Aromatic hydrocarbons are compounds that contain a ring of six carbon atoms with alternating double and single bonds and six attached hydrogen atoms. This type of structure is known as a benzene ring. They occur naturally in crude oil, and can also be created by the refining process.
The more carbon atoms a hydrocarbon molecule has, the "heavier" it is (the higher is its molecular weight) and the higher is its boiling point.
Small quantities of a crude oil may be composed of compounds containing oxygen, nitrogen, sulphur and metals. Sulphur content ranges from traces to more than 5 per cent. If a crude oil contains appreciable quantities of sulphur it is called a sour crude (at least 2.5% sulfur); if it contains little or no sulphur it is called a sweet crude (sulfur content less than 0.5%).
Ex.1 Answer the following questions:
1. Where can hydrocarbons exist?
2. What are the main hydrocarbon groups?
3. How does the number of carbon atoms influence hydrocarbon molecular properties?
4. What is a benzene ring?
5. How is crude oil classified into sweet and sour?