This question is about benzene, C6H6 , a colourless liquid first isolated in 1825, and some related compounds.
Three C6H6 structures proposed in the 1860s are shown.
The delocalised model for the structure of benzene has been accepted since the 1930s following the study of its X‐ray diffraction pattern and the understanding of electron delocalisation in bonding theory.
The Dewar and Ladenburg structures have since been isolated as stable compounds but there is no compound with the Kekulé structure.
Describe a chemical test, including the result, that could distinguish the Dewar structure from benzene.
State one similarity and one difference you would expect in the low resolution proton NMR spectrum of the Ladenburg structure and that of benzene.
You must include data from the Data Booklet to support your answer.
Explain how X‐ray diffraction shows that benzene has a delocalised structure and not a Kekulé structure.
The Ladenburg and Dewar structures both isomerise to benzene.
The enthalpy changes are –376 kJ mol–1 and –297 kJ mol–1 respectively.
Include the enthalpy change values in kJ mol–1.
Your diagram does not need to be to scale.
(2)
(1)
The enthalpy change of hydrogenation of hex‐3‐ene is –118 kJ mol–1.
The table shows the enthalpy changes of hydrogenation of two further alkenes containing six carbon atoms.
Use your knowledge of benzene thermochemistry to suggest explanations for both of these enthalpy changes of hydrogenation in relation to the value for hex‐3‐ene.
Methylbenzene, C6H5CH3 , reacts with ethanoyl chloride, CH3COCl, in the presence of the catalyst aluminium chloride, AlCl3 , to form a mixture of organic products with the formula CH3COC6H4CH3.
C6H5CH3 + CH3COCl → CH3COC6H4CH3 + HCl
Draw the skeletal formulae of three different arenes with the formula CH3COC6H4CH3 .
(2)
The 13C NMR spectrum of one of these arenes, compound X, is shown.
Identify compound X.
Use the number of peaks on the 13C NMR spectrum to justify your answer.
(2)
Include an equation for the regeneration of the catalyst.
(4)
CH3COCl + AlCl3 → CH3CO++ AlC
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