The Student Room Group

why are phenols less soluble in water than other alcohols

My book just says it's because of the 'presence of the benzene ring'. But how does this make it less soluble?
Reply 1
It's because the oxygen s electrons in the p orbital delocalise into the ring, this reduces the phenols ability to make hydrogen bonds, which is what solubility in water is about
the oxygen uses lone pairs to make h bonds
Reply 2
It's the same reason why aromatic amines are not as basic as the aliphatic ones,
hope I helped:smile:
Reply 3
Original post by Patel3000
It's because the oxygen s electrons in the p orbital delocalise into the ring, this reduces the phenols ability to make hydrogen bonds, which is what solubility in water is about
the oxygen uses lone pairs to make h bonds


Oh right, I was only thinking about the hydrogen in the OH group in phenol :tongue: Correct me if I'm wrong, but from your post are you saying that the oxygen in phenol can not hydrogen bond with water as well. What about the hydrogen, they're not affected right and can still bond with water, right?
Reply 4
The phenyl ring is also much more hydrophobic than say, an ethyl chain.
Reply 5
Original post by illusionz
The phenyl ring is also much more hydrophobic than say, an ethyl chain.


Oh right, so does the same concept apply to carboxylic acids i.e. the longer the chain the lower the solubility due to an increase in the length of the hydrophobic region of the acid?
Original post by tammie94
Oh right, so does the same concept apply to carboxylic acids i.e. the longer the chain the lower the solubility due to an increase in the length of the hydrophobic region of the acid?


yes.

Methanol, ethanol & propan-1-ol are miscible with water. The solubility in water then decreases as the homologous series increases in chain length ...
Reply 7
Original post by tammie94
Oh right, I was only thinking about the hydrogen in the OH group in phenol :tongue: Correct me if I'm wrong, but from your post are you saying that the oxygen in phenol can not hydrogen bond with water as well. What about the hydrogen, they're not affected right and can still bond with water, right?


Yes that's right the hydrogen can bond to water but so can a normal alcohol, phenol is partially soluble in water because of the electrons being delocalised...blah blah
Reply 8
Logically it sounds like a phenol should be highly soluble in water.

The benzene ring surely heavily deprives hydrogen atoms of electrons and makes them extremely susceptible to forming hydrogen bonds with oxygen in water.or does the high electron concentration to some extent repel the oxygen and either weaken its bonds with hydrogen or prevent the from happening.

Such a bizarre subject aha
Reply 9
Original post by tammie94
Oh right, I was only thinking about the hydrogen in the OH group in phenol :tongue: Correct me if I'm wrong, but from your post are you saying that the oxygen in phenol can not hydrogen bond with water as well. What about the hydrogen, they're not affected right and can still bond with water, right?

The oxygen is unable to for h- bonds with hydrogen atoms of water molecule due to delocalization of electrons and therefore phenol is only partially soluble cuz the hydrogen of oh group in phenol do form the h- bonds, plus the benzene ring is an hydrophobic group which further contributes towards lesser solubility
Reply 10
Original post by palashnick
The oxygen is unable to for h- bonds with hydrogen atoms of water molecule due to delocalization of electrons and therefore phenol is only partially soluble cuz the hydrogen of oh group in phenol do form the h- bonds, plus the benzene ring is an hydrophobic group which further contributes towards lesser solubility


So the benzene ring is non-polar?
Reply 11
Original post by Jam'
Logically it sounds like a phenol should be highly soluble in water.

The benzene ring surely heavily deprives hydrogen atoms of electrons and makes them extremely susceptible to forming hydrogen bonds with oxygen in water.or does the high electron concentration to some extent repel the oxygen and either weaken its bonds with hydrogen or prevent the from happening.

Such a bizarre subject aha


The delocalised ring consists of one electron from each carbon atom, but the carbon atoms have 4 electrons each, so the delocalised ring doesn't steal electrons from the C-H bond (if that's what you mean), the carbon-hydrogen bonds are unaffected by the delocalised ring. The benzene ring is non-polar as the overall dipoles cancel each other our. Non-polar parts of a compound can not form hydrogen bonds with polar water molecules. Hope this helps :smile: I was a little confused myself
Reply 12
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Original post by tammie94
So the benzene ring is non-polar?


Benzene is non-polar. Based on the STRUCTURE you have a very symmetrical compound of just carbon and hydrogen and any dipoles formed by the C-H are all counteracted by each other resulting in a net zero dipole. The main ring are all composed of bonds of the same element, Carbon which makes that bond virtually non-polar. Sure, there is a pi electron cloud which essentially hovers the entire ring and because of symmetry again, benzene is non-polar.

Based on its PHYSICAL Property - like solubility, it is soluble in other non-polar compounds LIKE hexane, etc and NOT soluble in a Polar solvent or substance like WATER.

I hope you are not confused now. So you see sometimes you can explain away based on just structure, sometimes thru its physical properties or chemical reactivities.
Reply 14
Original post by tammie94
The delocalised ring consists of one electron from each carbon atom, but the carbon atoms have 4 electrons each, so the delocalised ring doesn't steal electrons from the C-H bond (if that's what you mean), the carbon-hydrogen bonds are unaffected by the delocalised ring. The benzene ring is non-polar as the overall dipoles cancel each other our. Non-polar parts of a compound can not form hydrogen bonds with polar water molecules. Hope this helps :smile: I was a little confused myself


That's a really awesome reply thanks :smile: mega helpful
Reply 15
Original post by tammie94
So the benzene ring is non-polar?
the benzene ring is non polar as it consists of c-h bond which by assumption are non polar covalent bonds. Being a non polar it is not soluble in a polar solvent such as water. Remember the solubility of any organic compound is only determined by its functional group as hydrocarbons are insoluble in water. Plus the greater no. of carbon atoms in the substance the lesser chance of it being soluble in polar solvents. Its simple like dissolves like,
Reply 16
Original post by Jam'
That's a really awesome reply thanks :smile: mega helpful


No problem :smile: I'm glad you understand now
Reply 17
Original post by advice_guru
Benzene is non-polar. Based on the STRUCTURE you have a very symmetrical compound of just carbon and hydrogen and any dipoles formed by the C-H are all counteracted by each other resulting in a net zero dipole. The main ring are all composed of bonds of the same element, Carbon which makes that bond virtually non-polar. Sure, there is a pi electron cloud which essentially hovers the entire ring and because of symmetry again, benzene is non-polar.

Based on its PHYSICAL Property - like solubility, it is soluble in other non-polar compounds LIKE hexane, etc and NOT soluble in a Polar solvent or substance like WATER.

I hope you are not confused now. So you see sometimes you can explain away based on just structure, sometimes thru its physical properties or chemical reactivities.


Thank you :smile: this is really helpful I understand now

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