As far as I have been able to understand this, the sites of electrophilic substitution are majorly decided on basis of the fact that "Where the electron density is more, electrophilic substitution occurs there".

This resonated with my intuition, but while looking at it for 4-nitrobenzaldehyde, my teacher told me that major site of substitution is meta with respect to aldehyde.


Pondering over it, I thought that since the reaction proceeds such that positive charge develops on the position adjacent to the site of substitution, thus it must be a location where electron density is more, i.e. meta to the nitro group. But this "ended" my intuition and I am doubtful whether such a reasoning is correct or not.

  • $\begingroup$ I did a quick search of Chem. Abst. for monohalogenation ofp-nitro benzaldehyde, benzoic acid and benzoic esters. The only example I found that may not involve a chelation effect with the carboxyl group is the bromination of p-nitrobenzoic acid with a quaternary ammonium perbromide to give 2-bromo-4-nitrobenzoic acid. I do not have access to the Slovenia journal. This result would support your contention. $\endgroup$
    – user55119
    Jan 8, 2022 at 16:26
  • 1
    $\begingroup$ According to Moodie & Willmer JCS Perk 2 (1992) 229-233 the major products of attempted nitration of 4-nitrocarboxaldehyde are oxidation to nitrobenzoic acids, the minor dinitrobenzaldehyde is 2,4-dinitrobenzaldehyde i.e. meta to the nitro group. $\endgroup$
    – Waylander
    Jan 8, 2022 at 16:31


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