Join TSR now and get all your revision questions answeredSign up now
    • Thread Starter
    Offline

    12
    ReputationRep:
    If you protonate a weak acid e.g. benzoic acid.
    + +
    So c6h5cooh + H+ ==> c6h5c(oh)2 or c6h5cooh2


    which product do you get? both products have 1+ charge
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by Xenon17)
    If you protonate a weak acid e.g. benzoic acid.
    + +
    So c6h5cooh + H+ ==> c6h5c(oh)2 or c6h5cooh2


    which product do you get? both products have 1+ charge
    The oxygen of the carbonyl group will accept a proton.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by charco)
    The oxygen of the carbonyl group will accept a proton.
    The markscheme gives the product as c6h5cooh2
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by Xenon17)
    The markscheme gives the product as c6h5cooh2
    It's an interesting one ...

    I would go with the carbonyl, as this allows resonance delocalisation of the positive charge using the pi electrons.

    This can't happen with protonation of the hydroxyl oxygen.

    It is possible that the mark scheme is not actually showing the location of the proton, rather a general idea.

    The esterification mechanism shows protonation of the carbonyl. The following image is taken from chemguide:

    Name:  estermech2.gif
Views: 36
Size:  1.7 KB
    Offline

    10
    ReputationRep:
    (Original post by Xenon17)
    The markscheme gives the product as c6h5cooh2
    The most basic site of the two is definitely the carbonyl Oxygen's lone pairs (the lone pairs on the other oxygen are delocalised and hence less available to accept a proton) so I would agree that the mark scheme isn't really trying to be representative of the product. In reality the protonation would be an equilibirum based process and so both oxygen atoms would be rapidly protonated and deprotonated.
 
 
 
Poll
If you won £30,000, which of these would you spend it on?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.