A student performs the reaction of 2-ethyl-1,3-pentadiene with HBr at –55∘C and obtains the following mixture of products: 78% compound A and 22% compound B. She repeats the reaction the next day, and this time obtains the approximately reverse ratio of products: 26% compound A and 74% compound B. Puzzled, she reviews the procedure and realizes that she forgot to regulate the reaction temperature and that the reaction instead proceeded at room temperature (25∘C). Determine the structures of compounds A and B and elucidate the role of temperature in the reaction.