Agenda Today Quiz on Naming and Drawing Aliphatic Compounds Lesson on Naming and Structure of: – Aromatic Compounds Practice Problems

1.3 Aromatic Hydrocarbons

Are unsaturated hydrocarbons that have a ring structure and a chemical arrangement that causes them to be chemically stable. Benzene (C 6 H 6 ) is a flat 6-carbon ring with a hydrogen atom bonded to each carbon atom. It is the simplest aromatic compound.

The structural diagram often shows benzene as having 3 double bonds alternating with 3 single bonds, however this is NOT AN ACCURATE REPRESENTATION! The bonds are all equal in length, thus, all electrons are shared equally between all 6 carbons. The bond length is somewhere between that of a single or double bond.

Naming Aromatic Compounds The benzene ring is considered to be the parent molecule. The attached functional groups are named as side chains or branches. If there are multiple branches, number the ring beginning with the branch name that comes first alphabetically. The suffix “-benzene” is used Method 1

Method 2 Is used when a benzene ring is attached to some complex hydrocarbon chain (such as a chain with a multiple bond). The benzene ring is now considered a branch to the hydrocarbon chain, which functions as the parent chain. The prefix “phenyl-” is used. Example

Practice: Name the following aromatic compounds. b) 3-phenylhexane a) 1-ethyl-2,4-dimethylbenzene

Practice: Draw the following aromatic compounds. a)1,4-dichloro-2-ethylbenzene b)4-methyl-2-phenylpent-2-yne

Traditional Naming System (Greek): Ortho-, Meta-, Para-

Properties of Aromatic Hydrocarbons Some are liquid at room temperature where others are in solid form. Their symmetry causes them to be non-polar substances (exception: if they contain some highly electronegative branch). This causes aromatics to generally be insoluble in water.

Benzene Uses Benzene is a colorless, flammable liquid with a sweet odor. It is formed from natural processes but most exposure results from human activities. Benzene is a natural part of crude oil and gasoline and is present in motor vehicle exhaust as well as cigarette smoke.cigarette smoke It is used mainly as a starting material in making other chemicals, including plastics, lubricants, rubbers, dyes, detergents, drugs, and pesticides. In the past, benzene was commonly used as an industrial solvent and as a gasoline additive, but these uses have been greatly reduced in recent decades due to its carcinogenic nature. Benzene is known to cause cancer, based on evidence from studies in both people and lab animals. The link between benzene and cancer has largely focused on leukemia and cancers of other blood cells.

IUPAC Name = Methylbenzene Common Name = Toluene - Toluene is a colourless flammable liquid obtained from petroleum or coal tar. - It is used as a solvent for gums, lacquers, in high- octane fuels as well as medicines, dyes, explosives and detergents. - Is a less harmful replacement for benzene.

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