Chemistry - AMINES Question with Solution | TestHub

Basic strength depends upon availability of lone pairs. Greater the resonance of lone pairs lesser the basic strength. In $\left(\mathrm{II}\right) \text{and} \left(\mathrm{III}\right)$ lone pair is localised. $\left(\mathrm{III}\right)$ is more basic due to $+\mathrm{I}$ effect of carbon chain whereas in $\mathrm{II}$, negative mesomeric effect is operating. In $\left(\mathrm{I}\right) \text{and} \left(\mathrm{IV}\right)$ lone pair is delocalised, so their basic strength is less that former two amines. If $\left(\mathrm{IV}\right)$ donates its lone pair then its aromaticity will get lost therefore, its basic strength is less than that of $\mathrm{I}$.

Overall order of basic strength is  $\left(\mathrm{III}\right)>\left(\mathrm{II}\right)>\left(\mathrm{I}\right)>\left(\mathrm{IV}\right)$