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Introduction to organic chemistry

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Title: Introduction to organic chemistry


1
Introduction to Organic Chemistry
21.1 What is Organic Chemistry? 21.2 The Unique
Nature of Carbon 21.3 Classification of Organic
Compounds 21.4 Factors Affecting the Physical
Properties of Organic Compounds
2
What is Organic Chemistry?
3
21.1 What is Organic Chemistry (SB p.2)
Organic Chemistry
  • Chemistry of the compounds present in living
    organisms.
  • They all contain carbon.
  • Organic Chemistry is the Chemistry of Carbon.

4
21.1 What is Organic Chemistry (SB p.4)
Natural Sources of Organic Compounds
5
21.1 What is Organic Chemistry (SB p.4)
Natural Sources of Organic Compounds
6
21.1 What is Organic Chemistry (SB p.3)
Development of Organic Chemistry as a Science
In the past ,
Chemistry
7
21.1 What is Organic Chemistry (SB p.3)
Development of Organic Chemistry as a Science
In 1828, Wohler (a German chemist)
(Inorganic compound)
(Organic compound)
8
21.1 What is Organic Chemistry (SB p.3)
Development of Organic Chemistry as a Science
Redefining ...
Organic chemistry is the study of carbon
compounds (except CO, CO2, carbonates,
hydrogencarbonates, carbides and cyanides)
obtained from natural sources or synthesized in
the laboratories.
9
The Unique Nature of Carbon
10
21.2 The Unique Nature of Carbon (SB p.5)
Ability to form four strong covalent bonds
  • Electronic configuration of carbon (ground state)
    1s22s22p2

11
21.2 The Unique Nature of Carbon (SB p.5)
Ability to form four strong covalent bonds
  • Each carbon atom has four unpaired electrons when
    excited
  • Tend to form four strong covalent bonds

12
21.2 The Unique Nature of Carbon (SB p.5)
Ability to Catenate
  • Carbon atoms link together to form chains of
    varying length, branched chains and rings of
    different sizes
  • Catenation
  • ? Ability of atoms in forming stable bonds with
    itself, hence joining up into chains or rings

13
21.2 The Unique Nature of Carbon (SB p.5)
Ability to Catenate
C C gt Si Si gt Ge Ge gt Sn Sn
Bond strength ? as bond length ?
14
21.2 The Unique Nature of Carbon (SB p.5)
Ability to Catenate
C C gt N N gt O O
Bond strength ? as the number of lone pairs ?
15
21.2 The Unique Nature of Carbon (SB p.5)
Ability to Catenate
CnH2n2 n 1,2,3,(no limit for n) SinH2n2 n
1 to 6 only ? silanes GenH2n2 n 1 to 3 only ?
germanes SnnH2n2 Only SnH4 (stannane) exists
16
21.2 The Unique Nature of Carbon (SB p.5)
Ability to Form Multiple Bonds
17
21.2 The Unique Nature of Carbon (SB p.6)
Single bond Double bond Triple bond

X halogens
18
21.2 The Unique Nature of Carbon (SB p.6)
19
Classification of Organic Compounds
20
21.3 Classification of Organic Compounds (SB p.7)
Functional Groups
  • Organic compounds are classified by the the
    presence of characteristic functional groups.

21
21.3 Classification of Organic Compounds (SB p.7)
Functional Groups
A functional group is defined as an atom or a
group of atoms that effectively determines the
chemical properties of an organic compound.
22
21.3 Classification of Organic Compounds (SB p.7)
Functional Groups
23
21.3 Classification of Organic Compounds (SB p.7)
Functional Groups
  • Propane does not react with sodium
  • Ethanol and propan-1-ol react with sodium to give
    hydrogen gas

24
21.3 Classification of Organic Compounds (SB p.7)
Functional Groups
  • have similar chemical properties
  • ? they contain the same functional group OH
  • ? they are classified into the same homologous
    series alcohols

