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Chapter 24 An Introduction to Organic Chemistry
24.1 What are organic compounds?
24.2 Introducing organic chemistry
24.3 Organic molecules represented by structural formulae
24.4 Saturated and unsaturated hydrocarbons
24.5 Classification of organic compounds
24.6 Naming of organic compounds
24.7 Structural formulae from IUPAC names
CONTENTS OF CHAPTER 24
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24.1 WHAT ARE ORGANIC COMPOUNDS?
24.1 WHAT ARE ORGANIC COMPOUNDS?
Figure 24.2 A collection of substances containing organic compounds.
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ORGANIC COMPOUNDS are carbon compounds.
A24.1
CO, CO2, Na2CO3, KHCO3, H2O, NH3, KOH, HCl, HNO3, NaCl.
(Other answers may be given.)
24.1 WHAT ARE ORGANIC COMPOUNDS?
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24.2 INTRODUCING ORGANIC CHEMISTRY
24.2 INTRODUCING ORGANIC CHEMISTRY
WHAT IS ORGANIC CHEMISTRY?
ORGANIC CHEMISTRY is a branch of chemistry focusing on
carbon compounds.
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Figure 24.3 Organic chemistry is often studied as a separate branch of chemistry.
24.2 INTRODUCING ORGANIC CHEMISTRY
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GENERAL CHARACTERISTICS OF ORGANIC
COMPOUNDS
Constituent elements and bonding in organic compounds
Almost all organic compounds contain hydrogen besides carbon.
Most organic compounds are covalent compounds. Some
consist of simple molecules. Others consist of very large
molecules (macromolecules).
24.2 INTRODUCING ORGANIC CHEMISTRY
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Figure 24.4
Most organic compounds consist of molecules:
(a) Hexane consists of simple molecules. (b) Starch consists of macromolecules.
24.2 INTRODUCING ORGANIC CHEMISTRY
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A24.2
Tetrachloromethane CCl4.
(Other answers may be given.)
Reactions of organic compounds
In general, reactions involving organic compounds have the
following in common:
The reactions are usually slow (when compared with common
inorganic reactions).
In most cases, organic compounds can burn to give carbon
dioxide and water.
24.2 INTRODUCING ORGANIC CHEMISTRY
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Figure 24.5
Ethanol, an organic compound,
burns to form carbon dioxide
and water.
24.2 INTRODUCING ORGANIC CHEMISTRY
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UNIQUENESS OF CARBON
Carbon has the unique property of forming a very large number of
compounds (over 4 000 000). There are three reasons for this:
(1) Carbon atoms can form strong single, double and triple
covalent bonds with other carbon atoms.
(2) Each carbon atom can form four single covalent bonds.
(3) Carbon can form strong bonds with other elements.
24.2 INTRODUCING ORGANIC CHEMISTRY
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24.2 INTRODUCING ORGANIC CHEMISTRY
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24.3 ORGANIC MOLECULES REPRESENTED BY STRUCTURAL FORMULAE
24.3 ORGANIC MOLECULES REPRESENTED
BY STRUCTURAL FORMULAE
Table 24.1
Structures of a butane molecule and a 2-methylpropane molecule, as represented by
formulae and models.
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Table 24.2 Structural formulae and models of some organic compounds.
24.3 ORGANIC MOLECULES REPRESENTED BY STRUCTURAL FORMULAE
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A24.3
24.3 ORGANIC MOLECULES REPRESENTED BY STRUCTURAL FORMULAE
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24.4 SATURATED AND UNSATURATED HYDROCARBONS
24.4 SATURATED AND UNSATURATED
HYDROCARBONS
Hydrocarbons may be saturated or unsaturated. Hydrocarbons
containing only single bonds are said to be saturated. Those
containing one or more carbon-carbon multiple bonds (C = C,
C C) are unsaturated. For example,
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24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
24.5 CLASSIFICATION OF ORGANIC
COMPOUNDS
FUNCTIONAL GROUP
Figure 24.7 Structural formulae and models of butane, but-1-ene and butan-1-ol.
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A FUNCTIONAL GROUP is an atom or group of atoms
responsible for most of the chemical properties of a compound.
A24.4
(a) Yes. They have the same functional group (–OH).
(b) A < B < C < D in boiling point. Van der Waals’ forces are
greater between larger molecules.
HOMOLOGOUS SERIES
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
The hydrocarbons methane, ethane, propane and butane belong
to the same homologous series — the alkane series.
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Table 24.3 Names, formulae and models of the four hydrocarbons present in natural gas.
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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A HOMOLOGOUS SERIES is a family of compounds all having
the same general formula and with adjacent members differing by
a – CH2 – unit. The individual members of a homologous series
are referred to as HOMOLOGUES.
A24.5
(a) Put n = 5 in CnH2n+2.
The molecular formula is C5H12.
(b) Put n = 11 in CnH2n+2.
The molecular formula is C11H24.
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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Another homologous series is the alkanol (alcohol) series,
with the general formula CnH2n+1OH.
Figure 24.8
Methanol and ethanol are the first
two members of the alkanol series.
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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Table 24.4
Some common functional groups and homologous series, with the first member in each
series shown.
