Chemistry 9701 · AS & A Level · 2.3

2.3 — practice question

Cycloalkanes have chemical behaviour similar to alkanes, yet they possess the same empirical formula as alkenes.
(a)[1]

Define what is meant by empirical formula.

(b)[2]

Cyclopentane, $\mathrm{C_5H_{10}}$, has four cyclic structural isomers. One of them is C, which is drawn in Fig. 3.1. Complete Fig. 3.1 by showing two further cyclic structural isomers of $\mathrm{C_5H_{10}}$.

(c(i))[1]

Cyclopentane reacts with $\mathrm{Cl_2}$ under ultraviolet light to produce $\mathrm{C_5H_9Cl}$. The reaction begins with the bond fission of $\mathrm{Cl_2}$. State the type of bond fission shown in the initiation step.

(c(ii))[2]

Complete the equations to show the two propagation steps after initiation. 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 here: $\mathrm{C_5H_9}\bullet + \mathrm{Cl}\bullet \rightarrow \mathrm{C_5H_9Cl}$. State the name of this stage in the reaction.

(d(i))[1]

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

(d(ii))[2]

Use the data in Fig. 3.2 and in Table 3.1 to calculate the enthalpy change of reaction 2, $\Delta H_2$.

(e(i))[1]

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

(e(ii))[2]

The infrared spectrum of W is shown in Fig. 3.3. Identify two absorptions in the infrared spectrum of W that would not be present in the infrared spectrum of cyclopentene. Write 1 or 2 on Fig. 3.3 against each of these two absorptions. Complete Table 3.2 to show which bond is responsible for each absorption that 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 smallest whole-number (integer) ratio of atoms of each element in a compound or molecule

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