Transcript Hydrocarbons(

Hydrocarbons(烃): compounds composed
entirely of carbon and hydrogen
 alkanes(烷烃): have only single bond;
saturated (饱和) hydrocarbon;
have no reactive functional groups;
simplest and least reactive.
 alkenes(烯烃): have carbon-carbon double
bond (C＝C)
 alkynes(炔烃): have carbon-carbon triple bond
(C≡C)
 aromatic hydrocarbons(芳香烃): have
aromatic rings (resembling benzene)
Chapter 2
Alkanes and cycloalkanes
(烷烃和环烷烃)
Reading materials:
Text 1: Chapter 3, 4
Text 2: 第二、五章
Contents
2.1 Alkanes
1. Molecular formulas of alkanes
2. Nomenclature of alkanes
3. Physical properties of alkanes
4. Uses and sources of alkanes
5. Reactions of alkanes
6. The free-radical chain reactions
7. Structure and conformations of alkanes
2.2 Cycloalkanes
1. Molecular formulas
2. Nomenclature
3. Physical and chemical properties
4. cis-trans isomerism in cycloalkanes
5. Stabilities of cycloalkanes: ring strain
6. Cyclohexane conformations
7. Conformations of substituted cyclohexanes
2.1 Alkanes (烷烃)
1). Molecular formulas of alkanes
CH4
H—CH2—H
CH3CH3
H—(CH2)2—H
CH3CH2CH3
H—(CH2)3—H
CH3CH2CH2CH3
H—(CH2)4—H
…………
General formula (通式) for alkanes: CnH2n+2
—CH2—, methylene group (亚甲基)
Homologous series (同系列) , CH2 称为系差
Homolog(ue), homologous compound: (同系物)
Isomerism (异构现象) n > 3
Isomer (异构体)
Constitutional isomerism（structural isomerism,
构造异构 See p 54, 2-8）
Branched alkanes (支链烷烃), unbranched
(straight chain, 直链) alkanes
2). Nomenclature (命名) of alkanes (See 3-3)
• Common names (普通命名法)
H3C CH2 CH2 CH3
butane
丁烷
H3C CH2 CH2 CH2CH3
pentane
戊烷
CH3
H3C CH CH3
isobutane
异丁烷
CH3
CH3
H3C CH CH2 CH3 H3C C CH3
CH3
isopentane
neopentane
异戊烷
新戊烷

IUPAC or systematical names (系统命名法)
What is IUPAC?
The formal system of nomenclature used today is
one proposed by the International Union of Pure
and Applied Chemistry (IUPAC, 国际纯粹与应用
化学联合会). This system was first developed in
1892.
Each different compound should have a
different name and make a systematic set of
rules.
Nomenclature of the unbranched alkanes
No
1
2
3
4
5
6
7
8
9
10
Stucture
CH4
CH3CH3
CH3CH2CH3
CH3(CH2)2CH3
CH3(CH2)3CH3
CH3(CH2)4CH3
CH3(CH2)5CH3
CH3(CH2)6CH3
CH3(CH2)7CH3
CH3(CH2)8CH3
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Learn their name by heart !!!
甲烷
乙烷
丙烷
丁烷
戊烷
己烷
庚烷
辛烷
壬烷
癸烷
-ane
(See p 81, Table 3-2)
Nomenclature of branched-Chain alkanes
支链烷烃的命名
IUPAC
Nomenclature Rules:
Rule 1. Finding the main chain: Find the longest
continuous chain of carbon atoms, and use the name of
this chain as the base name or the alkane.（选母体 或 选主
链, 最长链;等长时使取代基最多的链）
Rule 2. Numbering the main chain: numbering the
longest chain, beginning with the end of the chain nearest
the substituent.(主链编号, 使取代基位次最小)
Rule 3. Naming alkyl groups: Name the substituent
groups attached to the longest chain as alkyl groups. Give
the location of each alkyl group by the number of the mainchain carbon atom to which it is attached. (取代基命名和定
位)
Rule 4. Organizing multiple groups: (多个取代
基的组织、排序)
When two or more substituents are present, list
them in alphabetical order（按字母顺序）. (注意！！！
中文按取代基由小到大、由简单到复杂排)
When two or more the same alkyl substituents
are present, use the prefixes di-, tri-, tetra-, penta-, hexa,etc. (ignored in alphabetizing) to avoid having to name
the alkyl group twice.
