22.0 Ortho effect

  General Organic Chemistry

If any electron withdrawing group present on ortho position of the benzoic acid. It always increases acidic nature of acid because this group increases the outer resonance of the ring towards acidic nature. Similarly if any group present on ortho position of aniline, it decreases basic nature. This effect is known as ortho effect.

Question: The correct order of acidity among the following compound is,

(a) II>III>IV>I
(b) IV>II>III>I
(c) II>IV>III>I
(d) IV>III>II>I

Solution: As we know that the nitro group is an electron withdrawing group. So, the nitro group at ortho and para position withdraw electron due to resonance and thus increases the acidity of the compound.

Therefore, ortho and para substituted acid is more acidic than para.

Also, ortho-substituted acid is more acidic due to ortho effect.

So, the order will be II>IV>III>I.