what should we consider if a circle is inside a benzene
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Answer:
Well to be precise, the benzene ring has two different structures, if you represent it by using three double bonds. So if you were to somehow chlorinate it, you would end up with two different products. But only one product is obtained when we chlorinate benzene. This can be explained by resonance effect.
When you form a covalent bond, you actually share electrons betwen two atoms with approx. same electronegativity i.e. the tendancy to pull an electron towards itself. A double bond consists of a sigma bond, and a pi bond. A sigma bond is formed when two s orbitals overlap i.e. the atoms share their sigma electrons. Similiarly, a pi bond is formed when two p orbitals overlap. So now we have 6 electrons which are pi bonded in a benzene molecule. But if you think a little higher, you can also see that the pi bonds are conjugated i.e. alternating between a single bond. Now whenever this type of bonding occurs, resonance takes place. Resonance simply means that the electrons gets distributed evenly over the conjugation, i.e. till the alternating pi bond-sigma bond occurs. Thus in a benzene ring, the electrons present in the pi bonding orbitals i.e. p orbitals gets spread evenly. So to show this spread of electrons, a ring is used instead of the double bonds. Resonance also is called delocalisation of electrons. The ring structure was first given by an Austrian chemist Johann Josef Loschmidt, though the explaination was provided by Agust Kekulé. Refer Solomons & Fryhle, Morrison &Boyd, Clayden or even simpler, NCERT textbooks for further reading.