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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A24.6
(a) A and C; alkanoic acid series
(b) H H H H H O
H— C— C— C— C— C— C— O— H
H H H H H
24.5 CLASSIFICATION OF ORGANIC COMPOUNDS
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24.6 NAMING OF ORGANIC COMPOUNDS
24.6 NAMING OF ORGANIC COMPOUNDS
NAMING ALKANES BY THE IUPAC SYSTEM
Naming straight-chain alkanes
All alkanes have names ending with the suffix -ane.
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Table 24.5 Structural formulae and names of the 10 simplest straight-chain alkanes.
24.6 NAMING OF ORGANIC COMPOUNDS
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Alkyl groups
Alkyl groups are derived from alkanes by the removal of a
hydrogen atom. They are often represented by the symbol R—.
Table 24.6 Some alkyl groups and their parent alkanes.
24.6 NAMING OF ORGANIC COMPOUNDS
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A24.7
(a) (i) Hexyl (ii) Octyl
(b) (i) CH3(CH2)3CH2—
(ii) CH3(CH2)5CH2—
Naming branched-chain alkanes
The IUPAC name for a branched-chain alkane consists of 2 parts:
(1) The prefixes which indicate the alkyl group substituents
(2) The ‘root’ which indicates the parent alkane (the main carbon
chain).
24.6 NAMING OF ORGANIC COMPOUNDS
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That is,
Prefixes Root
(alkyl groups) (main carbon chain)
The basic IUPAC rules of naming can be illustrated by the
example below:
24.6 NAMING OF ORGANIC COMPOUNDS
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The name of the compound is:
A24.8
(a) 2,3-dimethylbutane
(b) 4-ethyl-3-methylheptane
24.6 NAMING OF ORGANIC COMPOUNDS
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NAMING HALOGEN-SUBSTITUTED ALKANES
A24.9
2-bromo-1-iodo-3-methylpentane
NAMING ALKENES
Alkenes have the general formula CnH2n. We can name them with
the same general rules for alkanes, but using the suffix -ene
instead of -ane.
24.6 NAMING OF ORGANIC COMPOUNDS
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24.6 NAMING OF ORGANIC COMPOUNDS
For example,
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24.6 NAMING OF ORGANIC COMPOUNDS
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A24.10
(a) 2-methylbut-2-ene
(b) chloroethene
24.6 NAMING OF ORGANIC COMPOUNDS
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24.6 NAMING OF ORGANIC COMPOUNDS
NAMING ALKANOLS
Alkanols have the general formula CnH2n+1OH or ROH, where R–
is an alkyl group.
Names of some alkanols are given below:
CH3OH (methaneol) methanol; CH3CH2OH ethanol
3 2 1
CH3CH2CH2OH propan-1-ol
3 2 1
CH3CHCH3 propan-2-ol
OH
(not propan-3-ol, as the lowest possible numeral is given to the –OH group)
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CH3
1CH3—2C—3CH3 2-methylpropan-2-ol
OH
A24.11
(a) Butan-1-ol
(b) 4-chlorobutan-2-ol
(not 1-chlorobutan-3-ol)
24.6 NAMING OF ORGANIC COMPOUNDS
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NAMING ALKANOIC ACIDS
Alkanoic acids have the general formula CnH2n+1COOH or
R COOH, where R– is an alkyl group or hydrogen.
Names of some alkanoic acids are given below:
HCOOH (methaneoic acid) methanoic acid
CH3COOH ethanoic acid
CH3CH2COOH propanoic acid
CH3CH2CH2COOH butanoic acid
3 2 1
CH3CHCOOH 2-methylpropanoic acid
CH3
24.6 NAMING OF ORGANIC COMPOUNDS
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A24.12
3-chlorobutanoic acid.
24.6 NAMING OF ORGANIC COMPOUNDS
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
24.7 STRUCTURAL FORMULAE FROM IUPAC
NAMES
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
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A24.13
24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
A model of butane.
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
A model of but-1-ene.
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
A model of butan-1-ol.
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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES
A model of butanoic acid.
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SUMMARY
1. Organic compounds are carbon compounds.
2. Almost all organic compounds contain hydrogen besides
carbon. Many contain oxygen too. They are usually covalent
compounds.
3. In general, reactions involving organic compounds are slow.
In most cases, organic compounds can burn to give carbon
dioxide and water.
SUMMARY
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SUMMARY
4. Carbon forms a very large number of organic compounds
because
carbon can form strong bonds with itself and with other
elements
each carbon atom can form 4 single covalent bonds
5. Saturated hydrocarbons are compounds (with carbon and
hydrogen only) containing only single bonds.
Unsaturated hydrocarbons are compounds (with carbon and
hydrogen only) containing one or more carbon-carbon
multiple bonds (C=C or CC).
6. A functional group is an atom or group of atoms responsible
for most of the chemical properties of a compound.
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SUMMARY
7. A homologous series is a family of compounds having the
same general formula with adjacent members differing by a
– CH2 – unit. See Table 24.4 on p. 29.
8. Organic compounds are usually named by the IUPAC system
of naming. For rules and examples, refer to pp. 30 – 37.