Calorimetrically measurable enthalpic isotope effect

A measurable difference found in the heat released by the well-known Birch reduction of naphthalene and of its perdeuteriated analogue is reported. The results are coupled with the known enthalpy of electron transfer between naphthalene and its perdeuteriated analogue, implying that the heat of hydrogenation of naphthalene is decreased upon perdeuteriation of the naphthalene.