Doubt & Answer Explanation

Answer Explanation

Here are the characteristics that aromatic compounds must satisfy:

   1. A delocalized conjugated ? system, most commonly an arrangement of alternating single and double bonds must exist
   2. Coplanar structure, with all the contributing atoms in the same plane
   3. Contributing atoms arranged in one or more rings
   4. A number of ? delocalized electrons that is even, but not a multiple of 4. That is, 4n + 2 number of ? electrons, where n=0, 1, 2, 3, and so on. This is known as Hückel's Rule.

Whereas benzene is aromatic (6 electrons, from 3 double bonds), cyclobutadiene is not, since the number of ? delocalized electrons is 4, which of course is a multiple of 4. The cyclobutadienide (2?) ion, however, is aromatic (6 electrons). An atom in an aromatic system can have other electrons that are not part of the system, and are therefore ignored for the 4n + 2 rule. In furan, the oxygen atom is sp² hybridized. One lone pair is in the ? system and the other in the plane of the ring (analogous to C-H bond on the other positions). There are 6 ? electrons, so furan is aromatic.