Answer:
They are all formed in acidic solution.
Explanation:
The diagram for hemiacetal, acetal and imine is shown in the diagram below and a star is placed on the three of them since they are all form in acidic solution.
From the diagram; reaction of methanol with propanal leads to formation of hemiacetal. From CH₃OH(methanol), one hydrogen attaches itself to the Oxygen double bond on the propanal to form a new hydroxyl group, the other methoxyl (-O-CH₃) from methanol attaches itself to other part of the propanal.
The further addition of methanol to Hemiacetal yields to Acetal.
Imines are formed by Mannich Reaction which is the reaction of propanal with amine group and which is followed by the dehydration with a Schiff base.
