Loading...
Amines are related to ammonia by replacement of one or more hydrogen atoms with carbon groups. Primary, secondary and tertiary describe the number of carbon groups attached to nitrogen, which is a different counting rule from alcohol classification. Nitrogen’s lone pair accepts H+, so amines form ammonium salts with acids. Basicity depends on lone-pair availability, electron donation, delocalisation and solvation; a simple more-alkyl-groups rule is not reliable for every comparison in water.
Video by Eliot Rintoul. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain amine basicity
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What makes an amine a base?
Its nitrogen lone pair can accept H+. Protonation produces an ammonium ion.
After watching 2: How many carbon groups are directly attached to nitrogen in a secondary amine?
Two. This classification is based on attachments to nitrogen.
What you'll be able to do
Amines are related to ammonia by replacement of one or more hydrogen atoms with carbon groups. Primary, secondary and tertiary describe the number of carbon groups attached to nitrogen, which is a different counting rule from alcohol classification. Nitrogen’s lone pair accepts H+, so amines form ammonium salts with acids. Basicity depends on lone-pair availability, electron donation, delocalisation and solvation; a simple more-alkyl-groups rule is not reliable for every comparison in water.
An alkyl group can donate electron density toward nitrogen, making an aliphatic amine more basic than ammonia in the usual simple comparison. In phenylamine the lone pair is delocalised toward the benzene ring and is less available to accept a proton, so it is less basic. The explanation concerns electron-pair availability rather than bond strength alone. A lone pair is not eliminated by delocalisation; its distribution and ability to participate in proton acceptance are changed.
Heating a halogenoalkane with excess ethanolic ammonia can produce a primary amine, but further substitution may give secondary, tertiary and quaternary products. Excess ammonia helps favour the primary product. Reducing a nitrile forms a primary amine and retains the nitrile carbon in the chain. Amines react with acyl chlorides or anhydrides to form amides. For aromatic chemistry, specify the course’s required reduction or diazonium routes and the relevant conditions rather than treating all nitrogen reactions as interchangeable.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why is phenylamine less basic than ethylamine?
Ethylamine’s lone pair is more available in this comparison.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.