Data about the enthalpy of hydrogenation of cyclohexene and benzene are given:
(1) cyclohexene+H2→cyclohexane\text{cyclohexene} + \text{H}_2 \rightarrow \text{cyclohexane}cyclohexene+H2→cyclohexane, ΔH⊖=−120 kJ mol−1\Delta H^\ominus = -120\text{ kJ mol}^{-1}ΔH⊖=−120 kJ mol−1
(2) benzene+3H2→cyclohexane\text{benzene} + 3\text{H}_2 \rightarrow \text{cyclohexane}benzene+3H2→cyclohexane, ΔH⊖=−208 kJ mol−1\Delta H^\ominus = -208\text{ kJ mol}^{-1}ΔH⊖=−208 kJ mol−1
Explain the bonding in and the shape of a benzene molecule. Compare the stability of benzene with that of the hypothetical cyclohexa-1,3,5-triene molecule. Use the data in your answer.
The enthalpy of hydrogenation of cyclohexa-1,3-diene is not exactly double that of cyclohexene. Suggest a value for the enthalpy of hydrogenation of cyclohexa-1,3-diene and justify your value.
