Q.Match the acids given in Column I with their correct IUPAC names given in Column II.
Column I:

Concept: IUPAC Nomenclature of dicarboxylic acids — the parent chain is the longest carbon chain containing both carboxyl groups, numbered from one carboxyl carbon to the other.

Reasoning:

1. Phthalic acid has a benzene ring with two carboxyl groups at positions 1 and 2 → Benzene-1,2-dicarboxylic acid.
2. Oxalic acid has two carboxyl groups directly bonded (2 carbons total) → Ethane-1,2-dioic acid. …

Why IUPAC Nomenclature for Dicarboxylic Acids Works This Way

The IUPAC system names a dicarboxylic acid by identifying the longest continuous carbon chain that contains both carboxyl ($-\text{COOH}$) groups. The suffix "-dioic acid" replaces the "-e" of the parent alkane name. The two carboxyl carbons are always carbon 1 and the last carbon of the chain — so numbering is fixed, and locants (1,6- etc.) are mandatory to show the positions.

The common names you see in Column I are historical: they come from the source where each acid was first isolated (oxalic from wood sorrel, succinic from amber, etc.). But the IUPAC name tells you exactly how many carbons are in the backbone.

Step-by-Step Matching

1. Phthalic acid (i)

Phthalic acid has two carboxyl groups attached to a benzene ring at positions 1 and 2. The parent structure is benzene, and the functional groups are named as substituents. The IUPAC name is benzene-1,2-dicarboxylic acid. This matches Column II entry (b).

2. Oxalic acid (ii)

Oxalic acid is the simplest dicarboxylic acid: two carboxyl groups directly bonded to each other. The parent chain has only 2 carbon atoms (the two carboxyl carbons). The IUPAC name is ethane-1,2-dioic acid. This matches Column II entry (e).

3. Succinic acid (iii)

Succinic acid has a four-carbon chain with a carboxyl group at each end. The parent alkane is butane (4 carbons). The IUPAC name is butane-1,4-dioic acid. This matches Column II entry (d).

4. Adipic acid (iv) …

Concept: IUPAC Nomenclature of Dicarboxylic Acids

The systematic name for a dicarboxylic acid follows the pattern:

alkane chain length – positions of –COOH groups – dioic acid

The carbon atoms of both carboxyl groups are included in the parent chain.

Method: Chain-Length Matching Method

Steps

1. Identify the carbon skeleton of each common acid (excluding the –COOH carbons, then add them back).

2. Count total carbons in the parent chain (including both carboxyl carbons).

3. Write the IUPAC name as:

   alkane (with that total carbon count) – positions of –COOH groups – dioic acid

4. Match with Column II.

Applying the method

Here are the most common mistakes students make when matching these dicarboxylic acids with their IUPAC names, along with the reasoning to avoid them.

Mistake 1: Confusing the Common Name with the Carbon Chain Length

The Mistake:

Students often misjudge the number of carbon atoms in the parent chain. For example, they might think "Succinic acid" has 3 carbons (because it sounds like "succinct") or "Glutaric acid" has 4 carbons (because it sounds like "gluten" or "glutamate" which has 4 carbons in its backbone).

Why it happens:

The common names (phthalic, oxalic, succinic, etc.) are historical and don't directly tell you the carbon count. Relying on sound-alike words or memorization without understanding the structure leads to errors.

How to Avoid:

Memorize the carbon skeleton for each common name. The easiest way is to learn the systematic pattern:

• Oxalic → 2 carbons (Ox- = sharp, like oxalic acid is the simplest)
• Malonic → 3 carbons (not in this list, but good to know)
• Succinic → 4 carbons (Succ- = juice of amber, 4 carbons)
• Glutaric → 5 carbons (Glut- = related to glutamic acid, 5 carbons)
• Adipic → 6 carbons (Adip- = fat, 6 carbons)

Quick Trick: Write the common name and immediately write the number of carbons next to it:

• Oxalic → 2
• Succinic → 4
• Glutaric → 5
• Adipic → 6

Mistake 2: Forgetting that the Carboxyl Groups Count as Carbons

The Mistake:

When counting the carbon chain for the IUPAC name (e.g., "Hexane-1,6-dioic acid"), students sometimes count only the carbons between the two -COOH groups, forgetting that the carboxyl carbon itself is part of the chain.

Example of the error:

For Adipic acid, a student might think the chain between the two -COOH groups has 4 carbons (HOOC-CH₂-CH₂-CH₂-CH₂-COOH) and incorrectly match it with "Butane-1,4-dioic acid" (which has 4 carbons total). But the correct chain includes both carboxyl carbons, giving 6 carbons total → Hexane-1,6-dioic acid.

How to Avoid:

Always draw the full structure or count the total carbons in the parent chain including the -COOH groups.

• For a dicarboxylic acid, the IUPAC name tells you the total number of carbons in the longest continuous chain that includes both carboxyl groups.
• Formula: Total carbons = carbons between the two -COOH groups + 2 (the two carboxyl carbons).

Example:

• Oxalic acid: HOOC-COOH → 2 carbons total → Ethane-1,2-dioic acid (not "Methane").
• Succinic acid: HOOC-CH₂-CH₂-COOH → 4 carbons total → Butane-1,4-dioic acid.

Mistake 3: Mixing Up the Position of the Carboxyl Groups (1,2 vs 1,4 etc.)

The Mistake:

Students correctly identify the carbon count but then match the wrong positional isomer. For example, they might match Phthalic acid (benzene ring with two -COOH groups) with "Benzene-1,4-dicarboxylic acid" (which is terephthalic acid) instead of the correct Benzene-1,2-dicarboxylic acid.

Why it happens:

They remember "phthalic" is related to benzene but forget the specific position (ortho, meta, para).

How to Avoid:

Learn the positional relationship for common aromatic dicarboxylic acids:

• Phthalic acid → 1,2 (ortho) → Benzene-1,2-dicarboxylic acid
• Isophthalic acid → 1,3 (meta) → Benzene-1,3-dicarboxylic acid …