Carboxylic Acids - Structure and Nomenclature

In this article we will discuss about Structure and Nomenclature of Carboxylic acids in organic chemistry. The carboxylic acids have general formula R-COOH.  

Carboxylic acids are the organic compounds which consist of an alkyl / aryl group and one hydroxyl group bonded to a carbonyl group. IUPAC nomenclature of carboxylic acids is described herein.

Key words: Carboxylic acid, Common Names, IUPAC Nomenclature, Functional group.

Table of Contents

1. Introduction
2. Common Names of Carboxylic acids
3. IUPAC Nomenclature
4. Conclusion

1. Introduction

The carboxylic acids have general formula R-COOH; where R = alkyl / aryl group. The COOH group also known as carboxyl group.

Carboxylic Acid

2. Common Names of Carboxylic Acids

Many carboxylic acids are recognized by their common names. In general the common names of the carboxylic acids are given from the source from which they are found. Common names of few carboxylic acids are shown in Table 1.

Carboxylic acid	Source	Structure
Formic acid	Ant (Latin “formica”)
Acetic acid	Vinegar (Latin “Acetum”)
Propionic acid	Milk (Greek, protos = "first" and pion ="fat")
Butyric acid	Butter (Latin, “butyrum”)
Valeric acid	Minor constituent of flowering plant valerian
Caproic acid	Goat (Latin "caper / capra" )
Enanthic acid	Vines (Greek, “Oenanthe”)
Caprylic acid	Goat (Latin "caper / capra" )
Pelargonic acid	Oil of pelargonium. (genus of flowering plants)
Capric acid	Goat (Latin "caper / capra" )

Table : 1

Let’s see some examples:

	The carbon chain has 3 carbons, so it is propionic acid. Bromide is bonded to a carbon. Therefore name of the compound is a-bromopropionic acid.
	The carbon chain has 4 carbons, so it is butyric acid. Hydroxyl group is bonded to b carbon. Therefore name of the compound is b-hydroxybutyric acid.
	The carbon chain has 4 carbons, so it is butyric acid. Chloride is bonded to g carbon. Therefore name of the compound is g-chlorobutyric acid.
	The carbon chain has 5 carbons, so it is valeric acid. Hydroxyl group is bonded to d carbon. Therefore name of the compound is d-hydroxyvaleric acid.

3. IUPAC Nomenclature

To assign IUPAC name of the carboxylic acid; longest carbon chain is selected. From the number of carbon atoms in chain name of the parent alkane is chosen. Then –e ending of the parent alkane is replaced by oic acid. Here the carbonyl carbon is given number 1 and it is not included in the name of the compound. IUPAC names of some carboxylic acids are given in the Table 2. 

Structure	No. of carbons in chain; parent alkane	IUPAC name
	1; methane	Methanoic acid
	2; ethane	Ethanoic acid
	3; propane	Propanoic acid
	4; butane	Butanoic acid
	5; pentane	Pentanoic acid
	6; hexane	Hexanoic acid
	7; heptane	Heptanoic acid
	8; octane	Octanoic acid
	9; nonane	Nonanoic acid
	10; decane	Decanoic acid

Table :2

In IUPAC names of carboxylic acids; the carbons starting from carbonyl group are designated by numbers. The substituents are written in alphabetical order along with carbon numbers.

Let’s see some examples:

	The carbon chain has 3 carbons, so it is propanoic acid. Bromide is bonded to carbon 2. Therefore name of the compound is 2-bromopropanoic acid.
	The carbon chain has 4 carbons, so it is butanoic acid. Hydroxyl group is bonded to carbon 3. Therefore name of the compound is 3-hydroxybutanoic acid.
	The carbon chain has 4 carbons, so it is butanoic acid. Chloride is bonded to carbon 4. Therefore name of the compound is 4-chlorobutanoic acid.
	The carbon chain has 5 carbons, so it is pentanoic acid. Hydroxyl group is bonded to carbon 5. Therefore name of the compound is 5-hydroxypentanoic acid.

The carboxylic acid can also be bonded to cyclic ring. To assign IUPAC name of the carboxylic acid; the suffix –carboxylic acid is added to the name of cyclic compound. Names of some cyclic carboxylic acids are given in the Table 3.

Carboxylic acid	Common name	IUPAC Name
	cyclopropylcarboxylic acid	cyclopropanecarboxylic acid
	cyclopentylcarboxylic acid	cyclopentanecarboxylic acid
	Cyclohexylcarboxylic acid	Cyclohexanecarboxylic acid
	benzoic acid	Benzenecarboxylic acid
	Salicylic acid	2-hydroxybenzenecarboxylic acid OR 2-hydroxybenzoic acid (preferred)
	Gallic acid	3,4,5-trihydroxybenzenecarboxylic acid OR 3,4,5-trihydroxybenzoic acid (preferred)
	o-toluic acid	2-methylbenzenecarboxylic acid OR 2-methylbenzoic acid (preferred)
	Pthalic acid	Benzene-1,2-dicarboxylic acid

Table :3

Examples for practice: write the IUPAC names of following compounds.

4. Conclusion

To summarize this article, carboxylic acids are the organic compounds which consists of COOH functional group. We discussed common names and IUPAC names of carboxylic acids. In general the common names of the carboxylic acids are given from the source from which they are found. IUPAC names of carboxylic acids are given by the parent alkane followed by the suffix "oic acid". And if any substituent present in the molecule, then they are denoted by the carbon number and arranged in alphabetical order.

That's all for this topic. If you have any questions please feel free to ask me in the comment box. Thank you..!