Giving justification, categorise the following molecules/ions as nucleophile or electrophile: HS⁻, BF₃, C₂H₅O⁻, (CH₃)₃N:, Cl⁺, CH₃C⁺=O, H₂N⁻:, NO₂⁺.

Question

Accepted Answer

> [!TLDR]
> Nucleophiles are electron-rich species that donate electrons; electrophiles are electron-deficient species that accept electrons. **HS⁻, C₂H₅O⁻, (CH₃)₃N:, and H₂N⁻: are nucleophiles; BF₃, Cl⁺, CH₃C⁺=O, and NO₂⁺ are electrophiles.**

## The Electrophile–Nucleophile Concept

The distinction between nucleophiles and electrophiles rests on electron availability. A **nucleophile** ("nucleus-loving") carries excess electron density—either as a negative charge, lone pairs, or π-electrons—and seeks positively charged or electron-deficient centres. An **electrophile** ("electron-loving") is electron-deficient, often bearing a positive charge or an incomplete octet, and hunts for electrons to stabilise itself.

The key diagnostic: look for **charge**, **lone pairs**, and **octet completion**. Negative charges and lone pairs signal nucleophilic character; positive charges and vacant orbitals signal electrophilic character.

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## Classification with Justification

1. **HS⁻ (hydrosulphide ion)**  
   The negative charge places excess electron density on sulphur. Sulphur also carries lone pairs beyond the bonding pair with hydrogen. This species will readily donate electrons to an electron-deficient centre.  
   **Category:** Nucleophile

2. **BF₃ (boron trifluoride)**  
   Boron has only six electrons in its valence shell (three bonds to fluorine), leaving it two electrons short of an octet. The empty $p$-orbital on boron makes it a powerful Lewis acid, eager to accept an electron pair.  
   **Category:** Electrophile

3. **C₂H₅O⁻ (ethoxide ion)**  
   The negative charge resides on oxygen, which also has three lone pairs. Oxygen is highly electronegative and the negative charge makes this species strongly nucleophilic—it will attack electron-poor sites.  
   **Category:** Nucleophile

4. **(CH₃)₃N: (trimethylamine)**  
   Nitrogen has a lone pair of electrons (the colon represents this). Although neutral, the lone pair is available for donation. Amines are classi

Feature	Electrophile	Nucleophile
Charge	Often positive or neutral (with empty orbital)	Often negative or neutral (with lone pair)
Examples	$\ce{H+}$ , $\ce{AlCl3}$ , $\ce{BF3}$ , $\ce{CH3+}$ (carbocation), $\ce{CO2}$	$\ce{OH-}$ , $\ce{NH3}$ , $\ce{H2O}$ , $\ce{Cl-}$ , $\ce{CH3O-}$
Orbital	Empty orbital (can accept electrons)	Filled orbital (lone pair or pi bond)
Reaction type	Attacked by nucleophile	Attacks electrophile

Species	Type	Justification
$\ce{HS^-}$	Nucleophile	Negative charge + lone pairs on sulphur
$\ce{BF3}$	Electrophile	Boron has incomplete octet (6 electrons)
$\ce{C2H5O^-}$	Nucleophile	Negative charge + lone pairs on oxygen
$\ce{(CH3)3N:}$	Nucleophile	Lone pair on nitrogen available for donation
$\ce{Cl^+}$	Electrophile	Positive charge, electron-deficient
$\ce{CH3C^+=O}$	Electrophile	Positive charge on carbon (acylium cation)
$\ce{H2N^-:}$	Nucleophile	Negative charge + lone pairs on nitrogen

Q.Giving justification, categorise the following molecules/ions as nucleophile or electrophile: HS⁻, BF₃, C₂H₅O⁻, (CH₃)₃N:, Cl⁺, CH₃C⁺=O, H₂N⁻:, NO₂⁺.

Concept understanding — Electrophile Nucleophile Concept

The Electrophile–Nucleophile Concept: A First Look

The Intuition

The Precise Statement

How to Identify Them

The Arrow-Pushing Convention

The Electrophile–Nucleophile Concept

Classification with Justification

Q.Giving justification, categorise the following molecules/ions as nucleophile or electrophile: HS⁻, BF₃, C₂H₅O⁻, (CH₃)₃N:, Cl⁺, CH₃C⁺=O, H₂N⁻:, NO₂⁺.

The Electrophile–Nucleophile Concept

Classification with Justification

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