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,The first two chapters of the text cover aPA R T
variety of topics that you need to get started An Introduction
with your study of organic chemistry. to the Study
Chapter 1 reviews the topics from general chemistry
that will be important to your study of organic chemistry. of Organic
The chapter starts with a description of the structure of
atoms and then proceeds to a description of the structure
of molecules. Molecular orbital theory is introduced.
Chemistry
Acid–base chemistry, which is central to understanding
ONE
many organic reactions, is reviewed. You will see how the
structure of a molecule affects its acidity and how the
acidity of a solution affects molecular structure.
To discuss organic compounds, you must be able to name
them and visualize their structures when you read or hear
their names. In Chapter 2, you will learn how to name
five different classes of organic compounds. This will
give you a good understanding of the basic rules followed
in naming compounds. Because the compounds exam- Chapter 1
ined in the chapter are either the reactants or the products Electronic Structure and Bonding
of many of the reactions presented in the next 10 chap- • Acids and Bases
ters, you will have the opportunity to review the nomen-
clature of these compounds as you proceed through those Chapter 2
chapters. The structures and physical properties of these An Introduction to Organic
compounds will be compared and contrasted, which
makes learning about them a little easier than if each Compounds: Nomenclature,
compound were presented separately. Because organic Physical Properties, and
chemistry is a study of compounds that contain carbon, Representation of Structure
the last part of Chapter 2 discusses the spatial arrange-
ment of the atoms in both chains and rings of carbon
atoms.
1
, Electronic Structure and
1 Bonding • Acids and Bases
Ethane Ethene
T
o stay alive, early humans
must have been able to tell the
difference between two kinds of
materials in their world. “You can live
on roots and berries,” they might have
Jöns Jakob Berzelius (1779–1848) said, “but you can’t live on dirt. You can
not only coined the terms “organic” stay warm by burning tree branches, but
and “inorganic,” but also invented you can’t burn rocks.” Ethyne
the system of chemical symbols still
By the eighteenth century, scientists thought they
used today. He published the first list
of accurate atomic weights and
had grasped the nature of that difference, and in 1807, Jöns Jakob Berzelius gave
proposed the idea that atoms carry names to the two kinds of materials. Compounds derived from living organisms were
an electric charge. He purified or believed to contain an unmeasurable vital force—the essence of life. These he called
discovered the elements cerium, “organic.” Compounds derived from minerals—those lacking that vital force—were
selenium, silicon, thorium, titanium, “inorganic.”
and zirconium. Because chemists could not create life in the laboratory, they assumed they could not
create compounds with a vital force. With this mind-set, you can imagine how surprised
chemists were in 1828 when Friedrich Wöhler produced urea—a compound known to
German chemist Friedrich Wöhler
(1800–1882) began his professional
be excreted by mammals—by heating ammonium cyanate, an inorganic mineral.
life as a physician and later became
a professor of chemistry at the Uni- O
versity of Göttingen. Wöhler codis- + − heat
NH4 OCN C
covered the fact that two different ammonium cyanate H2N NH2
chemicals could have the same mo- urea
lecular formula. He also developed
methods of purifying aluminum—at
the time, the most expensive metal on For the first time, an “organic” compound had been obtained from something other
Earth—and beryllium. than a living organism and certainly without the aid of any kind of vital force. Clearly,
chemists needed a new definition for “organic compounds.” Organic compounds are
now defined as compounds that contain carbon.
Why is an entire branch of chemistry devoted to the study of carbon-containing
compounds? We study organic chemistry because just about all of the molecules that
2
, Section 1.1 The Structure of an Atom 3
make life possible—proteins, enzymes, vitamins, lipids, carbohydrates, and nucleic
acids—contain carbon, so the chemical reactions that take place in living systems, in-
cluding our own bodies, are organic reactions. Most of the compounds found in
nature—those we rely on for food, medicine, clothing (cotton, wool, silk), and energy
(natural gas, petroleum)—are organic as well. Important organic compounds are not,
however, limited to the ones we find in nature. Chemists have learned to synthesize
millions of organic compounds never found in nature, including synthetic fabrics,
plastics, synthetic rubber, medicines, and even things like photographic film and
Super glue. Many of these synthetic compounds prevent shortages of naturally occur-
ring products. For example, it has been estimated that if synthetic materials were not
available for clothing, all of the arable land in the United States would have to be used
for the production of cotton and wool just to provide enough material to clothe us.
Currently, there are about 16 million known organic compounds, and many more are
possible.
What makes carbon so special? Why are there so many carbon-containing com-
pounds? The answer lies in carbon’s position in the periodic table. Carbon is in the
center of the second row of elements. The atoms to the left of carbon have a tendency
to give up electrons, whereas the atoms to the right have a tendency to accept electrons
(Section 1.3).
Li Be B C N O F
the second row of the periodic table
Because carbon is in the middle, it neither readily gives up nor readily accepts elec-
trons. Instead, it shares electrons. Carbon can share electrons with several different
kinds of atoms, and it can also share electrons with other carbon atoms. Consequently,
carbon is able to form millions of stable compounds with a wide range of chemical
properties simply by sharing electrons.
When we study organic chemistry, we study how organic compounds react. When
an organic compound reacts, some old bonds break and some new bonds form. Bonds
form when two atoms share electrons, and bonds break when two atoms no longer
share electrons. How readily a bond forms and how easily it breaks depend on the par-
ticular electrons that are shared, which, in turn, depend on the atoms to which the elec-
trons belong. So if we are going to start our study of organic chemistry at the
beginning, we must start with an understanding of the structure of an atom—what
electrons an atom has and where they are located.
1.1 The Structure of an Atom
An atom consists of a tiny dense nucleus surrounded by electrons that are spread
throughout a relatively large volume of space around the nucleus. The nucleus con-
tains positively charged protons and neutral neutrons, so it is positively charged. The
electrons are negatively charged. Because the amount of positive charge on a proton
equals the amount of negative charge on an electron, a neutral atom has an equal num-
ber of protons and electrons. Atoms can gain electrons and thereby become negatively
charged, or they can lose electrons and become positively charged. However, the num-
ber of protons in an atom does not change.
Protons and neutrons have approximately the same mass and are about 1800 times
more massive than an electron. This means that most of the mass of an atom is in its
nucleus. However, most of the volume of an atom is occupied by its electrons, and that
is where our focus will be because it is the electrons that form chemical bonds.
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