McGraw-Hill Ryerson - High School Chemistry 12

623 Pages·2005·14.03 MB·English

Organic Chemistry
A
UNIT 1 CONTENTS
t this moment, you are walking,
CHAPTER 1
sitting, or standing in an “organic”
Classifying Organic Compounds
body. Your skin, hair, muscles, heart,
CHAPTER 2 and lungs are all made from organic
Reactions of Organic Compounds compounds. In fact, the only parts of
your body that are notmostly organic
UNIT 1 ISSUE
are your teeth and bones! When you
Current Issues Related to
study organic chemistry, you are
Organic Chemistry
studying the substances that make
up your body and much of the world
UNIT 1 OVERALL EXPECTATIONS around you. Medicines, clothing,
carpets, curtains, and wood and
How do the structures of
plastic furniture are all manufactured
various organic compounds
differ? What chemical from organic chemicals. If you look
reactions are typical of these out a window, the grass, trees, squir-
compounds? rels, and insects you may see are also
How can you name different composed of organic compounds.
organic compounds and Are you having a sandwich for
represent their structures? lunch? Bread, butter, meat, and lettuce
What do you need to know in are made from organic compounds.
order to predict the products
Will you have dessert? Sugar, flour,
of organic reactions?
vanilla, and chocolate are also organic.
How do organic compounds What about a drink? Milk and juice
affect your life? How do they
are solutions of water in which
affect the environment?
organic compounds are dissolved.
In this unit, you will study a
variety of organic compounds. You
Unit Issue Prep
will learn how to name them and how
Before beginning Unit 1, read to draw their structures. You will also
pages 110 to 111 to find out about learn how these compounds react, and
the unit issue. In the unit issue, you
you will use your knowledge to pre-
will analyze an issue that involves
dict the products of organic reactions.
chemistry and society. You can
In addition, you will discover the
start planning your research as you
amazing variety of organic compounds
go through this unit. Which topics
interest you the most? How does in your body and in your life.
society influence developments in
science and technology?
2

Classifying
Organic Compounds
A
Chapter Preview s you wander through the supermarket, some advertising claims catch
your eye. “Certified organic” and “all natural” are stamped on the labels
1.1 Bonding and the Shape
of some foods. Other labels claim that the foods are “chemical free.” As a
of Organic Molecules
chemistry student, you are aware that these labels may be misleading. Are
1.2 Hydrocarbons
all “chemicals” harmful in food, as some of the current advertising suggests?
1.3 Single-Bonded Many terms are used inaccurately in everyday life. The word “natural”
Functional Groups is often used in a manner suggesting that all natural compounds are safe
1.4 Functional Groups and healthy. Similarly, the word “chemical” is commonly used to refer to
With the C(cid:2)O bond 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
Prerequisite
Concepts and Skills properties of different types of organic compounds.
Before you begin this chapter,
review the following concepts What is the word “organic” intended to mean here?
and skills: How is this meaning different from the scientific
(cid:2) drawing Lewis structures meaning of the word?
(Concepts and Skills
Review)
(cid:2) writing molecular formulas
and expanded molecular
formulas (Concepts and
Skills Review)
(cid:2) drawing complete, con-
densed, and line structural
diagrams (Concepts and
Skills Review)
(cid:2) identifying structural
isomers (Concepts and
Skills Review)
4 MHR • Unit 1 Organic Chemistry
Bonding and the 1.1
Shape of Organic Molecules
Early scientists defined organic compounds as compounds that originate Section Preview/
from living things. In 1828, however, the German chemist Friedrich Wohler Specific Expectations
(1800–1882) made an organic compound called urea, CO(NH2)2, out of an In this section, you will
inorganic compound called ammonium cyanate, NH CN. Urea is found in
4 (cid:2) discussthe use of the
the urine of mammals. This was the first time in history that a compound terms organic, natural, and
normally made only by living things was made from a non-living sub- chemicalin advertising
stance. Since Wohler had discovered that organic compounds can be made
(cid:2) demonstratean under-
without the involvement of a life process, a new definition was required. standing of the three types
Organic compoundsare now defined as compounds that are based on of carbon-carbon bonding
carbon. They usually contain carbon-carbon and carbon-hydrogen bonds. and the shape of a molecule
around each type of bond
The Carbon Atom (cid:2) communicateyour under-
standing of the following
There are several million organic compounds, but only about a quarter
terms: organic chemistry,
of a million inorganic compounds (compounds that are not based on organic compounds,
carbon). Why are there so many organic compounds? The answer lies in tetrahedral, trigonal
the bonding properties of carbon. planar,linear,bent,
As shown in Figure 1.1, each carbon atom usually forms a total of electronegativity,bond
dipole, polar, molecular
four covalent bonds. Thus, a carbon atom can connect to as many as four
polarity
other atoms. Carbon can bond to many other types of atoms, including
hydrogen, oxygen, and nitrogen.
