Question

Arrange the compounds in an increasing order of their basic strengths:

• A. $I>II>III>IV$
• B. $II>I>IV>III$
• C. $II>I>III>IV$
• D. $III>II>I>IV$

Answer 1

The correct option is B $II>I>IV>III$

Basic strength $\propto$ Tendency to donate lone pair.
Now,
`I)` Here `'N'` bearing lone pair is $s{p}^2$ hybridised.
$\therefore$ It is more electronegative hence, has less tendency to donate.
`II) `Here `'N'` is very rich in electron density as it is surrounded by 3 $+I$ groups and also it is $s{p}^3$ hybridised.
$\therefore$It has a good tendency to donate a pair $e^{-}$.
`III)` Lone pair of $e^{-}$ on `'N'` are involved in conjugation with 'O' it is a weak base.
`IV)` Here also lp of `'N'` is involved in resonance with the benzene ring.
$\therefore$ the availability of 'lp' here is also less. But it is more compared to case `(III)` as in case `(III)` extent of delocalisation is more.
So, the correct order of basic strength is:
$II>I>IV>III$