Why are halogens deactivating but still ortho/para directing? And why does nitrating aniline give meta product?
Ishita GoyalDropper Sample
22 Sept 2026 · 1 min read
I'm building a one-page "directing groups" template for my plan, and two entries refuse to fit the neat pattern.
The pattern as I understand it: activating groups like –OH, –NH2, –OCH3, –CH3, –R are ortho/para directing; deactivating groups like –NO2, –CN, –CHO, –COOH, –SO3H are meta directing. That's neat and I can draw it. But halogens (–Cl, –Br) are deactivating (chlorobenzene reacts slower than benzene in nitration) and yet they're ortho/para directing. That breaks the pattern. NCERT says it's because of the two opposing effects, inductive and resonance. I want to see how those two combine to get "slow but o/p".
Second: aniline has –NH2, a strong activator and o/p director. But direct nitration of aniline with nitrating mixture gives a significant amount of the meta nitroaniline along with para and ortho. My answer was "that can't be right", but apparently it is. Why?
Third: why does nitrobenzene not undergo Friedel–Crafts alkylation or acylation? I have the line "strongly deactivated" but do I need more than that?
6 answers & replies
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[+][–]Kabir Joshi11thSample· 27d ago
Halogens are deactivating so they should be meta directing, no? Every deactivating group on the list is meta. Maybe the chlorobenzene o/p thing in the book is just an exception to memorise.
[+][–]Rahul DubeyDropperSample· 27d ago
Kabir, "deactivating = meta" is the rule of thumb and halogens are exactly the exception that has a reason. Two effects in chlorine:
- -I effect (inductive): Cl is electronegative and pulls electron density through the sigma bond. This lowers the electron density of the whole ring, making it less reactive than benzene. That is why it's deactivating.
- +R effect (resonance): Cl has lone pairs that can be donated into the ring by resonance. This donation puts negative charge specifically at the ortho and para positions.
The -I effect decides the overall rate (slower), but the +R effect decides the position (ortho/para), because the incoming electrophile prefers the positions where the intermediate (arenium ion) is stabilised by the lone pair. So you get "slower, but o/p".
[+][–]Ishita GoyalDropperSample· 27d agoAuthor
this is perfect, "rate vs position" is the idea I needed. Template updated and the halogen row is red 😄
[+][–]Nisha Verma12thSample· 27d ago
Aniline in nitrating mixture: strong acid, + . The –NH2 group is basic, it picks up a proton and becomes anilinium, . That group has a full positive charge on N, so it pulls electrons strongly (–I) and has no lone pair to donate. It becomes a meta director and strongly deactivating. A mixture of unreacted aniline (o/p) and anilinium (meta) reacts, so you get all three isomers. To avoid this you protect the amine by acetylation first (acetic anhydride, giving acetanilide), nitrate, and then hydrolyse. NCERT shows it that way.
[+][–]Kavya NaikDropperSample· 27d ago
For Friedel–Crafts on nitrobenzene: the ring is strongly deactivated by –NO2 (both -I and -R withdraw), so the ring isn't nucleophilic enough to attack the weak carbocation / acylium electrophile. Same logic applies to anything more deactivating than a halogen, like –COOH, –CHO, –SO3H, –CN.
Another one examiners like: aniline also fails in Friedel–Crafts, but for a different reason. The lone pair on N is a Lewis base and it attacks the Lewis acid catalyst to form a salt, so the catalyst is used up and the ring becomes deactivated by the positive N. Nitrobenzene is sometimes used as a solvent for Friedel–Crafts, which is a fun fact because it's unreactive to them.
[+][–]Tanvi Deshmukh12thSample· 27d ago
Chart for the template, two rows:
Group Effect on rate Directs to –OH, –NH2, –OCH3, –R activating o / p –Cl, –Br, –I deactivating o / p –NO2, –CN, –CHO, –COOH, –SO3H deactivating meta Halogens in the middle are the only deactivating o/p directors. Circle them in red and you'll never forget. In PYQ-style questions the trap is "which group deactivates but is o/p directing", and it's always a halogen.
