Structure A is 2,2-dimethylpropanal
Structure B is 2,2-dimethylpropanoic acid
Reactivity ==> A is an aldehyde or primary alcohol as it is oxidised to produce B which is a carboxylic acid as it gives off CO2 when Na2CO3 is added.
IR ==> Strong sharp peak at 1700 cm^-1 is a C=O, peaks at 3000...