Where should the nitro group sit?
"Where should the nitro group sit?" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the NCERT section "Reactions of haloarenes" in Haloalkanes and Haloarenes. Nucleophilic attack on a chlorobenzene ring: the carbanion's negative charge is pushed around the ring; an –NO₂ placed ortho or para takes the charge onto its oxygens, a meta –NO₂ never does. NEET has asked about this idea 1 time in 10 years of papers. JEE Main asked 62 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Reactions of haloarenes in Haloalkanes and Haloarenes. Change the values and watch what happens.
What it shows
NCERT §6.7.2
Nucleophilic attack on a chlorobenzene ring: the carbanion's negative charge is pushed around the ring; an –NO₂ placed ortho or para takes the charge onto its oxygens, a meta –NO₂ never does.
Controls
3 to try
- Clickplace –NO₂ at ortho / meta / para (up to three)
- Buttonstep through resonance forms
- Readoutsforms with charge on NO₂, relative rate, conditions needed (623 K/300 atm vs mild)
Try this
Place one nitro group so the intermediate's charge reaches its oxygens, then move it meta and see the help vanish.
Common mistake
Any –NO₂ on the ring activates it equally.
In NEET
10 years of papers
Asked 1 time in 10 years of NEET.
See the past questions: Nucleophilic Substitution, Haloalkanes and Haloarenes (chapter)
In JEE Main
42 shifts analysed
62 questions from Haloalkanes and Haloarenes across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §6.7.2
- Aryl halides are far less reactive than alkyl halides towards nucleophilic substitution, for four reasons listed below.
- Resonance: the halogen's lone pairs conjugate with the ring's π electrons, giving the C–X bond partial double bond character that is harder to break.
- Hybridisation: the sp² carbon has more s-character, is more electronegative and holds the bonding pair tighter than an sp³ carbon. C–Cl is 169 pm in a haloarene against 177 pm in a haloalkane, and the shorter bond is harder to break.
- A phenyl cation from self-ionisation gets no resonance stabilisation, which rules out SN1; and the electron-rich nucleophile is repelled by the electron-rich ring.
- Chlorobenzene becomes phenol only under harsh conditions: aqueous NaOH at 623 K and 300 atmospheres.
- An –NO₂ group ortho or para to the halogen raises reactivity by withdrawing electron density and stabilising, through resonance, the negative charge in the carbanion intermediate. A meta –NO₂ has no effect, because none of the resonance structures then puts the negative charge on the carbon carrying –NO₂.
- Haloarenes undergo the usual electrophilic substitutions of benzene: halogenation, nitration, sulphonation and Friedel-Crafts reactions. The halogen is slightly deactivating yet ortho, para-directing.
- Why both: the –I effect withdraws electrons and deactivates the ring, so reactions are slower and need harsher conditions than with benzene. Resonance releases electrons to the ortho and para positions and stabilises attack there. The stronger inductive effect sets reactivity; resonance sets orientation.
- Wurtz-Fittig reaction: an alkyl halide and an aryl halide with sodium in dry ether give an alkylarene. Fittig reaction: aryl halides alone with sodium in dry ether join two aryl groups (e.g. biphenyl).
Questions
5 answers
- What does the "Where should the nitro group sit?" simulation show?
- Nucleophilic attack on a chlorobenzene ring: the carbanion's negative charge is pushed around the ring; an –NO₂ placed ortho or para takes the charge onto its oxygens, a meta –NO₂ never does.
- What mistake does the "Where should the nitro group sit?" simulation fix?
- A common mistake it clears up: any –NO₂ on the ring activates it equally.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 1 time in 10 years of papers.
- Does JEE Main ask questions from Haloalkanes and Haloarenes?
- Yes. JEE Main asked 62 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Reactions of haloarenes" in Haloalkanes and Haloarenes (Class 12 Chemistry).
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