19.2
Nomenclature of Primary Amines
Primary, secondary, and tertiary amines are compounds consisting of one, two, and three alkyl groups connected to the amino group (–NH2), respectively…
Common nomenclature of primary amines is derived by adding -amine as a suffix to the alkyl substituent to give alkylamine.
The IUPAC nomenclature of primary amines is derived by replacing the final -e of the parent alkane with the suffix -amine to give alkanamines.
If a molecule bears two –NH2 groups, the final -e of the alkane is retained, and the parent name is suffixed with -diamine.
To use the IUPAC nomenclature, select the longest parent hydrocarbon chain bonded to the amine nitrogen. Then assign the lowest locant to the carbon atom bearing the amine nitrogen.
The substituents and their locant values are listed alphabetically and prefixed to the parent name. Prefixes di- or tri- are used to indicate identical substituents.
Chiral centers, if present, are specified at the beginning of the name.
If a molecule bears another functional group, except halogens, the –NH2 group is treated as a substituent and prefixed to the parent name.
Primary amines bearing cyclic alkyl groups are named cycloalkylamines or cycloalkanamines.
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Q1: How do you name a primary amine using common nomenclature?
Common nomenclature of primary amines is derived by adding the suffix -amine to the alkyl substituent bonded to the amino group. For example, methylamine has one methyl group attached to the NH2 group, and ethylamine has an ethyl group. This straightforward approach provides the alkylamine name directly from the alkyl substituent identity.
Q2: What is the difference between common and IUPAC nomenclature for primary amines?
Common nomenclature adds -amine to the alkyl substituent, while IUPAC nomenclature replaces the final -e of the parent alkane with -amine to give alkanamines. IUPAC requires selecting the longest parent hydrocarbon chain bonded to the amine nitrogen and assigning the lowest locant to the carbon bearing the NH2 group. Substituents are then listed alphabetically with their locant values.
Q3: How do you assign locants when naming a primary amine using IUPAC rules?
Select the longest parent hydrocarbon chain bonded to the amine nitrogen, then assign the lowest locant to the carbon atom bearing the NH2 group. This ensures the amine functional group receives priority in numbering. Substituents and their locant values are then listed alphabetically and prefixed to the parent alkanamine name.
Q4: How are primary amines with two amino groups named?
When a molecule bears two –NH2 groups, the final -e of the parent alkane is retained, and the parent name is suffixed with -diamine. For example, a two-carbon chain with amino groups at both ends is named ethanediamine. This nomenclature convention distinguishes diamines from monoamines in the systematic name.
Q5: How do you name a primary amine with a chiral center?
Chiral centers, if present, are specified at the beginning of the name using stereochemical descriptors such as R or S. The chiral descriptor is added with the appropriate locant to indicate the three-dimensional orientation of substituents around the stereogenic carbon. This ensures the complete structural identity is captured in the nomenclature.
Q6: What happens to the amino group when a primary amine has another functional group present?
If a molecule bears another functional group except halogens, the –NH2 group is treated as a substituent and prefixed to the parent name using the prefix amino-. This means the other functional group receives priority as the parent, and the amine is named as a substituent. Halogens remain lower in priority than the amino group.
Q7: How are primary amines with cyclic alkyl groups named?
Primary amines bearing cyclic alkyl groups are named cycloalkylamines or cycloalkanamines. The cycloalkane parent name is used, with the final -e replaced by -amine for IUPAC nomenclature. For example, cyclohexylamine contains a cyclohexyl group attached to the amino functional group.