Question

For the structures shown below, state the number of pi electrons present in the molecule.

Is the molecule aromatic according to the Huckel criteria? If the molecule were planar, would it be antiaromatic?

Answer 1

Solution :-

In the first structure we have 3 rigns

And it have 6 triple bonds

So pi electrons = 6*2 = 12

But for the 3 ring we need (4*3)+2 = 14 electrons so that it become aromatic

So the structure 1 is not aromatic

Because it do not matches with Huckel criteria.

In the structure 2

We have 1 ring which has 3 double bonds so the total pi electrons in the ring are 3*2 = 6

So it obeys the Huckel rule so it is aromatic

Structure 2 is aromatic    because it matches with Huckel criteria.