7-Bromo-1,3,5-cycloheptatriene exists as an ion whereas 5-bromo-1,3-cyclopentadiene does not form an ion even in presence of Ag^+. Explain

7-Bromo-1,3,5-cycloheptatriene exists as an ion whereas 5-bromo-1,3-cy

1.	7-Bromo-1,3,5-cycloheptatriene exists as an ion whereas 5-bromo-1,3-cyclopentadiene does not form an ion even in presence of Ag^+. Explain
Answer» Solution :7-Bromo-1,3,5-cycloheptatriene, on ionization, gives tropylium ion. Since , tropylium ion contains `6 PI`-electrons which are completely delocalized, therefore, according to Huckel rule, it is AROMATIC and HENCE stable .Being highly stable , it is easily FORMED . In contrast,5-bromo-1,3-cyclopentadiene, on ionization, will give 1,3-cyclopentadienyl cation which contains `4pi`-electrons and hence in antiaromatic. Being antiaromatic, it is highly unstable and hence is not formed even in the presence of `Ag^+` ion which otherwise facilitates ionization.