EasyChemistryHigh School (11–12)Organic Compounds with Functional Groups › Haloalkanes and HaloarenesNumerical

A primary alkyl bromide reacts with an iodide ion in acetone by the SN2 mechanism…

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A primary alkyl bromide reacts with an iodide ion in acetone by the $S_{\text{N}}2$ mechanism. The rate constant is $4.0 \times 10^{-3}\ \text{L/(mol s)}$ . In the first experiment, $[\text{RBr}] = 0.25\ \text{mol/L}$ and $[\text{I}^-] = 0.60\ \text{mol/L}$ . In a second experiment, the concentration of the bromide is doubled and that of the iodide is tripled. Find the rate of the first experiment, the rate of the second experiment, and the factor between them. Give the rates in $\text{mmol/(L s)}$ .

Need a reminder? The key ideaShow

$S_{\text{N}}2$ is one step with the rate law $\text{rate} = k[\text{RX}][\text{Nu}]$ , and it inverts the shape of the carbon. The speed falls from methyl to primary, secondary and tertiary. Rates of $S_{\text{N}}2$ reactions of different halides are compared through their rate constants. Time for the same conversion is inversely proportional to the rate constant. Yield calculations use the ratio of the balanced equation.

The worked solution

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← PreviousTextbooks quote typical relative SN2 rates of 30 for a methyl bromide, 1 for a primary bromide and… →

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