Giáo trình Hóa học bằng tiếng Anh - Chemistry 12 v2

At this moment, you are walking,

sitting, or standing in an “organic”

body. Your skin, hair, muscles, heart,

and lungs are all made from organic

compounds. In fact, the only parts of

your body that are not mostly organic

are your teeth and bones! When you

study organic chemistry, you are

studying the substances that make

up your body and much of the world

around you. Medicines, clothing,

carpets, curtains, and wood and

plastic furniture are all manufactured

from organic chemicals. If you look

out a window, the grass, trees, squir￾rels, and insects you may see are also

composed of organic compounds.

Are you having a sandwich for

lunch? Bread, butter, meat, and lettuce

are made from organic compounds.

Will you have dessert? Sugar, flour,

vanilla, and chocolate are also organic.

What about a drink? Milk and juice

are solutions of water in which

organic compounds are dissolved.

In this unit, you will study a

variety of organic compounds. You

will learn how to name them and how

to draw their structures. You will also

learn how these compounds react, and

you will use your knowledge to pre￾dict the products of organic reactions.

In addition, you will discover the

amazing variety of organic compounds

in your body and in your life.

Organic Chemistry

CHAPTER 1

Classifying Organic Compounds

CHAPTER 2

Reactions of Organic Compounds

UNIT 1 ISSUE

Current Issues Related to

Organic Chemistry

UNIT 1 CONTENTS

How do the structures of

various organic compounds

differ? What chemical

reactions are typical of these

compounds?

How can you name different

organic compounds and

represent their structures?

What do you need to know in

order to predict the products

of organic reactions?

How do organic compounds

affect your life? How do they

affect the environment?

UNIT 1 OVERALL EXPECTATIONS

2

Before beginning Unit 1, read

pages 110 to 111 to find out about

the unit issue. In the unit issue, you

will analyze an issue that involves

chemistry and society. You can

start planning your research as you

go through this unit. Which topics

interest you the most? How does

society influence developments in

science and technology?

Unit Issue Prep

4 MHR • Unit 1 Organic Chemistry

Classifying

Organic Compounds

What is the word “organic” intended to mean here?

How is this meaning different from the scientific

meaning of the word?

1.1 Bonding and the Shape

of Organic Molecules

1.2 Hydrocarbons

1.3 Single-Bonded

Functional Groups

1.4 Functional Groups

With the CO bond

Chapter Preview

Before you begin this chapter,

review the following concepts

and skills:

■ drawing Lewis structures

(Concepts and Skills

Review)

■ writing molecular formulas

and expanded molecular

formulas (Concepts and

Skills Review)

■ drawing complete, con￾densed, and line structural

diagrams (Concepts and

Skills Review)

■ identifying structural

isomers (Concepts and

Skills Review)

Prerequisite

Concepts and Skills

As you wander through the supermarket, some advertising claims catch

your eye. “Certified organic” and “all natural” are stamped on the labels

of some foods. Other labels claim that the foods are “chemical free.” As a

chemistry student, you are aware that these labels may be misleading. Are

all “chemicals” harmful in food, as some of the current advertising suggests?

Many terms are used inaccurately in everyday life. The word “natural”

is often used in a manner suggesting that all natural compounds are safe

and healthy. Similarly, the word “chemical” is commonly used to refer to

artificial compounds only. The food industry uses “organic” to indicate

foods that have been grown without the use of pesticides, herbicides,

fertilizers, hormones, and other synthetic chemicals. The original meaning

of the word “organic” refers to anything that is or has been alive. In this

sense, all vegetables are organic, no matter how they are grown.

Organic chemistry is the study of compounds that are based on

carbon. Natural gas, rubbing alcohol, aspirin, and the compounds that

give fragrance to a rose, are all organic compounds. In this chapter, you

will learn how to identify and name molecules from the basic families of

organic compounds. You will be introduced to the shape, structure, and

properties of different types of organic compounds.

