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Y ou now are starting the study of organic chemistry, which is the chemistry
of compounds of carbon. In this introductory chapter, we will tell you some-
is important for you to learn so that you will have a reasonable working knowl-
edge of the subject, whether you are just interested in chemistry or plan for a
career as a chemist, an engineer, a physician, a biologist, and so on. The subject
is very large; more than two million organic compounds have been isolated or
prepared and characterized, yet the number of guiding principles is relatively
small. You certainly will not learn everything about organic chemistry from
this book, but with a good knowledge of the guiding principles, you will be
able later to find out what you need to know either from the chemical literature,
or directly by experiment in the laboratory.
Unfortunately, learning about and learning how to use organic chemistry
is not a straightforward process, wherein one step leads to another in a simple,
logical way like Euclidean geometry. A more realistic analogy would be to
consider yourself thrust into and required to deal successfully with a sizable
group of strangers speaking a new and complex language. In such a situation,
one has to make many decisions- how much of the language to learn at the
2 1 Introduction. What is Organic Chemistry All About?

outset? Which people are the best to interact with first? Which will be the most
important to know in the long run? How well does one have to know each
person? How much does one have to know about the history of the group to
understand their interactions? These are difficult questions, and a period of
confusion, if not anxiety, is expected in any attempt to complete a task of this
kind in a set, brief period of time. Clearly, it would be difficult to learn all at
once the language, the people, and the interactions between them. Nonetheless,
this is pretty much what is expected of you in learning organic chemistry.
A number of approaches have been devised to help you become familiar
with and use organic chemistry. In terms of our analogy, one way is to learn
the language, then the relationships between the people, and finally, well pre-
pared, to proceed to interact with the people singly and then in groups. Such
an approach may be logical in concept, but is not to everyone's taste as a way
to learn. Many of us do better with an interactive approach, where language,
relationships, and people are worked out more or less in concert, with atten-
dant misunderstandings and ambiguities.
What we will try to do is to introduce some of the important basic con-
cepts and the elements of the language of organic chemistry, then show how
these are used in connection with various classes of compounds. The initial
round will be a fairly extensive one and you should not expect to be able to
master everything at once. This will take practice and we will provide oppor-
tunity for practice.
One of the appealing yet bothersome features of modern organic chemis-
try is its extraordinary vitality. Unlike Euclidean geometry or classical me-
chanics, it is evolving rapidly and many of the concepts introduced in this
book are either new or have been drastically modified in the past ten years.
Every issue of the current chemical journals has material of such basic interest
that one would like to include it in an introductory course. Truly, those who
write organic'textbooks write on water, with no hope of producing the definitive
book. Things just change too fast. Despite this, one of the great ideas of modern
civilization, namely that organic compounds can be described in terms of more
or less simple three-dimensional molecular structures with atoms held together
by chemical bonds, has persisted for more than one hundred years and seems
unlikely to be superseded, no matter how much it is refined and modified.


You may not be much interested in the way that organic chemistry developed,
but if you skip to the next section without reading further, you will miss some
of the flavor of a truly great achievement- of how a few highly creative chem-
ists were able, with the aid of a few simple tools, to determine the structures
of molecules, far too small and too elusive to be seen individually with the
finest optical microscope, manifesting themselves only by the collective be-
havior of at least millions of millions at once.
1-1 A Bit of History

Try to visualize the problems confronting the organic chemist of 100

years ago. You will have no more than reasonably pure samples of organic
compounds, the common laboratory chemicals of today, glassware, balances,
thermometers, means of measuring densities, and a few optical instruments.
You also will have a relatively embryonic theory that there are molecules in
those bottles and that one compound differs from another because its mole-
cules have different members or kinds of atoms and different arrangements
of bonds. Your task will be to determine what kinds and what numbers of
atoms they contain, that is, to determine their molecular formulas. Obviously,
a compound with formula C,H,O and one with C,H,O, are not the same com-
pound. But suppose two compounds from different sources both are C,H,O.
T o decide whether these are the same or different you could smell them (far
better to sniff than to inhale), taste them (emphatically not recommended),
see if they have the same appearance and viscosity (if liquids), or use more
sophisticated criteria: boiling point, melting point, density, or refractive index.
Other possibilities would be to see if they both have the same solubility in
water or other solvents and whether they give the same reaction products with
various reagents. Of course, all this gets a bit tough when the compounds are
not pure and no good ways are available to purify them, but that is part of the
job. Think about how you might proceed.
In retrospect it is surprising that in less than fifty years an enormous,
even if incomplete, edifice of structural organic chemistry was constructed
on the basis of the results of chemical reactions without determination of a
single bond distance, and with no electronic theory as a guide. Interestingly,
all of the subsequent developments of the quantum mechanical theory of chem-
ical bonds has not altered this edifice in significant ways. Indeed, for a long
time, a goal of molecular quantum mechanics was simply to be able to corrob-
orate that when an organic chemist draws a single line between two carbon
atoms to show that they are bonded, he in fact knows what he is doing. And
that when he draws two (or three) bonds between the carbons to indicate a
double (or triple) bond, quantum mechanics supports this also as a valid idea.
Furthermore, when modern tools for determining organic structures that
involve actually measuring the distances between the atoms became available,
these provided great convenience, but no great surprises. To be sure, a few
structures turned out to be incorrect because they were based on faulty or
inadequate experimental evidence. But, on the whole, the modern three-
dimensional representations of molecules that accord with actual measure-
ments of bond distances and angles are in no important respect different from
the widely used three-dimensional ball-and-stick models of organic molecules,
and these, in essentially their present form, date from at least as far back as
E. Paterno, in 1869.
How was all of this achieved? Not by any very simple process. The
essence of some of the important ideas follow, but it should be clear that what
actually took place was far from straightforward. A diverse group of people
was involved; many firmly committed to, if not having a vested interest in,
earlier working hypotheses or paradigms that had served as useful bases for
earlier experimentation, but were coming apart at the seams because they could
1 lntroduct~onWhat IS Organ~cChemistry All About?

not accommodate the new facts that kept emerging. As is usual in human en-
deavors, espousal of new and better ideas did not come equally quickly to all
those used to thinking in particular ways. To illustrate, at least one famous
chemist, Berthelot, still used H O as the formula for water twenty-five years
after it seemed clear that H,O was a better choice.

