GSCI 163
Lecture 12
Organic chemistry
What distinguishes organic chemistry from other areas of
chemistry?
The area of chemistry that studies carbon based
compounds, hydrocarbons and respective derivatives.
Origins – compounds from plants and animals
Organic compounds were though to have a “vital force” and
as such to be impossible to synthesize in laboratory.
Friedrich Wöhler debunked this notion by synthesizing
urea a common carbon based compound found in human
urine.
Common elements
In organic compounds, the bonds are covalent since the
elements are non-metals. The most common elements in
organic compounds are:
Element
Total number
of bonds
Distribution of total number of bonds and
examples
Carbon
4
4 single
2 single, 1
double
1 single, 1
triple
Nitrogen
3
3 singles
1 single, 1
double
1 triple
Oxygen or
sulfur
2
2 singles
1 double
-
Halogens (H,
Cl, F, etc)
1
1 single
-
-
Hydrocarbons: the simplest organic
compounds
Hydrocarbons are a combination of carbon and hydrogen
atoms. All other organic compounds are considered
derivative of hydrocarbons.
How can we combine carbon and hydrogen atoms to make
organic compounds?
• If they form a special ring they are classified as aromatic
hydrocarbons – fundamental characteristic: a distinctive
smell
• If they don’t they are classified as aliphatic
The benzene family
The most important aromatic compound is the
benzene ring. Benzene is a clear, colorless
liquid with a distinct odor. It is carcinogenic.
Other common aromatic hydrocarbons are:
Aliphatic family
If an organic compound does not have an benzene
ring, it is know as an aliphatic hydrocarbon.
They can be divided into four groups depending on
the types of bonds:
•
•
•
•
Alkanes – only single bonds
Cycloalkanes – rings of carbons with single bonds
Alkenes – double bond between carbon atoms
Alkynes – triple bond between carbon atoms
Alkanes clan
Gas
Liquid
Saturated = CnH2n+2
Where do we find alkanes?
• Methane: Natural gas
• Propane & butane
• Gasoline: alkanes n=5 to 10
• Kerosene: alkanes n=10 to 16
• Higher n: diesel, fuel oil, petroleum jelly, paraffin
wax, lubricating oil and asphalt
Combustible
Alkanes are highly combustible reacting with O2
forming carbon dioxide, water vapor and
releasing heat. If combustion is not complete,
carbon monoxide and black sooty carbon is
produced.
What is the octane rate?
100 = Trymethylpentane
Cycloalkanes
Rings of saturated hydrocarbons
Properties similar to the alkanes, but have higher boiling points,
melting point and densities than alkanes
Alkenes
These hydrocarbons have double bonds
between two carbon atoms.
Most common: ethylene
Alkenes are very reactive and known as
unsaturated hydrocarbons which react with H2
to form a corresponding alkane.
Alkynes
Hydrocarbons that have a triple bond
between two carbon atoms.
Most common: acetylene
Used for welding application because of
the high temperature of its flame: over
3000 C
Summary
Hydrocarbons
Aliphatic
Alkanes
Cycloalkanes
Aromatic
Alkenes
Alkynes
Next class
• Derivatives of hydrocarbons