Question

(a)Azulene has an appreciabel dipole moment.Write the reasonance structure that explains the dipole moment and its aromaticity.
(b)In the cse of halogen-substituted azulenes,a halogen atom on`C-6`can be displace bynucleophile while one on`C-1`is unreactive towards nucleophile .Rationalise this differemce in behaviou.

Answer 1

The major contribution to the hybrid must be one that involves charge separation ,having aromatic five-and seven-membered rings.
(b)
`ArSN` intermediate reaction is favoured by five-membered ring woth cyclopentadienyl anion character(aromatic).
In the second case`bar(e)`discoalisation into the other (seven-membered)ring result in eight`bar(e)`-in that ring ,which doesnot stablise it.