Wednesday, August 9, 2017

organic chemistry - Why does nitration of aromatic amines give meta directed nitro compounds?



Amines are activating groups and donate electrons to the resonance structure using the lone pair of electrons on Nitrogen. But when aromatic amines are nitrated, for example when benzyl amine is nitrated, it gives a meta nitro benzyl amine. Given the activating nature of amine groups, shouldn't the compound be an ortho-para directing variant? I tried figuring it out. One explanation I've come up with is that when it's nitrated, the proton from the nitrous acid forms a coordinate covalent bond with the amine group closing the lone pair electron to the bond. As a result it becomes an $\ce{NH3+}$ group. That would mean that it has a deactivating effect or electron withdrawing effect. That's why the incoming nitro groups are attached to the meta positions. But then why doesn't the same happen for nitration of hydroxide groups, for instance phenol?




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periodic trends - Comparing radii in lithium, beryllium, magnesium, aluminium and sodium ions

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