Pantalene is a most elusive molecule that has been Isolated only liquid-nitiogen

Question

Pantalene is a most elusive molecule that has been Isolated only liquid-nitiogen temperature. The pentalene dianion, however, is well known and quite stable. Explain. Indole is an aromatic heterocycle that has a benzene ring fused to pyrrole ring. Draw an orbital picture of indole. How many ir electrons does indole have? What is the electronic relationship of indole to naphthalene? Ribavirin, ail antiviral agent used against hepatitis C and viral pneumonia, contains a 1,2,4-triazole ring. Why is the ring aromatic?

Explanation / Answer

Solution :-

15.36 )

The pentanlene has 4 double bonds so it contains 8 pi electrons in two ring

According to the Huckels rule

We need (4n)+2 that is (4*2)+2 = 10 electrons in the two rings to make it aromatic

So pentalene is not aromatic

But in the pentalene dianion it have have -2 charge means 2 more electrons

So (4*2)+2 = 10 electrons

So pentalene diainion have the aromatic character therefore it is stable.

Therefore since pentalene dianion has aromatic character so it is stable and can be isolated.

15.37) a) In the idole structure we have 4 double bonds and the lone pair of electrons on the nitrogen atom also takes part in the ring therefore it makes (4*2) + 2 lone apir = 10 pi electrons in the indole.

b) the naphthalene ring also has 10 pi electrons as present in the indole so they are called isoelectronic.

15.38)

The ring containing 3 nitrogen in have the 2 double bonds and the N with 3 single bonds involves its lone pair of electron in the ring delocalization therefore it makes 6 pi electrons in the ring

(4*1)+2 = 6

So it meets the criteria of the aromatic character therefore the ring is aromatic.

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