The beats of combustion for(1) hippuric acid(c),(2) piperazine(c)and(3) azaeycloheptane(1) wore dotormined using a precision bomb calorimeter.The results of △H^-_o and △H⁰_f are:(1)-1008.30±0.22;(2)-707.79±0.27,-9.99±0.27 and(3)-987.03±0.39,-21.36±0.39 kcal/mol,respectively.Using values of latent heat from literature or by estimation,△H⁰_f valuos of these two cyclic compounds wore derived.According to the bond energy achomo,tho conventional ring strain energies for these compounds are estimated to be(2)-0.2±1.5 and(3)+5.6±0.4 kcal/mol,respectivoly,and comparison with thoso of other cyclic compounds is made.