25
21.3 Classification of Organic Compounds (SB
p.12)
Homologous Series
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.
26
21.3 Classification of Organic Compounds (SB
p.12)
Number of carbon atom(s) IUPAC name Molecular formula Condensed structural formula Structural formula
1 Methane CH4 CH4
2 Ethane C2H6 CH3CH3
3 Propane C3H8 CH3CH2CH3
4 Butane C4H10 CH3CH2CH2CH3
The first four members of straight-chain alkanes
27
21.3 Classification of Organic Compounds (SB
p.12)
Number of carbon atom(s) IUPAC name Molecular formula Condensed structural formula Structural formula
1 Methanol CH3OH CH3OH
2 Ethanol C2H5OH CH3CH2OH
3 Propan-1-ol C3H7OH CH3CH2CH2OH
4 Butan-1-ol C4H9OH CH3CH2CH2CH2OH
The first four members of straight-chain alcohols
28
21.3 Classification of Organic Compounds (SB
p.13)
Homologous Series
  • Members in the same series can be represented by
    a general formula.
  • e.g. alkanes CnH2n2
  • alkenes CnH2n
  • alkynes CnH2n-2

29
21.3 Classification of Organic Compounds (SB
p.13)
Homologous Series
  • Members in the same series can be represented by
    a general formula.

e.g. alkanols CnH2n1OH alkanals
CnH2n1CHO alkanoic acids CnH2n1COOH
30
21.3 Classification of Organic Compounds (SB
p.13)
Homologous Series
Functional group of an organic compound
Members of a homologous series have similar
chemical properties
31
21.3 Classification of Organic Compounds (SB
p.13)
Homologous Series
  • The physical properties change gradually along
    the homologous series
  • e.g. the longer the carbon chain in
    the molecule ( or the greater the molecular
    mass)
  • ? the greater the attractive force between
    molecules
  • ? the higher the melting point, boiling point
    and density

32
21.3 Classification of Organic Compounds (SB
p.13)
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 91 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
33
21.3 Classification of Organic Compounds (SB
p.13)
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
34
21.3 Classification of Organic Compounds (SB
p.13)
35
Factors Affecting the Physical Properties of
Organic Compounds
Refer to notes on Bonding and Structure
pp.77-92 intermolecular forces
36
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.17)
Main Factors Affecting the Physical Properties of
Organic Compounds
1. Structure of the functional group 1.1 Dipole
moment of the molecule 1.2 Formation of hydrogen
bonding 2. Length of carbon chains (London
dispersion forces)
37
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.17)
Structure of Functional Group
  • Molecules having a polar functional group have a
    higher b.p. than others with a non-polar
    functional group of similar molecular masses
  • ? Stronger intermolecular attraction among
    molecules

38
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.17)
Structure of Functional Group
Molecule Relative molecular mass Boiling point (oC)
Molecules with polar functional groups CH3CH2CH2OH 60 97.2
Molecules with polar functional groups CH3CH2CH2NH2 59 48.6
Molecules with polar functional groups CH3CH2Cl 64.5 12.5
Molecules with polar functional groups CH3CH2COOH 60 141
Molecules with non-polar functional groups CH3CH2CH2CH3 58 -0.5
Molecules with non-polar functional groups CH3CH2CHCH2 56 -6.2
Molecules with non-polar functional groups CH3CH2C?CH 54 8.1
39
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Dipole Moment of Molecule
  • Tetrachloromethane has 4 polar bonds in the
    molecule
  • M.p. and b.p. are very low
  • ? the molecule is non-polar
  • ? the molecule is tetrahedrally symmetrical
  • ? the dipole moments of the C ? Cl bond
    cancel each other

40
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Examples of Polar Molecules with Net Dipole Moment
41
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Examples of Non-polar Molecules with No Net
Dipole Moment
42
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Solubility of Organic Molecules
  • Depends on the polarity of organic molecules and
    the solvent
  • Non-polar or weakly polar compounds dissolve
    readily in non-polar or weakly polar solvents
  • Highly polar compounds dissolve readily in highly
    polar solvents
  • Like dissolves like