H
• •• Web LINK
+ →
C • 4H • H • C • H
• • •
www.mcgrawhill.ca/links/
• ••
H chemistry12
In the chapter opener, you
Figure 1.1 This Lewis structure shows methane, the simplest organic compound. The
considered how the terms
carbon atom has four valence electrons, and it obtains four more electrons by forming four
“natural” and “chemical” are
covalent bonds with the four hydrogen atoms.
used inaccurately. A natural
substance is a substance that
In addition, carbon atoms can form strong single, double, or triple bonds occurs in nature and is not
with other carbon atoms. In a single carbon-carbon bond, one pair of artificial. A chemicalis any
electrons is shared between two carbon atoms. In a double bond, two substance that has been made
pairs of electrons are shared between two atoms. In a triple bond, three using chemical processes in
a laboratory. A chemical can
pairs of electrons are shared between two atoms.
also be defined as any sub-
Molecules that contain only single carbon-carbon bonds are saturated.
stance that is composed of
In other words, all carbon atoms are bonded to the maximum number of
atoms. This definition covers
other atoms: four. No more bonding can occur. Molecules that contain
most things on Earth. Go to the
double or triple carbon-carbon bonds are unsaturated. The carbon atoms web site above, and click on
on either side of the double or triple bond are bonded to less than four Web Linksto find out where
atoms each. There is potential for more atoms to bond to each of these to go next. Look up some
carbon atoms. naturalpoisons, pesticides,
and antibiotics that are
Carbon’s unique bonding properties allow the formation of a
produced by animals, plants,
variety of structures, including chains and rings of many shapes and
and bacteria. Then look up
sizes. Figure 1.2 on the next page illustrates some of the many shapes
some beneficial chemicals
that can be formed from a backbone of carbon atoms. This figure includes
that have been synthesized
examples of three types of structural diagrams that are used to depict by humans. Make a poster to
organic molecules. (The Concepts and Skills Review contains a further illustrate your findings.
review of these types of structural diagrams.)
Chapter 1 Classifying Organic Compounds • MHR 5
CHEM A H B C
FACT
H C H
A few carbon compounds are
considered to be inorganic.
H C H
These include carbon dioxide, C C CH C CH
3
CO , and and carbon com-
2
pounds containing complex C C
H C H
negative ions (for example,
CO2−, HCO−, and OCN−).
3 3 H C H
H
Figure 1.2 (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.
ExpressLab Molecular Shapes
The type of bonding affects the shape and 4. Examine the shape of the molecule around
movement of a molecule. In this ExpressLab, each carbon atom. Draw diagrams to show your
you will build several molecules to examine the observations.
shape and character of their bonds.
Analysis
Procedure
1. Which bond or bonds allow rotation to occur?
1. Build a model for each of the following com- Which bond or bonds are fixed in space?
pounds. Use a molecular model kit or a chemical
2.(a) Describe the shape of the molecule around a
modelling computer program.
carbon atom with only single bonds.
CH CH CH CH H C CH CH CH (b) Describe the shape of the molecule around a
3 2 2 3 2 2 3
carbon atom with one double bond and two
butane 1–butene
single bonds.
(c) Describe the shape of the molecule around a
H C CH CH CH H C C C CH
2 2 3 3
carbon atom with a triple bond and a single
1,3–butadiene 2–butyne bond.
(d) Predict the shape of a molecule around
a carbon atom with two double bonds.
2. Identify the different types of bonds in each
3. Molecular model kits are a good representation
molecule.
of real atomic geometry. Are you able to make a
3. Try to rotate each molecule. Which bonds
quadruple bond between two atoms with your
allow rotation around the bond? Which bonds
model kit? What does this tell you about real
prevent rotation?
carbon bonding?
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.
