Carboxylic Acids: Structures and Names (2024)

Learning Objectives

1. Name carboxylic acids with common names.
2. Name carboxylic acids according to IUPAC nomenclature.

Note

Pure acetic acid solidifies at 16.6°C, only slightly below normal room temperature. In the poorly heated laboratories of the late 19th and early 20th centuries in northern North America and Europe, acetic acid often “froze” on the storage shelf. For that reason, pure acetic acid (sometimes called concentrated acetic acid) came to be known as glacial acetic acid, a name that survives to this day.

Figure 15.2 Ball-and-Stick Models of Carboxylic Acids

Carboxylic acids feature a carbon atom doubly bonded to an oxygen atom and also joined to an OH group. The four acids illustrated here are formic acid (a), acetic acid (b), propionic acid (c), and butyric acid (d).

Note

Greek letters are used with common names; numbers are used with IUPAC names.

Example 1

Give the common and IUPAC names for each compound.

1. ClCH₂CH₂CH₂COOH

2. 

Solution

1. The LCC contains four carbon atoms; the compound is therefore named as a substituted butyric (or butanoic) acid.

   

   The chlorine atom is attached to the γ-carbon in the common system or C4 in the IUPAC system. The compound is γ-chlorobutyric acid or 2-bromobutanoic acid.

2. The LCC contains four carbon atoms; the compound is therefore named as a substituted butyric (or butanoic) acid.

The bromine (Br) atom is at the α-carbon in the common system or C2 in the IUPAC system. The compound is α-bromobutyric acid or 4-chlorobutanoic acid.

Skill-Building Exercise

Give the IUPAC name for each compound.

1. ClCH₂CH₂CH₂CH₂COOH

2. (CH₃)₂CHCH₂CHBrCOOH

Example 2

Write the condensed structural formula for β-chloropropionic acid.

Solution

Propionic acid has three carbon atoms: C–C–COOH. Attach a chlorine (Cl) atom to the parent chain at the beta carbon atom, the second one from the carboxyl group: Cl–C–C–COOH. Then add enough hydrogen atoms to give each carbon atom four bonds: ClCH₂CH₂COOH.

Skill-Building Exercise

1. Write the condensed structural formula for 4-bromo-5-methylhexanoic acid.

Concept Review Exercises

1. What is the IUPAC name for the straight-chain carboxylic acid with six carbon atoms?

2. The straight-chain aldehyde with five carbon atoms has the common name valeraldehyde. What is the common name of the corresponding straight-chain carboxylic acid?

Answers

1. hexanoic acid

2. valeric acid

Key Takeaways

• Simple carboxylic acids are best known by common names based on Latin and Greek words that describe their source (e.g., formic acid, Latin formica, meaning “ant”).
• Greek letters, not numbers, designate the position of substituted acids in the common naming convention.
• IUPAC names are derived from the LCC of the parent hydrocarbon with the -e ending of the parent alkane replaced by the suffix -oic and the word acid.

Exercises

1. Draw the structure for each compound.

   1. heptanoic acid
   2. 3-methylbutanoic acid
   3. 2,3-dibromobenzoic acid
   4. β-hydroxybutyric acid

2. Draw the structure for each compound.

   1. o-nitrobenzoic acid
   2. p-chlorobenzoic acid
   3. 3-chloropentanoic acid
   4. α-chloropropionic acid

3. Name each compound with either the IUPAC name, the common name, or both.

   1. (CH₃)₂CHCH₂COOH
   2. (CH₃)₃CCH(CH₃)CH₂COOH
   3. CH₂OHCH₂CH₂COOH

4. Name each compound with its IUPAC name.

   1. CH₃(CH₂)₈COOH
   2. (CH₃)₂CHCCl₂CH₂CH₂COOH
   3. CH₃CHOHCH(CH₂CH₃)CHICOOH

Answers

1. 1. CH₃CH₂CH₂CH₂CH₂CH₂COOH

   2. 

   3. 

   4. 

3. 1. 3-methylbutanoic acid; β-methylbutyric acid
   2. 3,4,4-trimethylpentanoic acid
   3. 4-hydroxybutanoic acid; γ- hydroxybutyric acid