1-1A Determination of Molecular Formulas

Before structures of molecules could be established, there had to be a means
of establishing molecular formulas and for t h ~ spurpose the key concept was
Avogadro's hypothesis, which can be stated in the form "equal volumes of
gases at the same temperature and pressure contain the same number of mole-
cules." Avogadro's hypothesis allowed assignment of relative molecular
weights from measurements of gas densities. Then, with analytical techniques
that permit determination of the weight percentages of the various elements
in a compound, it became possible to set up a self-consistent set of relative
atomic weightsS1From these and the relative molecular weights, one can assign
molecular formulas. For example, if one finds that a compound contains 22.0%
carbon (atomic weight = 12.00), 4.6% hydrogen (atomic weight = 1.008), and
73.4% bromine (atomic weight = 79.90), then the ratios of the numbers of
atoms are (22.0/12.00):(4.6/1.008):(73.4/79.90) = 1.83:4.56:0.92. Dividing
each of the last set ofnumbers by the smallest (0.92)gives 1.99:4.96:1 2 2:5:1,
which suggests a molecular formula of C,H,Br, or a multiple thereof. If we
know that hydrogen gas is H, and has a molecular weight of 2 X 1.008 = 2.016,
we can compare the weight of a given volume of hydrogen with the weight of
the same volume of our unknown in the gas phase at the same temperature
and pressure. If the experimental ratio of these weights turns out to be 54,
then the molecular weight of the unknown would be 2.01 6 x 54 = 109 and the
formula C,H,Br would be correct (see Exer~ise1- 15).

1-1B Valence
If we assume that the molecule is held together by chemical bonds, without
knowing more, we could write numerous structures such as H-H-H-
H-H-C-C-Br, H-C-Br-H-H-C-H-H, and so on. How-
ever, if we also know of the existence of stable H,, but not H,; of stable Br,,
but not of Br,; and of stable CH,Br, CH,Br,, CHBr,, and CBr,, but not of
CH,Br, CHBr, CBr, and so on, a pattern of what is called valence emerges.

lWe will finesse here the long and important struggle of getting a truly self-consistent
table of atomic weights. If you are interested in the complex history of this problem
and the clear solution to it proposed by S. Cannizzaro in 1860, there are many accounts
available in books on the history of chemistry. One example is J. R. Partington, A
History of Chemistry, Vol. IV, Macmillan, London, 1964. Relative atomic weights
now are based on I2C = 12 (exactly).
1-1 C Structural Formulas

It will be seen that the above formulas all are consistent if hydrogen atoms
and bromine atoms form just one bond (are univalent) while carbon atoms form
four bonds (are tetravalent). This may seem almost naively simple today, but
a considerable period of doubt and uncertainty preceded the acceptance of the
idea of definite valences for the elements that emerged about 1852.

1-1C Structural Formulas

If we accept hydrogen and bromine as being univalent and carbon as tetra-
valent, we can write

as a structural formula for C,H,Br.2 However, we also might have written

Br-C-C-H H-C-C-H
H H Br H

There is a serious problem as to whether these formulas represent the same

or different compounds. All that was known in the early days was that every
purified sample of C,H,Br, no matter how prepared, had a boiling point of
38°C and density of 1.460 g ml-l. Furthermore, all looked the same, all
smelled the same, and all underwent the same chemical reactions. There was
no evidence that C,H,Br was a mixture or that more than one compound of
this formula could be prepared. One might conclude, therefore, that all of the
structural formulas above represent a single substance even though they
superficially, at least, look different. Indeed, because H-Br and Br-H are
two different ways of writing a formula for the same substance, we suspect

2Formulas such as this appear to have been used first by Crum Brown, in 1864, after
the originators of structural formulas, A. ~ e k u l 6and A. Couper (1858), came up with
rather awkward, impractical representations. It seems incredible today that even the
drawing of these formulas was severely criticized for many years. The pot was kept
boiling mainly by H. Kolbe, a productive German chemist with a gift for colorful
invective and the advantage of a podium provided by being editor of an influential
chemical journal.
1 Introduction What IS Organ~cChemistry All About?

that the same is true for

Br-C-C-H and H-C-C-~r


Br H H Br
as well as for H-C-C-H, H-C-C-H,
H-C-C-H, and H-C-C-H.
Br H H Br

There are, though, two of these structures that could be different from one
another, namely

H-6-C-~r and H-C-C-H


In the first of these, CH,- is located opposite the Br- and the H-'s on the
carbon with the Br also are opposite one another. In the second formula,
CM,- and Br- are located next to each other as are the H-'s on the same
carbon. We therefore have a problem as to whether these two different for-
mulas also represent different compounds.

1-1D Tetrahedral Carbon

A brilliant solution to the problem posed in the preceding section came in
1874 when J. H. van't Hoff proposed that all four valences of carbon are
equivalent and directed to the corners of a regular tetrahedron."f we redraw
the structures for C,H,Br as 1, we see that there is only one possible arrange-
ment and, contrary to the impression we got from our earlier structural formu-
las, the bromine is equivalently located with respect to each of the hydrogens
on the same carbon.

T h e name of J. A. Le Be1 also is associated with this particular idea, but the record
shows that Le Be1 actually opposed the tetrahedral formulations, although, simul-
taneously with van't Hoff, he made a related very important contribution, as will be
discussed in Chapter 5.
1-1 E The Question of Rotational lsomers

A convenient way of representing organic molecules in three dimensions,

which shows the tetrahedral relationships of the atoms very clearly, uses the
so-called ball-and-stick models 2. The sticks that represent the bonds or va-
lences form the tetrahedral angles of 109.47".

I - 1 E The Question of Rotational lsomers

The tetrahedral carbon does not solve all problems without additional postu-
lates. For example, there are two different compounds known with the same
formula C,H,Br,. These substances, which we call isomers, can be reasonably
written as

H Br H H
H-C-C-H and Br-C-C-Br

However, ball-and-stick models suggest further possibilities for the second

structure, for example 3, 4, and 5:
1 lntroduct~on What is Organ~cChem~stryAll About?