Nomenclature of unbranched alkyl groups (烷基)
No
1
2
3
4
5
6
7
8
9
10
Stucture
CH4
CH3CH3
CH3CH2CH3
CH3(CH2)2CH3
CH3(CH2)3CH3
CH3(CH2)4CH3
CH3(CH2)5CH3
CH3(CH2)6CH3
CH3(CH2)7CH3
CH3(CH2)8CH3
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Alkyl group
name abbrev
CH3
Methyl Me
CH3CH2 
Ethyl
Et
CH3CH2CH2 Propyl Pr
CH3(CH2)2CH2Butyl
Bu
-ane to -yl
CH3CH2CH2CH3CHCH3
CH3CH2CH2CH3CHCH3
CH3
2-Methylhexane
2-甲基己烷
CH3
CH2
3-Methylheptane
3-甲基庚烷
CH3 CH3
CH3
CH3CH2CCH2CH2CH3 CH CH CCH CH CH
3
2
2
2
3
CH2
CH3
CH3
CH3CH2CHCHCHCH3
CH3
CH3
3,3-dimethylhexane
3,3- 二甲基己烷
3-Ethyl-3-methylhexane
3-甲基-3-乙基己烷
2,3,4-trimethylhexane
2,3,4-三甲基己烷
CH3
CH3 CH
CH2
CH3
CH
CH
CH3 CH
CH3 CH3
CH2 CH3
CH3
CH3
3-ethyl-2,4,5-trimethylheptane
2,4,5-三甲基-3-乙基庚烷
CH3 CH
CH2 CH
CH
CH3
2,3,5-trimethylhexane
2,3,5-三甲基己烷
not 2,4,5-trimethylhexane
Nomenclature of branched alkyl groups
Three-Carbon groups
CH3CH2CH2
Propyl group ±û»ù
CH3CH2CH3
CH3CH
or (CH3)2CH
CH3
1-methylethyl group or isopropyl group
1-¼×»ùÒÒ
»ù £¨ Òì±û»ù£©
Degree of carbon atoms:
H
R
C
H
R
H
R
C
H
R
H
R
C
R
H
R
a primary carbon a secondary carbon a tertairy carbon
1°carbon
3° carbon
2°carbon
伯碳
叔碳
仲碳
一级碳
三级碳
二级碳
R
C
R
R
a quaternary carbon
4° carbon
季碳
四级碳
Four-Carbon groups
CH3CH2CH2CH2
Butyl group ¶¡ »ù
CH3CH2CH2CH3
Butane
CH3CH2CH
CH3
1-methylpropyl group or ( sec-butyl group)
1-¼×»ù±û»ù £¨ µÚ¶þ¶¡ »ù, 仲丁基£©
CH3
CH3
CH3CHCH3
Isobutane
CH3CHCH2
isobutyl group Ò춡 »ù
CH3
CH3C
CH3
1,1-dimethylethyl group or ( tert-butyl group)
1,1-¶þ¼×»ù乙»ù £¨ Ê嶡 »ù£©
4-isopropylheptane
4-异丙基庚烷
5-isobutylnonane
5-异丁基壬烷
4-tert-butylheptane
4-叔丁基庚烷
5-sec-butylnonane
5-仲丁基壬烷
Which name is correct？
3-tert-butyl-2,3-dimethylpentane
3-ethyl-2,2,3,4-tetramethylpentane
4-isopropyl-2,2,5-trimethylheptane
4-isopropyl-3,6,6-trimethylheptane
Nomenclature of complex substituents
CH2 CH3
2
3
1
CH CH CH3
CH3
CH3
2
1
3
4
C
CH2 CH CH3
CH3
CH3
a (1-ethyl-2-methylpropyl) group
2-甲基-1-乙基丙基
a (1,1,3-trimethylbutyl) group
1,1,3-三甲基丁基
CH3
CH
CH3 CH2
CH3 CH2 CH
CH
CH2 CH
CH3
CH2 CH3
3-ethyl-5-(1-ethyl-2-methylpropyl)nonane
3-乙基-5-(2-甲基-1-乙基丙基)壬烷
CH2 CH2 CH2 CH3
Chemdraw:
3-ethyl-5-(2-methylpentan-3-yl)nonane
CH3
CH2
CH CH3
CH3 CH2 CH3 C CH3
CH3 CH2 CH
CH2 CH
CH2 CH2 CH2 CH2 CH3
5-(2-ethylbutyl)-2,4,4-trimethyldecane
2,4,4-三甲基-5-(2-乙基丁基)癸烷
Problem:
Write structural formulas and IUPAC names for the nine isomers of
C7H16
Heptane
庚烷
2-methylhexane
2-甲基己烷
3-methylhexane
2,2-dimethylpentane
2,3-dimethylpentane
2,3-二甲基戊烷 2,4-dimethylpentane
3,3-dimethylpentane
2,2,3-trimethylbutane
3-ethylpentane
Summary of the IUPAC nomenclature
• 主链长，支链(取代基)多，位次小。
• CCS (Chinese chemical society) names：
中文系统命名法
取代基顺序: 先小后大 (顺序规则见中文教材第51页)
Problems: text 1: problem 3-3, 3-4, 3-7
text 2: p 43: 1, 2, 3
命名题要求同时给出英文和中文名称.
