Explain how amines can be classified as primary, secondary or tertiary based on their structure.

Amines can be classified as primary, secondary or tertiary by the number of alkyl or aryl groups attached to the nitrogen atom.

  • Primary: one alkyl or aryl group bonded to N.
  • Secondary: two alkyl or aryl groups bonded to N.
  • Tertiary: three alkyl or aryl groups bonded to N.

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What is the shape and bond angles around the nitrogen atom of an amine?

The nitrogen atom of an amine has a trigonal pyramidal shape with bond angles of ≈107°.

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What is the difference between aliphatic amines and aromatic amines?

In aliphatic amines, the nitrogen atom is bonded to at least one straight or branched carbon chain i.e. an alkyl group.

In aromatic amines, the nitrogen atom is bonded directly to a benzene ring.

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Why do amines behave as Brønsted-Lowry bases?

Amines behave as Brønsted-Lowry bases because the lone pair of electrons on the nitrogen atom can accept a proton, forming a dative covalent bond.


For example, ethylamine behaves as a Brønsted-Lowry base:

C2H5NH2 + H+ ➔ C2H5NH3+

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Describe the reactions of amines with acids.

Amines neutralise acids to form salts. 


For example, ethylamine reacts with hydrochloric acid to form ethylammonium choride:

C2H5NH2 + HCl ➔ C2H5NH3Cl

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What determines the strength of ammonia and amines as bases?

The availability of the lone pair of electrons on their N atom to bond with an H+ ion.


The more readily available the N lone pair, the stronger the base.

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Rank the following nitrogen-containing compounds in order of increasing base strength: ammonia; primary aliphatic amines; and primary aromatic amines.

Base strength increases in the order: primary aromatic amines < ammonia < primary aliphatic amines.

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Why are primary aromatic amines weaker bases than ammonia?

The lone pair of electrons on the nitrogen atom overlaps with the delocalised π-system of the benzene ring, making the nitrogen lone pair less available to donate.

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Why are primary aliphatic stronger bases than ammonia?

The positive inductive effect of the alkyl group increases the electron density on the nitrogen atom, making nitrogen's lone pair of electrons more readily available to bond with an H+ ion. 

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