Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

The conversion of 1-chloro-1-phenylethane into 1-phenylethanol by hydroxide ions is given by: $\mathrm{C_6H_5CHClCH_3 + OH^- \rightarrow C_6H_5CH(OH)CH_3 + Cl^-}$ The rate of this reaction may be investigated by monitoring how much hydroxide ion is still present in the solution at a chosen moment. If the mixture is diluted with an ice-cold solvent, the reaction can be effectively quenched.
(a)[4]

Describe a suitable method for investigating the rate of this reaction at $40^\circ\text{C}$, using the following: • a $0.10\,\mathrm{mol\,dm^{-3}}$ solution of 1-chloro-1-phenylethane, labelled A • a $0.10\,\mathrm{mol\,dm^{-3}}$ solution of sodium hydroxide, labelled B • $0.10\,\mathrm{mol\,dm^{-3}}$ HCl • volumetric glassware • ice-cold solvent • stopclock • access to standard laboratory equipment and chemicals

(b(i))[2]

Deduce the order of reaction with respect to each of $[\mathrm{C_6H_5CHClCH_3}]$ and $[\mathrm{OH^-}]$. Explain your answer.

(b(ii))[1]

Write the rate equation for this reaction, and state the units of the rate constant, $k$.

(b(iii))[1]

Calculate the relative rate for experiment 4.

(c(i))[3]

Use your answers in (b)(i) to help you draw the mechanism for the reaction of 1-chloro-1-phenylethane with hydroxide ions, including: • all relevant lone pairs and dipoles • curly arrows to indicate electron-pair movement • the structures of any transition state or intermediate

(c(ii))[1]

A single optical isomer of 1-chloro-1-phenylethane was used in this reaction. Use your mechanism in (i) to predict whether the product will be a single optical isomer or a mixture of two optical isomers. Explain your answer.

(d)[4]

A proton NMR spectrum of 1-phenylethanol contains four peaks: a multiplet for the $\mathrm{C_6H_5}$ protons and three additional peaks as listed in the table. After the sample is shaken with $\mathrm{D_2O}$ and the proton NMR spectrum is taken again, fewer peaks are observed. Complete the table for the proton NMR spectrum of 1-phenylethanol, $\mathrm{C_6H_5CH(OH)CH_3}$. Use the Data Booklet might be helpful.

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