Substitution of an -OH with a halogen in an alcohol by hydrogen halides?

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nonipaify
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Report Thread starter 7 years ago
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We were given two types of alcohols, one a phenolic (benzene ring with a hydroxyl group on position 1 and a hydrocarbon chain on position 4) and a similar looking cyclic alcohol which which was drawn looking exactly the same as the phenol but without the delocalisation ring i.e. there were extra hydrogens in it.

It asked which of the compounds would react with HBr. What is the reason the phenolic had no reaction but this other cyclic alcohol underwent a reaction? is it only the aliphatic and cyclic alcohols that undergo substitution of the -OH group? my teacher taught me that the halogenating agents such as phosphorus halides and thionyl chloride work by replacing the -OH group in ANY compound including water and carboxylic acids so why not in the phenolic? Hope my question is clear to you.
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charco
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Report 7 years ago
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(Original post by nonipaify)
We were given two types of alcohols, one a phenolic (benzene ring with a hydroxyl group on position 1 and a hydrocarbon chain on position 4) and a similar looking cyclic alcohol which which was drawn looking exactly the same as the phenol but without the delocalisation ring i.e. there were extra hydrogens in it.

It asked which of the compounds would react with HBr. What is the reason the phenolic had no reaction but this other cyclic alcohol underwent a reaction? is it only the aliphatic and cyclic alcohols that undergo substitution of the -OH group? my teacher taught me that the halogenating agents such as phosphorus halides and thionyl chloride work by replacing the -OH group in ANY compound including water and carboxylic acids so why not in the phenolic? Hope my question is clear to you.
The phenol has extra stability due to the interaction between the oxygen electron pairs and the benzene delocalised ring.

It preferentially loses the phenolic hydrogen making it acidic (carbolic acid)
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