3. Physical properties of alkanes （Read 3-4）
• State (状态):
At ordinary pressure(常压下),
C 1~4 gas
C 5~16 liquid
C >17 solid
• Solubility (溶解性): insoluble in water, hydrophobic (water
hating, 憎水的, 疏水的)
• Density (密度)：~0.7 g/mL, less than water.
• Boiling points (沸点)：
van der Waals attraction (范德华作用),
London force (dispersion force, 色散力)
(1) For unbranched alkanes, the bp increase smoothly with
increasing numbers of carbon atoms and increasing molecular
weights.
(2) with same carbons, unbranched alkane > branched alkane
Melting points (熔点)：
(1) For unbranched alkanes, the mp increase in a
sawtoooth-shaped (锯齿形 ) graph with increasing numbers of
carbon atoms and increasing molecular weights. Alkanes with
even numbers of carbon atoms have higher mp, alkanes
with odd numbers of carbon atoms have lower mp.
(2) With same carbons, branched alkane > unbranched
alkane
分子结构对称性越好，其熔点越高。因此偶数碳的直链烷烃高于
奇数碳的直链烷烃，甲烷高于丙烷，新戊烷高于戊烷。
bp / ℃
mp / ℃
60
-154
58
-135
50
-98
4. Uses and Sources of alkanes (See 3-5)
• 1) Alkane sources; petroleum refining
Alkanes derive mostly from petroleum
(often called crude oil) and petroleum byproducts.
Distillation (蒸馏)
Catalytic cracking (催化裂解), thermal
cracking (热裂解)
(Table 3-3 Typical fractions obtained from
distillation of crude petroleum)
2) Major uses of alkanes
Mixtures of alkanes are perfectly suitable for uses as
fuels, solvents, and lubricants (润滑剂), the primary
uses of petroleum.
Natural gas (天然气): C1~3, about 70% methane,
10% ethane. 15% propane, depending on the source of
the gas.
Liquified petroleum gas (LPG, 液化石油气): C3~C4
Gasoline (汽油): C5~C8
Kerosene (煤油): C9~C16
>C16, lubricant (润滑剂), paraffin (石蜡)
chemically raw materials (化工原料)
2,2,4-trimethylpentane (isooctane 异辛烷)
CH3
H3C
C
CH3
CH2 CH
CH3
CH3
Isooctane burns very smoothly without knocking,
but heptane burns to produce much knocking.
A mixture of 87% isooctane and 13% heptane would
be rated as 87-octane gasoline
汽油的标号又称为是汽油的辛烷值，同样容量的汽油，
标号越高其燃烧放出的热越高，燃烧的时间也越长。另外，
不同标号的汽油其抗暴值不同.
5. reactions of alkanes
• Alkanes, as a class, are characterized by a general
inertness to many chemical reagents.
• Carbon-carbon and carbon-hydrogen bonds are
quite strong.
• Carbon and hydrogen atoms have nearly the same
electronegativity, the carbon-hydrogen bonds of
alkanes are only slightly polarized
• It is of lower reactivity of alkanes toward many
reagents.
• When heated, alkanes also react with chlorine and
bromine, and they react explosively with fluorine
1) Combustion (燃烧): rapid oxidation taking place at high temperature
to convert alkanes to carbon dioxide and water.
