Introduction to
Organic Molecules
Organic Chemistry
 (1828) Friedrich Wohler first synthesized an
organic compound from an inorganic source
leading to the birth of Organic Chemistry.
 Organic chemistry is the study of carbon containing
compounds except elemental carbon (diamond,
graphite, coal), CO2, CO, carbonates (CO32- group)
and cyanides (CN- group); Which are all considered
inorganic molecules.
Organic Chemistry
• Carbon has the ability to form
long chains.
• Without this property, large
biomolecules such as proteins,
lipids, carbohydrates, and
nucleic acids could not form.
• Carbon easily forms bonds with
other non-metal atoms.
Molecular Representations
We use different representations to
describe organic molecules for different
purposes.
Hydrocarbons
• The simplest
organic molecules
containing only
carbon and hydrogen
atoms
• Four basic types:
Alkanes
Alkenes
Alkynes
Aromatic
hydrocarbons
• The Lewis structures of alkanes look like
this.
Also called structural formulas.
Often not convenient, though…
•The space-filling model shows the
theoretical overlapping electron clouds of
bonded atoms
1
…so more often than not, condensed
structural formulas are used.
• But, most of the time, I use line
structures
•Lines represent bonds connecting
carbons. Since all carbons contain
4 bonding electrons, all available
bonds are assumed to be hydrogen.
Alkanes can be
separated from the
complex hydrocarbon
mixture present in
petroleum. The
separation into
simpler mixtures is
accomplished by
means of a
fractionating
column called
fractional distillation.
– The simplest alkane is methane (CH4) – the primary
compound in natural gas.
– Ethane (C2H6) – a minor component of natural gas.
– Propane (C3H8) – a fuel for heating homes and
cooking.
– Octane (C8H18) – a fuel used for automobile
combustion
– Dodecadecane (C20H42) – solid wax used for making
candles and as a lubricant
All of these are straight-chained
hydrocarbons (CnH2n+2).
Alkanes
• Saturated hydrocarbons.
“Saturated” with hydrogens.
Only single bonds.
• Also called “Paraffins”
• Relatively unreactive; however, highly
combustible.
IUPAC Names for the First Ten ContinuousChain Alkanes.
IUPAC refers to the standard system of
chemical nomenclature set forth by the
International Union of Pure and Applied Chemistry.
Isomerism
–Isomers: Compounds that have identical
molecular formulas, but different arrangement of
atoms.
•Structural isomers: (AKA Constitutional
isomers) molecules having the same
molecular formula but different arrangement
of atoms and bonds
Many structural isomers of these exist,
known as branched alkanes.
2
Organic Nomenclature
Number of
Structural Isomers
Possible for Alkanes
of Various CarbonChain Lengths.
Organic Nomenclature
• Three parts to a compound name:
 Base: Tells how many carbons are in the
longest continuous chain.
 Suffix: Tells what type of compound it is.
Cycloalkanes
• Carbon can also form ringed structures.
• Five- and six-membered rings are most stable.
Can take on conformation in which angles
are very close to tetrahedral angle.
Smaller rings are quite strained.
• Three parts to a compound name:
 Base: Tells how many carbons are in the
longest continuous chain.
Organic Nomenclature
• Three parts to a compound name:
 Base: Tells how many carbons are in the
longest continuous chain.
 Suffix: Tells what type of compound it is.
 Prefix: Tells what groups are attached to
chain.
Alkenes
• Contain at least one carbon–carbon double bond.
• Unsaturated.
 Have fewer than maximum number of hydrogens.
 CnH2n
 Properties Similar to alkanes
• Non-polar
• Insoluble in water
• Soluble in non-polar solvents
• Less dense than water
3
•Which
isomer
would you
predict to
be more
stable, and
why?
Table 12-2, p.388
Alkynes
Properties of Alkenes
• Notice that geometric isomerism exists for alkenes when
the double bond is not on a terminal carbon.
• To determine the cis-/trans- geometric isomerism, draw a
line through the bond and identify same or different
“same”
“different”
• Contain at least one carbon–carbon triple
bond.
• Carbons in triple bond sp-hybridized and have
linear geometry.
• Also unsaturated.
• CnH2n-2
• Structure also affects physical properties of alkenes.
Alkynes
– Ethyne (commonly called acetylene) is the
simplest alkyne and is used as a fuel for torches
and in making plastics.
Aromatics
• Cyclic hydrocarbons based
on the benzene ring
• Many aromatic
hydrocarbons are known
by their common names.
CH3
NO2
NO2
CO2H
NO3
4
Properties of Aromatic
Compounds
Non-polar
Insoluble in water
Aromatic rings are relatively stable
chemically and often remain intact
during reactions.
Benzene and toluene are widely used
organic solvents.
Can not be produced by the human
body; therefore, must be part of our diet.
Organic Functional Groups
• The chemically reactive group, or groups, on
organic molecules where reactions tend to
occur.
Carboxylate
salt
- ate
: :
..
.. :
Sodium
methanate
-
Na+
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