This is a problem apparently first clearly recognized by Paterno, in 1869. We

call these rotational (or conformational) isomers, because one is converted to
another by rotation of the halves of the molecule with respect to one another,
with the C-C bond acting as an axle. If this is not clear, you should make a
ball-and-stick model and see what rotation around the C-C bond does to the
relationships between the atoms on the carbons.
The difficulty presented by these possibilities finally was circumvented by
a brilliant suggestion by van't Hoff of "free rotation," which holds that isomers
corresponding to different rotational angles, such as 3, 4, and 5, do not have
separate stable existence, but are interconverted by rotation around the C-C
bond so rapidly that they are indistinguishable from one another. Thus there
is only one isomer corresponding to the different possible rotational angles
and a total of only two isomers of formula C,H,Br,. As we shall see, the idea
of free rotation required extensive modification some 50 years after it was
first proposed, but it was an extremely important paradigm, which, as often
happens, became so deeply rooted as to become essentially an article of faith
for later organic chemists. Free rotation will be discussed in more detail in
Chapters 5 and 27.

1-1F The Substitution Method for Proof of Structure

The problem of determining whether a particular isomer of C,H,Br, is

could be solved today in a few minutes by spectroscopic means, as will be

explained in Chapter 9. However, at the time structure theory was being de-
veloped, the structure had to be deduced on the basis of chemical reactions,
which could include either how the compound was formed or what it could be
converted to. A virtually unassailable proof of structure, where it is applicable,
is to determine how many different substitution products each of a given group
of isomers can give. For the C,H,Br, pair of isomers, substitution of a bromine
jor a hydrogen will be seen to give only one possibility with one compound
and two with the other:
1-1G The Benzene Problem

Therefore, if we have two bottles, one containing one C,H,Br, isomer and one
the other and run the substitution test, the compound that gives only one
product is 6 and the one that gives a mixture of two products is 7. Further, it
will be seen that the test, besides telling which isomer is 6 and which is 7, es-
tablishes the structures of the two possible C,H3Br3 isomers, 8 and 9. Thus
only 8 can be formed from both of the different C,H,Br, isomers whereas 9 is
formed from only one of them.

Exercise 1-1 How many different isomers are there of C,H,Br,? (Assume free-ro-
tating tetrahedral carbon and univalent hydrogen and bromine.) How could one
determine which of these isomers is which by the substitution method?

Exercise 1-2 A compound of formula C3H,Br, is found to give only a single sub-
stance, C3H,Br3, on further substitution. What IS the structure of the C3H,Br, isomer and
of its substitution product?

Exercise 1-3 A compound of formula C,H, gives only a single monobromo sub-
stitution product of formula C,H,,Br. What is the structure of this C,H,, isomer? (Notice
that carbon can form both continuous chains and branched chains. Also notice that
structures such as the following represent the same isomer because the bonds to car-
bon are tetrahedral and are free to rotate.)


HI 1
HI 1 88

I I I 1

Exercise 1-4 A gaseous compound of formula C,H, reacts with liquid bromine
(Br,) to give a single C,H,Br, compound. The C,H4Br, so formed gives only one
C,H,Br3 substitution product. Deduce the structure of C,H4 and the bromo compounds
derived from it. (This was a key problem for the early organic chemists.)

. I-1G The Benzene Problem

There were already many interconversion reactions of organic compounds
known at the time that valence theory, structural formulas, and the concept
of the tetrahedral carbon came into general use. As a result, it did not take
long before much of organic chemistry could be fitted into a concordant whole.
One difficult problem was posed by the structures of a group of substitution
1 !ntroduction. What is Organic Chemistry All About?

products of benzene, C,H,, called "aromatic compounds," which for a long

time defied explanation. Benzene itself had been prepared first by Michael
Faraday, in 1825. An ingenious solution for the benzene structure was pro-
vided by A. KekulC, in 1866, wherein he suggested (apparently as the result
of a hallucinatory perception) that the six carbons were connected in a hex-
agonal ring with alternating single and double carbon-to-carbon bonds, and
with each carbon connected to a single hydrogen, 10:

H,C/ Cac/H

11 1 Kekule structure of benzene

/ \
/ \ 10

This concept was controversial, to say the least, mainly on two counts.
Benzene did not behave as expected, as judged by the behavior of other com-
pounds with carbon-to-carbon double bonds and also because there should
be two different dibromo substitution products of benzene with the bromine
on adjacent carbons (11 and 12) but only one such compound could be isolated.

KekulC explained the second objection away by maintaining that 11 and 12

were in rapid equilibrium through concerted bond shifts, in something like
the same manner as the free-rotation hypothesis mentioned previously:

However, the first objection could not be dismissed so easily and quite a num-
ber of alternative structures were proposed over the ensuing years. The con-
troversy was not really resolved until it was established that benzene is a
1-1G The Benzene Problem

regular planar hexagon, which means that all of its C-C bonds have the samq
length, in best accord with a structure written not with double, not with single,
but with 1.5 bonds between the carbons, as in 13:

This. in turn, generated a massive further theoretical controversy overjust how

13 should be interpreted, which, for a time, even became a part of "Cold-War"
politics!' We shall examine experimental and theoretical aspects of the benzene
structure in some detail later. It is interesting that more than 100 years after
Kekule's proposal the final story on the benzene structure is yet to be told.'

Exercise 1-5 Three differen1 dibrornobenzenes are kiown, here represented by just
one of the K e k u l ~stract~res,14, 15, and 16:

Show how the su3stltJtron metrlod described ir Seci~onI - I F could be usea :o de-
termlne l ~ h i c hisomer I S which and, In addrt~oi,establ sh the structures of the varlous
poss~bletr~bromobenzenesof formula C,H,Br,

T11e "resonance theory," to be discussed in detail in Chapters 6 and 21, was charac-
t e r i ~ e din 1949 as a physically and ideologically inadmissable theory formulated by
"decadent bourgeois 3cientists." See I,. K. Graham, Scipnce and Plzilosophy in rhe
Soviet Union, Vintage Book\, New York, 1973, Chapter VT11, for an intercsting ac-
count of this controversy.
"Modern organic chemistry should not be regarded at all as a settled science, free of
controversy. To be sure, personal attacks of the kind indulged in by Kolbe and others
often are not published, but profound and indecd acrimonious differences of scient~fic
interpretatton exist and can persist for many years.
1 lntroductlon What IS Organrc Chemistry All About?