In this section, you will

■ discuss the use of the

terms organic, natural, and

chemical in advertising

■ demonstrate an under￾standing of the three types

of carbon-carbon bonding

and the shape of a molecule

around each type of bond

■ communicate your under￾standing of the following

terms: organic chemistry,

organic compounds,

tetrahedral, trigonal

planar, linear, bent,

electronegativity, bond

dipole, polar, molecular

polarity

Section Preview/

Specific Expectations

1.1

Chapter 1 Classifying Organic Compounds • MHR 5

Bonding and the

Shape of Organic Molecules

Early scientists defined organic compounds as compounds that originate

from living things. In 1828, however, the German chemist Friedrich Wohler

(1800–1882) made an organic compound called urea, CO(NH2)2, out of an

inorganic compound called ammonium cyanate, NH4CN. Urea is found in

the urine of mammals. This was the first time in history that a compound

normally made only by living things was made from a non-living sub￾stance. Since Wohler had discovered that organic compounds can be made

without the involvement of a life process, a new definition was required.

Organic compounds are now defined as compounds that are based on

carbon. They usually contain carbon-carbon and carbon-hydrogen bonds.

The Carbon Atom

There are several million organic compounds, but only about a quarter

of a million inorganic compounds (compounds that are not based on

carbon). Why are there so many organic compounds? The answer lies in

the bonding properties of carbon.

As shown in Figure 1.1, each carbon atom usually forms a total of

four covalent bonds. Thus, a carbon atom can connect to as many as four

other atoms. Carbon can bond to many other types of atoms, including

hydrogen, oxygen, and nitrogen.

This Lewis structure shows methane, the simplest organic compound. The

carbon atom has four valence electrons, and it obtains four more electrons by forming four

covalent bonds with the four hydrogen atoms.

In addition, carbon atoms can form strong single, double, or triple bonds

with other carbon atoms. In a single carbon-carbon bond, one pair of

electrons is shared between two carbon atoms. In a double bond, two

pairs of electrons are shared between two atoms. In a triple bond, three

pairs of electrons are shared between two atoms.

Molecules that contain only single carbon-carbon bonds are saturated.

In other words, all carbon atoms are bonded to the maximum number of

other atoms: four. No more bonding can occur. Molecules that contain

double or triple carbon-carbon bonds are unsaturated. The carbon atoms

on either side of the double or triple bond are bonded to less than four

atoms each. There is potential for more atoms to bond to each of these

carbon atoms.

Carbon’s unique bonding properties allow the formation of a

variety of structures, including chains and rings of many shapes and

sizes. Figure 1.2 on the next page illustrates some of the many shapes

that can be formed from a backbone of carbon atoms. This figure includes

examples of three types of structural diagrams that are used to depict

organic molecules. (The Concepts and Skills Review contains a further

review of these types of structural diagrams.)

Figure 1.1

+ 4H → C

H

H

H H

• • •

•

•

• •

•

•

• • C •

• www.mcgrawhill.ca/links/

chemistry12

In the chapter opener, you

considered how the terms

“natural” and “chemical” are

used inaccurately. A natural

substance is a substance that

occurs in nature and is not

artificial. A chemical is any

substance that has been made

using chemical processes in

a laboratory. A chemical can

also be defined as any sub￾stance that is composed of

atoms. This definition covers

most things on Earth. Go to the

web site above, and click on

Web Links to find out where

to go next. Look up some

natural poisons, pesticides,

and antibiotics that are

produced by animals, plants,

and bacteria. Then look up

some beneficial chemicals

that have been synthesized

by humans. Make a poster to

illustrate your findings.

Web LINK

The type of bonding affects the shape and

movement of a molecule. In this ExpressLab,

you will build several molecules to examine the

shape and character of their bonds.

Procedure

1. Build a model for each of the following com￾pounds. Use a molecular model kit or a chemical

modelling computer program.

2. Identify the different types of bonds in each

molecule.

3. Try to rotate each molecule. Which bonds

allow rotation around the bond? Which bonds

prevent rotation?

4. Examine the shape of the molecule around

each carbon atom. Draw diagrams to show your

observations.

Analysis

1. Which bond or bonds allow rotation to occur?

Which bond or bonds are fixed in space?

2. (a) Describe the shape of the molecule around a

carbon atom with only single bonds.

(b) Describe the shape of the molecule around a

carbon atom with one double bond and two

single bonds.

(c) Describe the shape of the molecule around a

carbon atom with a triple bond and a single

bond.

(d) Predict the shape of a molecule around

a carbon atom with two double bonds.

3. Molecular model kits are a good representation

of real atomic geometry. Are you able to make a

quadruple bond between two atoms with your

model kit? What does this tell you about real

carbon bonding?

