Chemistry 30 Organic Chemistry NOTES

11. Reactivity of Alkanes, Alkenes and Alkynes  Most to least – alkynes (4 bonding electrons available), alkenes (2 bonding electrons), and alkanes (no bonding electrons).

III. Important Uses of Aliphatics 1. Alkanes – methane (natural gas), butane (lighter fluid) 1. Alkanes – methane (natural gas), butane (lighter fluid)

2. Alkenes – ethene: used in making plastic

3. Alkynes – ethyne (acetylene): used in welding

IV. Aromatics Definition: A special class of cyclic unsaturated hydrocarbons is known as aromatic hydrocarbons. The simplest of these is benzene (C 6 H 6 ). However, evidence indicates that the bonds between the C’s are equal in length and strength.

So, the actual structure is a mixture of:

Therefore, benzene is represented by:

2. Nomenclature of Alkyl-Benzene Compounds USE THE FOLLOWING STEPS: a) name the alkyl group followed by benzene Example: methylbenzene (toluene) (toluene)

phenyl b) if the alkyl group is attached by a middle carbon, consider, the benzene as an alkyl group called phenyl Example: 2-phenylpropane

c) if 2 H’s are replaced in benzene, the replaced groups can be arranged in 3 ways Example: 1. Ortho 2. Meta 3. Para (adjacent C’s) (1C between) (2C’s between ) O-ethylmethylbenzene or 1-ethyl-2-methylbenzene M-ethylmethylbenzene or 1-ethyl-3-methylbenzene P-ethylmethylbenzene or 1-ethyl-4-methylbenzene

d) if 3 H’s are replaced, number so that the lowest possible number combination is achieved. Then name alphabetically.

Example: i. 1-ethyl-3-methyl-5-propylbenzene NOT 3-ethyl-5-methyl-1-propylbenzene

ii. 4-ethyl-1,2-dimethylbenzene NOT 1-ethyl-3,4-dimethylbenzene

3. Properties of Benzene Liquid at room temperature, boils at 80.1 C Non-polar so insoluble in water Behaves like an alkane: addition reaction do NOT occur Substitution reactions DO occur

Example: This is because there is no definite double bond for the addition reaction to occur on.

3. Properties of Benzene Also found in number of explosives Example: trinitrotoluene (TNT)

A little more about Benzene benzin, benzol, benzene

Discovery Michael Faraday- first to isolate & identify Auguste Laurent (French) named it “phène” August Wilhelm Hofmann used the word “aromatic” to describe the family Friedrich August Kekulé (German) had a dream

Uses After-shave lotion Solvent for degreasing metals Decaffeinate coffee paint strippers rubber cements spot removers gasoline additive

Health Issues... “it’s generally considered that the only absolutly safe concentration for benzene is zero” (The American Petroleum Institute, 1948) Know carcinogen- causes leukemia Was first known to cause cancer in the 1920s but it wasn’t until 1979 until it was “conclusive”

Still used today... Max 1% as a gasoline additive to make styrene and Nylon rubbers lubricants dyes detergents drugs explosives & napalm pesticides

Learning Activities Groups of 2: Make six flash cards. Draw a diagram on one side, name it on the other! Don’t forget IUPAC! Homework Page 11 Go back through the workbook and find any aromatic question that we skipped!