Arrange the following in decreasing order of acidity : phenol and the ortho (I), meta (II) and para (III) nitrophenols.
(I)
(II)
(III)
(IV)

Question

Arrange the following in decreasing order of acidity : phenol and the ortho (I), meta (II) and para (III) nitrophenols. (I) (II) (III) (IV)

TestHub · Accepted Answer

Here (IV) is phenol. The -M and -I effects of NO₂ stabilise the phenoxide ion. -M acts only from ortho and para, so those isomers are much more acidic than the meta isomer, which has only -I. Every nitrophenol is more acidic than phenol.

Between ortho and para the -I effect favours ortho, but the para isomer is also stabilised by an undisturbed -M effect and wins by a small margin (pKa 7.15 for para and 7.23 for ortho).

Order : III $>$ I $>$ II $>$ IV.

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