H2C CH2 CH3

1–butene

H2C

1,3–butadiene

CH3 CH2 CH2 CH3

butane

H3C

2–butyne

CH CH CH2 C C CH3

CH

ExpressLab Molecular Shapes

6 MHR • Unit 1 Organic Chemistry

(A) This complete structural diagram shows all the bonds in the molecule.

(B) This condensed structural diagram shows only carbon-carbon bonds. (C) This line

structural diagram uses lines to depict carbon-carbon bonds.

Carbon compounds in which carbon forms only single bonds have a

different shape than compounds in which carbon forms double or triple

bonds. In the following ExpressLab, you will see how each type of bond

affects the shape of a molecule.

Figure 1.2

C

C

C

C

C

H C H

H

H

C H

H

H

H H C

H

CH3 C CH

A B C

A few carbon compounds are

considered to be inorganic.

These include carbon dioxide,

CO2, and and carbon com￾pounds containing complex

negative ions (for example,

CO3

2−, HCO3

−, and OCN−).

FACT

CHEM

As you observed in the ExpressLab, the shape of a molecule depends on

the type of bond. Table 1.1 describes some shapes that you must know for

your study of organic chemistry. In Unit 2, you will learn more about why

different shapes and angles form around an atom.

Chapter 1 Classifying Organic Compounds • MHR 7

Table 1.1 Common Molecular Shapes in Organic Molecules

Three-Dimensional Structural Diagrams

Two-dimensional structural diagrams of organic compounds, such as

condensed structural diagrams and line structural diagrams, work well

for flat molecules. As shown in the table above, however, molecules

containing single-bonded carbon atoms are not flat.

You can use a three-dimensional structural diagram to draw the tetra￾hedral shape around a single-bonded carbon atom. In a three-dimensional

diagram, wedges are used to give the impression that an atom or group is

coming forward, out of the page. Dashed or dotted lines are used to show

that an atom or group is receding, or being pushed back into the page. In

Figure 1.3, the Cl atom is coming forward, and the Br atom is behind. The

two H atoms are flat against the surface of the page.

(A) Three-dimensional structural diagram of the

bromochloromethane molecule, BrClCH2 (B) Ball-and-stick model

Figure 1.3

C

H

Cl

Br H

A B

carbon with one

double bond and

two single bonds

carbon with two

double bonds or

one triple bond and

one single bond

oxygen with two

single bonds

The shape around this carbon atom is trigonal

planar. The molecule lies flat in one plane around

the central carbon atom, with the three bonded

atoms spread out, as if to touch the corners of a

triangle.

The shape around this carbon atom is linear. The

two atoms bonded to the carbon atom are stretched

out to either side to form a straight line.

A single-bonded oxygen atom forms two bonds.

An oxygen atom also has two pairs of non-bonding

electrons, called lone pairs. Since there are a total

of four electron pairs around a single-bonded

oxygen atom, the shape around this oxygen atom

is a variation of the tetrahedral shape. Because

there are only two bonds, however, the shape

around a single-bonded oxygen atom is usually

referred to as bent.

C C

H

H CH3 H3C CH3

CH3

120˚

C

O

120˚

H C CH C 3

180˚

Central atom Shape Diagram

carbon with four

single bonds

The shape around this carbon atom is tetrahedral.

That is, the carbon atom is at the centre of an

invisible tetrahedron, with the other four atoms at

the vertices of the tetrahedron. This shape results

because the electrons in the four bonds repel each

other. In the tetrahedral position, the four bonded

atoms and the bonding electrons are as far apart

from each other as possible.

120˚

H

H

H

H

C

109.5˚

H

H

O

104.5˚

lone

pairs

The following diagram shows

1-bromoethanol. (You will learn

the rules for naming molecules

such as this later in the chap￾ter.) Which atom or group is

coming forward, out of the

page? Which atom or group is

receding back, into the page?

HO

CH3

C

Br H

8 MHR • Unit 1 Organic Chemistry

Molecular Shape and Polarity

The three-dimensional shape of a molecule is particularly important when

the molecule contains polar covalent bonds. As you may recall from your

previous chemistry course, a polar covalent bond is a covalent bond

between two atoms with different electronegativities.

Electronegativity is a measure of how strongly an atom attracts

electrons in a chemical bond. The electrons in a polar covalent bond are

attracted more strongly to the atom with the higher electronegativity. This

atom has a partial negative charge, while the other atom has a partial posi￾tive charge. Thus, every polar bond has a bond dipole: a partial negative

charge and a partial positive charge, separated by the length of the bond.

