Organic and biochemistry Assitance Lecturer Amjad Ahmed Jumaa  Aromatic hydrocarbon  Benzene 1

Aromatic hydrocarbons Benzene Aromatic hydrocarbons Benzene  Aromatic hydrocarbons: are benzene and compounds that resemble benzene in chemical behavior. Aromatic properties are those properties of benzene that distinguish it from aliphatic hydrocarbons. They are characterized by a tendency to undergo ionic substitution.

Molecular formula. Isomer number. KeKule' structure 1-benzene has the molecular formula C 6 H 6. Benzene was known to contain six carbon atoms and six hydrogen atoms. in 1865, he offered an answer to the question of benzene : these carbon chains can sometime be closed to form rings. KeKule' structure of benzene represented as today (I)

4 II-V. Of all these, KeKule's structure was accepted as the most nearly satisfactory Other structure consistent with the formula C 6 H 6. For example the structures

2-benzene yield only one monosubstitution product, C 6 H 5 Y.only one bromobenzene, C 6 H 5 Br. Similarly only one chlorobenzene, C 6 H 5 Cl. Or one nitrobenzene, C 6 H 5 NO 2. From this fact we see each hydrogen must be exactly equivalent to each other hydrogen.

6  Thus the structure (I) above is the acceptable structure for the benzene ring. Nomenclature of benzene and its derivatives  For many of these derivatives we prefix the name of the substituent group to the word – benzene, for example, chlorobenzene, bromobenzene, etc.

 Special names: we see methylbenzene is always known as toluene, amino benzene is called aniline, hydroxybenzene as phenol, and so on.

 For several substituents (more than one groups that attached benzene ring), the names are differentiated by use the names ortho, Meta, and para, for example:

9  If the two groups are different, we simply name the two groups successively and the end the word with – benzene, for example:

 For special name the compound is named as a derivatives of that special compound as for example, nitro toluene, bromophenol.  For more than two groups numbers are used to indicate their relative positions, for example:

11  For more than two groups numbers are used to indicate their relative positions, for example:

Solution:

13 Follow problem: draw the structure for the following benzene derivatives: 1-(3-ethyl-2-methylaniline). 2-(2, 4-dinitrobenzene). 3-(1-ethyl-3-nitrobenzene). 4-(3,4,6-tribromobenzene). 5-(1-iodobenzene). 6-(p-methylbenzene). 7-(ethylbenzene). 8-(isopropylbenzene). Follow problem: draw the structure for the following benzene derivatives: 1-(3-ethyl-2-methylaniline). 2-(2, 4-dinitrobenzene). 3-(1-ethyl-3-nitrobenzene). 4-(3,4,6-tribromobenzene). 5-(1-iodobenzene). 6-(p-methylbenzene). 7-(ethylbenzene). 8-(isopropylbenzene).