Question 22 of 26intermediate💡 UnderstandShort Answer2 marks

p-Dichlorobenzene has higher m.p. than those of o- and m-isomers. Discuss.

Correct Answer

The boiling points of isomeric dihalobenzenes are very nearly the same. However, the para-isomers are high melting as compared to their ortho- and meta-isomers. This distinction in melting points is a significant physical property difference among these isomers.

This phenomenon occurs due to the symmetry of the para-isomers. Because of this structural symmetry, the para-isomers fit in the crystal lattice better as compared to ortho- and meta-isomers. The better packing efficiency in the crystal lattice requires more energy to overcome, resulting in a higher melting point for p-Dichlorobenzene.

Exercise: EXERCISES | Q: 6.18 | (Page 32)
For More Understanding

Explanation

The answer is derived directly from the provided textbook context which states that while boiling points of isomeric dihalobenzenes are similar, the para-isomers have higher melting points. The text explicitly attributes this to the 'symmetry of para-isomers that fits in crystal lattice better as compared to ortho- and meta-isomers'. This fits into the crystal lattice better, leading to higher melting points.

Solution Steps

  1. Step 1: State that boiling points of isomeric dihalobenzenes are nearly the same, but para-isomers have higher melting points than ortho- and meta-isomers.

  2. Step 2: Explain that this difference is due to the symmetry of the para-isomers.

  3. Step 3: Conclude that the symmetry allows para-isomers to fit better in the crystal lattice, resulting in a higher melting point.

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