Question

Compare order basic strength of furan , pyrrole, thiophene, pyridine

Answer 1

Thiophene, pyrrole and Furan are all five membered heterocyclic aromatic compounds, with the hetero atom being sulfur (S), nitrogen (N) and oxygen (O) respectively. They are aromatic as they are planar ring systems, and resonance is possible due to delocalization of the two pi bonds and the lone pair of electrons of the heteroatom. However, if we compare the electronegativity of the heteroatoms, we will see that O is more electronegative as compared to N, S being the least electronegative. Hence, O will have the least tendency, among the three, to donate its lone pair of electrons for resonance, and will rather draw the electronic density of the ring towards itself. The concentration of electron density on the heteroatom makes it a good electron donor (Lewis base). Thus the order of basicity will be
Furan > Pyrrole > Thiophene


Pyridine more basic than pyrrole, because pyrrole C4H4NH (in which N contributes a lone pair) has a pKa - 3.8, but pyridine (where N is part of the ring's double bond) has a pKa 5.14. Electron pair availability indicates the strength of basicity. In this case, pyridine is the stronger base.

Answer 2

Answer:

THE ORDER OF BASCICITY WOULD BE

Furan > Pyrrole > Thiophene

Explanation:

The heteroatoms in thiophene, pyrrole, and furan, which each have five members, are sulphur (S), nitrogen (N), and oxygen (O), respectively. Since they are planar ring structures, they are aromatic, and resonance is made possible by the delocalization of the heteroatom's single electron pair and the two pi bonds. The heteroatoms' electronegativity can be compared, and we can observe that O is more electronegative than N, with S being the least electronegative. Therefore, O will be the one of the three that is least likely to donate its single pair of electrons for resonance and will instead pull the ring's electrical density toward it. The heteroatom functions well as an electron donor due to the electron density concentration on it.

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