Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Heteroatomic Functional Groups and Organic Nomenclature
3.10 Structure and Properties of Acid Chlorides

Compounds that have the ─COCl functionality are commonly called acid chlorides or acyl chlorides. They are very reactive compounds and are used primarily for the synthesis of other compounds. The reactivity of acid chlorides is due primarily to the presence of the very electronegative chlorine, which is bonded to a carbon atom of the carbonyl group, which produces a very polarized functional group. Acid chlorides are highly reactive with water, and if inhaled causes severe medical problems owing to a reaction with moisture of the respiratory track.

3.10.1 Nomenclature of Acid Chlorides

Acyl chlorides are named based on the longest continuous chain that has the acid chloride functionality, these compound are named as alkanoyl chlorides in the IUPAC system. Note that the e of the corresponding alkane is changed to oyl and the word chloride is added. The IUPAC nomenclature is based on the longest chain that contains this functional group, which is changed from the alkane to alkanoyl chloride. The acid chloride functional group, along with the nomenclature of selected examples, is shown below.

In naming acid chlorides, identify the longest chain that contains the acid chloride functional group, the carbonyl carbon is assigned #1.

The correct root name for the molecule above is pentanoyl chloride (and not butanoyl chloride). If that longest chain has groups (substituents) attached, the position of each substituent must be specified based on the numbering of the longest continuous chain. More examples of nomenclature are shown below.

Since the alkanoyl chloride is a terminal functionality, it is not necessary to indicate its position by the #1.

3.10.2 Nomenclature of Difunctional Acid Chlorides

It is possible to have the ─COCl functionality present in a molecule that has another functionality, such as an OH, alkene, or alkyne. For these molecules, the alkanoyl chloride functionality will always get priority and the carbonyl carbon is assigned #1. The position of the other functionality is specified based on the numbering system dictated by the location of the alkanoyl chloride functionality. An example of the nomenclature of an acid chloride, which also contains an alkene functionality is shown below.

Problem 3.18

i. Give IUPAC names for the compounds shown below.

ii. Give line-angle structure for the following molecules.

1. 2-Pentenoyl chloride

2. 3-Methyl-4-nitrohexanoyl chloride

3. 3-Chloro-3-butenoyl chloride

4. 4-Methyl-2-pentynoyl chloride