Amines
28.1 Introduction to Amines:
- Amines are nitrogen containing organic compounds that 28.1 introduction to amines
are derived from ammonia, where one or more 28.2 the properties of amines as bases
hydrogen atom have been replaced by alkyl or aryl
28.3 amines as nucleophiles and their synthesis
groups.
- In primary amines, 1 hydrogen is replaced by
an alkyl group.
- In secondary amines, 2 hydrogens are replaced
by an alkyl group.
- In tertiary amines, 3 hydrogens are replaced by
an alkyl group.
- Amines are shaped similarly to ammonia. They have a bond angle of 107o between groups on the
nitrogen atom.
- This is slightly less than a perfect tetrahedron (109.5o) because of the lone pair, which repels more
than bonding pairs.
- Naming amines:
o The suffix -amine is added to the alkyl chain e.g., methylamine, ethylamine
o The prefix amino- is used when there is another functional group attached to carbon-1 in the
alkyl group e.g., 3-aminobutanal, 2-aminoethanoic acid
o If there are two or three alkyl chains that are the same use the prefix di- or tri-
o When two or more different alkyl chains are attached to the nitrogen atoms, we use N- to
represent the alkyl chains are side chains attached to the N of the larger group e.g., N-methyl
propylamine, N,N-diethyl butylamine
- Boiling point:
o Primary amines have a higher boiling point than alkanes because they can form hydrogen
bonds with each other.
o Secondary amines also form hydrogen bonds, but as the nitrogen atom is in the middle of the
hydrocarbon chain the strength of the dipole is slightly less. This decreases the strength of the
dipole-dipole interactions.
o In tertiary amines, there are no hydrogens attached directly to the nitrogen, so hydrogen
bonding between molecules is impossible.
o The boiling points of amines are lower than alcohols as nitrogen is less electronegative than
oxygen, so the hydrogen bonds are stronger in alcohols.
o Short chain amines are gases
o Longer chain amines are volatile liquids with fishy smells.
- Solubility:
o Amines are soluble in both water and alcohols.
o Amines have a lone pair of electrons on an electronegative atom; therefore, they can form
hydrogen bonds with water.
o The more alkyl groups on the amine, the less hydrogen bonds it can form so the less soluble
the amine.
o Long chains are only sparingly soluble as larger R groups interfere with hydrogen bonds
- Reactivity:
o The lone pair can bond with a H+ ion when the amine acts as a base.
o The lone pair can also bond with an electron-deficient carbon atoms when the amine acts as a
nucleophile.
28.2 The Properties of Amines as Bases:
- Amines can accept a proton, so they are Br∅nsted-Lowry base.
28.1 Introduction to Amines:
- Amines are nitrogen containing organic compounds that 28.1 introduction to amines
are derived from ammonia, where one or more 28.2 the properties of amines as bases
hydrogen atom have been replaced by alkyl or aryl
28.3 amines as nucleophiles and their synthesis
groups.
- In primary amines, 1 hydrogen is replaced by
an alkyl group.
- In secondary amines, 2 hydrogens are replaced
by an alkyl group.
- In tertiary amines, 3 hydrogens are replaced by
an alkyl group.
- Amines are shaped similarly to ammonia. They have a bond angle of 107o between groups on the
nitrogen atom.
- This is slightly less than a perfect tetrahedron (109.5o) because of the lone pair, which repels more
than bonding pairs.
- Naming amines:
o The suffix -amine is added to the alkyl chain e.g., methylamine, ethylamine
o The prefix amino- is used when there is another functional group attached to carbon-1 in the
alkyl group e.g., 3-aminobutanal, 2-aminoethanoic acid
o If there are two or three alkyl chains that are the same use the prefix di- or tri-
o When two or more different alkyl chains are attached to the nitrogen atoms, we use N- to
represent the alkyl chains are side chains attached to the N of the larger group e.g., N-methyl
propylamine, N,N-diethyl butylamine
- Boiling point:
o Primary amines have a higher boiling point than alkanes because they can form hydrogen
bonds with each other.
o Secondary amines also form hydrogen bonds, but as the nitrogen atom is in the middle of the
hydrocarbon chain the strength of the dipole is slightly less. This decreases the strength of the
dipole-dipole interactions.
o In tertiary amines, there are no hydrogens attached directly to the nitrogen, so hydrogen
bonding between molecules is impossible.
o The boiling points of amines are lower than alcohols as nitrogen is less electronegative than
oxygen, so the hydrogen bonds are stronger in alcohols.
o Short chain amines are gases
o Longer chain amines are volatile liquids with fishy smells.
- Solubility:
o Amines are soluble in both water and alcohols.
o Amines have a lone pair of electrons on an electronegative atom; therefore, they can form
hydrogen bonds with water.
o The more alkyl groups on the amine, the less hydrogen bonds it can form so the less soluble
the amine.
o Long chains are only sparingly soluble as larger R groups interfere with hydrogen bonds
- Reactivity:
o The lone pair can bond with a H+ ion when the amine acts as a base.
o The lone pair can also bond with an electron-deficient carbon atoms when the amine acts as a
nucleophile.
28.2 The Properties of Amines as Bases:
- Amines can accept a proton, so they are Br∅nsted-Lowry base.
