IAQUK Resources - Basic Organic Chemistry
Specifying carbon chain length
The simplest organic compounds are built of
straight chains of carbon atoms which are named by means of prefixes that
denote the number of carbons in the chain. Using the convention Cn to denote a
straight chain of n atoms, the prefixes for chain lengths
from 1 through 10 are given here:
As you can see, chains from C5 onward use Greek number prefixes, so you
don't have a lot new to learn here. The simplest of these compounds are
hydrocarbons having the general formula CnH2n+.
They are known generically as alkanes, and their names all combine the
appropriate numerical prefix with the ending -ane:
Since organic (carbon) compounds constitute the vast majority of all known chemical substances, IAQUK have provided some basic details about understanding how each distinct compound has a unique molecular structure which has a unique characteristic and name.
Organic compounds are derived from three sources:
Nature: fibers, vegetable oils, animal oils and
fats, alkaloids, cellulose, starch, sugars, and so on.
Synthesis: A wide variety of compounds and
materials prepared by manufacturing processes.
Fermentation: Alcohols, acetone, glycerol,
antibiotics, acids, and the like are derived by the action of
microorganisms upon organic matter.
Carbon (C) appears in the second row of the
periodic table and has four bonding electrons. Organic chemicals get their
diversity from the many different ways carbon can bond to other atoms. The
simplest organic chemicals, called hydrocarbons, contain
only carbon and hydrogen atoms; the simplest hydrocarbon (called methane)
contains a single carbon atom bonded to four hydrogen atoms.
But carbon can bond to other carbon atoms in
addition to hydrogen. In fact, the uniqueness of carbon comes from the fact
that it can bond to itself in many different ways. Carbon atoms can form long
chains, branched chains and rings. There appears to be almost
no limit to the number of different structures that carbon can form. To
add to the complexity of organic chemistry, neighbouring carbon atoms can
form double and triple bonds in addition to single carbon-carbon bonds.
In organic chemistry, a hydrocarbon is an organic
compound consisting entirely of hydrogen and carbon.
There are two types, saturated and
unsaturated. Saturated hydrocarbons are those in which adjacent carbon atoms
are joined by a single covalent bond and all other bonds are satisfied by hydrogen.
Unsaturated hydrocarbons have at least two carbon
atoms that are joined by more than one covalent bond and all remaining
bonds are satisfied by hydrogen.
The saturated hydrocarbons form a whole series of
compounds starting with one carbon atom and increasing one carbon atom,
stepwise. These compounds are called alkanes, or the methane series.
The principal source is petroleum.
The hydrocarbons serve as feedstocks for the
preparation of a wide variety oforganic chemicals. This knowledge serves as the
basis of the great petrochemical industry within the petroleum industry.
Saturated hydrocarbons are quite inert toward most chemical reagents. For this
reason they were termed “paraffins” by early chemists (from the Latin parum
affinis, meaning “little affinity”).
Strong bases, acids, or aqueous solutions
of oxidizing agents do not react with saturated hydrocarbons at room
temperature. At elevated temperatures, strong oxidizing agents, such as
concentrated sulfuric acid, oxidize the compounds to carbon dioxide and water.
Other reactions of importance are as follows:
- Oxidation with oxygen or air.
- Substitution of hydrogen by halogens:
- This reaction does not ordinarily occur in
aqueous solutions and therefore is of little significance in environmental engineering
- Pyrolysis or cracking:
- High-molecular-weight hydrocarbons may be broken
into smaller molecules by heat treatment. The process is used in the petroleum
- Biological oxidation:
- Hydrocarbons are oxidized by certain bacteria under
The unsaturated hydrocarbons are usually separated
into four classes.
Each member of the alkane group except methane can
lose hydrogen to form an unsaturated compound or alkene. The alkenes
all contain one double bond between two adjacent carbon atoms, and their names
all end in -ylene or -ene. The alkenes are also called olefins.
Alkenes, particularly ethene, propene, and butene are formed in great
quantities during the cracking or pyrolysis of petroleum.
When aliphatic compounds contain two double bonds
in the molecule, they are called diolefins, some times dienes for short.
The compound 1,3-butadiene is an important example, which has been used to make
Some organic compounds contain more than two
double bonds per molecule. The red colouring matter of tomatoes, lycopene, and
the yellow colouring matter of carrots are examples.
The alkynes have a triple bond between adjacent
carbon atoms. These compounds are found to some extent in industrial wastes
from certain industries, particularly those from the manufacture of some types
of synthetic rubber.
Unsaturated linkages occur in many types of organic
compounds and exhibit many properties in common, regardless of the type of
compound in which they exist. Unsaturated compounds undergo several reactions
with relative ease.
- Oxidation: The compounds are easily oxidized in
aqueous solution by oxidizing agents such as potassium permanganate. A glycol
is the normal product.
- Reduction: Under special conditions of temperature,
pressure, and catalysis, hydrogen may be caused to add at double or triple
- Addition: Halogen acids, hypochlorous acid, and
halogens will add across unsaturated linkages. The reaction with hypochlorous
acid is most important. Industrial wastes containing appreciable amounts of
unsaturated compounds exhibit high chlorine-demand values because of such
- Polymerization: Molecules of certain compounds
having unsaturated linkages are prone to combine with each other to form
polymers of higher molecular weight. Similar reactions serve as the basis for many
industrial products, e.g. synthetic resins, synthetic fibre, synthetic rubber,
and synthetic detergents.
- Bacterial oxidation: It is
generally considered that organic compounds possessing unsaturated
linkages are more prone to bacterial oxidation than corresponding saturated
compounds because of the ease of oxidation at the double bonds.
Chains and Rings
In organic chemistry, there are a few basic structural
shapes that you will encounter. They are chains and rings.
There are also two types of chains, a straight chain, and a branched
chain. In a straight chain, one carbon atom holds no more than two other carbon
atoms. As its name implies, the straight chain is a straight link of carbon,
sometimes oxygen or nitrogen, atoms,
in structural formula that is. Because of twisting and contouring, they chain
may have several conformations.
Branched chains have at least one carbon holding more than two other
carbon atoms. It will, as its name implies, have branches of other chains
coming off another chain. Branching is one of the reasons why there are so many
isomers for each compound.
Rings (or cyclic compounds) are composed of
rings of carbon and sometimes oxygen or nitrogen. For example, Benzen.
Isomerism is another reason why there are so
compounds. Isomers are compounds with identical molecular composition but their
structures are arranged differently. Depending on how they are arranged, they
may have similar or different properties.
Because the number of carbons per molecule
increases as the compound gets more complex, the number of possible isomers for any given formula becomes very,
Number of Isomers
The nomenclature of substituted benzene ring
compounds is less systematic than that of the alkanes, alkenes and alkynes. A
few mono-substituted compounds are named by using a group name as a prefix to
"benzene", as shown by the combined names listed below. A majority of
these compounds, however, are referred to by singular names that are unique.
There is no simple alternative to memorization in mastering these names.