Figure 1.4 illustrates the polarity of a double carbon-oxygen bond. Oxygen

has a higher electronegativity than carbon. Therefore, the oxygen atom in

a carbon-oxygen bond has a partial negative charge, and the carbon atom

has a partial positive charge.

Dipoles are often represented using vectors. Vectors are arrows that have

direction and location in space.

Other examples of polar covalent bonds include CO, OH,

and NH. Carbon and hydrogen attract electrons to almost the same

degree. Therefore, when carbon is bonded to another carbon atom or

to a hydrogen atom, the bond is not usually considered to be polar. For

example, CC bonds are considered to be non-polar.

Predicting Molecular Polarity

A molecule is considered to be polar, or to have a molecular polarity,

when the molecule has an overall imbalance of charge. That is, the

molecule has a region with a partial positive charge, and a region with a

partial negative charge. Surprisingly, not all molecules with polar bonds

are polar molecules. For example, a carbon dioxide molecule has two

polar CO bonds, but it is not a polar molecule. On the other hand, a

water molecule has two polar OH bonds, and it is a polar molecule.

How do you predict whether or not a molecule that contains polar bonds

has an overall molecular polarity? To determine molecular polarity, you

must consider the shape of the molecule and the bond dipoles within the

molecule.

If equal bond dipoles act in opposite directions in three-dimensional

space, they counteract each other. A molecule with identical polar bonds

that point in opposite directions is not polar. Figure 1.5 shows two

examples, carbon dioxide and carbon tetrachloride. Carbon dioxide, CO2,

has two polar CO bonds acting in opposite directions, so the molecule

is non-polar. Carbon tetrachloride, CCl4, has four polar CCl bonds in

a tetrahedral shape. You can prove mathematically that four identical

dipoles, pointing toward the vertices of a tetrahedron, counteract each

other exactly. (Note that this mathematical proof only applies if all four

bonds are identical.) Therefore, carbon tetrachloride is also non-polar.

Figure 1.4

C

δ+ δ−

O

partial positive charge partial negative charge

dipole vector points

from positive charge

to negative charge

In this unit, you will encounter

the following polar bonds:

CI, CF, CO, OH,

NH, and CN. Use the

electronegativities in the

periodic table to discover

which atom in each bond has

a partial negative charge, and

which has a partial positive

charge.

Chapter 1 Classifying Organic Compounds • MHR 9

The red colour indicates a region of negative charge, and the blue colour

indicates a region of positive charge. In non-polar molecules, such as carbon dioxide (A) and

carbon tetrachloride (B), the charges are distributed evenly around the molecule.

If the bond dipoles in a molecule do not counteract each other exactly, the

molecule is polar. Two examples are water, H2O, and chloroform, CHCl3,

shown in Figure 1.6. Although each molecule has polar bonds, the bond

dipoles do not act in exactly opposite directions. The bond dipoles do not

counteract each other, so these two molecules are polar.

In polar molecules, such as water (A) and chloroform (B), the charges are

distributed unevenly around the molecule. One part of the molecule has an overall negative

charge, and another part has an overall positive charge.

The steps below summarize how to predict whether or not a molecule

is polar. The Sample Problem that follows gives three examples.

Note: For the purpose of predicting molecular polarity, you can assume

that CH bonds are non-polar. In fact, they have a very low polarity.

Step 1 Does the molecule have polar bonds? If your answer is no, see

below. If your answer is yes, go to step 2.

If a molecule has no polar bonds, it is non-polar.

Examples: CH3CH2CH3 , CH2CH2

Step 2 Is there more than one polar bond? If your answer is no, see below.

If your answer is yes, go to step 3.

If a molecule contains only one polar bond, it is polar.

Examples: CH3Cl, CH3CH2CH2Cl

Step 3 Do the bond dipoles act in opposite directions and counteract each

other? Use your knowledge of three-dimensional molecular shapes

to help you answer this question. If in doubt, use a molecular model

to help you visualize the shape of the molecule.

If a molecule contains bond dipoles that do not counteract each

other, the molecule is polar.

Examples: H2O, CHCl3

If the molecule contains dipoles that counteract each other, the

molecule is non-polar.

