19.3
Nomenclature of Secondary and Tertiary Amines
The secondary and tertiary amines are derivatives of ammonia, where two and three of its hydrogens are replaced by alkyl groups, respectively. Seconda…
Secondary and tertiary amines can be symmetrical with identical alkyl groups attached to the nitrogen atom or unsymmetrical when more than one type of alkyl group is present.
In common nomenclature, secondary and tertiary amines are named alkylamines. For symmetrical amines, prefixes, di- and tri- are used. In the case of unsymmetrical amines, individual substituents are identified and listed alphabetically.
In the IUPAC nomenclature, the amines are named N-alkylalkanamines.
To assign the IUPAC name, identify the alkyl groups attached to the nitrogen atom. Next, select the longest chain as the parent, while the other alkyl groups are listed as substituents.
Now, number the parent chain by assigning the lowest number to the carbon atom bearing nitrogen.
Assign locants to each substituent. The letter N is used as a locant for the alkyl groups attached to the nitrogen atom.
Finally, assemble the name and specify the configuration of the chiral center, if present, at the beginning of the name.
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Q1: What is the difference between symmetrical and unsymmetrical secondary and tertiary amines?
Symmetrical secondary and tertiary amines have identical alkyl groups attached to the nitrogen atom, while unsymmetrical amines contain more than one type of alkyl group. In common nomenclature, symmetrical amines use prefixes di- and tri-, whereas unsymmetrical amines require individual substituents to be identified and listed alphabetically.
Q2: How are secondary and tertiary amines named in common nomenclature?
Secondary and tertiary amines are named as alkylamines in common nomenclature. For symmetrical amines with identical alkyl groups, the prefixes di- and tri- are used respectively. For unsymmetrical amines containing different alkyl groups, each substituent is identified and listed in alphabetical order.
Q3: What is the IUPAC naming convention for secondary and tertiary amines?
In IUPAC nomenclature, secondary and tertiary amines are named N-alkylalkanamines. The longest carbon chain becomes the parent, other alkyl groups are substituents, and the parent chain is numbered to give the lowest number to the carbon bearing nitrogen. The letter N designates alkyl groups attached to nitrogen.
Q4: How do you assign an IUPAC name to a secondary or tertiary amine structure?
First, identify all alkyl groups attached to nitrogen. Select the longest carbon chain as the parent structure. Number the parent chain to assign the lowest number to the carbon bearing nitrogen. Assign locants to each substituent, using N as the locant for nitrogen-attached groups. Finally, assemble the name and specify any chiral center configuration at the beginning.
Q5: What role does the letter N play in IUPAC amine nomenclature?
The letter N serves as a locant in IUPAC nomenclature to indicate that alkyl groups are attached directly to the nitrogen atom rather than to the carbon chain. This distinguishes N-substituted amines from carbon-chain-substituted compounds and clarifies the structure's connectivity.
Q6: How are quaternary ammonium ions named in IUPAC nomenclature?
Quaternary ammonium ions are named similarly to secondary and tertiary amines, but the suffix -amine is replaced with -ammonium, followed by the name of the counterion. This nomenclature reflects the positive charge on the nitrogen atom and identifies the associated anion.
Q7: Why is numbering the parent chain important when naming secondary and tertiary amines?
Numbering the parent chain to assign the lowest number to the carbon bearing nitrogen ensures a standardized, unambiguous IUPAC name. This convention prioritizes the amine functional group's position, allowing chemists to quickly identify the structure and communicate compound identity accurately.