Using the approximate resonance stabilization energies given below, arrange the heterocycles in decreasing order of stabilization. These energies are model-dependent estimates, not a universal measure of aromaticity.
(1) 122 kJ $mol^{- 1}$
(2) 68 kJ $mol^{- 1}$
(3) 90 kJ $mol^{- 1}$
(4) 117 kJ $mol^{- 1}$

Question

Using the approximate resonance stabilization energies given below, arrange the heterocycles in decreasing order of stabilization. These energies are model-dependent estimates, not a universal measure of aromaticity.

(1) Electronic Displacement Effect diagram 609 122 kJ $mol^{- 1}$

(2) Electronic Displacement Effect diagram 610 68 kJ $mol^{- 1}$

(3) Electronic Displacement Effect diagram 611 90 kJ $mol^{- 1}$

(4) Electronic Displacement Effect diagram 612 117 kJ $mol^{- 1}$

TestHub · Accepted Answer

All four rings have six pi electrons and are aromatic. Electron counting alone does not rank the extent of aromatic stabilization. For the stated reference energies, thiophene (122) > pyridine (117) > pyrrole (90) > furan (68), hence 1 > 4 > 3 > 2. Other aromaticity measures need not give the same order.

Chemistry - GOC Question with Solution | TestHub

Options:

Doubts & Discussion