L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
FUNDAMENTALS OF ORGANIC
Chpt. 24: p.1
CHEMISTRY 有機化學
Organic Chemistry is the chemistry of compounds containing carbon.
Most of these compounds also contain hydrogen, oxygen or other elements.
Note: Carbon containing compounds such as carbon monoxide and dioxide, carbonic acid, metal
carbides, carbonates and hydrogencarbonates are not classified as organic compounds.
(I)
NATURAL SOURCES OF ORGANIC COMPOUNDS
Organic compounds are extremely important as they are found in living things. Many products and
materials are also organic products.
Naturally occurring
Synthetic
Fuels (e.g. coal crude oil)
in living orgainisms
Carbohydrates
plastics
gasoline
proteins
cosmetics, perfumes
kerosene
fats and oils
anaesthetics
many petroleum products
vitamins
dyes, explosives
(II)
THE UNIQUE NATURE OF CARBON 碳的獨特性
1.
Introduction
The carbon atoms has a unique property of forming many naturally occurring and synthetic
compounds with a narrow range of elements than all other elements.
Reasons : Carbon is able
<1> to extend its maximum covalency to four 均有形成四個共價鍵的趨勢
<2> to form stable bonds with itself.
e.g.
Chain structures
straight chain :
butane
polythene
<3>
(A)
branched chain :
2-methylbutane
Ring structures :
cyclohexane
form double and triple bonds amongst themselves or with other elements .
可與碳或其他元素形成雙鍵，及三鍵
e.g
ethene
propyne
butanone
Physical properties
Organic compounds are usually
<1> covalent gases, volatile liquids or low melting solids
<2> insoluble in water (polar solvent) unless with the presence of some polar groups such as
-OH, -COOH, and –SO3H in the compounds
<3> more soluble in organic, non-polar solvents such as ethoxyethane/ether, trichloromethane.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
(B)
(III)
1.
Chpt. 24: p.2
Chemical properties
<1> The products yielded when burnt in excess oxygen are usually ,carbon dioxide
and water.
<2> They usually react more slowly than inorganic compounds. Energy in the
form of heat is usually required.
<3> The reactions are seldom complete reacted. Purification is usually
required to obtain the desired product.
<4> Organic compounds are often exist in groups or families (Homologous series)
having similar chemical properties and graduation of physical properties.
<5> They can exist in large amounts is due to the possibility of catenation and
isomerism in their compounds.
FUNCTIONAL GROUP AND HOMOLOGOUS SERIES 官能基及同系列
Functional Groups of Organic Compounds
The diversity of organic molecules are very often classified by the presence of functional, groups in the
molecules.
The functional group represents the part of molecule which gives a characteristic type of reactivity
upon the compound and effectively determines the compound’s chemical properties and many of its
physical properties as well.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
2.
Chpt. 24: p.3
Homologous Series
A homologous series is a series of compounds with adjacent
members differing in their formula by a —CH2— unit.
Examples
Alkanes series 烷烴
CH4
Alkanols series 烷醇
CH3OH
Alkenes series 烯烴
C2H4
Note : <1>
e.g.
Members of a homologous series exhibit similar chemical properties but have a
gradation physical properties (melting points, viscosity, density etc.)
Alkanes
C1-C4 : gases
C5-C16 : liquids
C17 above : solids
<2> Members in the same series have a general formula
e.g.
Alkanes
Alkenes
IV.
Alkanols
General Introduction to the major families of Organic Compounds
(A) Hydrocarbons 碳氫化合物:
The families of organic compounds whose molecules contain
carbon and hydrogen only.
Alkanes — contain only C—C single bond between carbon atoms
Alkenes — contain a C=C double bond
Alkynes — contain a CC triple bond
Aromatic Hydrocarbons — contain an aromatic ring
Alkanes 烷烴
These molecules are saturated hydrocarbons with only C—C bond and C—H single
bond inside. The carbon atoms form four single bonds with other atoms and have
unshared electrons in their valence orbitals.
Examples :
(a)
Chain structures 鍊狀結構:
1.
no
Methane
Propane
2—methylbutane
(b) Ring structures 環狀結構:
Cyclopentane
Cyclohexane
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
2.
Chpt. 24: p.4
Alkenes 烯烴
The two carbon atoms in such hydrocarbons share two pairs of electrons to form a C=C
double bond. This C=C double bond is therefore a centre of unsaturation in the molecule
and can undergo addition reaction to utilize its covalency to the full (four).
