Bondline / Reactions

Amine from a halogenoalkane and ammonia

Ammonia substitutes for bromide, then a second ammonia molecule removes a proton. Excess ammonia keeps the amine from reacting again.

Substitution · 2 steps

Conditions

Excess concentrated NH₃ in ethanol, heated in a sealed tube.

Mechanism in 3 steps

Red curly arrows show where each pair of electrons moves.

NH3BrNH2+HNH3++
Step 1The nitrogen lone pair attacks the δ+ carbon and bromide leaves (SN2).
NH2+HNH3NH2NH4+NH₃++
Step 2A second ammonia molecule removes a proton from the ethylammonium ion.

About substitution reactions

In a substitution, a nucleophile replaces a leaving group on a saturated carbon. Whether it happens in one step (SN2) or through a carbocation (SN1) depends on the substrate, the nucleophile and the solvent.

Practise this mechanismDraw the curly arrows yourself and Bondline checks each one. Or add it to your notes and watch it in 3D.

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