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

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!!

• 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. – yasir Jul 10 '15 at 6:54
• @yasir can you please explain why? – user14857 Jul 10 '15 at 7:14

• 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. – yasir Jul 10 '15 at 7:51