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In meta hydroxy benzaldehyde which position (w.r.t hydroxy group) is more prone to electrophilic attack ?

My approach:I considered hydroxy group as the stronger +M group.So my guess was para position w.r.t hydroxy group.But that's not the correct answer.

The answer is actually given as ortho w.r.t hydroxy and para w.r.t -CHO group!!

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  • $\begingroup$ This is known as the ortho effect. According to it if an ortho/para and meta directing group are meta to each other, then the incoming electrophile prefers to come on ortho of meta directing group. $\endgroup$ – yasir Jul 10 '15 at 6:54
  • $\begingroup$ @yasir can you please explain why? $\endgroup$ – user14857 Jul 10 '15 at 7:14
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This is known as the ortho effect. According to it if an ortho/para and meta directing group are meta to each other, then the incoming electrophile prefers to come on ortho of meta directing group.

See the reference.

enter image description here

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  • $\begingroup$ I wanted t0 know for m-hydroxy benzaldehyde $\endgroup$ – user14857 Jul 10 '15 at 7:40
  • $\begingroup$ The same applies for m-hydroxy benzaldehyde too.In this case, you have $\ce{Cl}$ which is ortho/para directing meta to $\ce{NO2}$ group which is meta directing.In your case, $\ce{OH}$ which is ortho/para directing is also meta to $\ce{CHO}$ group which is meta directing. $\endgroup$ – yasir Jul 10 '15 at 7:51
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    $\begingroup$ @yasir Please edit in the complete reference. Give credit where credit is due. $\endgroup$ – Martin - マーチン Jul 10 '15 at 8:02
  • $\begingroup$ So are you saying that the OP's stated 'correct' answer is wrong? $\endgroup$ – bon Jul 10 '15 at 10:57
  • $\begingroup$ @Bon That's what i have learnt from my text.I would like someone to kindly elaborate on ortho effect as my knowledge of it is limited. $\endgroup$ – yasir Jul 10 '15 at 11:35

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