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Chapter 24
Introduction to
Organic Chemistry
24.1 What is Organic Chemistry?
24.2 The Unique Nature of Carbon
24.3 Classification of Organic Compounds
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24.1 What is Organic Chemistry (SB p.2)
Organic Chemistry: The chemistry of the compounds of
carbon
Carbon compounds: DNA, proteins in our body, carbohydrates,
wool, cotton, petrol, medicines, pesticides, etc.
Organic chemicals
• make our life easy
• but also cause serious environmental problems
(e.g. organic compounds used as aerosol propellent damage
the ozone layer, insecticide is harmful to human
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24.1 What is Organic Chemistry (SB p.3)
Development of Organic Chemistry as a Science
In the past …,
Chemistry
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Organic
Compounds
Inorganic
Compounds
obtained from
living
organisms
obtained from
non-living
sources
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24.1 What is Organic Chemistry (SB p.3)
In 1828, Wohler (a German chemist)
(Inorganic compound)
(Organic compound)
Redefining …...
Organic chemistry is the study of carbon compounds except carbon
monoxide, carbon dioxide, carbonates, hydrogencarbonates,
carbides and cyanide.
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24.1 What is Organic Chemistry (SB p.4)
Natural Sources of Organic Compounds
Crude oil / coal
Living things
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Fractional distillation /
destructive distillation
Alkanes / Alkenes /
Alkynes / Aromatic
hydrocarbons
Carbohydrates / Proteins /
Fats / Vitamins / Antibiotics
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24.2 The Unique Nature of Carbon (SB p.5)
Ability to Catenate
Carbon atoms can link themselves together to form chains of
varying length, branched chains and rings of different sizes
Catenation:The ability of atoms in forming stable bonds with
itself and joining up in chains or rings.
e.g.
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24.2 The Unique Nature of Carbon (SB p.5)
Ability to Form Multiple Bonds
• Electronic configuration of carbon (ground state) : 1s22s22p2
Carbon (ground state)
• Each carbon atom has four unpaired electrons when excited
• tend to form 4 covalent bonds
Carbon (excited state)
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24.2 The Unique Nature of Carbon (SB p.6)
Single bond
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Double bond
Triple bond
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24.2 The Unique Nature of Carbon (SB p.6)
Example 24-1
Would you expect silicon, which is just below carbon in the
Periodic Table, to catenate to form diverse molecular
structures? Explain your answer.
Answer
Solution:
Silicon, unlike carbon, does not catenate to form diverse
molecular structures. Carbon is able to catenate because
carbon atoms have a relatively small atomic size. This
enables a carbon atom to form strong covalent bonds
with other carbon atoms. However, due to the greater
atomic size of silicon, its ability to catenate is much lower
than that of carbon.
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24.2 The Unique Nature of Carbon (SB p.7)
Check Point 24-1
Would you expect sulphur, which has an electronegativity
value very close to carbon, to catenate? Why?
Answer
The electronic configuration of sulphur is
1s22s22p63s23p4. It has only two unpaired electrons.
Its atomic size is larger than that of carbon. So it has
a much lower tendency to catenate than carbon.
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24.3 Classification of Organic Compounds (SB p.7)
Functional Groups
The compounds in a particular family are characterized by the
presence of a certain arrangement of atoms called a functional group
A functional group is defined as an atom or a group of atoms that
effectively determines the chemical properties of an organic
compound.
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24.3 Classification of Organic Compounds (SB p.7)
e.g.
and
have similar chemical properties because they contain
the same functional group –OH. They are classified
into the same homologous series — Alcohols.
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24.3 Classification of Organic Compounds (SB p.8)
Family
General
formula
Functional
group
Alkane
RH
C – H and
C – C bonds
Alkene
RCH = CH2
RCH = CHR
R2C = CHR
R2C = CR2
Alkyne
RC  CH
RC  CR
–CC–
Aromatic
hydrocarbon
ArH
Aromatic ring
Haloalkane
RX
Specific example
Formula
IUPAC name
CH3CH3
Ethane
CH2 = CH2
Ethene
HC  CH
Ethyne
Benzene
CH3Cl
R = CnH2n+1 –
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Chloromethane
24.3 Classification of Organic Compounds (SB p.8)
Functional
group
Specific example
Formula
IUPAC name
Family
General
formula
Alcohol
ROH
CH3OH
Methanol
Ether
R–O–R
CH3 – O – CH3
Methoxymethane
Aldehyde
Methanal
Ketone
Propanone
R = CnH2n+1 –
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24.3 Classification of Organic Compounds (SB p.8)
Family
General
formula
Functional
group
Specific example
Formula
Carboxylic acid
Ethanoic acid
Amine
RNH2
R2NH
R3N
Nitrile
RC  N
–CN
CH3NH2
Methylamine
CH3CN
Ethanenitrile
Ester
Methyl
ethanoate
Acyl halide
Ethanoyl
chloride
R = CnH2n+1 –, X = F, Cl, Br or I
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IUPAC
name
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24.3 Classification of Organic Compounds (SB p.9)
Family
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General formula
Functional
group
Specific example
IUPAC
Formula
name
Amide
Ethanamide
Acid
anhydride
Ethanoic
anhydride
R =
CnH2n+1 –
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24.3 Classification of Organic Compounds (SB p.9)
A homologous series is a series of compounds that have the same
functional group, and each member differs from the next member
by a – CH2 – unit in their formulae.
