Acrolein (CH2== CHCH==O) reacts with sodium azide (NaN3) in aqueous acetic acid to form a compound, C3H5N3O

Question:

Acrolein (CH2== CHCH==O) reacts with sodium azide (NaN3) in aqueous acetic acid to form a compound, C3H5N3O in 71% yield. Propanal (CH3CH2CH==O), when subjected to the same reaction conditions, is recovered unchanged. Suggest a structure for the product formed from acrolein, and offer an explanation for the difference in reactivity between acrolein and propanal.