The order of basicity among the following compounds is
(see structure) I
(see structure) II
(see structure) III
(see structure) IVIIIIIIIV
(A)II > I > IV > III
(B)IV > II > III > I
(C)IV > I > II > III✓ Correct
(D)I > IV > III > II
Answer: (C)
Solution
Basicity depends on the stability of the conjugate acid formed after protonation.
Compound IV (Guanidine): The conjugate acid has three equivalent resonance structures due to delocalization over three nitrogen atoms, making it the most stable and IV the most basic.
Compound I (Amidine): The conjugate acid has two equivalent resonance structures, making it moderately basic.
Compound II (Imidazoline): The conjugate acid has two resonance structures, but the basicity is lower than I due to ring strain.
Compound III (Imidazole): The conjugate acid has two resonance structures, but the aromatic character is lost upon protonation, making it the least basic.
Order: IV > I > II > III
JEE Advanced · 2017 · 21 May 2017 · Paper 2 · Single correct option
