Final answer:
A reaction between HCl and 1,3-butadiene involves an addition reaction with the potential for both 1,2-addition and 1,4-addition products, with 1,2-addition favored at room temperature.
Step-by-step explanation:
The reaction between HCl and 1,3-butadiene at room temperature typically involves an addition reaction where HCl adds across the conjugated diene system of 1,3-butadiene. This can lead to either 1,2-addition (kinetic product) or 1,4-addition (thermodynamic product), with the 1,2-addition being more prevalent at lower temperatures. However, to provide a step-by-step mechanism, more context is needed, such as whether you are focusing on the kinetic control (faster reaction at lower temperatures favoring 1,2-addition) or thermodynamic control (slower reaction at higher temperatures favoring 1,4-addition) of the reaction.