The Student Room Group

Which mechanism? & Prediction of products?

Hi guys,

Having a bit of trouble...but how can you tell which mechanism the question wants when it gives you just the reactants and solvent? Also how do you what is going to react with what to get the right product?

Does any one have tips/ steps on how tackle such questions?

E.g these two questions IMAG0856.jpg
Original post by Princess Kawaii
Hi guys,

Having a bit of trouble...but how can you tell which mechanism the question wants when it gives you just the reactants and solvent? Also how do you what is going to react with what to get the right product?

Does any one have tips/ steps on how tackle such questions?

E.g these two questions IMAG0856.jpg


I think that you just have to learn the conditions.

The first one is the iodoform reaction. It's a fairly standard test for the CH3CO- group.

The second one looks like the conditions for sulphonation, substitution of an HSO3 group to the ring.
Original post by charco
I think that you just have to learn the conditions.

The first one is the iodoform reaction. It's a fairly standard test for the CH3CO- group.

The second one looks like the conditions for sulphonation, substitution of an HSO3 group to the ring.



Original post by Princess Kawaii
Hi guys,

Having a bit of trouble...but how can you tell which mechanism the question wants when it gives you just the reactants and solvent? Also how do you what is going to react with what to get the right product?

Does any one have tips/ steps on how tackle such questions?

E.g these two questions IMAG0856.jpg


Yeah second that. You need to think about sterics for the position of sulphonation.
Original post by Princess Kawaii
Hi guys,

Having a bit of trouble...but how can you tell which mechanism the question wants when it gives you just the reactants and solvent? Also how do you what is going to react with what to get the right product?

Does any one have tips/ steps on how tackle such questions?

E.g these two questions IMAG0856.jpg


The first reaction is the iodoform reaction. This reaction occurs with methyl ketones or alcohols which when oxidised give methyl ketones. In this reaction, the methyl ketone group on the ring will be converted into that of methanoic acid.

The second reaction is sulfonation. You have to rationalise where the pi electrons will attack the S03H+ ion. OMe is o/p directing and NO2 is meta directing, so where both those positions coincide is the para position, hence directly opposite to the OMe substituent.
(edited 10 years ago)
Original post by LeonVII
The first reaction is the iodoform reaction. This reaction occurs with methyl ketones or alcohols which when oxidised give methyl ketones. In this reaction, the methyl ketone group on the ring will be converted into that of methanoic acid.

The second reaction is sulfonation. You have to rationalise where the pi electrons will attack the S03H+ ion. OMe is o/p directing and NO2 is meta directing, so where both those positions coincide is the para position, hence directly opposite to the OMe substituent.


Well there are 2 positions if you justify it on those grounds... That explanation is true but as I said you need to account for steric effects which leads to the selectivity over the position para to the oxygen.

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Original post by JMaydom
Well there are 2 positions if you justify it on those grounds... That explanation is true but as I said you need to account for steric effects which leads to the selectivity over the position para to the oxygen.

Posted from TSR Mobile


Of course, but the steric interactions would make it extremely unfavourable, I thought maybe that was too obvious to post. Maybe i should be a bit more thorough :biggrin:
Reply 6
Original post by LeonVII
Of course, but the steric interactions would make it extremely unfavourable, I thought maybe that was too obvious to post. Maybe i should be a bit more thorough :biggrin:


Unfavourable yes, but I think you would still get a mixture.
(edited 10 years ago)
Original post by illusionz
You would still get a mixture, despite the sterics.


Indeed, but the percentage of the 1,2 product would be dwarfed by the other, no?
Reply 8
Original post by LeonVII
Indeed, but the percentage of the 1,2 product would be dwarfed by the other, no?


Minor product indeed but any exam answer should, in my opinion, state that both are formed as it gives a more detailed description of the reaction and shows you understand what is going on.

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