[vanderwaals]

Could someone explain why the order of acidity (with 1 being the most acidic) is what it is in the attached photo? All I could figure out was that the second was the most acidic because the larger sulfur atom is less stable with the positive charge. I'm completely confused about the rest of the rankings, so any explanation would be appreciated thanks

[Dan]

Think about inductive and resonance stabilisation of the cation. Start by comparing the ketone to the amide - what is it about that N atom that stabilises the +ve charge?

The order of acidity in this series parallels the order of electrophilicity of carbonyls and can be explained using the same logic. So to approach from a different angle, why is a ketone more electrophilic than an amide?