An alternative mechanism for \(E_{2}\) elimination is the following: (a) Would this mechanism lead to a first-order kinetics with respect to the concentrations of \(\mathrm{OH}\) and ethy1 chloride? Explain. (b) This mechanism has been excluded for several halides by carrying out the reaction in deuterated solvents such as \(\mathrm{D}_{2} \mathrm{O}\) and \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OD}\). Explain how such experiments could be relevant to the reaction mechanism.

E2 elimination reactions occur when a proton adjacent to a leaving group is removed, and at the same time, the leaving group departs. This generates a double bond between the carbon atoms. The rate of the E2 elimination is second-order overall, depending on both the concentration of the substrate and the base.

We are asked to determine whether the given E2 mechanism would lead to a first-order kinetics concerning the concentrations of OH⁻ and ethyl chloride. For this, we will analyze the individual steps of the mechanism to determine the reaction order: 1. In the first step, the base (OH⁻) removes a proton from the substrate (ethyl chloride). Let's denote the rate constant for this step as k1. The rate of this step would be given by: Rate = k1[OH⁻][ethyl chloride] 2. In the second step, the ethyl chloride undergoes elimination to generate the final products. Let's denote the rate constant for this step as k2. The rate of this step would be given by: Rate = k2[Intermediate] We need to consider the rate-determining step (slowest step) to determine the overall reaction order. Suppose the first step is the slowest. In that case, the overall rate depends on the concentration of OH⁻ and ethyl chloride, which means the reaction would be first-order with respect to both reactants. If the second step is slower, it only depends on the intermediate concentration, and it wouldn't be first-order with respect to both reactants. 3. To verify this experimentally, one should vary the concentrations of OH⁻ and ethyl chloride and measure the rate of the reaction. If the rate depends only on the concentrations of OH⁻ and ethyl chloride, the given mechanism leads to first-order kinetics.

Deuterated solvents, such as D2O and C2H5OD, are used to study reaction mechanisms because they can help identify the involvement of protic groups in reactions. Deuterium, a heavy isotope of hydrogen (D), has much larger mass than hydrogen and therefore has different kinetic properties. By carrying out the E2 elimination reaction in a deuterated solvent, one can track the participation of solvent protons in the overall mechanism. If there is a significant difference in reaction rates between protic and deuterated solvents, it suggests a strong involvement of solvent protons in the reaction mechanism, thus providing valuable insights into the reaction mechanism. For example, if the reaction rate slowed significantly in D2O, it could imply deuterium is involved in transferring from the protic solvent to the reactants, such as through a proton transfer. Analyzing the final products can help verify if an H-D exchange occurred and compare the reaction rates in different solvents, which can confirm or disprove the proposed mechanism.