H
H
C C
H
H
+
Br
Br
C C
Br Br
The C=C double bond can be regarded as the functional group of alkene since most of
the chemical reactions take place here. Examples
Propene
cis—But—2—ene
cis—1, 2—dibromoethene
Cyclohexene
trans—But—2—ene
trans—1 , 2—dibromoethene
Alkynes 炔烴
These are hydrocarbons in which two of the carbon atoms share 3 pairs of electrons
between them and are thus bonded by a CC triple bond. The reactive site is the CC
triple bond at which the addition reactions take place.
Examples :
H-CC-H
Ethyne
Propyne
3—Methylbutyne
3.
4.
Aromatic Hydrocarbons 芳香烴
This is a class of cyclic hydrocarbons in which benzene is typical example .
Benzene derivatives : (substitution of the —H group)
Methylbenzene
1. 2—dibromobenzene
1, 3—dibromobenzene
Chlorobenzene
1,4—dibromobenzene
When benzene ring is attached to some other groups of atoms in a molecule, it is called a phenyl group.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
(B)
1.
Chpt. 24: p.5
Hydroxyl Compounds 羥基化合物:
Such family of compounds have the functional group —OH. There are two large groups
of hydroxyl compounds : alcohols and phenols
Alcohols 酒精
This group of compounds can either be regarded as hydroxyl derivatives of alkanes or as alkyl
derivatives of water.

RH
Example
CH3CH2-H

ROH

CH3CH2—OH 
ethanol
(ethyl alcohol)
HOH
H2O
Based on the condition of the carbon atom to which he —OH group is directly attached,
alcohols are generally classified into
three groups : primary (1°) , secondary (2°) and tertiary (30) alcohols.
a primary alcohol
e.g. ethanol 乙醇
a second alcohol
propan-2-ol 丙-2-醇
a tertiary alcohol 2-methylpropan-2-ol 2-甲基丙-2-醇
2.
Phenols 酚
This is a hydroxyl derivatives of benzene and is almost always called phenol.
OH
(C)
Ethers 醚:
Such family of compounds can be thought as derivatives of water in which both hydrogen have
been replaced by alkyl groups. They have the general formula R—O—R, and the bond angle of
R—O—R is slightly larger than H—O—H.
H
R
O
O
H
R
water
ether
(D) Carbonyl Compounds 羰基化合物: Such family of compounds contain the carbonyl group
C O
in their
1.
structures.
Aldehydes 醛
The carbonyl group bonded to at least one hydrogen atom. The general formula is
O
C
R
H
where R may also be H
Examples
Methanal 甲醛
(formaldehyde)
Ethanal 乙醛
(Acetaldehyde)
propanal 丙醛
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.6
Ketones 酮
The carbonyl group is attached to alkyl groups. The general formula is
2.
O
C
R'
R
Examples
Propanone 丙酮
(Acetone)
Butanone 丁酮
3-methylbutanone 3-甲基丁酮
(E) Carboxylic Acids : The family of compounds have the carboxyl group.
O
C
OH as
the functional group.
The general formula is
O
C
OH
R
or RCOOH or RCO2 H
Examples
Methanoic acid
甲酸
Ethanoic acid
乙酸
Benzoic acid
Ethandioic acid
乙二酸
(F) Acid Derivatives 酸的衍生物 :These refers to the acid halides 酉先鹵, amides 酉先胺,
esters 酯 and acid anhydrides 酉先酐. They are derived from the substitution of the hydroxyl
group of -COOH by -X, - NH2 , - OR and -COOR
Carboxylic Acid Derivatives
Structure
Name
Structure
O
R
R
C
Cl
Acyl(acid)chloride
O
O
C
O C
R
C
C NH2
O
R'
Acid anhydride
R
C NHR
Amides
O
O
R
Name
O
OR
Ester
R
C NR2
Halogen Hydrocarbons : Any —H group(s) in a hydrocarbon skeleton is substituted by one or
more halogen atoms
(i.e. Cl, Br, I etc.)
Examples
(G)
2, 2-Dibrombutane
3-chlorobut-1-ene
Bromobenzene
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
(H)
Amines 烷基胺
Chpt. 24: p.7
: These are organic derivatives of ammonia 為氨的有基衍生物.
H N H
R N H
R N H
R N R''
H
H
R'
R'
primary(1°)
amine (2H)
secondary(2°)
amine (1H)
tertiary(3°)
amine (no H)
Examples
Ethyl amine
(I)
V.
Propylamine
Polyfunctional Compounds : Compounds contain more than one typical functional groups.
