Organic Chemistry 4th ed - Paula Bruice.pdf - ANGIELSKIE - Nekromantis

The first two chapters of the text cover a

variety of topics that you need to get started

with your study of organic chemistry.

An Introduction

to the Study

of Organic

Chemistry

Chapter 1 reviews the topics from general chemistry

that will be important to your study of organic chemistry.

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.

Acid–base chemistry, which is central to understanding

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-

ined in the chapter are either the reactants or the products

of many of the reactions presented in the next 10 chap-

ters, you will have the opportunity to review the nomen-

clature of these compounds as you proceed through those

chapters. The structures and physical properties of these

compounds will be compared and contrasted, which

makes learning about them a little easier than if each

compound were presented separately. Because organic

chemistry is a study of compounds that contain carbon,

the last part of Chapter 2 discusses the spatial arrange-

ment of the atoms in both chains and rings of carbon

atoms.

Chapter 1

Electronic Structure and Bonding

• Acids and Bases

Chapter 2

An Introduction to Organic

Compounds: Nomenclature,

Physical Properties, and

Representation of Structure

Electronic Structure and

Bonding • Acids and Bases

Ethane

Ethene

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

said, “but you can’t live on dirt. You can

stay warm by burning tree branches, but

you can’t burn rocks.”

By the eighteenth century, scientists thought they

had grasped the nature of that difference, and in 1807, Jöns Jakob Berzelius gave

names to the two kinds of materials. Compounds derived from living organisms were

believed to contain an unmeasurable vital force—the essence of life. These he called

“organic.” Compounds derived from minerals—those lacking that vital force—were

“inorganic.”

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

be excreted by mammals—by heating ammonium cyanate, an inorganic mineral.

Jöns Jakob Berzelius (1779–1848)

not only coined the terms “organic”

and “inorganic,” but also invented

the system of chemical symbols still

used today. He published the first list

of accurate atomic weights and

proposed the idea that atoms carry

an electric charge. He purified or

discovered the elements cerium,

selenium, silicon, thorium, titanium,

and zirconium.

Ethyne

German chemist Friedrich Wöhler

(1800–1882) began his professional

life as a physician and later became

a professor of chemistry at the Uni-

versity of Göttingen. Wöhler codis-

covered the fact that two different

chemicals could have the same mo-

lecular formula. He also developed

methods of purifying aluminum—at

the time, the most expensive metal on

Earth—and beryllium.

NH 4 OCN

ammonium cyanate

heat

H 2 N

NH 2

urea

For the first time, an “organic” compound had been obtained from something other

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

T o stay alive, early humans

+ −

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).

NOF

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.

4 CHAPTER 1 Electronic Structure and Bonding • Acids and Bases

Louis Victor Pierre Raymond duc

de Broglie (1892–1987) was born in

France and studied history at the

Sorbonne. During World War I, he

was stationed in the Eiffel Tower as a

radio engineer. Intrigued by his expo-

sure to radio communications, he re-

turned to school after the war, earned

a Ph.D. in physics, and became a

professor of theoretical physics at the

Faculté des Sciences at the Sorbonne.

He received the Nobel Prize in

physics in 1929, five years after ob-

taining his degree, for his work that

showed electrons to have properties

of both particles and waves. In 1945,

he became an adviser to the French

Atomic Energy Commissariat.

The atomic number of an atom equals the number of protons in its nucleus. The

atomic number is also the number of electrons that surround the nucleus of a neutral

atom. For example, the atomic number of carbon is 6, which means that a neutral car-

bon atom has six protons and six electrons. Because the number of protons in an atom

does not change, the atomic number of a particular element is always the same—all

carbon atoms have an atomic number of 6.

The mass number of an atom is the sum of its protons and neutrons. Not all carbon

atoms have the same mass number, because, even though they all have the same num-

ber of protons, they do not all have the same number of neutrons. For example,

98.89% of naturally occurring carbon atoms have six neutrons—giving them a mass

number of 12—and 1.11% have seven neutrons—giving them a mass number of 13.

These two different kinds of carbon atoms and are called isotopes. Isotopes

have the same atomic number (i.e., the same number of protons), but different mass

numbers because they have different numbers of neutrons. The chemical properties of

isotopes of a given element are nearly identical.

Naturally occurring carbon also contains a trace amount of which has six pro-

tons and eight neutrons. This isotope of carbon is radioactive, decaying with a half-life

of 5730 years. (The half-life is the time it takes for one-half of the nuclei to decay.) As

long as a plant or animal is alive, it takes in as much as it excretes or exhales.

When it dies, it no longer takes in so the in the organism slowly decreases.

Therefore, the age of an organic substance can be determined by its content.

The atomic weight of a naturally occurring element is the average weighted

mass of its atoms. Because an atomic mass unit (amu) is defined as exactly

of the mass of the atomic mass of is 12.0000 amu; the atomic

mass of is 13.0034 amu. Therefore, the atomic weight of carbon is 12.011 amu

The molecular weight is the

sum of the atomic weights of all the atoms in the molecule.

( 12 C

13 C)

14 C,

14 C

14 C,

14 C

12 C,

12 C

13 C

0.9889 * 12.0000 + 0.0111 * 13.0034

12.011

PROBLEM 1

Oxygen has three isotopes with mass numbers of 16, 17, and 18. The atomic number of

oxygen is eight. How many protons and neutrons does each of the isotopes have?

1.2 The Distribution of Electrons in an Atom

Erwin Schrödinger (1887–1961)

was teaching physics at the Universi-

ty of Berlin when Hitler rose to

power. Although not Jewish,

Schrödinger left Germany to return

to his native Austria, only to see it

taken over later by the Nazis. He

moved to the School for Advanced

Studies in Dublin and then to Oxford

University. In 1933, he shared the

Nobel Prize in physics with Paul

Dirac, a professor of physics at Cam-

bridge University, for mathematical

work on quantum mechanics.

Electrons are moving continuously. Like anything that moves, electrons have kinetic

energy, and this energy is what counters the attractive force of the positively charged

protons that would otherwise pull the negatively charged electrons into the nucleus.

For a long time, electrons were perceived to be particles—infinitesimal “planets” or-

biting the nucleus of an atom. In 1924, however, a French physicist named Louis de

Broglie showed that electrons also have wavelike properties. He did this by combining

a formula developed by Einstein that relates mass and energy with a formula devel-

oped by Planck relating frequency and energy. The realization that electrons have

wavelike properties spurred physicists to propose a mathematical concept known as

quantum mechanics.

Quantum mechanics uses the same mathematical equations that describe the wave

motion of a guitar string to characterize the motion of an electron around a nucleus.

The version of quantum mechanics most useful to chemists was proposed by Erwin

Schrödinger in 1926. According to Schrödinger, the behavior of each electron in an

atom or a molecule can be described by a wave equation . The solutions to the

Schrödinger equation are called wave functions or orbitals . They tell us the energy of

the electron and the volume of space around the nucleus where an electron is most

likely to be found.

According to quantum mechanics, the electrons in an atom can be thought of as oc-

cupying a set of concentric shells that surround the nucleus. The first shell is the one

An orbital tells us the energy of the

electron and the volume of space

around the nucleus where an electron

is most likely to be found.

Organic Chemistry 4th ed - Paula Bruice.pdf

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: