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We know that the Electron Donating effect of the benzene ring in benzoic acid makes it less acidic than formic acid!

And we also now that whenever an ortho substituent is present in benzoic acid there would be ortho effect which makes benzoic acid more acidic.This is precisely because the resonance doesn't occur anymore because planarity of the molecule is lost. So,now since we don't have any electron donating effect due to resonance is ortho-nitro benzoic acid more acidic than formic acid?

Moreover can we now consider Electron withdrawing effects of benzene ring and the nitro substituent to support of claim?

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o-NO2-benzoic aid pKa 2.19 1

Formic acid pKa 3.75 2

Nitro is a very powerful electron-withdrawing group and profoundly affects the properties of aromatics when it is present. According to this paper 3 the ortho effect does also contribute to the acidity of o-nitro benzoic acid.

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  • $\begingroup$ so,is o-nitro benzoic acid stronger acid than fromic acid only beacause of Electron withdrawing effect ?Is ortho efffect playing no role in increasing its acidic nature?... $\endgroup$ – Banchin Jul 12 '18 at 9:26
  • $\begingroup$ @Banchin Answer edited to address this $\endgroup$ – Waylander Jul 12 '18 at 10:18
  • $\begingroup$ Well actually all the nitrobenzoic acids are more acidic than formic acid // 3-nitrobenzoic_acid, pka = 3.46 // 4-nitrobenzoic_acid, pKa = 3.44 $\endgroup$ – MaxW Jul 12 '18 at 14:10
  • $\begingroup$ @MaxW Could you explain the reasons and is ortho effect one of them? $\endgroup$ – Banchin Jul 12 '18 at 14:50
  • $\begingroup$ The pKa's speak for themselves. Compare similar acids. Are apples tastier than oranges? $\endgroup$ – user55119 Jul 12 '18 at 19:34

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