Here, the formation enthalpies obtained from the W1 21 method from Gaussian16 22 are compared with state-of-the-art tables for validation and to shed light on the limitations of these tables. From the W1 21 method, we obtain the total electronic energy along with thermal enthalpy at 0K, denoted by ε 0 (M) in Eqn. 1, which is used to compute the atomization energy of the molecule. Following this calculation, the formation enthalpy of the molecule is computed using Eqn. 2 where the atomic formation enthalpies are taken from Ref. 36. Besides determining ∆ f H (0 K) from atomization energies, other reactions can be used as well, for example, C 4 ← C 2 +C 2 . Computing this quantity using various reactions provides a consistency check. Therefore, validation for the data computed in this paper is done using Active Thermochemical Tables (ATcT). ATcT is a database of thermochemical properties for molecules developed at the Argonne National Laboratory. The properties are calculated by taking a weighted average of values from literature, which include experimental and computational results for various reaction mechanisms. The thermochemical data is also compared to JANAF Tables 40 and Gurvich Thermodynamic Tables whose values are widely used for the prediction of mixture composition in the boundary layer of an ablating heat shield.