Examples: CO2, CCl4

Figure 1.6

A B

H H

O

• • • •

Cl

H

C

Cl Cl

Figure 1.5

O C • •

• •

O• •

• •

A B

Cl

Cl

C

Cl Cl

10 MHR • Unit 1 Organic Chemistry

Problem

Use your knowledge of molecular shape and polar bonds to predict

whether each molecule has an overall molecular polarity.

(a)

(b)

(c)

Solution

(a) Step 1 Does the molecule have polar bonds? HC and CC

bonds are usually considered to be non-polar. Thus, this molecule

is non-polar.

(b) Steps 1 and 2 Does the molecule have polar bonds? Is there more

than one polar bond? The CO and OH bonds are polar.

Step 3 Do the bond dipoles counteract each other? The shape around

oxygen is bent, and the dipoles are unequal. Therefore, these dipoles

do not counteract each other. The molecule has an overall polarity.

(c) Steps 1 and 2 Does the molecule have polar bonds? Is there more

than one polar bond? The CCl bonds are polar.

Step 3 Do the bond dipoles counteract each other? If you make a

model of this molecule, you can see that the CCl dipoles act in

opposite directions. They counteract each other. Thus, this molecule

is non-polar.

H

H Cl

Cl

C C

CH3 CH2 O H

CH3 CH3

Sample Problem

Molecular Polarity The polarity of a molecule

determines its solubility. Polar

molecules attract each other,

so polar molecules usually

dissolve in polar solvents,

such as water. Non-polar

molecules do not attract

polar molecules enough to

compete against the strong

attraction between polar

molecules. Therefore, non￾polar molecules are not

usually soluble in water.

Instead, they dissolve in

non-polar solvents, such

as benzene.

FACT

CHEM

1. Predict and sketch the three-dimensional shape around each

single-bonded atom.

(a) C and O in CH3OH

(b) C in CH4

2. Predict and sketch the three-dimensional shape of each

multiple-bonded molecule.

(a) HCCH

(b) H2CO

3. Identify any polar bonds that are present in each molecule in

questions 1 and 2.

4. For each molecule in questions 1 and 2, predict whether the molecule

as a whole is polar or non-polar.

Practice Problems

Chapter 1 Classifying Organic Compounds • MHR 11

Section Summary

In this section, you studied carbon bonding and the three-dimensional

shapes of organic molecules. You learned that you can determine the

polarity of a molecule by considering its shape and the polarity of its

bonds. In Unit 2, you will learn more about molecular shapes and

molecular polarity. In the next section, you will review the most basic

type of organic compound: hydrocarbons.

How are the following statements misleading? Explain your

reasoning.

(a) “You should eat only organic food.”

(b) “All-natural ingredients make our product the healthier choice.”

(c) “Chemicals are harmful.”

Classify each bond as polar or non-polar.

(a) CO (c) CN (e) CO

(b) CC (d) CC

Describe the shape of the molecule around the carbon atom

that is highlighted.

(a) (b)

Identify each molecule in question 3 as either polar or non-polar.

Explain your reasoning.

Identify the errors in the following structural diagrams.

(a) (b)

Use your own words to explain why so many organic

compounds exist.

6 C

HC CH CH2 CH3

5 I

4 K/U

C C

H

H O

C C

H

H

H

H

C C H H

H

H

H

H

H

H

3 K/U

2 K/U

1 MC

Section Review

12 MHR • Unit 1 Organic Chemistry

1.2

In this section, you will

■ distinguish among the

following classes of organic

compounds: alkanes,

alkenes, alkynes, and

aromatic compounds

■ draw and name hydro￾carbons using the IUPAC

system

■ communicate your under￾standing of the following

terms: hydrocarbons,

aliphatic hydrocarbon,

aromatic hydrocarbon,

alkane, cycloalkane, alkene,

functional group, alkyne,

alkyl group

Section Preview/

Specific Expectations

Hydrocarbons

In this section, you will review the structure and names of hydrocarbons.

As you may recall from your previous chemistry studies, hydrocarbons

are the simplest type of organic compound. Hydrocarbons are composed

entirely of carbon and hydrogen atoms, and are widely used as fuels.

Gasoline, propane, and natural gas are common examples of hydrocarbons.

Because they contain only carbon and hydrogen atoms, hydrocarbons are

non-polar compounds.

