Introduction to Organic Chemistry

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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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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
Alkanes / Alkenes / Alkynes / Aromatic
hydrocarbons
Crude oil / coal
Carbohydrates / Proteins / Fats / Vitamins /
Antibiotics
Living things
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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

• Each carbon atom has four unpaired electrons
  when excited
• tend to form 4 covalent bonds

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24.2 The Unique Nature of Carbon (SB p.6)
Single bond 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
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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.
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 Specific example Specific example
Family General formula Functional group Formula IUPAC name
Alkane RH C H and C C bonds CH3CH3 Ethane
Alkene RCH CH2 RCH CHR R2C CHR R2C CR2 CH2 CH2 Ethene
Alkyne RC ? CH RC ? CR C ? C HC ? CH Ethyne
Aromatic hydrocarbon ArH Aromatic ring Benzene
Haloalkane RX CH3Cl Chloromethane
R CnH2n1
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24.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Specific example Specific example
Family General formula Functional group Formula IUPAC name
Alcohol ROH CH3OH Methanol
Ether R O R CH3 O CH3 Methoxymethane
Aldehyde Methanal
Ketone Propanone
R CnH2n1
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24.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Specific example Specific example
Family General formula Functional group Formula IUPAC name
Carboxylic acid Ethanoic acid
Amine RNH2 R2NH R3N CH3NH2 Methylamine
Nitrile RC ? N C ? N CH3CN Ethanenitrile
Ester Methyl ethanoate
Acyl halide Ethanoyl chloride
R CnH2n1 , X F, Cl, Br or I
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24.3 Classification of Organic Compounds (SB p.9)
Family General formula Functional group Specific example Specific example
Family General formula Functional group Formula IUPAC name
Amide Ethanamide
Acid anhydride Ethanoic anhydride
R CnH2n1
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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.
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24.3 Classification of Organic Compounds (SB
p.10)
Number of carbon atom(s) IUPAC name Molecular formula Condensed structural formula Structural formula
1 Methanol CH3OH CH3OH
2 Ethanol C2H5OH CH3CH2OH
3 Propanol C3H7OH CH3CH2CH2OH
4 Butanol C4H9OH CH3CH2CH2CH2OH
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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 CnH2n2 General formula of
alcohols CnH2n1OH
Functional group of an organic compound
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 seriese.g. the longer the carbon
chain in molecule ( or the greater the molecular
mass) ? 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 of carbon atom(s) Molecular formula State (at room temperature and pressure) Melting point (C) Boiling point (C) Density of solid / liquid at 20C (g cm3)
1 2 3 4 5 6 7 8 9 10 CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 Gas Gas Gas Gas Liquid Liquid Liquid Liquid Liquid Liquid 183 172 188 135 130 95 31 57 54 30 161 89 42 0 36 69 98 126 151 174 0.626 0.657 0.684 0.703 0.718 0.730
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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 of carbon atom(s) Molecular formula State (at room temperature and pressure) Melting point (C) Boiling point (C) Density of solid / liquid at 20C (g cm3)
11 12 13 14 15 16 17 18 19 20 C11H24 C12H26 C13H28 C14H30 C15H32 C16H34 C17H36 C18H38 C19H40 C20H42 Liquid Liquid Liquid Liquid Liquid Liquid Liquid Solid Solid Solid 26 10 7 3 10 18 22 28 32 37 196 216 233 260 271 287 302 316 330 344 0.740 0.749 0.753 0.761 0.769 0.773 0.778 0.777 0.777 0.785
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24.3 Classification of Organic Compounds (SB
p.11)
Example 24-2 Identify the functional group(s) in
the following compound (a)
Answer
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24.3 Classification of Organic Compounds (SB
p.11)
Example 24-2 Identify the functional group(s) in
the following compound (b)
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)
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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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)
Answer
Solution (b) Yes, both of them are alcohols.
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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. (c)
Answer
Solution (c) No, the first one is an amide and
the second one is an amine.
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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
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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
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
Answer
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The END