GSCI 163

Lecture 12

Organic chemistryWhat distinguishes organic chemistry from other areas of chemistry?

Origins – compounds from plants and animalsOrganic 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.

The area of chemistry that studies carbon based compounds, hydrocarbons and respective derivatives.

Common elementsIn 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

Saturated = CnH2n+2

Gas

Liquid

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 Aromatic

Alkanes Cycloalkanes Alkenes Alkynes

Next class

• Derivatives of hydrocarbons