6 MHR • Unit 1 Organic Chemistry
Table 1.1 Common Molecular Shapes in Organic Molecules
Central atom Shape Diagram
carbon with four The shape around this carbon atom is tetrahedral. H
single bonds 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 109.5˚
because the electrons in the four bonds repel each C
H
other. In the tetrahedral position, the four bonded H
atoms and the bonding electrons are as far apart
from each other as possible. H
carbon with one The shape around this carbon atom is trigonal O
H CH
double bond and planar. The molecule lies flat in one plane around 3
two single bonds the central carbon atom, with the three bonded 120˚ C C C
atoms spread out, as if to touch the corners of a
H 120˚ CH H C CH
triangle. 3 3 120˚ 3
carbon with two The shape around this carbon atom is linear. The
double bonds or two atoms bonded to the carbon atom are stretched 180˚
one triple bond and out to either side to form a straight line. H C C CH3
one single bond
oxygen with two A single-bonded oxygen atom forms two bonds.
single bonds An oxygen atom also has two pairs of non-bonding lone
pairs
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
O
is a variation of the tetrahedral shape. Because
H
there are only two bonds, however, the shape
104.5˚
around a single-bonded oxygen atom is usually H
referred to as bent.
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. The following diagram shows
1-bromoethanol. (You will learn
the rules for naming molecules
A B
such as this later in the chap-
ter.) Which atom or group is
H
coming forward, out of the
page? Which atom or group is
C
receding back, into the page?
Br H
Cl CH3
C
Br H
HO
Figure 1.3 (A) Three-dimensional structural diagram of the
bromochloromethane molecule, BrClCH (B) Ball-and-stick model
2
Chapter 1 Classifying Organic Compounds • MHR 7
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.
partial positive charge partial negative charge
δ+ δ−
C O
dipole vector points
from positive charge
to negative charge
In this unit, you will encounter Figure 1.4 Dipoles are often represented using vectors. Vectors are arrows that have
the following polar bonds: direction and location in space.
C(cid:3)I, C(cid:3)F, C(cid:3)O, O(cid:3)H,
N(cid:3)H, and C(cid:3)N. Use the Other examples of polar covalent bonds include C(cid:3)O, O(cid:3)H,
electronegativities in the and N(cid:3)H. Carbon and hydrogen attract electrons to almost the same
periodic table to discover
degree. Therefore, when carbon is bonded to another carbon atom or
which atom in each bond has
to a hydrogen atom, the bond is not usually considered to be polar. For
a partial negative charge, and
example, C(cid:3)C bonds are considered to be non-polar.
which has a partial positive
charge.
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 C(cid:2)O bonds, but it is not a polar molecule. On the other hand, a
water molecule has two polar O(cid:3)H 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, CO ,
2
has two polar C(cid:2)O bonds acting in opposite directions, so the molecule
is non-polar. Carbon tetrachloride, CCl , has four polar C(cid:3)Cl bonds in
4
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.
8 MHR • Unit 1 Organic Chemistry
A B
Cl
•• ••
O C O C
•• ••
Cl Cl
Cl
Figure 1.5 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, H O, and chloroform, CHCl ,
2 3
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.
A B
H
••O•• C
H H Cl Cl
Cl
Figure 1.6 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 C(cid:3)H 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: CH CH CH , CH (cid:2)CH
3 2 3 2 2
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: CH Cl, CH CH CH Cl
3 3 2 2
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: H O, CHCl
2 3
If the molecule contains dipoles that counteract each other, the
molecule is non-polar.
Examples: CO , CCl
2 4
Chapter 1 Classifying Organic Compounds • MHR 9
CHEM Sample Problem
FACT
Molecular Polarity
The polarity of a molecule
determines its solubility. Polar
molecules attract each other, Problem
so polar molecules usually Use your knowledge of molecular shape and polar bonds to predict
dissolve in polar solvents,
whether each molecule has an overall molecular polarity.
such as water. Non-polar
(a) CH CH
molecules do not attract 3 3
polar molecules enough to (b) CH CH O H
3 2
compete against the strong
attraction between polar
H Cl
molecules. Therefore, non-
(c) C C
polar molecules are not
Cl H
usually soluble in water.
Instead, they dissolve in
Solution
non-polar solvents, such
as benzene. (a) Step 1 Does the molecule have polar bonds? H(cid:3)C and C(cid:3)C
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 C(cid:3)O and O(cid:3)H 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 C(cid:3)Cl 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 C(cid:3)Cl dipoles act in
opposite directions. They counteract each other. Thus, this molecule
is non-polar.
Practice Problems
1. Predict and sketch the three-dimensional shape around each
single-bonded atom.
(a) C and O in CH OH
3
(b) C in CH
4
2. Predict and sketch the three-dimensional shape of each
multiple-bonded molecule.
(a) HC(cid:4)CH
(b) H C(cid:2)O
2
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.
10 MHR • Unit 1 Organic Chemistry