The values for bond enthalpies are found in the data book. For some bonds, the mean bond enthalpy is quoted. This is to give an average value to work from since the precise enthalpy value for a ...

A database of 290,664 bond dissociation energies for small molecules (10 or fewer heavy atoms) consisting of C, H, O, or N atoms. Enthalpy calculations were carried out using the M06-2X/def2-TZVP ...