GSCI 163 Lecture 12 Organic chemistry What distinguishes

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 Distribution of total number of bonds and of bonds 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 = Cn. H 2 n+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 O 2 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 H 2 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