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

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

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Textbooks quote typical relative $S_{\text{N}}2$ rates of $30$ for a methyl bromide, $1$ for a primary bromide and $0.03$ for a secondary bromide, with the same nucleophile and solvent. They are illustrative values and depend on the case. Under the conditions of an experiment the primary bromide reaches a given conversion in $60\ \text{min}$ . Use the relative rates to estimate the time that the methyl bromide needs for the same conversion, and the time that the secondary bromide needs, in minutes and in hours.

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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