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JEE Main levelSingle correct optionDifficulty 2 of 3nc029

Guanidine, $(H X_{2} N) X_{2} C = NH$ , is a very strong organic base because:

Aits conjugate acid is nonplanar and has no resonance
Bit has no lone pair of electrons on any nitrogen
Cit contains an acidic hydrogen on carbon
Dits conjugate acid is strongly stabilised by resonance with three equivalent nitrogen atoms sharing the charge

Answer: D

Protonation at the imine nitrogen gives the guanidinium ion, in which the positive charge is delocalised equally over three nitrogens. This resonance stabilisation of the conjugate acid makes the base very strong.

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