Determination of The Enthalpy of Formation of Three- and Eight- Membered Heterocyclic Ethers in Ideal Gas by Diffe-rent Theoretical Methods via Atomization Energy and Bond Separation Schemes

Enthalpies of formation for three- and eight- membered heterocyclic ethers (15 compounds) in gas state have been determined by different theoretical methods: levels of theory B3LYP/6-31g(d), MP2/6-31g(d) and chemical composite methods (Gn and CBS) via two approach’s: atomization energy (AE) and bond separations (BS). Median absolute deviations (MAD) and standard deviations (SD) of calculated values from experimental data have been determined for every using method’s. The bond separation method has the smallest MAD at most of theoretical methods in comparison to the atomization energy approach. The 6-31g(d,p) basis set doesn’t seen clear effect in the theoretical results.