Amines as Bases
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Order these bases from strongest to weakest: aliphatic amines aromatic amies ammonia
• aliphatic amine • ammonia • aromatic amine
How is the strength of a base measured?
Using pH, a higher pH indicates a stronger base
If a base is strong, what will the pH value range between?
pH values ranging from 12 - 14
If a base is weak, what will the pH value range between?
pH values ranging from 7.1 - 11
What determines the basic strength of an amine? (aval. lp. e- N atom)
The availability of the lone pair of electrons on the nitrogen atom
How does lone pair availability affect basic strength? (+aval. lp. acc. p = strng. bse.)
The more available the lone pair is to accept a proton, the stronger the base
Why are aliphatic amines stronger bases than ammonia? (alk. don. ED - N - inc lp. aval. - N bttr. acc. pro.)
Alkyl groups donate electron density to nitrogen, increasing lone pair availability and making nitrogen better at accepting a proton
How do alkyl groups affect electron density in aliphatic amines?
They increase electron density on nitrogen, making the lone pair more readily available
How does the basicity of phenylamine compare with ammonia?
Phenylamine is a weaker base than ammonia
Why is phenylamine a weaker base than ammonia? (N lp. - deloc. benz. rng. - lss. aval. acc. pro.)
The nitrogen lone pair becomes delocalised into the benzene ring, making it less available to accept a proton
How does delocalisation affect the lone pair in phenylamine? (lp - prt. deloc. pi. sys. - red. aval. + dec. b stngth.)
The lone pair becomes part of the delocalised π system, reducing its availability and decreasing basic strength
Compare the basic strength of phenylamine, ammonia and aliphatic amines AA - strng - alk. grps. + don. e A - lss bsc. - no e don. alk. grps PA - wkst. - lp delo. benz. rng. - lss. aval. acc. p
Aliphatic amines are the strongest bases because alkyl groups donate electron density to nitrogen, increasing lone pair availability. Ammonia is less basic because it has no electron donating alkyl groups. Phenylamine is the weakest base because the nitrogen lone pair is delocalised into the benzene ring, making it less available to accept a proton