开链烃
饱和烃
不饱和烃
烃
环状烃
脂环烃
芳香烃
烷烃
烯烃、炔烃
Chapter 5
ALICYCLIC HYDROCARBON
(CYCLOALIPHATES)
Cyclopentane and cyclohexane are present in
petroleum, but as a rule, unsubstituted cycloalkanes
are rarely found in natural sources. Compounds that
contain rings of various types, however, are quite
abundant.
5.1 MONOCYCLIC HYDROCARBON
5.1.1 Naming and Isomery
Cycloalkanes are named, under the IUPAC system,
by adding the prefix cyclo- to the name of the
unbranched alkane with the same number of carbons
as the ring. Substituent groups are identified in the
usual way.
When the ring contains fewer carbon atoms than an
alkyl group attached to it, the compound is named as
an alkane, and the ring is treated as a cycloalkyl
substituent:
Ex:
Cl
Cyclohexa-1,3-diene
Cl
1,4-Dichlorocyclopentene
4-Isopropyl-1-methylcyclohexene
1,4-Dimethylcyclohexane
Ethylcyclohexane
These two compounds are constitutional isomers.
trans-1,4-Dimethylcyclohexane
cis-1,4-Dimethylcyclohexane
These two compounds are cis-/trans- isomers.
脂环烃产生顺反异构体的条件：
①阻碍单键自由旋转的因素 ②同一个碳上所连基团不同
5.1.2 Properties
1. Physical Properties
环烷烃的熔点、沸点和相对密度都较含同数碳
原子的脂肪烃为高。
2. Chemical Properties
Cycloalkanes :
Co-Cat.
100℃, 10atm
‹
Oxidation:
‹
Free-radical Substitution:
+ O2
+ Br2
光照
COOH
COOH
Br
Cycloalkenes :
‹ Electrophilic Addition
+ Br2
H Br
Br H
anti addition
+ HBr
‹
Br
碳原子数不变说明
双键在环上。
Ozonolysis:
O3
Zn/H2O
CH2 CHO
CH2
CH2 CHO
‹
Hydroboration-Oxidation:
① (BH3)2
② H2O2, OH
-
H CH3
OHH
顺式反马氏加成
Special Properties of Cycloalkanes
1. Addition Reaction
+ Br2
CCl4
+ Cl2
加成在连接最少和最
多烷基的碳原子之间
Br
Br
Cl
Cl
CH3
CH
CH2 + HBr
r.t.
CH2
CH3CH CH2CH3
Br
符合马氏规则
环丁烷常温时与HX、X2不加成，加热可以反应。
环戊烷可以加氢，但不可以其它加成。
2. The Stability to Oxidant of Cyclopropane and
Cyclobutane
KMnO4
COOH
可用于区别烯烃和环丙烷的衍生物。
Ex：Please distinguish the following gases using a
reasonale method.
CH3CH2CH3
CH3CH CH2
KMnO4 /H+
(-)
(+) 褪色
(-)
(-)
Br2 / CCl4
(+) 红棕色褪去
5.1.3 Structures of Alicyclic Hydrocarbon
1. Baeyer Strain Theory
During the nineteenth century it was widely
believed—incorrectly, as we’ll soon see—that
cycloalkane rings are planar.
109.5°
C
60°
60°
24° 44′
Angle strain is the strain a molecule has because
one or more of its bond angles deviate from the ideal
value; in the case of alkanes the ideal value is 109.5°.
According to Baeyer, cyclopentane should be the
most stable of all the cycloalkanes because the ring
angles of a planar pentagon, 108°, are closer to the
tetrahedral angle than those of any other cycloalkane.
A prediction of the Baeyer strain theory is that the
cycloalkanes beyond cyclopentane should become
increasingly strained and correspondingly less stable.
The angles of a regular hexagon are 120°, and the
angles of larger polygons deviate more and more
from the ideal tetrahedral angle.
2. Heats of Combustion
Cyclopropane has the highest heat of combustion
per methylene group, which is consistent with the idea
that its potential energy is raised by angle strain.
Cyclobutane has less angle strain at each of its
carbon atoms and a lower heat of combustion per
methylene group.
