Question 15 of 39intermediate🔧 ApplyShort Answer2 marks

Give the structures and IUPAC names of monohydric phenols of molecular formula, C₇H₈O.

Correct Answer

The molecular formula C₇H₈O corresponds to methylphenols (cresols), which are monohydric phenols derived from phenol by replacing one hydrogen atom of the benzene ring with a methyl group (—CH₃).

There are three isomers possible based on the position of the methyl group relative to the —OH group:

1. Ortho-isomer (o-Cresol)

  • IUPAC Name: 2-Methylphenol
  • Structure: Benzene ring with —OH at position 1 and —CH₃ at position 2.

2. Meta-isomer (m-Cresol)

  • IUPAC Name: 3-Methylphenol
  • Structure: Benzene ring with —OH at position 1 and —CH₃ at position 3.

3. Para-isomer (p-Cresol)

  • IUPAC Name: 4-Methylphenol
  • Structure: Benzene ring with —OH at position 1 and —CH₃ at position 4.
Exercise: EXERCISES | Q: 7.7 | (Page Page 30)
For More Understanding

Explanation

The question asks for monohydric phenols with formula C₇H₈O. Monohydric means one —OH group attached to the benzene ring. The formula indicates a phenol (C₆H₅OH) with one additional methyl group (CH₃), giving methylphenols commonly known as cresols. The textbook context explicitly lists all three isomers: o-Cresol (2-Methylphenol), m-Cresol (3-Methylphenol), and p-Cresol (4-Methylphenol). The ortho, meta, and para positions correspond to 1,2-; 1,3-; and 1,4-disubstituted benzene respectively.

Solution Steps

  1. Step 1: Identify that C₇H₈O represents a phenol with one methyl substituent (methylphenol/cresol).

  2. Step 2: Determine the three possible positional isomers based on ortho (1,2), meta (1,3), and para (1,4) arrangements.

  3. Step 3: Write the IUPAC names: 2-Methylphenol, 3-Methylphenol, and 4-Methylphenol.

  4. Step 4: Draw structures showing —OH at position 1 and —CH₃ at positions 2, 3, and 4 respectively.

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