What is the reason for the boiling point of benzene-1,4-diol being higher than that of benzene-1,3-diol?
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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Can you take a guess? Have you not been provided with other examples? https://chemistry.stackexchange.com/help/how-to-ask – Buck Thorn Aug 07 '21 at 10:41
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see https://chemistry.stackexchange.com/questions/112078/what-effect-on-boiling-and-melting-points-does-intramolecular-hydrogen-bonding-h – Lalit Aug 07 '21 at 13:43
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1@Lllt: Not related question. None of these two can make intramolecular hydrogen bonding. – Mathew Mahindaratne Aug 07 '21 at 17:26
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@MathewMahindaratne I think benzene 1,3 diol can do so – Lalit Aug 07 '21 at 17:28
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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. – napstablook Aug 09 '21 at 04:40
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@napstablook By symmetry, I meant its packing and all in liquid state – Robin Singh Aug 09 '21 at 12:05
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@RobinSingh packing in liquid state? – napstablook Aug 10 '21 at 05:01
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@napstablook I'm sorry I don't have a way with words. I mean the ease with which they can form h bonds – Robin Singh Aug 10 '21 at 11:30
1 Answers
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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.
Aathesh Vigram
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