Cyclopentane, as expected, has a lower value still.
Notice, however, that contrary to the prediction of
the Baeyer strain theory, cyclohexane has a smaller
heat of combustion per methylene group than
cyclopentane.
Furthermore, the heats of combustion per
methylene group of the very large rings are all about
the same and similar to that of cyclohexane. Rather
than rising because of increasing angle strain in large
rings, the heat of combustion per methylene group
remains constant at approximately 653 kJ/mol.
The Baeyer strain theory is useful to us in
identifying angle strain as a destabilizing effect. Its
fundamental flaw is its assumption that the rings of
cycloalkanes are planar.
3. Theory of Covalent Bond
The less effective overlap
that does occur leads to what
chemists refer to as “bent”
bonds. The electron density in
the carbon–carbon bonds of
cyclopropane does not lie along
the internuclear axis but is
distributed along an arc
between the two carbon atoms.
The ring bonds of cyclopropane
are weaker than other carbon–
carbon σ bonds.
In addition to angle strain, cyclopropane is
destabilized by torsional strain. Each C-H bond of
cyclopropane is eclipsed with two others.
Cyclobutane has less angle strain than
cyclopropane and can reduce the torsional strain
that goes with a planar geometry by adopting the
nonplanar “puckered” (折叠)conformation.
5.1.4 Stereochemistry of Alicyclic
Hydrocarbons
1. cis-trans-isomer
When a cycloalkane bears two substituents on
different carbons—methyl groups, for example—
these substituents may be on the same or on opposite
sides of the ring. When substituents are on the same
side, we say they are cis to each other; if they are on
opposite sides, they are trans to each other.
The methyl groups on the same side of the ring in cis-1,2dimethylcyclopropane crowd each other and increase the
potential energy of this stereoisomer. Steric hindrance between
methyl groups is absent in trans-1,2-dimethylcyclopropane.
2. Conformations of Cyclohexane
构象是指由于单键旋转，改变了各原子和原子团
的相对位置，形成各原子和原子团的空间排布。
‹
Ultimate Conformation
There is considerable evidence that six-membered
rings are nonplanar and the most stable conformation
of the cyclohexane ring is the “chair” conformation.
With C－C－C bond angles of 109.5°, the chair
conformation is thereby free of angle strain. All its
bonds are staggered, making it free of torsional strain
as well.
The staggered arrangement of bonds in the chair
conformation of cyclohexane is apparent in a
Newman-style projection.
A second, but much less stable, nonplanar
conformation called the boat is shown in Figure as
follows. Like the chair, the boat conformation has
bond angles that are approximately tetrahedral and is
relatively free of angle strain.
As noted in Figure, however, the boat is
destabilized by van der Waals strain involving its two
“flagpole” hydrogens, which are within 180 pm of
each other.
An even greater contribution to the estimated 27
kJ/mol energy difference between the chair and the
boat is the torsional strain associated with eclipsed
bonds on four of the carbons in the boat.
The various conformations of cyclohexane are in
rapid equilibrium with one another, but at any moment
almost all of the molecules (more than 99%) exist in the
chair conformation.
Axial and Equatorial Bonds in Cyclohexane
One of the most important findings to come from
conformational studies of cyclohexane is that its 12
hydrogen atoms are not all identical but are divided
into two groups.
‹
Six of the hydrogens, called axial
hydrogens, have their bonds parallel to
a vertical axis that passes through the
ring’s center. These axial bonds
alternately are directed up and down
on adjacent carbons.
The second set of six
hydrogens, called equatorial
hydrogens, are located
approximately along the
equator of the molecule.
Notice that the four bonds
to each carbon are arranged
tetrahedrally, consistent with
an sp3 hybridization of carbon.
‹
Conformational Inversion in Cyclohexane
(Ring Flipping)
We have seen that alkanes are not locked into a
single conformation. Cyclohexane, too, is
conformationally mobile. Through a process known
as ring inversion, chair–chair interconversion, or,
more simply, ring flipping, one chair conformation is
converted to another chair.
The activation energy for cyclohexane ring
inversion is 45 kJ/mol (10.8 kcal/mol). It is a very
rapid process with a half-life of about 10-5s at 25°C.