Exercise 1-6 The German chem~stLadenburg, In 1868, suggested the pr~smatrc

formula 17 for benzene

Assumrng the C-C bonds of the prlsm all are the same length, determ~nehow many
mono-, dl-, and trrbrom~ne-subst~tuted Isomers are poss~blefor 17 Compare the re-
sults wlth those expected for benzene w ~ t hstructure 13 If you have molecular models
l very helpful A s~mplealternative model for
of the ball-and-strck type, these w ~ l be
17 would be a plece of strff paper folded and fastened as In 18 to glve a prlsm wrth
three equal square faces

1-1H Proof of Structure through Reactions

The combination of valence theory and the substitution method as described
in Section 1-1F gives, for many compounds, quite unequivocal proofs of
structure. Use of chemical transformations for proofs of structure depends on
the applicability of a simple guiding principle, often called the "principle of
least structural change." As we shall see later, many exceptions are known and
care is required to keep from making serious errors. With this caution, let us
see how the principle may be applied. The compound C,H,Br discussed in
Section 1-1A reacts slowly with water to give a product of formula C,H60.
The normal valence of oxygen is two, and we can write two, and only two,
different structures, 19 and 20, for C,H60:
I - 1 H Proof of Structure through Reactions

The principle of least structural change favors 19 as the product, because the
reaction to form it is a simple replacement of bromine bonded to carbon by
-OH, whereas formation of 20 would entail a much more drastic rearrange-
ment of bonds. The argument is really a subtle one, involving an assessment
of the reasonableness of various possible reactions. On the whole, however, it
works rather well and, in the specific case of the C,H,O isomers, is strongly
supported by the fact that treatment of 19 with strong hydrobromic acid (HBr)
converts it back to C,H,Br. In contrast, the isomer of structure 20 reacts with
HBr to form two molecules of CH,Br:

+ HBr - H-C-C-Br
+ HzO

In each case, C-O bonds are broken and C-Br bonds are formed.
We could conceive of many other possible reactions of CzH,O with
HBr, for example

H-C-C-OH + HBr -A+ Br-C-C-OH + H,

which, as indicated by +, does not occur, but hardly can be ruled out by the
principle of least structural change itself. Showing how the probability of such
alternative reactions can be evaluated will be a very large part of our later

Exercise 1-7 The compound C,H,Br reacts slowly with the compound CH40 to
yield a single substance of formula C,H,O. Assuming normal valences throughout,
write structural formulas for CH40 and the three different possible structural (not
rotational) isomers of C,H,O and show how the principle of least structural change
favors one of them as the reaction product. What would you expect to be formed from
each of these three C,H,O isomers with strong hydrobromic acid?
1 Introduction. What is Organic Chemistry All About?

1-1I Reactivity, Saturation, Unsaturation,

and Reaction Mechanisms
The substitution method and the interconversion reactions discussed for proof
of structure possibly may give you erroneous ideas about the reactions and
reactivity of organic compounds. We certainly do not wish to imply that it is
a simple, straightforward process to make all of the possible substitution prod-
ucts of a compound such as


In fact, as will be shown later, direct substitution of bromine for hydrogen with
compounds such as this does not occur readily, and when it does occur, the
four possible substitution products indeed are formed, but in far from equal
amounts because there are diferences in reactivity for substitution at the
different positions. Actually, some of the substitution products are formed
only in very small quantities. Fortunately, this does not destroy the validity
of the substitution method but does make it more difficult to apply. If direct
substitution fails, some (or all) of the possible substitution products may have
to be produced by indirect means. Nonetheless, you must understand that
the success of the substitution method depends on determination of the total
number of possible isomers-it does not depend on how the isomers are
Later, you will hear a lot about compounds or reagents being "reactive"
and "unreactive." You may be exasperated by the loose way that these terms
are used by organic chemists to characterize how fast various chemical changes
occur. Many familiar inorganic reactions, such as the neutralization of hydro-
chloric acid with sodium hydroxide solution, are extremely fast at ordinary
temperatures. But the same is not often true of reactions of organic compounds.
For example, C,H,Br treated in two different ways is converted to gaseous
compounds, one having the formula C,H, and the other C,H4. The C2H4com-
pound, ethene, reacts very quickly with bromine to give C,H,Br,, but the
C,H, compound, ethane, does not react with bromine except at high tempera-
tures or when exposed to sunlight (or similar intense light). The reaction
products then are HBr and C,H,Br, and later, HBr and C,H4Br,, C,H,Br,,
and so on.
We clearly can characterize C,H, as "reactive" and C,H, as "unreac-
tive" toward bromine. The early organic chemists also used the terms "un-
saturated" and "saturated" for this behavior, and these terms are still in wide
use today. But we need to distinguish between "unsaturated" and "reactive,"
and between "saturated" and "unreactive," because these pairs of terms are
not synonymous. The equations for the reactions of ethene and ethane with
1-11 Reactivity, Saturation, Unsaturation, and Reaction Mechanisms

bromine are different in that ethene adds bromine, C2H4 Br, -+ C,H,Br,,
whereas ethane substitutes bromine, C2H6 Br, ---t C,H,Br HBr. +
You should reserve the term "unsaturated" for compounds that can,
at least potentially, react by addition, and "saturated7' for compounds that
can only be expected to react by substitution. The difference between addition
and substitution became much clearer with the development of the structure
theory that called for carbon to be tetravalent and hydrogen univalent. Ethene
then was assigned a structure with a carbon-to-carbon double bond, and ethane
a structure with a carbon-to-carbon single bond:

ethene ethane

Addition of bromine to ethene subsequently was formulated as breaking one

of the carbon-carbon bonds of the double bond and attaching bromine to
these valences. Substitution was written similarly but here bromine and a
C-H bond are involved:

- H-C-C-H
1 1
(dashed lines indcate
bonds broken and made)

We will see later that the way in which these reactions actually occur
is much more complicated than these simple equations indicate. In fact, such
equations are regarded best as chemical accounting operations. The number of
bonds is shown correctly for both the reactants and the products, and there
is an indication of which bonds break and which bonds are formed in the overall
process. However, do not make the mistake of assuming that no other bonds
are broken or made in intermediate stages of the reaction.
Much of what comes later in this book will be concerned with what we
know, or can find out, about the mechanisms of such reactions-a reaction
mechanism being the actual sequence of events by which the reactants be-
come converted to the products. Such information is of extraordinary value
in defining and understanding the range of applicability of given reactions for
practical preparations of desired compounds.
The distinction we have made between "unsaturated" and "reactive" is
best illustrated by a definite example. Ethene is "unsaturated" (and "reactive")
1 Introduction. What is Organic Chemistry All About?

toward bromine, but tetrachloroethene, C2C1,, will not add bromine at all un-
der the same conditions and is clearly "unreactive." But is it also "saturated"?

