1,3-Butadiene can react with NBS (conditions generating Br2), producing 1,2 and 1,4- addition products. At different reaction temperature, the ratio of the two products is different. (a) Write the reaction equation, (b) indicate which product is predominant at low temperature, (c) which product is predominant at high temperature, and (d) draw a reaction energy diagram explaining your answers in b and c.