Chapter F, Problem F.1P

Interpretation Introduction

Interpretation:

The IUPAC name of $\text{L-asparagine}$ is to be written.

Concept introduction:

The IUPAC name of a compound is made up of three parts: prefix, root, and suffix. If the compound contains different functional groups, the highest priority group is determined. This determines the suffix. The longest continuous chain of carbons that contains the highest priority group forms the root. The final ‘e’ in the name of the corresponding alkane is replaced by the suffix corresponding to the highest priority group, except in the case of nitriles, when the suffix ‘nitrile’ is simply added to the root name. The position (locant) of the highest priority group on the longest chain is inserted between the root name and the suffix unless redundant. The longest carbon chain is numbered in the direction that gives the highest priority group the lowest possible locant. If the root is a ring, the position of the highest priority group is always 1. For any other, low priority groups are treated as substituents and listed alphabetically in the prefix along with their locants. In the case of rings, the numbering of ring carbons is done in the direction that gives the substituents lowest possible locants. If more than one instance of any functional group (including highest priority) is present, their numbers are specified by adding a di, tri, etc. to the respective functional group name.

If any chiral carbons are present, their absolute configurations are determined on the basis of Cahn-Ingold-Prelog rules and listed at the start along with the carbon number.

Answer to Problem F.1P

The IUPAC name of $\text{L-asparagine}$ is $\text{(2S)-2-amino-3-carbamoylpropanoic acid}$.

Explanation of Solution

The structure of $\text{L-asparagine}$ is

The highest priority function group in $\text{L- asparagine }$ is carboxylic acid, $-{\text{CO}}_{\text{2}}\text{H}$_. Thus the suffix of the root is oic acid and numbering starts from the carbon of the $-{\text{CO}}_{\text{2}}\text{H}$ group. The longest carbon chain that includes this group is three carbon long, therefore, the root is propane.

There are two other functional groups, amine ($-{\text{NH}}_2$) and amide ($-{\text{CONH}}_{\text{2}}$). These are listed as prefixes, amino, and carbamoyl respectively. As carbamoyl is a substituent, the carbon atom in it is not treated as part of the root.

The root carbons are numbered from the carboxylic acid carbon as shown below.

This puts the amino group on C2 and the carbamoyl on C3. The carbon to which the amine group is attached is a chiral carbon. Based on the Cahn-Ingold-Prelog rules, the absolute configuration at this carbon is S.

Apparently, the three highest priority groups are arranged clockwise, but with the lowest priority hydrogen pointing toward the observer. Therefore, the actual configuration is S.

Therefore, the complete IUPAC name of $\text{L-asparagine}$ is $\text{(2S)-2-amino-3-carbamoylpropanoic acid}$

Conclusion

The highest priority functional group is considered as suffix, and the other remaining groups are considered as substituents for writing IUPAC name of the molecule.