\ 7'+ I
Br, ++ CI-C-C-CI

?="\C 1

The answer is definitely no, because if we add a small amount of aluminum

bromide, AlBr,, to a mixture of tetrachloroethene and bromine, addition does
occur, although sluggishly:

Obviously, tetrachloroethene is "unsaturated" in the sense it can undergo ad-

dition, even if it is unreactive to bromine in the absence of aluminum bromide.
The aluminum bromide functions in the addition of bromine to tetra-
chloroethene as a catalyst, which is something that facilitates the conversion
of reactants to products. The study of the nature and uses of catalysts will
concern us throughout this book. Catalysis is our principal means of control-
ling organic reactions to help form the product we want in the shortest pos-
sible time.

Exercise 1-8 There are a large number of known isomers of C,H,, and some of
these are typically unsaturated, like ethene, while others are saturated, like ethane.
One of the saturated isomers on bromine substitutiori gives only one compound of
formula C,H,Br. Work out a structure for this isomer of C,H, and its monobromo sub-
stitution product.


We have tried to give you a taste of the beginnings of organic chemistry and
a few of the important principles that brought order out of the confusion that
existed as to the nature of organic compounds. Before moving on to other
matters, it may be well to give you some ideas of what kind of preparation will
be helpful to you in learning about organic chemistry from this textbook.
The most important thing you can bring is a strong desire to master the
subject. We hope you already have some knowledge of general chemistry and
1-2 What Preparat~onShould You Have? 17

that you already will have had experience with simple inorganic compounds.
That you will know, for example, that elemental bromine is Br, and a noxious,
dark red-brown, corrosive liquid; that sulfuric acid is H,SO,, a syrupy color-
less liquid that reacts with water with the evolution of considerable heat and
is a strong acid; that sodium hydroxide is NaOH, a colorless solid that dis-

solves in water to give a strongly alkaline solution. It is important to know
the characteristics of acids and bases, how to write simple, balanced chemical
reactions, such as 2H2 0, -+ 2H20, and 2NaOH H,SO, + Na,SO,
+ 2H,O, what the concept of a mole of a chemical substance is, and to be
somewhat familiar with the periodic table of the elements as well as with the
metric system, at least insofar as grams, liters, and degrees centigrade are
concerned. Among other things, you also should understand the basic ideas of
the differences between salts and covalent compounds, as well as between
gases, liquids, and solids; what a solution is; the laws of conservation of mass
and energy; the elements of how to derive the Lewis electron structures of
simple molecules such as H :0 :H =water; that P V = nR T; and how to calculate
molecular formulas from percentage compositions and molecular weights. We
shall use no mathematics more advanced than simple algebra but we do cx-
pect that you can use logarithms and are able to carry through the following
conversions forward and backward:

The above is an incomplete list, given to illustrate the level of prepara-

tion we are presuming in this text. If you find very much of this list partly or
wholly unfamiliar, you don't have to give up, but have a good general chemistry
textbook available for study and reference-and use it! Some useful general
chemistry books are listed at the end of the chapter. A four-place table of
logarithms will be necessary; a set of ball-and-stick models and a chemical
handbook will be very helpful, as would be a small electronic calculator or
slide rule to carry out the simple arithmetic required for many of the exercises.
In the next section, we review some general chemistry regarding salt-
like and covalent compounds that will be of special relevance to our later


Let us consider some of the factors that make so much of chemistry center on
a single element, carbon. One very important feature is that carbon-carbon
bonds are strong, so long chains or rings of carbon atoms bonded to one another
are possible. Diamond and graphite are two familiar examples, the diamond
lattice being a three-dimensional network of carbon atoms, whereas graphite
more closely resembles a planar network. The lubricating properties of graph-
ite actually are related to its structure, which permits the planes to slide one
past the other.
1 Introduction. What is Organic Chemistry All About?

d~amondlattice graphite

( 0 carbon atom)

But carbon is not unique in forming bonds to itself because other elements
such as boron, silicon, and phosphorus form strong bonds in the elementary
state. The uniqueness of carbon stems more from the fact that it forms strong
carbon-carbon bonds that also are strong when in combination with other ele-
ments. For example, the combination of hydrogen with carbon affords a re-
markable variety of carbon hydrides, or hydrocarbons as they usually are
called. In contrast, none of the other second-row elements except boron gives
a very extensive system of stable hydrides, and most of the boron hydrides
are much more reactive than hydrocarbons, especially to water and air.
\ 7 (typical hydrocarbons)
I I I /"="\
methane ethane ethene

Carbon forms bonds not only with itself and with hydrogen but also
with many other elements, including strongly electron-attracting elements
such as fluorine and strongly electropositive metals such as lithium:

F-C-F H-C-F H-C-~i

tetrafluoromethane methyl fluoride methyllithium
(carbon tetrafluorlde)

Why is carbon so versatile in its ability to bond to very different kinds of ele-
ments? The special properties of carbon can be attributed to its being a
relatively small atom with four valence electrons. To form simple saltlike
compounds such as sodium chloride, NaBC1@,carbon would have to either
lose the four valence electrons to an element such as fluorine and be con-
verted to a quadripositive ion, C4@,or acquire four electrons from an element
such as lithium and form a quadrinegative ion, C40. Gain of four electrons
would be energetically very unfavorable because of mutual repulsion between
the electrons.
1-3 Why is Organic Chemistry Special? 19

Customarily, carbon completes its valence-shell octet by sharing elec-

trons with other atoms. In compounds with shared electron bonds (or covalent
bonds) such as methane, ethane, or tetrafluoromethane, each of the bonded
atoms including carbon has its valence shell filled, as shown in the following
electron-pair or Lewis6 structures:

.. H .. .. :F:
.. ..
.. : H H:C
..: C..: H : ..
F : c..: F..:
H H H ..
: F:
methane ethane tetrafluoromethane

In this way, repulsions between electrons associated with completion of the

valence shell of carbon are compensated by the electron-attracting powers
of the positively charged nuclei of the atoms to which the carbon is bonded.
However, the electrons of a covalent bond are not necessarily shared
equally by the bonded atoms, especially when the affinities of the atoms for
electrons are very different. Thus, carbon-fluorine and carbon-lithium bonds,
although they are not ionic, are polarized such that the electrons are asso-
ciated more with the atom of higher electron afinity. This is usually the atom
with the higher effective nuclear charge.
C :F c: Li (SO, 6 0 denote partial ionic bonds)

