Aromatic Hydrocarbons

Aromatic Hydrocarbons Dr. MarwaEid

Aromatic Compounds Unsaturatedhydrocarbons Some of them have pleasantodors. Aromatic compounds

Aromatic hydrocarbons 1. Unsaturated ring compounds which contain a benzene ring in their molecules, C6H6 . 2. Compounds that are far more stable than they should be and resist the addition reactions typical of unsaturated aliphatic compounds.

Aromatic Compounds Arene:A compound containing one or more benzene rings. benzene Aryl group:When we remove a H atom from an arene (Ar-) Phenyl C6H5-

Aromatic hydrocarbons • Benzene C6H6 • Methylbenzene C7H8 • Ethylbenzene C8H10

Benzene C6H6

Methylbenzene C7H8

EthylbenzeneC8H10

Aromatic Compounds in Nature and Health Many aromatic compounds are common in nature and in medicine. Aspirine

Benzene Molecule • Six carbon atoms joined to form a hexagonal ring. • Each carbon has four valence electrons • One of these is used to form a bond with a hydrogen atom. • Two other electrons are used to form sigma bonds with the carbon atoms on the either side.

Naming of Aromatic Compounds Aromatic compounds are named with benzene as the parent chain. One side group is named in front of the name benzene. methylbenzene chlorobenzene

Naming Aromatic Compounds • A benzene substituent is called a phenyl group, and it can be abbreviated in a structure as “Ph-”. • Therefore, benzene can be represented as PhH, and phenolwould be PhOH.

Naming Aromatic Compounds • To name a benzene ring with one substituent, name the substituent and add the word benzene. • Many monosubstituted benzenes have common names which you must also learn.

Some substituted benzenes have common names CH3 Toluene

Naming Aromatic Compounds • There are three different ways that two groups can be attached to a benzene ring, so a ortho, meta, or para—can be used to designate the relative position of the two substituent. para-dibromobenzene or p-dibromobenzene or 1,4-dibromobenzene ortho-dibromobenzene or o-dibromobenzene or 1,2-dibromobenzene meta-dibromobenzene or m-dibromobenzene or 1,3-dibromobenzene

Naming Aromatic Compounds • If the two groups on the benzene ring are different, alphabetize the names of the substituents preceding the word benzene. • If one substituent is part of a common root, name the molecule as a derivative of that monosubstituted benzene.

Naming Aromatic Compounds • For three or more substituents on a benzene ring: • Number to give the lowest possible numbers around the ring. • Alphabetize the substituent names. • When substituents are part of common roots, name the molecule as a derivative of that monosubstituted benzene. The substituent that comprises the common root is located at C1.

Naming Aromatic Compounds

Learning Check (1) Select the names for each structure: 1. Chlorocyclohexane 2. Chlorobenzene 3. 1-chlorobenzene 1. Meta-methyltoluene 2. Meta-dimethylbenzene 3. 1,3-dimethylbenzene

Solution (1) Select the names for each structure: 2. Chlorobenzene 1. Meta-methyltoluene 2. Meta-dimethylbenzene 3. 1,3-dimethylbenzene

Learning Check (2) Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. Ortho-chlorotoluene

Solution Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. Ortho-chlorotoluene

Learning Check (3) Identify the organic family for each:

Solution(3) Identify the organic family for each: alkane cycloalkane aromatic

Stability of Benzene • Benzene’s unusual behavior is not limited to hydrogenation. Benzene does not undergo addition reactions typical of other highly unsaturated compounds. • Benzene does not react with Br2 to yield an addition product. Bromine substitutes for a hydrogen atom, yielding a product that retains the benzene ring.

Aromatic physical properties • Physical state: Benzene, methylbenzene and ethylbenzene are liquids. • Insoluble in water. • Soluble in non-polar solvents such as cyclohexane.

HW Give Reasons Benzene does not undergo addition reaction

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Aromatic Hydrocarbons