Examples
2—Hydroxylpropanoic acid
(Lactic acid)
Ethane—1.2—diol
2—Aminoethanoic acid
(Glycine)
Phenyl ethyne
Representation of structural formula
<1> Dot formula — to show the number of valence electrons and the way they are shared.
<2> Dash formula — to show the way atoms are attached to one another.
<3> Condensed formula — to impart all the information implied in the dot and dash formula.
<4> bond—line formula — to show only the carbon skeleton. Hydrogen atoms are omitted. N, O ,Cl
are written in.
Examples :
Dot formula
Dash formula
Condensed formula
CH3CH2CH2CH2CH2OH
Bond—line formula
(CH3)2CHCH2OH
<5> Three-dimensional formula — to show the arrangement of atoms in space and give the 3dimensional structure of a molecule.
(i)
(ii)
.
(iii)
Dash—line—wedge formula : bond lines notation bonds directed behind the plane of the page
bonds projected out of the plane of the page
bonds on the plane of the page
Sawhorse projection : to show the carbon skeleton by solid lines with
indications of the terminal group attached
to it
Newman projection : to show the structure by looking down one
particular carbon—carbon bond axis.
Bonds of the front carbon are depicted as
Bonds of the back carbon are depicted as
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.8
Exercises :
CH3 CH CH2 CH CH CH3
CH3
H
CH3 C
and
CH3
CH3 CH
CH3 CH3
CH3
CH2
CH3
1. Identify,
groups in each of the following compounds.
as far as possible, all the functional
OH
H
COOH
O
a)
O
OH
C
OH
N
c) O
b)
C
Cl
O
CH3
C
Cl
C
O
d)
2.
e)
Which of the following pairs of structure represent the same compound and which are different
compounds?
CH3 CH CH2 CH CH CH3
CH3
CH3 CH3
and
H
CH3 C
CH3
CH3 CH
CH2
a)
CH3
CH3
C2H5
OCH3
and
b)
CH3
c)
Cl
H3C O
C2H5
Cl
and
CH3
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.9
VI. STRUCTURE AND SHAPE OF HYDROCARBONS
(A).
Tetravalent Carbon in Saturated Compounds
The electronic configuration of Carbon is 1s2 2s2 2p2
It is not divalent (the 2 unpaired 2p electrons forming covalent bonds by overlapping with the
orbitals of two unpaired electrons from other atoms) but tetravalent because hybridization of the
atomic orbitals takes place at the carbon atom.
The hybrid orbitals are in tetravalent arrangement in order to minimize the repulsion among
them. For such sp3 orbitals overlapping with is orbitals from four hydrogen atoms, methane is
formed.
Note
<1> The carbon atom prefers the tetravalent state because large amount of bond energy is
released by form two extra ‘bonds. Such energy can outweigh the energy required
for
excitation and hybridization.
<2> The strong covalent bonds formed is called a bond. The bonding electrons are localized
symmetrically along the internuclear axis of boding atoms.
<3> The tetrahedral configuration around an sp3 carbon is retained in any compound where
carbon forms four single covalent bonds with other atoms.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.10
<4>The atoms joined by a a bond can rotate with respect to one another.
Example :
For ethane molecule, C—H and C—C bonds can be rotated.
Conformations (conformers) of the molecules can be obtained by
rotation about the C—C bond. The two extreme cases are staggered and
eclipsed forms.
<i> staggered form : The molecule is lower in
Reason :
energy and more stable.
<ii> eclipsed form : The molecule is higher in energy and less stable.
Reason :
<5> In the case of cyclic compounds, the tetrahedral configuration around sp3 carbon also tend to
preserve other additional interactions have to be taken into account.
(i)
Cyclohexane:
The ring is slightly puckered from a planar form (regular hexagon with interior angle
1200 ) to a puckered form in order to relieve the 12 C—H bonds interaction.
It has two conformations :
<a> Chair form —
—
—
<b> Boat form —
—
the
The ring is puckered that all sp carbons have tetrahedral
configuration.
It is free of ring strain.
All the C—H bonds are perfectly staggered so that there will be
no H—H interaction.
Hydrogens of the side carbons are eclipsed
Two of the hydogens on C1 and C4 exert repulsion on each other.
Such repulsion cause the form to have higher energy than
chair form.
chair form
boat form
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
(B).
Chpt. 24: p.11
Unsaturated Hydrocarbons — Double and Triple Bonds
(1)
Formation of C=C Double Bond
In forming the C=C bond, carbon atoms undergo sp2 hybridization.