Scientists classify hydrocarbons as either aliphatic or aromatic. An

aliphatic hydrocarbon contains carbon atoms that are bonded in one or

more chains and rings. The carbon atoms have single, double, or triple

bonds. Aliphatic hydrocarbons include straight chain and cyclic alkanes,

alkenes, and alkynes. An aromatic hydrocarbon is a hydrocarbon based

on the aromatic benzene group. You will encouter this group later in

the section. Benzene is the simplest aromatic compound. Its bonding

arrangement results in special molecular stability.

Alkanes, Alkenes, and Alkynes

An alkane is a hydrocarbon that has only single bonds. Alkanes that do not

contain rings have the formula CnH2n + 2. An alkane in the shape of a ring is

called a cycloalkane. Cycloalkanes have the formula CnH2n. An alkene is a

compound that has at least one double bond. Straight-chain alkenes with

one double bond have the same formula as cycloalkanes, CnH2n.

A double bond involves two pairs of electrons. In a double bond, one

pair of electrons forms a single bond and the other pair forms an addition￾al, weaker bond. The electrons in the additional, weaker bond react faster

than the electrons in the single bond. Thus, carbon-carbon double bonds

are more reactive than carbon-carbon single bonds. When an alkene

reacts, the reaction almost always occurs at the site of the double bond.

A functional group is a reactive group of bonded atoms that appears

in all the members of a chemical family. Each functional group reacts in a

characteristic way. Thus, functional groups help to determine the physical

and chemical properties of compounds. For example, the reactive double

bond is the functional group for an alkene. In this course, you will

encounter many different functional groups.

An alkyne is a compound that has at least one triple bond. A straight￾chain alkyne with one triple bond has the formula CnH2n − 2. Triple bonds

are even more reactive than double bonds. The functional group for an

alkyne is the triple bond.

Figure 1.7 gives examples of an alkane, a cycloalkane, an alkene, and

an alkyne.

Figure 1.7 Identify each compound as an alkane, a cycloalkane, an alkene, or an alkyne.

CH3CH2CH2CH3

cyclopentane, C5H10 butane, C4H10 2-hexyne, C6H10

propene, C3H6

H

H

H H

C C

H

C H CH3 C C CH2 CH2 CH3

The molecular formula of

benzene is C6H6. Remember

that each carbon atom must

form a total of four bonds. A

single bond counts as one

bond, a double bond counts

as two bonds, and a triple

bond counts as three bonds.

Hydrogen can form only

one bond. Draw a possible

structure for benzene.

Chapter 1 Classifying Organic Compounds • MHR 13

General Rules for Naming Organic Compounds

The International Union of Pure and Applied Chemistry (IUPAC) has set

standard rules for naming organic compounds. The systematic (or IUPAC)

names of alkanes and most other organic compounds follow the same

pattern, shown below.

The Root: How Long Is the Main Chain?

The root of a compound’s name indicates the number of carbon atoms in

the main (parent) chain or ring. Table 1.2 gives the roots for hydrocarbon

chains that are up to ten carbons long. To determine which root to use,

count the carbons in the main chain, or main ring, of the compound. If the

compound is an alkene or alkyne, the main chain or ring must include the

multiple bond.

Table 1.2 Root Names

Figure 1.8 shows some hydrocarbons, with the main chain or ring

highlighted.

(A) There are six carbons in the main chain. The root is -hex-. (B) There are five

carbons in the main ring. The root is -pent-.

The Suffix: What Family Does the Compound Belong To?

The suffix indicates the type of compound, according to the functional

groups present. (See Table 1.4 on page 22.) As you progress through this

chapter, you will learn the suffixes for different chemical families. In your

previous chemistry course, you learned the suffixes -ane for alkanes, -ene

for alkenes, and -yne for alkynes. Thus, an alkane composed of six carbon

atoms in a chain is called hexane. An alkene with three carbons is called

propene.

Figure 1.8

HC CH CH3

CH3

CH2

H3C C

CH3

CH

CH2

H2C CH2

H2C

CH3

A B

1

-meth￾2

-eth￾3

-prop￾4

-but￾5

-pent￾6

-hex￾7

-hept￾8

-oct￾9

-non￾10

-dec￾Number of

carbon atoms

Root

prefix root suffix + +

14 MHR • Unit 1 Organic Chemistry

The Prefix: What Is Attached to the Main Chain?

