Q.Which of the following is not a nucleophile ?
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The Electrophile–Nucleophile Concept: A First Look
Imagine you are in a crowded room. Some people are constantly reaching out to shake hands — they want to connect, to grab something. Others are holding their hands close, waiting for someone to come to them. In organic chemistry, molecules behave the same way.
The Intuition
Every chemical reaction is about electron movement. Some species are electron-poor — they want to accept electrons to become stable. Others are electron-rich — they have extra electrons and are happy to donate them.
- Electrophile (from Greek philos = loving, electron = electron): "Electron-loving" — a species that loves electrons and seeks them out. It is electron-deficient (positive charge, partial positive charge, or an empty orbital).
- Nucleophile (from Greek nucleus = nucleus, philos = loving): "Nucleus-loving" — a species that loves positive nuclei because it has excess electrons to donate. It is electron-rich (negative charge, lone pairs, or pi bonds).
Think of an electrophile as a hungry guest at a party (wants food = electrons) and a nucleophile as a generous host (has food to give). The reaction happens when the host offers food to the hungry guest.
The Precise Statement
Electrophile: Any atom, ion, or molecule that accepts a pair of electrons to form a new covalent bond. It is Lewis acid (electron-pair acceptor).
Nucleophile: Any atom, ion, or molecule that donates a pair of electrons to form a new covalent bond. It is Lewis base (electron-pair donor).
How to Identify Them
| Feature | Electrophile | Nucleophile |
|---|---|---|
| Charge | Often positive or neutral (with empty orbital) | Often negative or neutral (with lone pair) |
| Examples | HX+, AlClX3, BFX3, CHX3X+ (carbocation), COX2 | OHX−, NHX3, HX2O, ClX−, CHX3OX− |
| Orbital | Empty orbital (can accept electrons) | Filled orbital (lone pair or pi bond) |
| Reaction type | Attacked by nucleophile | Attacks electrophile |
The Arrow-Pushing Convention
In organic chemistry, we show electron movement with curved arrows:
- Arrow starts at the nucleophile (where electrons come from) — usually a lone pair or a pi bond.
- Arrow ends at the electrophile (where electrons go) — usually at a positive charge or an empty orbital.
Example: Reaction of hydroxide ion with methyl bromide
HOX−+CHX3BrHO−CHX3+BrX−
The arrow goes from the lone pair on O (nucleophile) to the carbon atom in CHX3Br (electrophile, because Br pulls electron density away, making carbon partially positive). …
A nucleophile donates an electron pair. BF3 is electron-deficient and accepts electron pairs, so it is not a nucleophile (it is an electrophile). …
BF3 is not a nucleophile (it is an electrophile).
Nucleophiles are electron-rich species that donate a lone pair, e.g. CN-, CH3O- and NH3 (lone pair on N). BF3 has boron with an incomplete octet (only 6 electrons), so it accepts …
- CBSE 2026Set ANNUAL1 markMCQQ.Which of the following is not a nucleophile ?(a) CN^-(b) CH3O^-(c) BF3(d) NH3
›Reveal solutionSolution
BF3 is not a nucleophile (it is an electrophile).
Nucleophiles are electron-rich species that donate a lone pair, e.g. CN-, CH3O- and NH3 (lone pair on N). BF3 has boron with an incomplete octet (only 6 electrons), so it accepts …
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following is an electrophile?(a) BCl3(b) CH3OH(c) NH3(d) AlCl4⁻
›Reveal solutionSolution
BCl3 is the electrophile because boron has an incomplete octet and is electron-deficient.
An electrophile ("electron-loving") is a species that is electron-deficient and accepts an electron pair.
- BCl3: boron has only 3 bond pairs (6 electrons) around it — an incomplete octet — so it readily accepts an electron pair; it is a classic electrophile/Lewis acid. …
- CBSE 2019Set ANNUAL1 markMCQQ.In the following Nucleophiles are:(a) OH-, H2O(b) CH3+, NC-(c) >C=O, CH3+(d) OH-, R3C+
›Reveal solutionSolution
Nucleophiles are electron-pair donors; OH⁻ and H₂O both have available lone pairs and are classic nucleophiles, while the other options mix in electrophiles.
A nucleophile ('nucleus-loving') is a species rich in electron density — usually bearing a lone pair and/or a negative charge — that attacks an electron-deficient (electrophilic) centre, forming a new bond by donating its electron pair.
- (a) OH⁻, H₂O: OH⁻ carries a negative charge and lone pairs; H₂O is neutral but has two lone pairs on oxygen. Both readily donate electrons — both are nucleophiles. ✓ …
- CBSE 2018Set ANNUAL1 markMCQQ.Electrophile is:(a) C2H5O-(b) OH-(c) NC-(d) CH3+
›Reveal solutionSolution
Electrophiles are electron-poor species (often positively charged or with an incomplete octet) that attack electron-rich centres; CH3+ is the only such species among the options.
An electrophile ("electron-loving") is a reagent that is deficient in electrons and hence seeks out a pair of electrons from another species during a reaction. Electrophiles are typically positively charged, or neutral species with an incomplete octet/empty orbital.
A nucleophile ("nucleus-loving"), in contrast, is electron-rich — usually bearing a lone pair or a negative charge — and donates electrons to an electrophilic centre.
Checking the options:
- C2H5O- (ethoxide ion): negatively charged, has lone pairs to donate → nucleophile. …
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