The three sp2 hybridized orbitals are in a trigonal planar arrangement with 120° between
any two orbitals. The unhybridized 2p orbital is in a plane at right angle to them.
In forming the ethane (C2H4) molecule,
<a> A strong sp2—sp2 __________ is formed between the carbon atoms
<b> Four sp2—s __________ are formed between the sp2 carbons and hydrogens by
overlapping with their is orbitals.
<c> The two unhybridized 2p orbitals of carbon overlap laterally to form a _______ bond
above and below the plane.
Note
<i>
<ii>
The Lateral overlap in  bond is ______ effective than the linear overlap in a bond.
The electrons in the  bond are delocalized over both carbon atoms, moving freely
throughout an orbital above and below the plane of the carbon framework. Such carbon
framework is the nodal plane of the it bond.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
<iii>
Chpt. 24: p.12
The rotation of the  bond through 90° would result in the breakage of the  bond.
The breakage if usually involves a large amount of energy (220 kJmol-1) and the
temperature required should be above 300°C.
The  bond is rigid that prevents double bond rotation and keep the structure of the
ethene molecular planar, with all the hydrogen atoms lying in the same plane.
<iv>
The rigidity of mm bond is till maintained in the structure of cyclohexene,
C=C bond in which carbons are sp2 hybridized :
planar
3
C—C bond in which carbons are sp hybridized : tetrahedral
(2)
Formation of —CC— Triple Bond
In forming —CC— bond, carbon atoms undergo sp hybridization by utilizing their 2s
and 2p orbitals. The sp hybrid orbitals are co-linear and are at 180° to one another. The
other two unhybridized orbitals of each carbon atom remain in planes at right angles to
one another.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.13
In forming the ethyne (C2H2) molecule,
<1> One sp—sp ________ is formed between two carbon atoms.
<2> Two pairs of unhybridized. 2p orbitals overlap each other laterally to form two it bonds
which are mutually at right angles to each other.
<3> The difference in bonding and electronic structure of the C— C, C=C and CC bonds is
reflected in their bond energy and bond lengths.
Table - Values of bond length and bond energy in ethane, ethene and ethyne
Carbon-carbon bond
Carbon-carbon bond
Compound
‘
length/nm
energy/kJ mol-1
in ethane
0.154
350
in ethene
0.134
600
in ethyne
0.120
815
Interpretation
(i)
The carbon—carbon bond length decreases from C—C to CC
Reason:
The formation of double and triple bonds is accompanied by an increase in overlap of the
electron clouds of the combining atoms. The increases electron density enhances the
electrostatic binding between the two nuclei. As a result, the bonds are shorter.
(ii)
The carbon—carbon bond energy increases from C—C to CC
Reason :
More energy is required to rupture the bond from C—C bond to CC bond.
VII.
Aromatic Hydrocarbons — Special case of Benzene
(A)
Electronic Structure and Special Distribution of Bonds
The structure of benzene can be considered as a further extension of delocalisation from the
conjugated dienes.
<1>
<2>
Each carbon atom undergoes sp2 hybridization and form 2  bonds with another two
carbon atoms as well as 1 bond with hydrogen atom. All the 6 carbon atoms and 6
hydrogen atoms form a planar hexagon.
The 6 unhybridized 2p orbitals overlap each other on both side to give an annular
electron cloud above and below the plane of the ring. This extended delocalisation of the
p orbitals accounts for the planar nature of the ring.
Note: <1> Benzene can be regarded as the resonance hybrid of two Kelule structures. The true
structure is the intermediate between them.
L.S.T. Leung Chik Wai Memorial School
F.6 Chemistry
Chapter 24-25
Chpt. 24: p.14
<2>
The  electrons are delocalized around the whole system and the structure of benzene is
better represented as follow :
<3>
Due to the delocalization of the electron cloud, the C—C bond lengths in benzene are
exactly the same (0.140 nm). Such value lies between the value for a CC triple bond
(0.154 nm) and a C=C double bond (0.134 nm).
Exercise
Explain why the benzene molecule is planar, whereas the cyclohexane molecule is puckered.
Exercise
Certain bond angles have been marked in the compound shown below. The 2—dimensional diagram
does not indicate the true angles.
(a)
(b)
Suggest approximate values for the bond angles marked 1, and 4 in the three dimensional
structure, and explain any difference between these values.
Arrange the bonds C—Cl, C=O, C—O, CC, CN and C—H (in H—CC—H) in order of
increasing length. Give explanation when necessary.
SOLUTION
,