1 chapter 24an introduction to organic chemistry 24.1what are organic compounds? 24.2introducing...

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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?


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.)


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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.


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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).


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Figure 24.4

Most organic compounds consist of molecules:

(a) Hexane consists of simple molecules. (b) Starch consists of macromolecules.


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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.


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Figure 24.5

Ethanol, an organic compound,

burns to form carbon dioxide

and water.


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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.


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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.


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A24.3


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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


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.


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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.


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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.


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Table 24.4

Some common functional groups and homologous series, with the first member in each

series shown.


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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


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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.


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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.


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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).


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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:


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The name of the compound is:

A24.8

(a) 2,3-dimethylbutane

(b) 4-ethyl-3-methylheptane


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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.


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For example,

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A24.10

(a) 2-methylbut-2-ene

(b) chloroethene


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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)


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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


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A24.12

3-chlorobutanoic acid.


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24.7 STRUCTURAL FORMULAE FROM IUPAC NAMES

24.7 STRUCTURAL FORMULAE FROM IUPAC

NAMES

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40

A24.13


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A model of butane.

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A model of but-1-ene.

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A model of butan-1-ol.

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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.

1 chapter 24an introduction to organic chemistry 24.1what are organic compounds? 24.2introducing...

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