Final answer:
In the reaction between HBr and 1,3-butadiene, a low-temperature reaction favors a 1,4-addition product, which may change to a 1,2-addition product upon heating due to thermodynamic control. In a general substitution reaction of butane with excess bromine, butane can be fully converted to tetrabromobutane.
Step-by-step explanation:
When a mixture of products from a reaction between HBr and 1,3-butadiene is formed at a low temperature and then heated, an interesting shift occurs. At low temperatures, the addition of HBr to 1,3-butadiene tends to occur in a 1,4-addition manner, leading to the formation of a more substituted, stable product. However, as the temperature is increased, the reaction can lead to a 1,2-addition product. The reason for this change can be attributed to thermodynamic control at higher temperatures, where the more stable product formed from the 1,4-addition can revert to the reactants and then form the less substituted 1,2-addition product.
Speaking generally about reactions with bromine, when a hydrocarbon like butane reacts with an excess of bromine, a substitution reaction occurs where all hydrogen atoms on the hydrocarbon could be replaced by bromine atoms, depending on the conditions. This could be depicted in a simple balanced reaction showing the conversion of butane to tetrabromobutane:
CH3CH2CH2CH3 + 8Br2 → CBr4 + 8HBr