Aromatic hydrocarbons are unusually stable compounds with ring structures in which electrons are shared by many atoms. Section 5: Aromatic Hydrocarbons K What I Know W What I Want to Find Out L What I Learned

7(A) Name ionic compounds containing main group or transition metals, covalent compounds, acids, and bases, using International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules. 3(F) Research and describe the history of chemistry and contributions of scientists. Aromatic Hydrocarbons Copyright © McGraw-Hill Education

Essential Questions How do the properties of aromatic and aliphatic hydrocarbons compare and contrast? What is a carcinogen and what are some examples? Aromatic Hydrocarbons Copyright © McGraw-Hill Education

Review hybrid orbitals New aromatic compound aliphatic compound Aromatic Hydrocarbons Copyright © McGraw-Hill Education Vocabulary

The Structure of Benzene Michael Faraday first isolated benzene in Chemists knew the formula was C 6 H 6 and proposed several models which would have all be very reactive, but benzene is unusually stable. German chemist Friederich Kekulé claimed to have had a dream in which he realized the flat, hexagonal shape ring structure for benzene. This structure explained some of benzene's properties, but not its lack of reactivity. Linus Pauling’s hybrid orbital theory explained benzene’s lack of reactivity. Aromatic Hydrocarbons Copyright © McGraw-Hill Education The double bonds in benzene are not fixed, but rather the electrons are delocalized and shared among all six carbon atoms.

Aromatic Compounds Organic compounds that contain benzene rings as part of their structure are called aromatic compounds. Aromatic was originally used because many benzene related compounds were found in pleasant smelling oils that came from plants and plant parts. Aliphatic compounds are the alkane, alkene, and alkyne hydrocarbons, coming from the Greek word for fat because they were obtained by heating animal fat. Aromatic Hydrocarbons Copyright © McGraw-Hill Education

Aromatic Compounds Substituted benzene compounds are named in the same way as cyclic alkanes. Aromatic Hydrocarbons Copyright © McGraw-Hill Education

Aromatic Compounds Many aromatic compounds were commonly used as industrial and laboratory solvents. Health risks linked to aromatics include respiratory ailments, liver problems, and damage to the nervous system. Some aromatic compounds cause cancer. Aromatic Hydrocarbons Copyright © McGraw-Hill Education

Aromatic Hydrocarbons Copyright © McGraw-Hill Education NAMING AROMATIC COMPOUNDS EVALUATE THE ANSWER The benzene ring is numbered to give the branches the lowest possible set of numbers. The names of the substituent groups are correctly identified. Use with Example Problem 4. Problem Name the aromatic compound shown. Response ANALYZE THE PROBLEM You are given an aromatic compound. Follow the rules to name the aromatic compound. As you can see, the numbers 1 and 3 are lower than the numbers 1 and 5. So the numbers used to name the hydrocarbon should be 1 and 3. Step 2. Determine the name of the substituents. If the same substituent appears more than once, add the prefix to show the number of groups present. Step 3. Put the name together. Alphabetize the substituent names, and use commas between numbers and hyphens between numbers and words. Write the name as 1,3-dipropylbenzene. SOLVE FOR THE UNKNOWN Step 1. Number the carbon atoms to give the lowest numbers possible.

Aromatic Hydrocarbons Copyright © McGraw-Hill Education Review Essential Questions How do the properties of aromatic and aliphatic hydrocarbons compare and contrast? What is a carcinogen and what are some examples? Vocabulary aromatic compound aliphatic compound