Presentation on theme: "Organic Chemistry CE 541. Aromatic Hydrocarbons They are hydrocarbons that include benzene and compounds containing aliphatic or aromatic groups attached."— Presentation transcript:
Aromatic Hydrocarbons They are hydrocarbons that include benzene and compounds containing aliphatic or aromatic groups attached to aromatic rings. Benzene is the simplest aromatic hydrocarbon (C6H6)
More recently, the following is used to represent the structure of Benzene
Nomenclature The monocyclic aromatic hydrocarbons are named as derivatives of the parent benzene. Trivial names of some of the compounds are still recognized by the IUPAC T olueneo-xylenem-xylenep-xylene T olueneo-xylenem-xylenep-xylene (ortho-xylene)(meta-xylene)(para-xylene)
In the IUPAC system, aromatic compounds with one group attached to them are named by combining the name of the group with benzene. All these structures are named as Chlorobenzene, and all represent the same compound.
There are three different ISOMERIC compounds with two substituents on the ring. The positions of the substituents on these compounds are indicated as follows: ortho (or 1, 2 - ) meta (1, 3 - )para (or 1, 4 - ) ortho (or 1, 2 - ) meta (1, 3 - )para (or 1, 4 - ) abbreviated o- abbreviated m-abbreviated p- abbreviated o- abbreviated m-abbreviated p-
Using benzene or toluene as parent structure, the following examples illustrate the use of the system o-dichlorobenzenem-dichlorobenzene p-dichlorobenzene o-dichlorobenzenem-dichlorobenzene p-dichlorobenzene o-chlorotoluenem-chlorotoluene p-chlorotoluene o-chlorotoluenem-chlorotoluene p-chlorotoluene
For compounds with three or more substituents on the ring, we must use numbers to indicate the position on the ring and apply the following rules: 1. The parent structure is benzene or toluene 2. For benzene, the group name written next to the word “benzene” becomes position number 1 on the ring and the ring is numbered in a direction that will give the lowest possible numbers to the substituents. 3. For toluene, the methyl group becomes position number 1 on the ring and the ring is numbered in a direction that will give the lowest possible numbers to the substituents. The number 1 position is assumed in both benzene and toluene derivatives, but is not indicated in the name. 4. All groups are placed in alphabetical order except the group in the number 1 position.
Hydrocarbons 1. Benzene Series BenzeneC6H6 BenzeneC6H6 TolueneC6H5 + CH3 TolueneC6H5 + CH3 XyleneC6H4 (CH3)2 XyleneC6H4 (CH3)2 EthylbenzeneC6H5 + C2H5 EthylbenzeneC6H5 + C2H5 They : Are used extensively as solvents Are used extensively as solvents Are insoluble in water (relatively) Are insoluble in water (relatively) Are common constituents of petroleum products Are common constituents of petroleum products Cause cancers to human Cause cancers to human
Styrene is a benzene derivative used in the production of polystyrene products Styrene
Chlorinated Aromatic Hydrocarbon (1) Chlorinated Benzenes They are benzene with one or more of the hydrogen are replaced by chlorine (2) Polychlorinated Biphenyls (PCBs) They are chlorinated benzenes with the following general structure: X can be H or Cl X can be H or Cl There are 209 possible PCBs There are 209 possible PCBs Stable compounds (some can be biodegraded) Stable compounds (some can be biodegraded) Used widely as coolants in transformers, solvents, and hydraulic fluids Used widely as coolants in transformers, solvents, and hydraulic fluids Bio-concentrate Bio-concentrate
Derivatives of the Hydrocarbons 1. Organic Halides Examples DDT (dichlorodiphenyltrichloroethane) DDT (dichlorodiphenyltrichloroethane) Chlorofluorocarbons (CFC, CF2Cl2, CFCl3) Chlorofluorocarbons (CFC, CF2Cl2, CFCl3) Organic Halides Alkyl halides Alkyl group attached to a halogen atom such as F, Cl, Ba, I. General formula: R – X R = alkyl group X = halogen atom Aryl halides Halogen atom attached to an aromatic ring. General formula: Ar – X Ar = Aromatic ring X = halogen atom
Nomenclature (1) If both groups attached to the carbonyl group are alkyl groups, they are named as follows: Name the alkyl groups attached to the carbonyl group. If both groups are the same, the prefix -di is used Name the alkyl groups attached to the carbonyl group. If both groups are the same, the prefix -di is used Add the word “ketone” Add the word “ketone”
to name compounds as phenones, the follwing should be done: Name the cyl group as given above Name the cyl group as given above Add phenone to the name of the acyl group Add phenone to the name of the acyl group
Nomenclature (1) when trivial names of carboxylic acids are used, the –ic acid part of the name is replaced by the ending –amide (i.e. the amide of acetic acid is acetamide) (2) the IUPAC name is obtained by dropping the –oic acid ending of the IUPAC name of the acid and replacing it with the ending –amide.