CnH2n+2 +
excess O2
heat
n CO2 + (n+1) H2O
2) Cracking and hydrocracking (裂解和氢化裂解)
catalytic cracking:
heat
catalyst
long-chain alkane
short-chain alkanes and alkenes
catalytic hydrocracking:
H2, heat
catalyst
long-chain alkane
short-chain alkanes
3) Halogenation (卤化或卤代)
Alkanes can react with halogens (F2, Cl2, Br2, I2) to form alkyl
halides (烷基卤, 卤代烷)
Reaction conditions: heat or light
CH4 + Cl2
heat or light
CH3Cl + CH2Cl2 + CHCl3 + CCl4 + HCl
Reactivity (反应活性): X2: F2 > Cl2 > Br2 > I2 ?
C-H: 3°>2°> 1°
?
Reaction mechanism (反应机理):
free-radical chain reaction (自由基链反应)
[The mechanism is the complete, step-by-step description of exactly
which bonds breaks and which bonds form in what order to give the
observed products.]
6. The free-radical chain reactions (chaper 4)
h¦Í
Initiation steps
step
(链引发)
Cl
Cl
Propagation steps
(链增长)
Cl
+ CH4
Rate
determining
step (决速步骤)
Cl2 +
or ¡÷
CH3
CH3Cl + Cl
CH2Cl
Termination steps
(链终止)
Cl
Cl
+ Cl2
+ Cl
CH3 + CH3
Cl + CH3
+ Cl
？
CH3 + HCl
CH3Cl + Cl
CH2Cl
+ HCl
CH2Cl2 + Cl
Cl2
CH3CH3
CH3Cl
Reactionenergy diagram
for chlorination
of methane
(甲烷氯化反应
的能线图)
①
②
H3C
H +
CH3 +
Cl
Cl
H3C
Cl
H3C
H
Cl
Cl
Cl
CH3 + HCl
CH3Cl +
Cl
Transition state (过渡态)：在能线图的峰顶，无法证实。
Intermediate (中间体)：在能线图的峰谷，实验方法可证实。
Activation energy (活化能)：过渡态与初始态之间的能量差。
Reaction heat (反应热)：生成物与反应物之间的能量差。
正值为吸热，负值为放热。
Which hydrogen is more easily substituted?
哪个氢更容易被取代?
CH3CH2CH3 + Cl2
hv
CH3CH2CH2Cl
yield:
CH3
CH3C H + Cl2
Cl
57%
43%
CH3
hv
CH3C
CH3
Cl
CH3
yield:
+ CH3CHCH3
36%
CH3
+ CH3CH
CH2Cl
64%
仲氢的反应活性是伯氢的4倍。
叔氢的反应活性是伯氢的5倍
Reactivity: C-H: 3°>2°> 1°
Reactivity: C-H: 3°>2°> 1°
Why?
Reason 1: bond dissociation energy （键离解能）
1°C-H
410.3Kj / mol
2°C-H
3°C-H
397.7Kj / mol
389.4Kj / mol
键离解能越小，键越弱，越易均裂。
Reason 2: free-radical stability （自由基的稳定性）:
在自由基链反应中，决定速度步骤中的中间体是烷基自由基，自
由基越稳定，反应越易进行。自由基稳定性:
(CH3)3C
＞ (CH3)2CH
Why?
＞ CH3CH2 ＞ CH 3
① 热力学角度：
键离解能越小，键越弱，越易均裂，自由基越易形成，即自由基
稳定。
② 结构角度：由于“超共轭效应” （hyperconjugation）
烷基上的碳原子与体积极小的氢原子结合，对电子云屏蔽作用很
小，所以C-H上的σ电子比较容易与邻近的π电子（或p轨道）共轭
（电子离哉），使电子重新分配，基团稳定。这种σ键与π键（或p轨
道）的共轭称为超共轭效应，σ键与π键的共轭叫σ- π超共轭效应，σ
键与p轨道的共轭叫σ- p 超共轭效应。
H
•.
C
•.
H
H
H
C
H
sp3
sp2
·CH2CH3
·CH3
C
H
C
H
sp2
H3C
H
有3个C-H σ电子同P轨道交盖
H3C
H
H3C
C
CH 3
H3C
接近sp2
·CH2(CH3)2
.