The most important result of ring inversion is that
any substituent that is axial in the original chair
conformation becomes equatorial in the ring-flipped
form and vice versa.
原来在平面上方的键依然在上方；反之亦然。
Conformational Analysis of Substituted Cyclohexanes
Ring inversion in methylcyclohexane differs from
that of cyclohexane in that the two chair conformations
are not equivalent. In one chair the methyl group is
axial; in the other it is equatorial.
At room temperature approximately 95% of the
molecules of methylcyclohexane are in the chair
conformation that has an equatorial methyl group
whereas only 5% of the molecules have an axial methyl
group.
‹
Q: Why is equatorial methylcyclohexane more
stable than axial methylcyclohexane?
A methyl group is less crowded when it is
equatorial than when it is axial.
A. 多元取代环己烷最稳定的构象是e键取代基最多
的椅式构象。
B. 环上有不同取代基时，大的取代基在e键的椅式
构象最稳定。
Problem：Please give the more stable conformations
for cis-4-tert-butylcyclohexanol and 1-methyl-4isopropyl-cyclohexane, respectively.
OH
H
H
H
H
3. Stereochemistry of Electrophilic Addition
to Cycloalkenes
Br-
+ Br2
H
+ Br2/H2O
Br
Br H
H
H Br
+
H Br
Br H
+ H Br
H OH
H2O
H+
+ RCO3H
O
Br H
OH H
OH
OH
+ KMnO4
OHOH
OH
+ H2
H
Pt
H
CH3
CH3
H2O2, OH-
B2H6
H3 C
H
BH2
CH3 H
H
OH
+
H
OH
CH3 H
Problem: 以1-甲基环己烯为代表，写出加成、氧化、
还原和硼氢化氧化等反应的主产物。
5.2 POLYCYCLIC RING SYSTEMS
Organic molecules in which one carbon atom is
common to two rings are called spirocyclic (螺环)
compounds.
Naming：根据成环碳原子的总数称为“螺某烷”，
在螺字后面的方括号中用阿拉伯数字标出两个碳
环除了螺原子以外的碳原子数目，将小的数字排
在前面。编号从较小环中与螺原子相邻的一个碳
原子开始，经过共有碳原子而到较大的环，数字
之间用原点隔开。
Ex：
5
6
4
3
7
1
2
4-甲基-螺[2.4]庚烷
2,6-二甲基-螺[3.3]庚烷
When two or more atoms are common to more
than one ring, the compounds are called polycyclic
ring systems. They are classified as bicyclic, tricyclic,
tetracyclic etc., according to the minimum number of
bond cleavages required to generate a noncyclic
structure.
Naming：Bicyclic compounds are named in the
IUPAC system by counting the number of carbons
in the ring system, assigning to the structure the
base name of the unbranched alkane having the
same number of carbon atoms, and attaching the
prefix “bicyclo-.” The number of atoms in each of
the bridges connecting the common atoms is then
placed, in descending order, within brackets.
Ex：
双环[4.3.0]壬烷
1,7,7-三甲基-双环[2.2.1]庚烷
命名步骤：
⑴首先编号
⑵确定碳环中的总碳原子数
⑶确定碳环数（把碳环化合物转变为链状化合物
需要打断的C-C键数目）
⑷确定方括号中的碳原子数目，由大到小排列
⑸命名取代基
双环[2.2.2]-2-辛烯
Among the most important of the bicyclic
hydrocarbons are the two stereoisomeric
bicyclo[4.4.0]decanes, called cis- and trans-decalin.
The hydrogen substituents at the ring junction
positions are on the same side in cis-decalin and on
opposite sides in trans-decalin. Both rings adopt the
chair conformation in each stereoisomer.
合成路线的选择
Ex：Please give a reasonable synthetic
route for the following molecule.
Analysis:
CH3
Br
CH3
‹
若用光照加溴，则主产物为:
‹
若用烯烃加溴化氢，则设计以下两种烯烃为前体：
CH3
(1)
Poor selectivity
CH3
(2)
对于(2):
可以，反应需要加温和加压
+
反应的选择性不好
+
或者：
CH3
CH3
Br
Br
+
Br
The better method