43
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Solubility of Organic Molecules
44
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.19)
Why does Hexane Dissolve Readily in
Tetrachloromethane?
45
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.19)
Why is Hexane Insoluble in Water?
46
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.19)
Formation of Hydrogen Bonding
  • Molecules having ?OH or ? NH2 groups are able to
    form hydrogen bonds
  • Hydrogen bonds affect the physical properties of
    alcohols and amines with low molecular masses

47
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
Why does Propan-1-ol have a Higher Boiling Point?
48
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
Formation of Hydrogen Bonding
  • Also affect the solubility of a molecule
  • Molecules with ?OH groups are able to form
    hydrogen bonds with surrounding water molecules
  • ? Soluble in water

49
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
50
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
Length of Carbon Chains
  • Molecules with higher molecular masses have
    higher m.p., b.p. and density
  • ? Higher molecular masses
  • ? Large molecular sizes
  • ? Stronger London dispersion forces among
    molecules

51
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
Length of Carbon Chains
  • Molecules with branched chains
  • ? b.p. and density lower than its
    straight-chain isomer
  • Straight-chain isomers have greater surface area
    in contact with each other
  • ? Greater attractive force among the molecules

52
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
Length of Carbon Chains
  • Molecules with branched chains
  • ? m.p. higher than its straight-chain isomer
  • Branched-chain isomers are more spherical
  • ? Packed more efficiently in solid state
  • ? Extra energy is needed to break down the
    efficient packing

53
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
54
21.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Example Example
Family General formula Functional group Formula IUPAC name
Alkane RH (Nil) CH3CH3 Ethane
Alkene RCH CH2 RCH CHR R2C CHR R2C CR2 Carbon-carbon double bond CH2 CH2 Ethene
Alkyne RC ? CH RC ? CR C ? C Carbon-carbon triple bond HC ? CH Ethyne
Aromatic hydrocarbon ArH Phenyl group Benzene
R CnH2n1
55
21.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Example Example
Family General formula Functional group Formula IUPAC name
Haloalkane RX X halo group CH3Cl Chloromethane
Alcohol ROH ? OH hydroxyl group CH3OH Methanol
Ether R?O ? R ? O ? oxy group CH3 ? O ? CH3 Methoxymethane
Aldehyde carbonyl group Methanal
R CnH2n1
56
21.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Example Example
Family General formula Functional group Formula IUPAC name
Ketone carbonyl group Propanone
Carboxylic acid carboxyl group Ethanoic acid
Amine RNH2 R2NH R3N amino group CH3NH2 Methylamine
Nitrile RC?N ? C ? N nitrile group CH3CN Ethanenitrile
R CnH2n1
57
21.3 Classification of Organic Compounds (SB p.8)
Family General formula Functional group Example Example
Family General formula Functional group Formula IUPAC name
Ester ester group Methyl ethanoate
Acyl halide acyl halide group Ethanoyl chloride
Amide amide group Ethanamide
R CnH2n1
58
21.3 Classification of Organic Compounds (SB p.9)
Family General formula Functional group Example Example
Family General formula Functional group Formula IUPAC name
Acid anhydride acid anhydride group Ethanoic anhydride
R CnH2n1
59
The END
60
21.1 What is Organic Chemistry (SB p.4)
Check Point 21-1
  1. How was organic chemistry defined before 1800s?

