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What is the reason for the boiling point of benzene-1,4-diol being higher than that of benzene-1,3-diol?

Resorcinol

Quinol

Both have hydrogen bonds. I think it is due to quinol's symmetry but can't point out exactly why this is the case.

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  • $\begingroup$ Can you take a guess? Have you not been provided with other examples? chemistry.stackexchange.com/help/how-to-ask $\endgroup$
    – Buck Thorn
    Aug 7, 2021 at 10:41
  • $\begingroup$ see chemistry.stackexchange.com/questions/112078/… $\endgroup$
    – Lalit
    Aug 7, 2021 at 13:43
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    $\begingroup$ @Lllt: Not related question. None of these two can make intramolecular hydrogen bonding. $\endgroup$ Aug 7, 2021 at 17:26
  • $\begingroup$ @MathewMahindaratne I think benzene 1,3 diol can do so $\endgroup$
    – Lalit
    Aug 7, 2021 at 17:28
  • $\begingroup$ symmetry makes it have a lot less dipole moment than resorcinol. I think this has to do with larger surface area of quinol leading to higher Vander Waal forces. $\endgroup$ Aug 9, 2021 at 4:40

1 Answer 1

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Benzene-1,4-diol has a boiling point of 287°C and Benzene-1,3-diol has a boiling point of 277°C and Benzene-1,2-diol has a boiling point of 245.5°C. This could be attributed to the ease of formation of 2 intermolecular hydrogen bonds with the 2 hydroxy groups of these molecules increasing when the hydroxy groups are placed apart, to minimise steric hindrance and repulsion. Benzene-1,4-diol could form intermolecular hydrogen bonds with more stability than Benzene-1,3-diol or Benzene-1,2-diol as these two will get destabilised by steric repulsion when large groups have to reach nearer to form hydrogen bonds.

Thus, the extent of intermolecular hydrogen bonding in : Benzene-1,4-diol > Benzene-1,3-diol > Benzene-1,2-diol

To overcome this attraction, more energy is needed. Hence the same is the order of their Boiling Points.

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  • $\begingroup$ Is that good enough of a reason for a 10°C rise? $\endgroup$ Aug 10, 2021 at 11:27

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