Chemistry - GOC Question with Solution | TestHub

Guanidine (4) is the strongest base : its conjugate acid is stabilised by resonance over three nitrogens (pKaH ≈ 13.6). The amidine (3) comes next, with the charge shared by two nitrogens (pKaH ≈ 12.5). Ethylamine (1) is an ordinary amine (pKaH ≈ 10.6). The imine (2) is the weakest : its lone pair sits in an sp2 orbital with more s-character and is held more tightly (pKaH ≈ 7). Hence 4 $>$ 3 $>$ 1 $>$ 2.