We see then a gradation from purely ionic to purely covalent bonding in differ-
ent molecules, and this is manifest in their chemical and physical properties.
Consider, for instance, the hydrides of the elements in the second horizontal
row of the periodic table. Their melting and boiling point^,^ where known, are
given below.


rnp,"C 680 (decomposes at 125) - -182 -78 0 -83.7

bp, "C - - -161 -33 100 +19.7

0 0
Lithium hydride can be regarded as a saltlike ionic compound, Li :H.
Electrostatic attractions between oppositely charged ions in the crystal lattice

6G. N. Lewis (1876-1946), the renowned U.S. chemist, was the first to grasp the sig-
nificance of the electron-pair in molecular structure. H e laid the foundation for modern
theory of structure and bonding in his treatise on Valence and the Structure o f A t o m s
and Molecules (1923).
7Throughout this text all temperatures not otherwise designated should be understood
to be in "C; absolute temperatures will be shown as OK.
1 Introductron. What is Organic Chemistry All About?

are strong, thereby causing lithium hydride to be a high-melting, nonvolatile

solid like sodium chloride, lithium fluoride, and so on.
Methane, CH,, is at the other extreme. It boils at --161°, which is about
800" lower even than the melting point of lithium hydride. Because carbon
and hydrogen have about the same electron-attracting power, C-H bonds
have little ionic character, and methane may be characterized as a nonpolar
substance. As a result, there is relatively little electrostatic attraction between
methane molecules and this allows them to "escape7' more easily from each
other as gaseous molecules - hence the low boiling point.
Hydrogen fluoride has a boiling point some 200" higher than that of
methane. The bonding electron pair of H F is drawn more toward fluorine
so so
than to hydrogen so the bond may be formulated as H----F. In liquid hydrogen
fluoride, the ~noleculestend to aggregate through what is called hydrogen
bonding- in chains and rings arranged so the positive hydrogen on one molecule
attracts a negative fluorine on the next:

When liquid hydrogen fluoride is vaporized, the temperature must be raised

sufficiently to overcome these intermolecular electrostatic attractions; hence
the boiling point is high compared to liquid methane. Hydrogen fluoride is
best characterized as a polar, but not ionic, substance. Although the 0-H
and N-H bonds of water and ammonia have somewhat less ionic character
than the H-F bonds of hydrogen fluoride, these substances also are relatively
polar in nature and also associate through hydrogen bonding in the same way
as does hydrogen fluoride.
The chemical properties of lithium hydride, methane, and hydrogen
fluoride are in accord with the above formulations. Thus, when the bond to
the hydrogen is broken, we might expect it to break in the senseLiB ;:Hafor
so ..so
lithium hydride, and H j : F : for hydrogen fluoride so that the electron pair
goes with the atom of highest electron affinity. This is indeed the case as the
following reaction indicates:

Methane, with its relatively nonpolar bonds, is inert to almost all re-
agents that could remove hydrogen as H @or H : @exceptunder anything but
extreme conditions. As would be expected, methyl cations CH,@and methyl
anions CH, :Oare very difficult to generate and are extremely reactive. For this
reason, the following reactions are not observed:
1-4 The Breadth of Organic Chemistry

From the foregoing you may anticipate that the chemistry of carbon
compounds will be largely the chemistry of covalent compounds and will not
at all resemble the chemistry of inorganic salts such as sodium chloride. You
also may anticipate that the major differences in chemical and physical proper-
ties of organic compounds will arise from the nature of the other elements
bonded to carbon. Thus methane is not expected to, nor does it have, the same
chemistry as other one-carbon compounds such as methyllithium, CH,Li,
or methyl fluoride, CH,F.

Exercise 1-9 Lithium hydride could be written as either Li@:Hoor Ha: LiG depend-
ing on whether lithium or hydrogen is more electron-attracting. Explain why hydrogen
is actually more electron-attracting, making the correct structure Lia: HO

Exercise '1-10 An acid (HA) can be defined as a substance that donates a proton
to a base, for example water. The proton-donation reaction usually is an equilibrium
reaction and is written as

Predict which member of each of the following pairs of compounds would be the
stronger acid. Give your reasons.
a. LiH, HF c. H20,, H 2 0
b. NH,, H 2 0 d. CH,, CF,H


Organic chemistry originally was defined as the chemistry of those substances

formed by living matter and, for quite a while, there was a firm belief that it
would never be possible to prepare organic compounds in the laboratory out-
side of a living system. However, after the discovery by Wohler, in 1828, that
a supposedly typical organic compound, urea, could be prepared by heating
an inorganic salt, ammonium cyanate, this definition gradually lost significance
and organic chemistry now is broadly defined as the chemistry of carbon-
containing compounds. Nonetheless, the designation "organic" is still very
pertinent because the chemistry of organic compounds is also the chemistry
of living organisms.
22 1 lntroductlon What IS Organic Chernrstry Ail About?

Each of us and every other living organism is comprised of, and end-
lessly manufactures, organic compounds. Further, all organisms consume
organic compounds as raw materials, except for those plants that use photo-
synthesis or related processes to synthesize their own from carbon dioxide.
To understand every important aspect of this chemistry, be it the details of
photosynthesis, digestion, reproduction, muscle action, memory or even the
thought process itself, is a primary goal of science and it should be recognized
that only through application of organic chemistry will this goal be achieved.
Modern civilization consumes vast quantities of organic compounds.
Coal, petroleum, and natural gas are primary sources of carbon compounds
for use in production of energy and as starting materials for the preparation
of plastics, synthetic fibers, dyes, agricultural chemicals, pesticides, fertilizers,
detergents, rubbers and other elastomers, paints and other surface coatings,
medicines and drugs, perfumes and flavors, antioxidants and other preserva-
tives, as well as asphalts, lubricants, and solvents that are derived from pe-
Much has been done and you soon may infer from the breadth of the
material that we will cover that most everything worth doing already has been
done. However, many unsolved scientific problems remain and others have not
even been thought of but, in addition, there are many technical and social prob-
lems to which answers are badly needed. Some of these include problems of
pollution of the environment, energy sources, overpopulation and food pro-
duction, insect control, medicine, drug action, and improved utilization of
natural resources.