Answer
(a) The knowledge of organic and inorganic
compounds was raised during the 1780s. Scientists
defined organic chemistry as the study of
compounds that could be obtained from living
organisms. They believed that the synthesis of
organic compounds took place in living organisms
only.
61
21.1 What is Organic Chemistry (SB p.4)
Back
Check Point 21-1
(b) How is organic chemistry defined nowadays?
Answer
(b) Nowadays, scientists have discovered that
many organic compounds can be synthesized from
inorganic substances. The updated definition of
organic chemistry is the study of carbon
compounds, except for carbon monoxide, carbon
dioxide, carbonates, hydrogencarbonates, carbides
and cyanides. These compounds have been
traditionally classified under inorganic
chemistry.
62
21.2 The Unique Nature of Carbon (SB p.5)
Let's Think 1
Why is carbon able to catenate?
Answer
The ability to catenate of carbon is chiefly due
to the high strength of the C?C single bond (bond
enthalpy of C ? C single bond is 356 kJ mol-1).
Back
63
21.2 The Unique Nature of Carbon (SB p.6)
Example 21-2
Would you expect silicon, which is just below
carbon in the Periodic Table, to catenate to form
diverse molecular structures? Explain your answer.
Answer
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.
Back
64
21.2 The Unique Nature of Carbon (SB p.7)
Back
Check Point 21-2
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.
65
21.3 Classification of Organic Compounds (SB
p.14)
Example 21-3A
Identify the functional group(s) in the following
compounds (a)
Answer
66
21.3 Classification of Organic Compounds (SB
p.14)
Example 21-3A
Identify the functional group(s) in the following
compounds (b)
Answer
67
21.3 Classification of Organic Compounds (SB
p.14)
Back
Example 21-3A
Identify the functional group(s) in the following
compounds (c)
Answer
68
21.3 Classification of Organic Compounds (SB
p.15)
Example 21-3B
To which homologous series does each of the
following compounds belong? (a)
(a) Ester
Answer
69
21.3 Classification of Organic Compounds (SB
p.15)
Example 21-3B
To which homologous series does each of the
following compounds belong? (b)
(b) Amide
Answer
70
21.3 Classification of Organic Compounds (SB
p.15)
Back
Example 21-3B
To which homologous series does each of the
following compounds belong? (c)
(c) Acid anhydride
Answer
71
21.3 Classification of Organic Compounds (SB
p.15)
Example 21-3C
State whether each of the following pairs of
compounds belongs to the same homologous series.
Explain your answer. (a)
Answer
(a) No, the first one is a carboxylic acid and
the second one is an ester.
72
21.3 Classification of Organic Compounds (SB
p.15)
Example 21-3C
State whether each of the following pairs of
compounds belongs to the same homologous series.
Explain your answer. (b)
Answer
(b) Yes, both of them are alcohols.
73
21.3 Classification of Organic Compounds (SB
p.15)
Back
Example 21-3C
State whether each of the following pairs of
compounds belongs to the same homologous series.
Explain your answer. (c)
Answer
(c) No, the first one is an amide and the second
one is an amine.
74
21.3 Classification of Organic Compounds (SB
p.16)
Check Point 21-3
(a) Name the homologous series of organic
compounds that contain oxygen atoms in their
functional groups.
Answer
(a) Alcohol, ether, aldehyde, ketone, carboxylic
acid, ester, acyl halide, amide and acid anhydride
75
21.3 Classification of Organic Compounds (SB
p.16)
Check Point 21-3
  • Identify and name the functional groups in
    glucose which has the following structure.

(b) ?OH (hydroxyl group) and ? O ? (oxy group)
Answer
76
21.3 Classification of Organic Compounds (SB
p.16)
Back
Check Point 21-3
  • (c) Identify and name the functional groups in
    the following compounds