The prefix indicates the name and location of each branch and functional

group on the main carbon chain. Most organic compounds have branches,

called alkyl groups, attached to the main chain. An alkyl group is obtained

by removing one hydrogen atom from an alkane. To name an alkyl group,

change the -ane suffix to -yl. For example, CH3 is the alkyl group that is

derived from methane, CH4. It is called the methyl group, taken from the

root meth-. Table 1.3 gives the names of the most common alkyl groups.

Read the steps below to review how to name hydrocarbons. Then examine

the two Sample Problems that follow.

How to Name Hydrocarbons

Step 1 Find the root: Identify the longest chain or ring in the hydrocarbon.

If the hydrocarbon is an alkene or an alkyne, make sure that you

include any multiple bonds in the main chain. Remember that the

chain does not have to be in a straight line. Count the number of

carbon atoms in the main chain to obtain the root. If it is a cyclic

compound, add the prefix -cyclo- before the root.

Step 2 Find the suffix: If the hydrocarbon is an alkane, use the suffix -ane.

Use -ene if the hydrocarbon is an alkene. Use -yne if the hydrocarbon

is an alkyne. If more than one double or triple bond is present, use

the prefix di- (2) or tri- (3) before the suffix to indicate the number

of multiple bonds.

Step 3 Give a position number to every carbon atom in the main chain.

Start from the end that gives you the lowest possible position

number for the double or triple bond, if there is one. If there is no

double or triple bond, number the compound so that the branches

have the lowest possible position numbers.

Step 4 Find the prefix: Name each branch as an alkyl group, and give it

a position number. If more than one branch is present, write the

names of the branches in alphabetical order. Put the position

number of any double or triple bonds after the position numbers

and names of the branches, just before the root. This is the prefix.

Note: Use the carbon atom with the lowest position number to give

the location of a double or triple bond.

Step 5 Put the name together: prefix + root + suffix.

Table 1.3 Common Alkyl Groups

methyl propyl isopropyl ethyl

CH3 CH2CH3 CH2CH2CH3

butyl iso-butyl tert-butyl sec-butyl

CH2CH2CH2CH3 CH CH

CH3

CH2CH3

CH3

CH3

CH

CH3

CH3

CH2 CH3

CH3

CH3

C

Chapter 1 Classifying Organic Compounds • MHR 15

• Use hyphens to separate

words from numbers.

Use commas to separate

numbers.

• If there is a ring, it is

usually taken as the main

chain. Follow the same

rules to name cyclic

compounds that have

branches attached.

Include the prefix -cyclo￾after the names and

position numbers of the

branches, directly before

the root: for example,

2-methyl-1-cyclohexene.

PROBLEM TIPS

Problem

Name the following alkene.

Solution

Step 1 Find the root: The longest chain in the molecule has seven carbon

atoms. The root is -hept-.

Step 2 Find the suffix: The suffix is -ene. The root and suffix together are

-heptene.

Step 3 Numbering the chain from the left, in this case, gives the smallest

position number for the double bond.

Step 4 Find the prefix: Two methyl groups are attached to carbon number

2. One ethyl group is attached to carbon number 3. There is a

double bond at position 3. The prefix is 3-ethyl-2,2-dimethyl-3-.

Step 5 The full name is 3-ethyl-2,2-dimethyl-3-heptene.

CH3 C

CH3

CH3

C CH CH2 CH2 CH3

CH2CH3

1 2 34 567

Sample Problem

Naming an Alkene

Problem

Name the following alkanes.

(a) (b)

Solution

(a) Step 1 Find the root: The longest chain has three carbon atoms, so the

root is -prop-.

Step 2 Find the suffix: The suffix is -ane.

Steps 3 and 4 Find the prefix: A methyl group is attached to carbon

number 2. The prefix is 2-methyl.

Step 5 The full name is 2-methylpropane.

(b) Steps 1 and 2 Find the root and suffix: The main ring has five carbon

atoms, so the root is -pent-. Add the prefix -cyclo-. The suffix is -ane.

Steps 3 and 4 Find the prefix: Start numbering at the ethyl branch. The

prefix is 1-ethyl, or just ethyl.

Step 5 The full name is 1-ethylcyclopentane.

CH2CH3

1 2

5 3

4

CH3

CH3

CH CH3

3 2 1

Sample Problem

Naming Alkanes