有6个C-H 键σ电子同P轨道交盖
接近sp2
·CH2(CH3)3
有9个C-H 键σ电子同P轨道交盖
卤素对取代反应的选择性(selectivity)
CH3CH2CH3 + X2
yield:
hv
CH3CH2CH2X
X=Cl
X=Br
CH3
CH3C H + Br2
CH3
hv
+ CH3CHCH3
X
57%
97%
43%
3%
CH3
CH3C Br
yield: 99.5%
CH3
因此溴化具有很高的选择性，在合成上有应用价值。
7. Structure and conformations of alkanes
Constitution (构造): 分子式相同，原子的成键顺序不同。
Conformation (构象): The different arrangements formed by rotation
about a single bond are called conformations. (分子构型相同，由于
单键的自由旋转，原子或原子团在空间的排列不同。)
Conformer (构象异构体): Pure conformers cannot be isolated in
most cases.
For examples:
ethane molecule, have two important conformers (有两种极限构
象):
Dashes and wedges structure (楔形式)
H
H
H
H
H
H
H
H
H
The staggered conformation of ethane
乙烷的交叉式构象
H
H
H
The eclipsed conformation of ethane
乙烷的重叠式构象
Sawhorse structure (锯架透视式)
H
H H
H
H
H
H
H
H
H
H
H
Newman Projections (纽曼投影式)
H H
H
H
H
H
H
H
H
H
H
H
H
H H
H H
H
H
H
H
H
H
H
H
模型
锯架式
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
纽曼式
H
楔型式
H
Conformational analysis of ethane
12.5
Energy
(kJ/mol)
0
12.5 kJ/mol
the torsional energy
(单键的扭转能磊）
60
120
Rotation/(°)
H
H
H
H
H
H
H H
H
H
H
H
H
H
H
H
H
H
H
Conformation
of propane
H
H
C
H
H
CH3
H
H
H
H
H
H
H
H
CH3
The staggered conformation of propaneane
丙烷的交叉式构象
H
C
H
CH3
H
H
CH3
H
H
H
H
H
H
H
CHH3
The eclipsed conformation of propane
丙烷的重叠式构象
Conformational analysis of butane
C4H10
H
H
H
H
H
C
C
C
C
H
H
H
H
H
CH3
H
H
C
C
H
H
CH3
the important conformations of butane
(四种极限构象式)
CH3
H
H
H
H
H
H
CHH3
CH3
anti 对位交叉式（反错式）
eclipsed 部分重叠式（反叠式）
H
H
H
H
CH3
CH3
gauche邻位交叉式（顺错式）
CH3
H
H
H
H
H
CHCH
3 3
totally eclipsed全重叠式（顺叠式）
H
25
CH3
H
H
H
20
H
H
H
23
CHCH
3 3
H
H
CHH3
14.6
15
CH3
H
CHH3
14.6
10
5
3.5
0
3.5
0
0
60
120
180
240
H
CH3
0
360
300
H
420
CH3
H
H
H
H
H
H
H
H
H
H
H
CH3
H
CH3
H
H
CH3
CH3
CH3
CH3
CH3
H
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
H
H
H
CHH3
Potential energy λÄÜ
H
H
H
H
CHCH
3 3
Summary of alkane
1. General molecular formulas
2. Nomenclature of alkanes
3. Physical properties of alkanes: bp, mp
4. Reactions of alkanes: halogenation
5. The free-radical chain reactions
6. Conformations of ethane and butane
Assignments: text 2: p 44-45: 7, 8, 10, 11, 12, 15
2.2 Cycloalkanes
1. Molecular formulas
General formula: CnH2n
2. Nomenclature of cycloalkane
Monocyclic
compounds
(单环化合物）
cyclopropane
cyclohexane
cyclobutane
cycloheptane
cyclopentane
cyclooctane
Monosubstituted
cycloalkanes
(单取代环烷烃)
Methylcyclohexane
甲基环己烷
Isopropylcyclohexane
异丙基环己烷
polysubstituted
cycloalkanes
(多取代环烷烃)
1-ethyl-3-methylcyclohexane
1-甲基-3-乙基环己烷
注意区别！！
1,3-dimethylcyclobutane
1,3-二甲基环丁烷
Cycloalkyl环烷基
Cyclopropylcyclopentane
环丙基环戊烷
Butylcyclopropane
丁基环丙烷
1-cyclopropylbutane
1-环丙基丁烷
1,4-dicyclohexylbutane
1，4-二环己基丁烷
Pentylcyclobutane
戊基环丁烷
1-cyclobutylpentane
1-环丁基戊烷
Bicyclic compounds
（双环化合物）
bridged bicycloalkanes
桥环
fused bicycloalkanes
稠环
Spirocycloalkanes