Answer
77
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.18)
Let's Think 2
Why is oil immiscible with water?
Answer
Oil molecules do not have free ?OH groups, so
they cannot form hydrogen bonds with water
molecules.
Back
78
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
Let's Think 3
The relative molecular mass of glucose is 180.0,
but it is soluble in water. Why?
Answer
Glucose molecules have ?OH groups, so they are
able to form hydrogen bonds with water molecules.
Therefore, glucose is soluble in water despite it
has a high molecular mass.
Back
79
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
Example 21-4A
Despite the fact that butan-1-ol and ethoxyethane
have the same relative molecular mass, they have
very different boiling points. The boiling points
of butan-1-ol and ethoxyethane are 117oC and 35oC
respectively. Explain the difference.
Answer
80
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.20)
Back
Example 21-4A
81
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
Back
Example 21-4B
Explain why propan-1-ol is soluble in water but
1-chloropropane is insoluble in water.
Answer
The ? OH group of propan-1-ol molecules enables
it to form hydrogen bonds with water molecules.
Thus it is soluble in water. Although
1-chloropropane is a polar molecule, it does not
form hydrogen bonds with water molecules. So it
is insoluble in water.
82
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.21)
Let's Think 4
Which molecule would have a higher boiling point,
1-bromobutane or 2-bromobutane? Why?
Answer
1-bromobutane would have a higher boiling point.
1-bromobutane is a straight-chain molecule while
2-bromobutane is a branched-chain molecule.
Straight-chain molecules have a greater surface
area in contact with each other, so greater
intermolecular forces exist among the molecules.
Higher energy is required to break down the
intermolecular forces among the molecules of
1-bromobutane.
Back
83
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.22)
Example 21-4C
1-Chlorobutane and 2-chloro-2-methylpropane have
the same molecular mass, yet their melting points
differ. The melting point of 1-chlorobutane is
123oC while that of 2-chloro-2-methylpropane is
27.1oC. Explain the difference.
Answer
84
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.22)
Back
Example 21-4C
Melting point is a measure of how efficient the
molecules are packed together in the solid state
instead of just comparing the van der Waals
forces among molecules. Hence melting point is a
function of the efficient packing of molecules
but not the contact surface area. 1-Chlorobutane
is a straight-chain molecule while
2-chloro-2-methylpropane is a branched-chain
molecule. As 2-chloro-2-methylpropane is more
spherical and symmetrical, its molecules are
packed more efficiently in the solid state.
1-Chlorobutane is linear in shape and flattened,
its packing in the solid state is not so
efficient. Hence, it has a lower melting point
than 2-chloro-2-methylpropane.
85
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
(a) What are the major factors that affect the
physical properties of organic compounds?
Answer
(a) The physical properties of organic compounds
are mainly affected by the structure of the
functional groups, dipole moment of the molecule,
the formation of hydrogen bonding between
molecules, and the length of carbon chains of the
molecule.
86
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
  1. The melting point and boiling point of pentane
    are 130oC and 36.3oC respectively while the
    melting point and boiling point of
    2,2-dimethylpropane are 15.9oC and 9.5oC
    respectively. Account for the difference in
    melting point and boiling point between the two
    isomers.

Answer
87
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
(b) Pentane is a straight-chain molecule, while
2,2-dimethylpropane is a branched-chain molecule.
Straight-chain molecules have a greater surface
area in contact with each other than
branched-chain molecules. Straight-chain
molecules are held together by stronger
intermolecular forces. Therefore, pentane has a
higher boiling point than 2,2-dimethylpropane.
Molecules of 2,2-dimethylpropane are more
spherical in shape and are packed more
efficiently in the solid state. Molecules of
pentane are linear in shape and flattened, so
their packing in the solid state is not
efficient. Since extra energy is required to
break down the efficient packing of
2,2-dimethylpropane, 2,2-dimethylpropane has a
higher melting point than pentane.
88
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
  • (c) Which molecule, hexane or cyclohexane, would
    have a higher melting point? Explain your answer.

Answer
89
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
(c) Cyclohexane has a higher melting point than
hexane. Molecules of cyclohexane are more
spherical in shape and are packed more eff
iciently in the solid state. Molecules of hexane
are linear in shape and flattened, so their
packing in the solid state is not efficient.
Since extra energy is required to break down the
efficient packing of cyclohexane, cyclohexane has
a higher melting point than hexane.
90
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
  • (d) Arrange the following molecules in increasing
    order of boiling points. Explain your answer.

Answer
91
21.4 Factors Affecting the Physical Properties
of Organic Compounds (SB p.24)
Check Point 21-4
Back
(d) The boiling points increase in the
order butane lt propanal lt propan-1-ol Molecules
of butane are non-polar. Their molecules are held
together by weak instantaneous dipole-induced
dipole interactions. A relatively small amount of
energy is required to separate the molecules in
the process of boiling. Both propanal and
propan-1-ol are polar molecules. Molecules of
propanal are held together by relatively weak
dipole-dipole interactions, while molecules of
propan-1-ol are held together by intermolecular
hydrogen bonds. Since the intermolecular forces
present in molecules of propan-1-ol are stronger
than those present in molecules of propanal, a
larger amount of energy is required to separate
the propan-1-ol molecules in the process of
boiling.
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