Q.Nucleophiles and electrophiles are reaction intermediates having electron rich and electron deficient centres respectively. Hence, they tend to attack electron deficient and electron rich centres respectively. Classify the following species as electrophiles and nucleophiles.

The key idea is that electrophiles are electron-deficient (seek electrons) and nucleophiles are electron-rich (donate electrons). A neutral species can be either depending on its structure.

Step 1 – Identify charge and lone pairs.

1. $\ce{H3CO-}$ has a negative charge and lone pairs → nucleophile.
2. $\ce{CH3-C(=O)-O-}$ has a negative charge on oxygen → nucleophile.
3. $\ce{Cl.}$ is a free radical with an unpaired electron; it is electron-deficient and seeks an electron → electrophile.
4. $\ce{:CCl2}$ has a lone pair on carbon but also an empty p-orbital; it acts as both, but in typical reactions it is an electrophile (carbene).
5. $\ce{(H3C)3C+}$ has a positive charge → electrophile.
6. $\ce{Br-}$ has a negative charge and lone pairs → nucleophile.
7. $\ce{H3COH}$ (methanol) has lone pairs on oxygen but is neutral; it can act as a weak nucleophile. …

The core idea is simple: a nucleophile is "nucleus-loving" — it has a lone pair or a negative charge and seeks a positive or electron-deficient centre. An electrophile is "electron-loving" — it is electron-deficient (positive charge, incomplete octet, vacant orbital) and seeks a region of high electron density.

Let’s go through each species one by one.

1. H₃CO⁻ (methoxide ion)

   This is the conjugate base of methanol. It carries a full negative charge on oxygen, and oxygen already has two lone pairs. That’s a textbook nucleophile — electron-rich, ready to donate a pair.

   → Nucleophile

2. CH₃–C(=O)–O⁻ (acetate ion)

   The negative charge is delocalised over the two oxygen atoms (resonance), but the species still has a net negative charge and lone pairs on oxygen. It can donate electrons, though it’s a weaker nucleophile than methoxide because the charge is spread out. Still, it’s electron-rich.

   → Nucleophile

3. Cl· (chlorine free radical)

   A free radical has an unpaired electron — it’s not electron-rich in the sense of a lone pair, and it’s not electron-deficient like a carbocation. Radicals are electrophilic because they seek an electron to complete their octet. They attack electron-rich centres (like double bonds) to pair up the odd electron.

   → Electrophile

4. :CCl₂ (dichlorocarbene)

   Carbenes have a divalent carbon with only six electrons in its valence shell. The carbon has a lone pair and a vacant p-orbital. It can act as both, but in most reactions (like cyclopropanation), it behaves as an electrophile — the vacant p-orbital accepts electron density from a π-bond.

   → Electrophile

5. (H₃C)₃C⁺ (tert-butyl carbocation)

   A carbocation has a positively charged carbon with only six electrons — a classic electron-deficient species. It desperately wants a pair of electrons.

   → Electrophile

6. Br⁻ (bromide ion)

   A full negative charge and three lone pairs — extremely electron-rich. A strong nucleophile (and also a good leaving group, but that’s another story).

   → Nucleophile

7. H₃COH (methanol) …