3.4.6—Lewis acid-base theory

A Lewis acid accepts an electron pair; a Lewis base donates an electron pair. Nucleophiles correspond to Lewis bases and electrophiles to Lewis acids.

In BF₃ + NH₃ → F₃B←NH₃, NH₃ donates the pair and is the Lewis base; BF₃ accepts it and is the Lewis acid. Classify the roles from electron-pair movement rather than from whether H⁺ appears.

Representative question

[Maximum number: 1]

What is the role of the $\mathrm{CN}^{-}$ ion in the reaction of 1-chloropropane with excess KCN in ethanol?

\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Cl}+\mathrm{KCN} \rightarrow \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{CN}+\mathrm{KCl}

Electrophile and Lewis base

Nucleophile and Lewis acid

Electrophile and Lewis acid

Nucleophile and Lewis base

Retrieve the route: classify nucleophiles and electrophiles, show heterolysis, write substitution and addition mechanisms, map Lewis coordination, compare SN1/SN2, and restore aromaticity in benzene substitution.

Check electron-pair arrow origin and destination, leaving-group departure, intermediate identity, carbocation stability and the assessed mechanism boundary.

3.4.6—Lewis acid-base theory

Lewis Acids and Bases

Classifying Lewis Acids and Bases

Assessment in practice

Electron-Pair Sharing Summary

Question 1