Q.Match the structures of the compounds given in Column I with the names of the compounds given in Column II. (In the Exemplar the Column I entries are drawn structures; their carriable names are given inline below.)
Column I:

The key idea is that common names (like cresol, anisole) correspond to specific IUPAC systematic names based on the substitution pattern on the benzene ring.

Step 1 – Identify the functional group and substituents for each common name.

• o-cresol = 2-methylphenol (methyl at ortho position to –OH).
• catechol = 1,2-dihydroxybenzene (two –OH groups adjacent).
• resorcinol = 1,3-dihydroxybenzene (two –OH groups meta).
• hydroquinone = 1,4-dihydroxybenzene (two –OH groups para).
• anisole = methoxybenzene (–OCH₃).
• phenetole = ethoxybenzene (–OC₂H₅).

Step 2 – Match each Column I entry to its correct IUPAC name in Column II.

(i) o-cresol → (d) 2-methylphenol …

The question tests your ability to translate between the traditional common names still used in organic chemistry and the systematic IUPAC nomenclature. Each compound in Column I is a well-known aromatic derivative. Let's go through them one by one.

1. o-cresol

The prefix o- (ortho) means the two substituents are adjacent on the benzene ring. Cresol is the common name for methylphenol. So o-cresol is 2-methylphenol — a methyl group at position 1 and a hydroxyl group at position 2 (or vice versa; the hydroxyl gets priority in numbering). This matches option (d).

2. catechol

Catechol is the traditional name for benzene-1,2-diol — two hydroxyl groups on adjacent carbons. The IUPAC name is 1,2-dihydroxybenzene. That's option (c).

3. resorcinol

Resorcinol is benzene-1,3-diol — hydroxyl groups at positions 1 and 3. The systematic name is 1,3-dihydroxybenzene, which is option (f).

4. hydroquinone

Hydroquinone is benzene-1,4-diol — hydroxyl groups opposite each other. The IUPAC name is 1,4-dihydroxybenzene, option (a).

5. anisole

Anisole is the common name for methoxybenzene — a benzene ring with a methoxy ($-OCH_3$) substituent. That's option (e).

6. phenetole

Phenetole is the common name for ethoxybenzene — a benzene ring with an ethoxy ($-OC_2H_5$) group. That's option (b). …

Method: IUPAC Name-to-Structure Matching by Functional Group & Substituent Position

This method uses the IUPAC systematic name to identify the parent ring, functional groups, and substituent positions, then matches it to the common name.

Steps

1. Identify the parent ring

   All compounds in Column II contain a benzene ring (phenol derivatives or ethers).

2. Locate the principal functional group

   • -ol → phenol (hydroxy group, –OH)
   • -oxybenzene → ether (alkoxy group, –OR)

3. Count and number substituent positions

   • For dihydroxybenzenes: numbers indicate –OH positions (1,2-; 1,3-; 1,4-).
   • For methylphenol: methyl is at position 2 (ortho).
   • For alkoxybenzenes: ethoxy = –OCH₂CH₃, methoxy = –OCH₃.

4. Match to common names

   Use the standard common names for these well-known compounds.

Matching Table

Here are the most common mistakes students make when matching these structures with their IUPAC names, along with how to avoid each.

Mistake 1: Confusing the Positions of the Hydroxyl Groups

This is the most frequent error. Students mix up the three dihydroxybenzene isomers: catechol (1,2-), resorcinol (1,3-), and hydroquinone (1,4-).

• The Mistake: Matching catechol with 1,3-dihydroxybenzene or resorcinol with 1,4-dihydroxybenzene.
• How to Avoid:
  • Visualize the "Ortho, Meta, Para" rule. The common names directly hint at the relative positions.
    • Catechol = ortho (1,2-). Think "C" for "Close" or "C" for "ortho" (the first vowel is 'o').
    • Resorcinol = meta (1,3-). Think "R" for "Remote" or "R" for "meta" (the vowel is 'e').
    • Hydroquinone = para (1,4-). Think "H" for "Hydrogen" or "H" for "para" (the vowel is 'a').
  • Draw it out. If you are unsure, quickly sketch the benzene ring and place the two -OH groups at the 1,2-, 1,3-, and 1,4- positions. The pattern is:
    • 1,2- → Catechol
    • 1,3- → Resorcinol
    • 1,4- → Hydroquinone

Mistake 2: Misidentifying the Parent Chain in Cresol

Students often forget that the methyl group is the substituent on the phenol ring, not the other way around.

• The Mistake: Matching o-cresol with 1-methyl-2-hydroxybenzene or similar, instead of 2-methylphenol.
• How to Avoid:
  • Remember the priority rule: The -OH group (phenol) is the parent functional group. The methyl group is a substituent.
  • The name "cresol" implies a methylphenol. The "o-" (ortho) tells you the methyl is at the 2-position relative to the -OH.
  • Correct IUPAC name: 2-methylphenol (not 1-hydroxy-2-methylbenzene, though that is also acceptable, the standard is to name it as a substituted phenol).

Mistake 3: Confusing Anisole and Phenetole

These are both ethers, but students mix up the alkyl group attached to the oxygen.

• The Mistake: Matching anisole with ethoxybenzene or phenetole with methoxybenzene.
• How to Avoid:
  • Focus on the alkyl group's name.
    • Anisole = Methyl phenyl ether. The IUPAC name is methoxybenzene.
    • Phenetole = Ethyl phenyl ether. The IUPAC name is ethoxybenzene.
  • Mnemonic: "Anisole" sounds like "An-isole" → "An-is" → "An-is" → "M-ethyl"? No. Better: "Anisole" has an 'A' for "Alkyl" but the alkyl is methyl. "Phenetole" has an 'E' for "Ethyl". Think: Anisole = Methyl; Phenetole = Ethyl.

Mistake 4: Forgetting the "1-methoxy-4-methylbenzene" Distractor

This is a trick. It looks like anisole but has an extra methyl group.

• The Mistake: Matching anisole with 1-methoxy-4-methylbenzene.
• How to Avoid:
  • Read the name carefully. "1-methoxy-4-methylbenzene" has two substituents: a methoxy group and a methyl group. Anisole (methoxybenzene) has only one substituent (the methoxy group). …