Chemistry - GOC Question with Solution | TestHub

The basicity depends on stabilization of the conjugate acid and on electron withdrawal from the accepting nitrogen. In c, charge redistribution can give an aromatic two-pi-electron cyclopropenyl unit, making donation from the lower ring particularly favorable. The saturated cyclopropyl group in b provides weaker sigma delocalization. The extra aza nitrogen in a withdraws electron density and makes a weaker than b. In d, the cyclopentadienyl unit favors a charge-separated contributor with negative charge on its aromatic six-pi-electron ring and positive charge on the nitrogen system, reducing lone-pair availability. Thus c > b > a > d.