Chemistry 9701 · AS & A Level · 6.1

6.1 — practice question

Cycloalkanes have chemical properties similar to alkanes, yet their empirical formula is the same as that of alkenes.
(a)[1]

Define the empirical formula.

(b)[2]

Cyclopentane, $\mathrm{C_5H_{10}}$, has four cyclic structural isomers. One of these isomer is C, shown in Fig. 3.1. Finish Fig. 3.1 so that it displays two other cyclic structural isomers of $\mathrm{C_5H_{10}}$.

(c(i))[1]

The reaction starts with bond fission of $\mathrm{Cl_2}$. State the kind of bond fission shown in the initiation step.

(c(ii))[2]

Complete the equations to show the two propagation steps that come after the initiation step. Propagation 1: $\mathrm{C_5H_{10}} + \underline{\hspace{1cm}} \rightarrow \mathrm{C_5H_9}\bullet + \underline{\hspace{1cm}}$. Propagation 2: $\mathrm{C_5H_9}\bullet + \underline{\hspace{1cm}} \rightarrow \underline{\hspace{1cm}}$.

(c(iii))[1]

The final stage is shown: $\mathrm{C_5H_9}\bullet + \mathrm{Cl}\bullet \rightarrow \mathrm{C_5H_9Cl}$. Give the name of this step in the reaction.

(d(i))[1]

Fig. 3.2 displays a reaction cycle linking cyclopentane, cyclopentene and $\mathrm{C_5H_9Cl}$. Identify a suitable reagent for reaction 3.

(d(ii))[2]

Use the information in Fig. 3.2 and Table 3.1 to work out the enthalpy change for reaction 2, $\Delta H_2$.

(e(i))[1]

Cyclopentene, $\mathrm{C_5H_8}$, reacts with hot concentrated acidified $\mathrm{KMnO_4}$ to produce compound W, $\mathrm{C_5H_8O_4}$. Draw the structure of W.

(e(ii))[2]

The infrared spectrum of W appears in Fig. 3.3. Identify two absorptions in the infrared spectrum of W that would not appear in the infrared spectrum of cyclopentene. Put 1 or 2 on Fig. 3.3 beside each of these two absorptions. Complete Table 3.2 to show which bond causes each absorption you have identified in Fig. 3.3.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: The lowest whole-number (integer) ratio of atoms of each element in a compound/molecule

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