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noradrenaline reaction with an acid and a base

Consider the structure of noradrenaline. A question asked to draw the structures of the products when noradrenaline reacts with HCl and NaOH separately.

Now I know from the study of hydroxyl compounds that the proton in an -OH group is replaceable. In the case of NaOH, the H from the OH is replaced by a Na+ ion. My answer consisted of a structure where ALL THREE -OH became -ONa but as per the mark scheme only the -OH attached to the ring became -ONa. Please tell me why not the hydroxyl group in the hydrocarbon chain as well?

I also remember that alcohols are amphoteric and accept a proton too. My answer was a structure where all three -OH became -OH2+ and ofcourse the -NH2 became -NH3+. again the mark scheme showed a structure with only the amine group having gained a proton. Help.


Maybe I should post this in biochemistry section aswell?
(edited 9 years ago)
Reply 1
A hydroxyl group in an alcohol and a hydroxyl group in a phenol have different chemistry.

Loss of a proton from the hydroxyl group in the hydrocarbon chain would make the molecule unstable, because the negative charge is concentrated at one atom (the oxygen). I don't know whether you've learnt about the chemistry of a benzene ring, but in phenol the negatively charged oxygen can distribute it's charge across the ring, thereby stabilising it.

I don't remember being taught about alcohols accepting protons, so maybe check that? Even if it was possible, -OH2+ is not a stable molecule, so it would only be formed in very acid conditions (i.e. when there's a lot of H+ in solution).

I don't want to overcomplicate the answer by talking about equilibriums and pKa values (since I don't know which stage of education you're in), but if you need me to expand on anything, let me know :smile:
Reply 2
Original post by kanra
A hydroxyl group in an alcohol and a hydroxyl group in a phenol have different chemistry.

Loss of a proton from the hydroxyl group in the hydrocarbon chain would make the molecule unstable, because the negative charge is concentrated at one atom (the oxygen). I don't know whether you've learnt about the chemistry of a benzene ring, but in phenol the negatively charged oxygen can distribute it's charge across the ring, thereby stabilising it.

I don't remember being taught about alcohols accepting protons, so maybe check that? Even if it was possible, -OH2+ is not a stable molecule, so it would only be formed in very acid conditions (i.e. when there's a lot of H+ in solution).

I don't want to overcomplicate the answer by talking about equilibriums and pKa values (since I don't know which stage of education you're in), but if you need me to expand on anything, let me know :smile:


Thanks alot for your reply. I got the answer to my question. I am doing the cie A2 chemistry right now what level are you?
Reply 3
Original post by nonipaify
Thanks alot for your reply. I got the answer to my question. I am doing the cie A2 chemistry right now what level are you?


You're welcome :smile: And I've just finished my first year of biochemistry at ICL.

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