定性
P电子数环烯烃
IV,Aromaticity and Hückel’s Rule
? Molecular Orbital theory
? ------- in benzene
6
IV,Aromaticity and Hückel’s Rule
? Molecular Orbital theory
? ------- in cyclooctatetraene
?从分子轨道处理的情况看：环辛四烯应具有反芳香性，但实际上不是平面分子分子内单双键交替，
属于非芳香分子
8
IV,Aromaticity and Hückel’s Rule
? Other member rings
0
-1
-2
1
2
0.618
-1.618
1.247
-.445
-1.802
1.414
-1.414
IV,Aromaticity and Hückel’s Rule
? Other aromatic molecular
IV,Aromaticity and Hückel’s Rule
请思考：
1、为什么[10]-轮烯没有芳香性？而1，6-桥连[10]-轮烯具有芳香性？
2、[14]-轮烯，[18]-轮烯，[22]-轮烯又如何？
第三章重点内容一、不饱和碳氢化合物的命名二、不饱和碳氢化合物的稳定性三、共振理论和分子轨道理论简介四、芳香性与Hückel’s规则
