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Naming Organic Compounds
It was once believed that compounds found in and produced by living things were infused with a “vital
force” setting them apart from inorganic compounds. In 1828 German Chemist Friedrich Wöhler
synthesized urea (an important component of urine) in his lab from inorganic reactants without the use
of a “vital force”. This was a turning point that paved the way for the synthesis of complex organic
compounds throughout the 19th century and into the present. Rather than being classified by their
method of production, today, organic compounds are defined as any compound containing carbon.
Though it is now known that carbon containing compounds do not possess a unique force, these
versatile molecules are still the subject of their own subdivision of chemistry.
Properties of Carbon:
Lewis diagram
bonding
capacity
significance
Hydrocarbons: The simplest organic compounds
The simplest organic compounds are composed exclusively of carbon and hydrogen. These are called
hydrocarbons. Hydrocarbons containing only single bonds between the carbon atoms are known as
alkanes. Alkanes are said to be saturated because all of the possible bonds to carbon are occupied by
an individual atom or molecule. The presence of one or more double or triple bonds between carbon
atoms will result in an unsaturated hydrocarbon. Double bonds denote an alkene and triple bonds
denote an alkyne.
H H
H
H
H
C
C
H H
ethane
C2H6
C
H
H
H
C
C
C
H
H
ethene
C2H4
ethyne
C2H2
Organic compounds can be represented in a variety of ways:
structural formula
ball-and-stick model
space-filling model
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For convenience, long hydrocarbon chains may be drawn in their most simplified form as a line diagram:
C8H18 =
=
C5H10 =
=
Each line represents a bond with a carbon at each end. Hydrogens are implied in line diagrams.
Naming Alkanes:
To indicate the number of carbons in a chain, we use the following prefixes
meth
eth
prop
but
pent
hex
hept
oct
non
dec
1
2
3
4
5
6
7
8
9
10
Straight-chain alkanes
Alkanes are not always in straight-chain configurations. In fact, alkanes are quite variable. Cycloalkanes
form rings. Furthermore, both straight-chain alkanes and cycloalkanes may substitute one more of their
hydrogens with either a different element (eg. haloalkanes contain halogens) or even side chains called
alkyl groups. Any element or alkyl group replacing a hydrogen is known as a substituent group.
CH3
CH3
H3C CH2 CH CH2 CH2 CH2 CH3
CH2
CH3
cyclopentane
1,1-dimethylcyclopentane
3-ethylheptane
a cycloalkane
a cycloalkane with two alkyl groups
A straight-chain alkane with an alkyl group