ORGANIC
CHEMISTRY AND
MODERN
LIFE
Photo by: Sandra Cunningham
At first glance, the term "organic chemistry" might
sound like something removed from
A
NOTHER BYPRODUCT OF ORGANIC CHEMISTRY
:
PETROLEUM JELLY
.
(Laura Dwight/Corbis
.
Reproduced by permission.)
everyday life, but this could not be further from the truth. The
reality of the role played by organic chemistry in modern existence is
summed up in a famous advertising slogan used by E. I. du Pont de
Nemours and Company (usually referred to as "du Pont"):
"Better Things for Better Living Through Chemistry."
Often rendered simply as "Better Living Through
Chemistry," the advertising campaign made its debut in 1938,
just as du Pont introduced a revolutionary product of organic
chemistry: nylon, the creation of a brilliant young chemist named
Wallace Carothers (1896-1937). Nylon, an example of a polymer
(discussed below), started a revolution in plastics that was still
unfolding three decades later, in 1967. That was the year of the film
The Graduate
, which included a famous interchange between the character of
Benjamin Braddock (Dustin Hoffman) and an adult named Mr. McGuire
(Walter Brooke):
-
Mr. McGuire: I just want to say one word to you… just one
word.
-
Benjamin Braddock: Yes, sir.
-
Mr. McGuire: Are you listening?
-
Benjamin Braddock: Yes, sir, I am.
-
Mr. McGuire: Plastics.
The meaning of this interchange was that plastics were the wave of the
future, and that an intelligent young man such as Ben should invest
his energies in this promising new field. Instead, Ben puts his
attention into other things, quite removed from
"plastics," and much of the plot revolves around his
revolt against what he perceives as the "plastic" (that
is, artificial) character of modern life.
In this way,
The Graduate
spoke for a whole generation that had become ambivalent concerning
"better living through chemistry," a phrase that
eventually was perceived as ironic in view of concerns about the
environment and the many artificial products that make up modern life.
Responding to this ambivalence, du Pont dropped the slogan in the late
1970s; yet the reality is that people truly do enjoy "better
living through chemistry"—particularly organic
chemistry.
APPLICATIONS OF ORGANIC CHEMISTRY.
What would the world be like without the fruits of organic chemistry?
First, it would be necessary to take away all the various forms of
rubber, vitamins, cloth, and paper made from organically based
compounds. Aspirins and all types of other drugs; preservatives that
keep food from spoiling; perfumes and toiletries; dyes and
flavorings—all these things would have to go as well.
Synthetic fibers such as nylon—used in everything from
toothbrushes to parachutes—would be out of the picture if it
were not for the enormous progress made by organic chemistry. The same
is true of plastics or polymers in general, which have literally
hundreds upon hundreds of applications. Indeed, it is virtually
impossible for a person in twenty-first century America to spend an
entire day without coming into contact with at least one, and more
likely dozens, of plastic products. Car parts, toys, computer
housings, Velcro fasteners, PVC (polyvinyl chloride) plumbing pipes,
and many more fixtures of modern life are all made possible by
plastics and polymers.
Then there is the vast array of petrochemicals that power modern
civilization. Best-known among these is gasoline, but there is also
coal, still one of the most significant fuels used in electrical power
plants, as well as natural gas and various other forms of oil used
either directly or indirectly in providing heat, light, and electric
power to homes. But the influence of petrochemicals extends far beyond
their applications for fuel. For instance, the roofing materials and
tar that (quite literally) keep a roof over people's heads,
protecting them from sun and rain, are the product of
petrochemicals—and ultimately, of organic chemistry.
H
YDROCARBONS
Carbon, together with other elements, forms so many millions of
organic compounds that even introductory textbooks on organic
chemistry consist of many hundreds of pages. Fortunately, it is
possible to classify broad groupings of organic compounds. The largest
and most significant is that class of organic compounds known as
hydrocarbons—chemical compounds whose molecules are made up of
nothing but carbon and hydrogen atoms.
Every molecule in a hydrocarbon is built upon a
"skeleton" composed of carbon atoms, either in closed
rings or in long chains. The chains may be straight or branched, but
in each case—rings or chains, straight chains or branched
ones—the carbon bonds not used in tying the carbon atoms
together are taken up by hydrogen atoms.
Theoretically, there is no limit to the number of possible
hydrocarbons. Not only does carbon form itself into apparently
limitless molecular shapes, but hydrogen is a particularly good
partner. It has the smallest atom of any element on the periodic
table, and therefore it can bond to one of carbon's valence
electrons without getting in the way of the other three.