螺环
Bridged ( and fused ) cycloalkanes (桥环和稠环烷烃 )
bridgehead
one-carbon
bridge
two-carbon bridge
two-carbon
bridge
bridgehead
bicyclo[2.2.1]heptane
(二环[2.2.1]庚烷）
先大环，后小环
bicyclo[1.1.0]butane
（二环[1.1.0]丁烷）
If substituents are present, we number the bridged ring
system beginning at one bridgehead first
1
6
2
7
3
5
4
1,7-dimethylbicyclo[2.2.1]heptane
(1,7-二甲基二环[2.2.1]庚烷）
2-ethyl-1-methylbicyclo[1.1.0]butane
（1-甲基-2-乙基二环[1.1.0]丁烷）
1
5
2
6
3
4
1,5,6-trimethylbicyclo[2.1.1]hexane
(1,5,6-三甲基二环[2.1.1]己烷
5
6
7
Spiro[4.4]nonane
螺[4.4]壬烷
1
4
8
2
3
Spiro[3.4] octane
螺[3.4]辛烷
3. Physical and chemical properties
• Physical properties:
Resemble the open-chain (noncyclic，acyclic) alkanes.
nonpolar, bp and mp depending on their molecular
weights, inert.
• Chemical properties: （中文104-106页，自学）
free-radical substituted（自由基取代）
oxidation（氧化）
addition （加成）：三元环和四元环易发生加成开环，原
因是环张力。
4. Cis-tran isomerism (顺反异构)in
cycloalkanes
=
H
H
H
CH3 CH3
CH3 CH3
=
H
H
H
CH3
H
CH3 CH3
CH3 H
cis-1,2-dimethylcyclopentane
顺-1，2-二甲基环戊烷
trans-1,2-dimethylcyclopentane
反-1，2-二甲基环戊烷
5. Stabilities of cycloalkanes;
Ring strain (环张力）
Why are five-membered and six-membered rings more
common than the other sizes?（五元环和六元环比其它
环稳定）
Experimental facts:
Heats of combustion (燃烧热）for cycloalkanes
(Table 3-5, p 104)
Heats of combustion (kcal/mole) for some simple cycloalkanes
Ring
cycloalkane
size
Molar heat of
combustion
Heat of
combustion
per CH2
group
3
cyclopropane
499.8
166.6
9.2
27.6
4
cyclobutane
655.9
164.0
6.6
26.4
5
cyclopentane
793.5
158.7
1.3
6.5
6
cyclohexane
944.5
157.4
0.0
0.0
7
cycloheptane
1108.3
158.3
0.9
6.3
8
cyclooctane
1268.9
158.6
1.2
9.6
157.4
0.0
0.0
Reference: long-chain alkane
Ring strain
per CH2
group
Total ring
strain
E
C
B
A
reactant
∆Hc = E(p) – E(r)
Product, CO2+ H2O
Stability: A>B>C
heat of combustion: A<B<C
Analyze Table 3-5, p 104
Conclusion:
stability: 6>5>4>3
The origin of ring strain
in cyclopropane and cyclobutane:
Angle strain(角张力) and torsional strain（扭力）
Adolf von Baeyer first attempted to explain the
relative stabilities of cyclic molecules in the late
nineteenth century, and he was awarded a Nobel
Prize for this work in 1905.
The normal tetrahedral bond angle of an sp3hybridized atom is 109.5o.
How about the angle of the cyclopropane and
cyclobutane ?
H
Cyclopropane
H
H
H H
H
60o
H
H
109.5o-60o = 49.5o
H
H
H
Angle strain is; 49.5o / 2 =24.7o
H
Orbital overlap is less effective in cyclopropane
这种由于键角偏离正常键角而引起的张力称为角张力
（angle strain）
H
H
H
H
H
H
H
H
HH
H
H
A Newman projection formula
eclipsed hydrogens
torsional strain（扭力）
Angle strain >> torsioal strain
Cyclobutane also has considerable angle strain
88o
Angle strain >> torsioal strain
Slightly folded conformation
The ‘Bent’ or ‘envelope’ form of
cyclopentane
H
o
H
108
Pentagon
五边形
H
H
H
H H
H
H
H
Envelope conformation
“信封式”构象
Important!
