Organic and biochemistry
Aromatic hydrocarbon
Benzene
Assitance Lecturer Amjad Ahmed Jumaa
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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.
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Molecular formula. Isomer number. KeKule' structure
1-benzene has the molecular formula C6H6. 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)
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Other structure consistent with the formula C6H6. For example
the structures
II-V. Of all these, KeKule's structure was accepted as the most
nearly satisfactory
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2-benzene yield only one monosubstitution product, C6H5Y.only
one bromobenzene, C6H5Br. Similarly only one chlorobenzene,
C6H5Cl . Or one nitrobenzene, C6H5NO2. From this fact we see
each hydrogen must be exactly equivalent to each other
hydrogen.
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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.
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Special names: we see methylbenzene is always known as
toluene, amino benzene is called aniline, hydroxybenzene as
phenol, and so on.
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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:
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If the two groups are different, we simply name the two
groups successively and the end the word with –benzene, for
example:
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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:
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For more than two groups numbers are used to indicate their
relative positions, for example:
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Solution:
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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).
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