A double bond in a six-membered ring is usually more stable in an endocyclic position than in an exocyclic position. Hydrogenation data on two pairs of compounds follow. One pair suggests that the energy difference between endocyclic and exocyclic double bonds is about 9 kJ mol. The other pair suggests an energy difference of about 5 kJ mol. Which number do you trust as being more representative of the actual energy difference? Explain your answer.

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116 heats of hydrogenation (kJ/mol) endocyclic exocyclic 107 105 110