There are two basic varieties of hydrocarbon, distinguished by shape:
aliphatic and aromatic. The first of these forms straight or branched
chains, as well as rings, while the second forms only benzene rings,
discussed below. Within the aliphatic hydrocarbons are three
varieties: those that form single bonds (alkanes), double bonds
(alkenes), and triple bonds (alkynes.)
ALKANES.
The alkanes are also known as saturated hydrocarbons, because all the
bonds not used to make the skeleton itself are filled to their
capacity (that is, saturated) with hydrogen atoms. The formula for any
alkane is C
n
H
2n+2
, where n is the number of carbon atoms. In the case of a linear,
unbranched alkane, every carbon atom has two hydrogen atoms attached,
but the two end carbon atoms each have an extra hydrogen.
What follows are the names and formulas for the first eight normal, or
unbranched, alkanes. Note that the first four of these received common
names before their structures were known; from C
5
onward, however, they were given names with Greek roots indicating
the number of carbon atoms (e.g., octane, a reference to
"eight.")
-
Methane (CH
4
)
-
Ethane (C
2
H
6
)
-
Propane (C
3
H
8
)
-
Butane (C
4
H
10
)
-
Pentane (C
5
H
12
)
-
Hexane (C
6
H
14
)
-
Heptane (C
7
H
16
)
-
Octane (C
8
H
18
)
The reader will undoubtedly notice a number of familiar names on this
list. The first four, being the lowest in molecular mass, are gases at
room temperature, while the heavier ones are oily liquids. Alkanes
even heavier than those on this list tend to be waxy solids, an
example being paraffin wax, for making candles. It should be noted
that from butane on up, the alkanes have numerous structural isomers,
depending on whether they are straight or branched, and these isomers
have differing chemical properties.
Branched alkanes are named by indicating the branch attached to the
principal chain. Branches, known as substituents, are named by taking
the name of an alkane and replacing the suffix with yl—for
example, methyl, ethyl, and so on. The general term for an alkane
which functions as a substituent is alkyl.
Cycloalkanes are alkanes joined in a closed loop to form a ring-shaped
molecule. They are named by using the names above, with cyclo-as a
prefix. These start with propane, or rather cyclopropane, which has
the minimum number of carbon atoms to form a closed shape: three
atoms, forming a triangle.
ALKENES AND ALKYNES.
The names of the alkenes, hydrocarbons that contain one or more double
bonds per molecule, are parallel to those of the alkanes, but the
family ending is-ene. Likewise they have a common formula: C
n
H
2n
. Both alkenes and alkynes, discussed below, are unsaturated—in
other words, some of the carbon atoms in them are free to form other
bonds. Alkenes with more than one double bond are referred to as being
polyunsaturated.
As with the alkenes, the names of alkynes (hydrocarbons containing one
or more triple bonds per molecule) are parallel to those of the
alkanes, only with the replacement of the suffix -yne in place of-ane.
The formula for alkenes is C
n
H
2n-2
. Among the members of this group are acetylene, or C
2
H
2
, used for welding steel. Plastic polystyrene is another important
product from this division of the hydrocarbon family.
AROMATIC HYDROCARBONS.
Aromatic hydrocarbons, despite their name, do not necessarily have
distinctive smells. In fact the name is a traditional one, and today
these compounds are defined by the fact that they have benzene rings
in the middle. Benzene has a formula C
6
H
6
, and a benzene ring is usually represented as a hexagon (the six
carbon atoms and their attached hydrogen atoms) surrounding a circle,
which represents all the bonding electrons as though they were
everywhere in the molecule at once.
In this group are products such as naphthalene, toluene, and dimethyl
benzene. These last two are used as solvents, as well as in the
synthesis of drugs, dyes, and plastics. One of the more famous (or
infamous) products in this part of the vast hydrocarbon network is
trinitrotoluene, or TNT. Naphthalene is derived from coal tar, and
used in the synthesis of other compounds. A crystalline solid with a
powerful odor, it is found in mothballs and various
deodorant-disinfectants.
PETROCHEMICALS.
As for petro-chemicals, these are simply derivatives of petroleum,
itself a mixture of alkanes with some alkenes, as well as aromatic
hydrocarbons. Through a process known as fractional distillation, the
petrochemicals of the lowest molecular mass boil off first, and those
having higher mass separate at higher temperatures.
Among the products derived from the fractional distillation of
petroleum are the following, listed from the lowest temperature range
(that is, the first material to be separated) to the highest: natural
gas; petroleum ether, a solvent; naphtha, a solvent (used for example
in paint thinner); gasoline; kerosene; fuel for heating and diesel
fuel; lubricating oils; petroleum jelly; paraffin wax; and pitch, or
tar. A host of other organic chemicals, including various drugs,
plastics, paints, adhesives, fibers, detergents, synthetic rubber, and
agricultural chemicals, owe their existence to petrochemicals.