As you proceed with your study of organic chemistry, you may well feel con-
fused as to what it is you are actually dealing with. On the one hand, there will
be exhortations to remember how organic chemistry pervades our everyday
life. And yet, on the other hand, you also will be exhorted to think about or-
ganic compounds in terms of abstract structural formulas representing mole-
cules when there is absolutely no way at all to deal with molecules as single
entities. Especially if you are not studying organic compounds in the laboratory
concurrently, you may come to confuse the abstraction of formulas and ball-
and-stick models of the molecules with the reality of organic compounds, and
this would be most undesirable. At each stage of the way, you should try to
make, or at least visualize, a juncture between a structural formula and an
actual substance in a bottle. This will not be easy-it takes time to reach the
level of experience that a practicing organic chemist has so that he can tell
you with some certainty that the structural formula 21 represents, in actuality,
a limpid, colorless liquid with a pleasant odor, slightly soluble in water, boiling
somewhere about 100".
1-5 Some Philosophical Observations


A useful method for developing this sort of feeling for the relationship between
structures and actual compounds is to check your perception of particular
substances with their properties as given in a chemical handbook.
One, perhaps comforting, thought for you at this time is that differences
between the chemical behaviors of relative]y similar organic compounds usually
are ascribed to just three important and different kinds of effects- two of which
have root in common experience. One, called steric hindrance, is a manifes-
tation of experience that two solid objects cannot occupy the same space at
once. Another is the electrical effect, which boils down to a familiar cate-
chism that like electrical charges repel each other and unlike charges attract
each other. The remaining important effect, the one that has no basis in com-
mon experience, derives from quantum mechanics. The quantum mechanical
effect explains why benzene is unusually stable, how and why many reactions
occur in special ways and, probably most important of all, the ways that or-
ganic compounds interact with electromagnetic radiation of all kinds -from
radio waves to x rays.
We shall try to give as clear explanations as possible of the quantum
mechanical effect, but some of it will just have to be accepted as fact that we
cannot ourselves experience directly nor understand intuitively. For example,
when a grindstone rotates, so far as our experience goes, it can have an in-
finitely variable rate of rotation and, consequently, infinitely variable rota-
tional (angular) momentum. However, molecules in the gas phase have only
specijic rotation rates and corresponding specijic rotational momentum values.
No measurement technique can detect in-between values of these quantities.
Molecules are "quantized rotators." About all you can do is try to accept
this fact, and if you try long enough, you may be able to substitute familiarity
for understanding and be happy with that.
All of us have some concepts we use continually (even perhaps uncon-
sciously) about energy and work. Thermodynamics makes these concepts
quantitative and provides very useful information about what might be called
the potential for any process to occur, be it production of electricity from a
battery, water running uphill, photosynthesis, or formation of nitrogen oxides
in combustion of gasoline. In the past, most organic chemists seldom tried to
apply thermodynamics to the reactions in which they were interested. Much
of this was due to the paucity of thermodynamic data for more than a few
organic compounds, but some was because organic chemists often liked to
think of themselves as artistic types with little use for quantitative data on
their reactions (which may have meant that they didn't really know about
thermodynamics and were afraid to ask).
24 1 Introduction. What is Organic Chemistry All About?

Times have changed. Extensive thermochemical data are now available,

the procedures are well understood, and the results both useful and interesting.
We shall make considerable use of thermodynamics in our exposition of or-
ganic chemistry. We believe it will greatly improve your understanding of why
some reactions go and others do not.
Finally, you should recognize that you almost surely will have some
problems with the following chapters in making decisions as to how much time
and emphasis you should put on the various concepts, principles, facts, and so
an, that we will present for you. As best we can, we try to help you by pointing
out that this idea, fact, and so on, is "especially important," or words to that
effect. Also, we have tried to underscore important information by indicating
the breadth of its application to other scientific disciplines as well as to tech-
nology. In addition, we have caused considerable material to be set in smaller
type and indented. Such material includes extensions of basic ideas and de-
partments of fuller explanation. In many places, the exposition is more com-
plete than it needs to be for you at the particular location in the book. However,
you will have need for the extra material later and it will be easier to locate
and easier to refresh your memory on what came before, if it is in one place.
We will try to indicate clearly what you should learn immediately and
what you will want to come back for later.
The problem is, no matter what we think is important, you or your
professor will have your own judgments about relevance. And because it is
quite impossible to write an individual text for your particular interests and
needs, we have tried to accommodate a range of interests and needs through
providing a rather rich buffet of knowledge about modern organic chemistry.
Hopefully, all you will need is here, but there is surely much more, too. So,
to avoid intellectual indigestion, we suggest you not try to learn everything as
it comes, but rather try hardest to understand the basic ideas and concepts
to which we give the greatest emphasis. As you proceed further, the really
important facts, nomenclature, and so on (the kind of material that basically
requires memorization), will emerge as that which, in your own course of study,
you will find you use over and over again. In hope that you may wish either to
learn more about particular topics or perhaps gain better understanding through
exposure to a different perspective on how they can be presented, we have
provided supplementary reading lists at the end of each chapter.
Our text contains many exercises. You will encounter some in the
middle of the chapters arranged to be closely allied to the subject at hand.
Others will be in the form of supplementary exercises at the end of the chap-
ters. Many of the exercises will be drill; many others will extend and enlarge
upon the text. The more difficult problems are marked with a star (*).

Additional Reading

Useful general chemistry textbooks:

R. E. Dickerson, H. B. Gray, and G. P. Haight, Jr., Chemical Principles, 2nd ed., W. A
Benjamin, Inc., Menlo Park, Calif., 1974.
Additional Read~ng

M. J, Sienko and R. A Plane, Chemical Principles and Properties, 2nd ed., McGraw-
Hill Book Company, New York, 1974.
L. Pauling, General Chemistry, 3rd ed., W. H. Freeman and Company, San Francisco,
B. H. Mahan, University Chemistry, 2nd ed., Addison-Wesley Publishing Company,
Reading, Mass., 1969,
G. C. Pimentel and R. 0 . Spratley, Understanding Chemistry, Holden-Day, Inc., San
Francisco, 1971.
R. H. Eastman, General Chemistry, Experiment and Theory, Holt, Rinehart and Winston,
New York, 1970.
W. L. Masterton and E, J. Slowinski, Chemical Principles, 3rd ed., W. B. Saunders
Company, Philadelphia, 1973,

A useful book on quantitative relationships:

S. W. Benson, Chemical Calculations, 3rd ed., John Wiley and Sons, Inc., New York,

A very detailed book on the history of organic chemistry:

