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When halogen atoms are attached to a benzene ring (aromatic), they are less reactive than when in an aliphatic (no benzene) halogenoalkane. This is because the p-orbital of the halogen atom can enter into the delocalised π- electrons of the benzene ring.

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Electrophilic Substitution

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Electrophilic Substitution

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Electrophilic Substitution

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Electrophilic Substitution

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X-ray diffraction studies give us data on the bond lengths and angles.
The carbon-carbon bonds in benzene exist as a hybrid between a single and a double bond. All of these bonds are equivalent.
The atoms making up benzene are all placed in one plane, making the molecule flat/planar.
The fact that all bond lengths are the same indicate no single or double bonds.

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If we add more that one type of functional group to our root compound (benzene or a straight chain) then we need to know which addition is the principle group.
The principle group is names using its suffix.
The other groups eg. side chains are named using prefixes.

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If we make additions to the structure of the benzene ring, the resulting compounds are called benzene derivatives.
In the case of benzene derivatives, the ring is numbered from where the principle group is attached. (This is carbon number 1).

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Compounds based upon the benzene ring are called aromatic compounds or arenes.

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C₆H6
Use Number 3