AQA · OCR A · Year 13
Aromatic Chemistry Explanation Questions
Practise benzene stability, nitration equations and substitution explanations. OCR A also includes phenol. This set does not assess mechanism drawings.
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Worked answer
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Use evidence to explain benzene stability. Its hydrogenation is less exothermic than a model with three isolated double bonds. In electrophilic substitution, delocalisation is temporarily disrupted and then restored; it is not preserved throughout every step.
A worked example
If one isolated C=C bond gives −120 kJ mol⁻¹ on hydrogenation, three predict −360 kJ mol⁻¹. A benzene value of −208 kJ mol⁻¹ indicates 152 kJ mol⁻¹ of extra stability relative to that comparison.