(a) How can you proof that the following compounds are aromatic? (i) Benzene and (ii) Phenol (b) What is aromaticity? What are the necessary conditions to be aromatic?
(a.)
(i) Benzene
Benzene is an aromatic compound, as the C-C bonds formed in the ring are not exactly single or double, rather they are of intermediate length.
Aromatic compounds are divided into two categories :
benzenoids (one containing benzene ring) and non-benzenoids (those not containing benzene ring), provided they follow Huckel rule.
According to Huckel rule, for a ring to be aromatic it should have the following property :
- Planarity
- Complete delocalization of the π electrons in the ring
- Presence of (4n + 2) π electrons in the ring where n is an integer (n = 0, 1, 2, . . .)
The best proof for benzene being an aromatic compound is the total number of pi electrons in the benzene molecule depicted below can be found to be 6, by obeying the 4n+2 ? electron rule where n=1.
By Huckle's rule,
(4n + 2 ) π electrons
= (4 × 1 + 2 ) π electrons
= 6 π electrons
Thus, the aromaticity of the benzene molecule is established since it obeys the Huckel rule.
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