Number of
carbon atom(s)
IUPAC
name
Molecular
formula
Condensed
structural formula
1
Methane
CH4
CH4
2
Ethane
C2H6
CH3CH3
3
Propane
C3H8
CH3CH2CH3
4
Butane
C4H10
CH3CH2CH2CH3
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Structural formula
24.3 Classification of Organic Compounds (SB p.10)
Number of
carbon
atom(s)
IUPAC
name
1
Methanol
CH3OH
CH3OH
2
Ethanol
C2H5OH
CH3CH2OH
3
Propanol
C3H7OH
CH3CH2CH2OH
4
Butanol
C4H9OH CH3CH2CH2CH2OH
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Molecular Condensed structural
formula
formula
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Structural formula
24.3 Classification of Organic Compounds (SB p.10)
Members in the same series can be represented by a general formula.
e.g. General formula of alkanes: CnH2n+2
General formula of alcohols: CnH2n+1OH
Functional group of
an organic compound
Chemical
properties
Members of a homologous series have similar
chemical properties
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24.3 Classification of Organic Compounds (SB p.10)
The physical properties change gradually along the homologous
series
e.g. the longer the carbon chain in molecule ( or the greater the
molecular mass)
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
the greater the attractive force between molecules

the higher the melting point and boiling point
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24.3 Classification of Organic Compounds (SB p.11)
Some physical properties of the first 20 members of straight-chain alkanes
Number
State (at room
Molecular
Melting
of carbon
temperature
point (°C)
formula
atom(s)
and pressure)
1
CH4
Gas
–183
2
C2H6
Gas
–172
3
C3H8
Gas
–188
4
C4H10
Gas
–135
5
C5H12
Liquid
–130
6
C6H14
Liquid
–95
7
C7H16
Liquid
–31
8
C8H18
Liquid
–57
9
C9H20
Liquid
–54
10
C10H22
Liquid
–30
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Boiling
point (°C)
–161
–89
–42
0
36
69
98
126
151
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Density of solid
/ liquid at 20°C
(g cm–3)
–
–
–
–
0.626
0.657
0.684
0.703
0.718
0.730
24.3 Classification of Organic Compounds (SB p.11)
Some physical properties of the first 20 members of straight-chain alkanes
Number
State (at room
Molecular
Melting
of carbon
temperature
point (°C)
formula
atom(s)
and pressure)
11
C11H24
Liquid
–26
12
C12H26
Liquid
–10
13
C13H28
Liquid
–7
14
C14H30
Liquid
–3
15
C15H32
Liquid
10
16
C16H34
Liquid
18
17
C17H36
Liquid
22
18
C18H38
Solid
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19
C19H40
Solid
32
20
C20H42
Solid
37
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Boiling
point (°C)
196
216
233
260
271
287
302
316
330
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Density of solid
/ liquid at 20°C
(g cm–3)
0.740
0.749
0.753
0.761
0.769
0.773
0.778
0.777
0.777
0.785
24.3 Classification of Organic Compounds (SB p.11)
Example 24-2
Identify the functional group(s) in the following compound:
(a)
Solution:
(a) Carbon-carbon double bond (
chloro (
) group
) and
Answer
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New Way Chemistry for Hong Kong A-Level Book 3A
24.3 Classification of Organic Compounds (SB p.11)
Example 24-2
Identify the functional group(s) in the following compound:
(b)
Solution:
(b) Carbonyl group (
)
Answer
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24.3 Classification of Organic Compounds (SB p.12)
Example 24-2
Identify the functional group(s) in the following compound:
(c)
Solution:
(c) Amino group (
group (
) and carboxyl
)
Answer
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24.3 Classification of Organic Compounds (SB p.12)
Example 24-3
To which homologous series does each of the following
compounds belong?
(a)
Solution:
(a) Ester
Answer
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24.3 Classification of Organic Compounds (SB p.13)
Example 24-3
To which homologous series does each of the following
compounds belong?
(b)
Solution:
(b) Amide
Answer
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24.3 Classification of Organic Compounds (SB p.13)
Example 24-3
To which homologous series does each of the following
compounds belong?
(c)
Solution:
(c) Acid anhydride
Answer
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24.3 Classification of Organic Compounds (SB p.13)
Example 24-4
State whether each of the following pairs of compounds belongs
to the same homologous series. Explain your answers.
(a)
Answer
Solution:
(a) No, the first one is a carboxylic acid and the
second one is an ester.
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New Way Chemistry for Hong Kong A-Level Book 3A
24.3 Classification of Organic Compounds (SB p.13)
Example 24-4
State whether each of the following pairs of compounds belongs
to the same homologous series. Explain your answers.
(b)
Solution:
(b) Yes, both of them are alcohols.
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Answer
24.3 Classification of Organic Compounds (SB p.13)
Example 24-4
State whether each of the following pairs of compounds belongs
to the same homologous series. Explain your answers.
(c)
Solution:
(c) No, the first one is an amide and the second
one is an amine.
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Answer
24.3 Classification of Organic Compounds (SB p.14)
Check Point 24-2
(a) Name the homologous series of organic compounds that
contain the element oxygen in their functional groups.
Answer
(a) Alcohol, ether, aldehyde, ketone, carboxylic acid,
ester, acyl halide, amide and acid anhydride
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24.3 Classification of Organic Compounds (SB p.14)
Check Point 24-2
(b) Identify and name the functional groups in glucose
which has the structure:
(b) – OH (hydroxyl) and – O – (oxy) groups
Answer
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24.3 Classification of Organic Compounds (SB p.14)
Check Point 24-2
(c) Identify and name the functional groups in the following
compound:
(c) – Br (bromo),
(aldehyde),
(acyl chloride) and
(carbon-carbon double bond) group
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Answer
The END
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