Section 3 : Organic Chemistry
Amines
Amines are compounds based on ammonia where hydrogen atoms have been replaced by alkyl or aryl
groups.
• There is some H-bonding between molecules, but weaker than in alcohols.
• The presence of the lone pair of electrons on the N atom dominates much of amine chemistry
meaning they can act as nucleophiles + bases to greater or less extents.
Classi cation of Amines
Amines can be classi ed as primary, secondary or tertiary.
• Ammonia can be regarded as the simplest amine.
• Quaternary ammonium ions are not amines + they do not possess a lone pair of electrons on the N.
They are named after the alkyl group(s) attached to the N atom, w/ the ending -amine. For example…
Base Properties
Ammonia + the amines are weak bases (proton acceptors).
• They are weak bases because the lone pair of electrons on
the N atom is able to accept a H+.
• The ability of amines to act as bases depends on the
availability of the lone pair of electrons on the N atom.
- ↑ electron density of the lone pair on the N atom ➜ ↑
ability to accept H+ ➜ stronger bases
Explaining Base Strength of Amines
Primary, Secondary + Tertiary Amines Compared to Ammonia
• Alkyl groups are more electron releasing than H atoms (have a greater ‘inductive effect’).
• The more alkyl groups substituted on to the N atom in place of H atoms, the more electron density is
pushed on to the N atom.
• ∴ the more alkyl groups attached to the N atom, the greater the electron density of the lone pair on
the N atom + the stronger a base the amine is.
• This means in order of ↑ base strength: NH3 < 1° < 2° < 3°
Aromatic Amines Compared to Aliphatic Amines
• The lone pair on the N atom is partially delocalised into the benzene ring.
• This means the electron density of the lone pair on the N atom is reduced meaning that aromatic
amines are weaker bases than aliphatic amines.
• ∴ in order of ↑ base strength: Aromatic < NH3 < 1° < 2° < 3°
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Amines
Amines are compounds based on ammonia where hydrogen atoms have been replaced by alkyl or aryl
groups.
• There is some H-bonding between molecules, but weaker than in alcohols.
• The presence of the lone pair of electrons on the N atom dominates much of amine chemistry
meaning they can act as nucleophiles + bases to greater or less extents.
Classi cation of Amines
Amines can be classi ed as primary, secondary or tertiary.
• Ammonia can be regarded as the simplest amine.
• Quaternary ammonium ions are not amines + they do not possess a lone pair of electrons on the N.
They are named after the alkyl group(s) attached to the N atom, w/ the ending -amine. For example…
Base Properties
Ammonia + the amines are weak bases (proton acceptors).
• They are weak bases because the lone pair of electrons on
the N atom is able to accept a H+.
• The ability of amines to act as bases depends on the
availability of the lone pair of electrons on the N atom.
- ↑ electron density of the lone pair on the N atom ➜ ↑
ability to accept H+ ➜ stronger bases
Explaining Base Strength of Amines
Primary, Secondary + Tertiary Amines Compared to Ammonia
• Alkyl groups are more electron releasing than H atoms (have a greater ‘inductive effect’).
• The more alkyl groups substituted on to the N atom in place of H atoms, the more electron density is
pushed on to the N atom.
• ∴ the more alkyl groups attached to the N atom, the greater the electron density of the lone pair on
the N atom + the stronger a base the amine is.
• This means in order of ↑ base strength: NH3 < 1° < 2° < 3°
Aromatic Amines Compared to Aliphatic Amines
• The lone pair on the N atom is partially delocalised into the benzene ring.
• This means the electron density of the lone pair on the N atom is reduced meaning that aromatic
amines are weaker bases than aliphatic amines.
• ∴ in order of ↑ base strength: Aromatic < NH3 < 1° < 2° < 3°
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