Introduction to Carboxylic Acids – Structure, Nomenclature & Properties

Table of Contents

• General Formula & Structure
• Nomenclature
• Sources of Carboxylic Acids
• Physical Properties
• Chemical Characteristics
• FAQs
• Quiz

Carboxylic acids are an important class of organic compounds, identified by the presence of a carboxyl group (–COOH). This consists of a carbonyl group (C=O) bonded to a hydroxyl group (–OH), making them acidic in nature.

General Formula and Structure

The general formula is R–COOH, where R = alkyl/aryl group.

The carboxyl group is planar and stabilized by resonance between carbonyl and hydroxyl groups.

Nomenclature

• IUPAC: Replace alkane -e with -oic acid. Example: methane → methanoic acid.
• Common: Historical names such as formic acid (HCOOH), acetic acid (CH₃COOH).

Formula	Common Name	IUPAC Name
HCOOH	Formic acid	Methanoic acid
CH3COOH	Acetic acid	Ethanoic acid
CH3CH2COOH	Propionic acid	Propanoic acid

Sources of Carboxylic Acids

• Formic acid → ant/bee stings
• Acetic acid → vinegar
• Citric acid → citrus fruits
• Fatty acids (oleic acid) → oils & fats

Physical Properties

• Low carboxylic acids = liquids with pungent odor.
• Polar, hydrogen bonding → high boiling points.
• Highly soluble (small acids), solubility decreases with chain length.

Chemical Characteristics

Carboxylic acids are weak acids but stronger than alcohols/phenols. Reactions include:

• Formation of salts with bases
• Esterification with alcohols
• Reduction to alcohols
• Decarboxylation

FAQs

Q1: Why are carboxylic acids acidic?

Because the –COOH group can donate a proton (H⁺) and the conjugate base is resonance-stabilized.

Q2: Which is stronger – acetic acid or ethanol?

Acetic acid, because its conjugate base (acetate ion) is stabilized by resonance.

Q3: What is the pKa range of carboxylic acids?

Typically between 4 and 5, making them weak acids but stronger than alcohols and phenols.

Quick Quiz

MCQ

1. Which of the following is the IUPAC name of acetic acid?

• A) Methanoic acid
• B) Propanoic acid
• C) Ethanoic acid ✅
• D) Butanoic acid

Fill in the Blanks

2. The general formula of carboxylic acids is ______.

Answer: R–COOH

3. Formic acid is found in ______ stings.

Answer: Ant and bee

Conclusion: Carboxylic acids are biologically and industrially vital compounds, showing versatile reactivity due to their –COOH group.