6. Conformations of cyclohexane
• There are two important conformations for cyclhexane
chair and boat
• The chair form is most stable conformation
1) Chair conformation 椅式构象
Axial bond直立键（a键）：
6个（3上、3下）
Equatorial 平伏键（e键）：
The chair conformation, stable
椅式构象, 稳定
6个（3上、3下）
H
H
1
H
H
H
2 3
6
H
5
H
H
4
H
H
相邻原子：交叉式
非键合原子：交叉式
How to write the chair conformation?( see p 309 )
a
e e
a
The inversion of chair conformation
构象翻转
a
a
a
e
e
e
e
e
a
a
a
a-bond
e-bond
e-bond
a-bond
e
2）The boat conformation,
unstable
船式构象, 不稳定
4
1
2
6
3
5
HH
1
4
H
H
H
H
2
HH
3
6
HH
5
相邻原子：重叠式
非键合原子：重叠式
The inversion of conformations
H
H
H
Chair
Chair
Boat
Half-chair
半椅式
Twist boat
扭船式
H
7. Conformations of substituted cyclohexanes
CH3
methylcyclohexane
H
CH3
H
H
HH
H
H
H
H
H
H
H
H
H
H
HH
H
H
H
H
H
CH3
1,2-, 1,3-, and 1,4-Dimethylcyclohexane
H
H
H
CH3
CH3
CH3
CH3
H
Cis-1,2-Dimethylcyclohexane
trans-1,2-Dimethylcyclohexane
H
H
CH3
CH3
H
CH3
CH3
H
1,3-Dimethylcyclohexane
H
CH3
H
H
CH3
H
CH3
CH3
Cis-1,3-Dimethylcyclohexane
trans-1,3-Dimethylcyclohexane
H
H
CH3
CH3
H
H3C
CH3
H
1,4-Dimethylcyclohexane
trans-1,4Dimethylcycloh
exane
H
CH3
CH3
H
H
H3C
H
CH3
(Stable)
(less stable)
cis-1,4Dimethylcyclo
hexane
CH3
CH3
CH3
H3C
H
H
H
H
Sample problem
H
H
Cl
H
Cl
Cl
H
Cl
Cl
Cl
H
H
(a)
(b)
a. cis-1,2-Dichlorocyclohexane
b. cis-1,3-Dichlorocyclohexane
c. trans-1,2-Dichlorocyclohexane
(c)
Cis-1-tert-butyl-4-methylcyclohexane
C(CH3)3
CH3
CH3
(H3C)3C
H
H
(Stable)
H
H
(Less stable)
Remember!! The large group puts in the equatorial
position as soon as possible
But
OH
a
a
OH
HO
e
e
H
H
O
a
HO
O
a
stable
1,4-di-tert-butylcyclohexane
C(CH3)3
C(CH3)3
(H3C)3C
H
(H3C)3C
H
“Chair”, unstable
“Twist boat”, stable
1,3-di-tert-butylcyclohexane
C(CH3)3
H
C(CH3)3
C(CH3)3
H
“Chair”, unstable
“boat”, stable
C(CH3)3
Bicyclo and polycyclic alkanes
Decalin shows cis-trans conformations isomerism
H
H
H
H
H
e
e
e
e
e
H
H
e
e
a
cis-bicyclo[4.4.0]decane
bp. 195 oC
H
trans-bicyclo[4.4.0]decane
bp.185.5oC
trans, stable
Adamantane (金刚烷） is a tricyclic system that
contains a three dimensional array of cyclohexane
Adamantane ½ð¸ÕÍé
A portion of the diamond structure
Summary of cycloalkanes
Nomenclature
Stabilities of cycloalkanes: ring strain; angle strain, torsional
strain
Conformations of cyclohexane and substituted
cyclohexanes
chair（椅式）, boat（船式）;
a bond （a键，直立键）, e bond（e键，平伏键）
Assignments
• Text 1: 3-37， 39，44 (p-123)