Obviously, petroleum is not just for making gasoline, though of course
this is the first product people think of when they hear the word
"petroleum." Not all hydrocarbons in gasoline are
desirable. Straight-chain or normal heptane, for instance, does not
fire smoothly in an internal-combustion engine, and therefore disrupts
the engine's rhythm. For this reason, it is given a rating of
zero on a scale of desirability, while octane has a rating of 100.
This is why gas stations list octane ratings at the pump: the higher
the presence of octane, the better the gas is for one's
automobile.
HYDROCARBON
DERIVATIVES
With carbon and hydrogen as the backbone, the hydrocarbons are capable
of forming a vast array of hydrocarbon derivatives by combining with
other elements. These other elements are arranged in functional
groups—an atom or group of atoms whose presence identifies a
specific family of compounds. Below we will briefly discuss some of
the principal hydrocarbon derivatives, which are basically
hydrocarbons with the addition of other molecules or single atoms.
Alcohols are oxygen-hydrogen molecules wedded to hydrocarbons. The two
most important commercial types of alcohol are methanol, or wood
alcohol; and ethanol, which is found in alcoholic beverages, such as
beer, wine, and liquor. Though methanol is still known as "wood
alcohol," it is no longer obtained by heating wood, but rather
by the industrial hydrogenation of carbon monoxide. Used in adhesives,
fibers, and plastics, it can also be applied as a fuel. Ethanol, too,
can be burned in an internal-combustion engine, when combined with
gasoline to make gasohol. Another significant alcohol is cholesterol,
found in most living organisms. Though biochemically important,
cholesterol can pose a risk to human health.
Aldehydes and ketones both involve a double-bonded carbon-oxygen
molecule, known as a carbonyl group. In a ketone, the carbonyl group
bonds to two hydrocarbons, while in an aldehyde, the carbonyl group is
always at the end of a hydrocarbon chain. Therefore, instead of two
hydrocarbons, there is always a hydrocarbon and at least one other
hydrogen bonded to the carbon atom in the carbonyl. One prominent
example of a ketone is acetone, used in nail polish remover. Aldehydes
often appear in nature—for instance, as vanillin, which gives
vanilla beans their pleasing aroma. The ketones carvone and camphor
impart the characteristic flavors of spearmint leaves and caraway
seeds.
CARBOXYLIC ACIDS AND ESTERS.
Carboxylic acids all have in common what is known as a carboxyl group,
designated by the symbol -COOH. This consists of a carbon atom with a
double bond to an oxygen atom, and a single bond to another oxygen
atom that is, in turn, wedded to a hydrogen. All carboxylic acids can
be generally symbolized by RCOOH, with R as the standard designation
of any hydrocarbon. Lactic acid, generated by the human body, is a
carboxylic acid: when a person overexerts, the muscles generate lactic
acid, resulting in a feeling of fatigue until the body converts the
acid to water and carbon dioxide. Another example of a carboxylic acid
is butyric acid, responsible in part for the smells of rancid butter
and human sweat.
When a carboxylic acid reacts with an alcohol, it forms an ester. An
ester has a structure similar to that described for a carboxylic acid,
with a few key differences. In addition to its bonds (one double, one
single) with the oxygen atoms, the carbon atom is also attached to a
hydrocarbon, which comes from the carboxylic acid. Furthermore, the
single-bonded oxygen atom is attached not to a hydrogen, but to a
second hydrocarbon, this one from the alcohol. One well-known ester is
acetylsalicylic acid—better known as aspirin. Esters, which are
a key factor in the aroma of various types of fruit, are often noted
for their pleasant smell.
POLYMERS
Polymers are long, stringy molecules made of smaller molecules called
monomers. They appear in nature, but thanks to Carothers—a
tragic figure, who committed suicide a year before Nylon made its
public debut—as well as other scientists and inventors,
synthetic polymers are a fundamental part of daily life.
The structure of even the simplest polymer, polyethylene, is far too
complicated to discuss in ordinary language, but must be represented
by chemical symbolism. Indeed, polymers are a subject unto themselves,
but it is worth noting here just how many products used today involve
polymers in some form or another.
Polyethylene, for instance, is the plastic used in garbage bags,
electrical insulation, bottles, and a host of other applications. A
variation on polyethylene is Teflon, used not only in nonstick
cookware, but also in a number of other devices, such as bearings for
low-temperature use. Polymers of various kinds are found in siding for
houses, tire tread, toys, carpets and fabrics, and a variety of other
products far too lengthy to enumerate.
