An structural isomer of bromobutane (C4H9Br) can be hydrolysed using aqueous sodium hydroxide to produce butanol. This can be represented by the following equation:

C4H9Br(l) + OH-(aq)  C4H9OH(l) + Br-(aq)
This reaction was investigated experimentally and the following results
were obtained:
Experiment
Initial [bromobutane], mol dm-3 Initial [OH-], mol dm-3 Initial rate, mol dm-3s-1
A 0.01 0.01 4.3 x 10-4
B 0.01 0.02 8.6 x 10-4
C 0.02 0.02 1.7 x 10-3

question Suggest which isomer of bromobutane is likely to react via this rate-limiting step. Explain your answer fully.

To determine which isomer of bromobutane reacts via the rate-limiting step, we need to analyze the experimental data and identify any patterns or trends. The rate of a chemical reaction can often provide clues about the reaction mechanism and which step is rate-determining.

In this case, we have three experiments with varying initial concentrations of bromobutane ([bromobutane]) and hydroxide ions ([OH-]). The initial rate of the reaction is given for each experiment.

Experiment A:
Initial [bromobutane] = 0.01 mol dm-3
Initial [OH-] = 0.01 mol dm-3
Initial rate = 4.3 x 10-4 mol dm-3s-1

Experiment B:
Initial [bromobutane] = 0.01 mol dm-3
Initial [OH-] = 0.02 mol dm-3
Initial rate = 8.6 x 10-4 mol dm-3s-1

Experiment C:
Initial [bromobutane] = 0.02 mol dm-3
Initial [OH-] = 0.02 mol dm-3
Initial rate = 1.7 x 10-3 mol dm-3s-1

Comparing the experiments, we can see that the initial concentrations of bromobutane ([bromobutane]) and hydroxide ions ([OH-]) are kept constant in experiments A and B while being doubled in experiment C. However, the initial rates of reaction are not directly proportional to the changes in concentration.

In experiment C, where the concentration of bromobutane is doubled while keeping the concentration of hydroxide ions constant, the initial rate also doubles. This suggests that the reaction is first-order with respect to bromobutane concentration.

In experiment B, where the concentration of hydroxide ions is doubled while keeping the concentration of bromobutane constant, the initial rate also doubles. This suggests that the reaction is first-order with respect to hydroxide ion concentration.

However, in order for both reactions (A and C) to be first-order, regardless of which reactant is being doubled, the reaction can be assumed to be a second-order reaction. This indicates that the reaction likely proceeds via a bimolecular mechanism, involving the collision of two reactant species.

Considering all these factors, we can conclude that the isomer of bromobutane that reacts via the rate-limiting step is the one that shows a first-order dependence on bromobutane concentration. Comparing experiments A and C, where the concentration of hydroxide ions ([OH-]) and bromobutane ([bromobutane]) is constant, the initial rate doubles when the concentration of bromobutane is doubled (C), indicating that the [bromobutane] term takes part in the rate equation. Therefore, the isomer that reacts via the rate-limiting step is the one used in experiment C, which has an initial concentration of 0.02 mol dm-3.

To determine the exact mechanism and further insights into why this isomer reacts via the rate-limiting step, additional experiments and analysis may be needed.