J. R. Partington, A History of Chemistry, Macmillan, London, 1964

Supplementary Exercises
~ ~ - ~ ~ ~ x * ~ a . ~ ~ ~ ~ ~ ~ ~ * ~ ~ ~ ~ ~ ~ , c ~ * A , s~<,n-,a.a"%~*bwP&,:~*~w
~ ~ ~ u , , , L ~~ ~ ~~ ~~ . ~. =. > ~~ -, r ~. ~~ A *~ ~ ...' . . "~--
~ t ~ k, ~~ ~ ~~ .-
~ \W%,<U* ~ ~
> ~~ ~ ~~ *, w~ ~ k w~
% ~

1-11 (This problem is in the nature of review of elementary inorganic chemistry and
may require reference to a general chemistry book.) Write Lewis structures for each
of the following compounds. Use distinct, correctly placed dots for the electrons.
Mark all atoms that are not neutral with charges of the proper sign.
a. ammonia, NH, f. hydrogen peroxide, HOOH
b. ammonium bromide, NH,Br g. hydroxylamine, HONH,
c. hydrogen cyanide, HCN h. nitric acid, HNO,
d. ozone ( L 0-0-0 = 120') i. hydrogen sulfide, H,S
e. carbon dioxide, CO, j. boron trifluoride, BF,

1-12 Use ball-and-stick models or suitable three-dimensional drawings to determine

which members of the following sets of formulas represent identical compounds,
provided "free rotation" is considered to be possible around all single bonds (except
when these bonds are present in a cyclic structure):

26 1 Introduction. What is Organic Chemistry All About?

b. H H H H
I I l l

H-c-H H-C-H

I I 1 8
1 H H H

I l l I

1-13 Write structures for all of the different monobromo substitution products (of
Br for H) you would expect for each of the following compounds, (Where CH,- ap-
pears in these structures it is an abbreviation for H-C-.)

b. H H
Supplementary Exerc~ses

C. CH3 d. CH3

H \>'

\c/ \c/

/ \C/ \H
H/ \H

1-14 There are two isomers of C3H6 with normal carbon and hydrogen valences.
Each adds bromine-one rapidly and the other very sluggishly -to give different
isomers of C3H6Br,. The C3H,Br2 derived from the C3H6isomer that reacts sluggishly
with bromine can give just two different C3H,Br3 isomers on further bromine substitu-
tion, whereas the other C3H6Br2compound can give three different C3H,Br3 isomers
on further substitution. What are the structures of the C3H6isomers and their C3H6Br,
addition products?

1-15* (Remember that here and elsewhere, * denotes a more difficult exercise.)
The vast majority of organic substances are compounds of carbon with hydrogen,
oxygen, nitrogen, or the halogens. Carbon and hydrogen can be determined in com-
bustible compounds by burning a weighed sample in a stream of oxygen (Figure 1-1)
and absorbing the resulting water and carbon dioxide in tubes containing anhydrous
magnesium perchlorate and soda lime, respectively. The gain in weight of these
tubes corresponds to the weights of the water and the carbon dioxide formed.
The molecular weight of a moderately volatile substance can be determined
by the historically important Victor Meyer procedure, by which the volume of gas
produced by vaporization of a weighed sample of an unknown is measured at a given

sample in
platinum boat /CuO pellets
p K q /
* - P w P'

-3 m A A w. r J
- . & S E E ? ? 4 excess

0 2
9. -g
,, .p
~lLb<a,d ,.e
% @ ujs
Mg(CIO,), soda lime

Figure 1-1 Schematic representation of a combustion train for deter-

mination of carbon and hydrogen in combustible substances
1 Introduction. What is Organic Chemistry All About?

oven at gas burette at

temperature i, temperature 7,

arr + vapor

Figure 1-2 Schematic diagram of a Victor Meyer apparatus for deter-
mination of the vapor dens~tyof a substance that is volatile at the oven
temperature T,. The air displaced from the heated chamber by the vol-
atilization of the sample in the bulb is measured in the gas burette at tem-
perature T2 as the difference in the burette readings V2 and V,.

temperature (Figure 1-2). The relationship PV = nRT is used here, in which P is the
pressure in mm of mercury, V is the volume in ml, T is the absolute temperature in OK
[= 273.15 T("C)], n is the number of moles, and R is the gas constant = 62,400 in
units of (mm Hg x ml)/(moles x OK). The number of moles, n, equals rnlM in which rn
is the weight of the sample and M is the gross molecular weight. An example of the
use of the Victor Meyer method follows.
A 0.005372-g sample of a liquid carbon-hydrogen-oxygen compound on com-
bustion gave 0.01222 g of CO, and 0.00499 g of H,O. In the Victor Meyer method,
0.0343 g of the compound expelled a quantity of air at 100" (373°K) which, when col-
lected at 27" (300°K) and 728 mm Hg, amounted to 15.2 ml.
Show how these results lead to the empirical and molecular formula of C,H,O.
Write at least five isomers that correspond to this formula with univalent H, divalent 0,
and tetravalent C.

1-16 Determine the molecular formula of a compound of molecular weight 80 and

elemental percentage composition by weight of C = 45.00, H = 7.50, and F = 47.45.
Write structures for all the possible isomers having this formula. (See Exercise 1-15
for a description of how percentage composition is determined by combustion

1-17 Why is the boiling point of water (100") substantially higher than the boiling
point of methane (-16Io)?
Supplementary Exercises 29

1-18 Dimethylmercury, CH3-Hg-CH,, is a volatile compound of bp 96", whereas

mercuric fluoride F-Hg-F is a high-melting solid having mp 570". Explain what
differences in bonding in the two substances are expected that can account for the
great differences in physical properties.

1-19* There are four posslble Isomers of C4H,Br Let us call two of these A and B
Both A and B react with water to give the same isomer of C4H,,0 and this isomer of
C4Hl,0 reacts with strong HBr to give back only A Substitution of A wlth bromine
gives only one of the posslble C4H,Br2 lsomers Subst~tutronof B with bromlne gives
three different C,H,Br2 Isomers, and one of these IS identical with the C4H,Br2 from
the subst~tutionof A Write structural formulas for A and 6, and the lsomers of C4H,Br2
formed from them with bromlne, and for the lsomers of C4Hl,0 expected to be formed
from them with water lndlcate In which reaction the principle of least structural change
breaks down