Isodesmic reaction studies on five-memebered heterocyclic C4H4M (M = O, S, Se, Te, NH, PH, AsH and SbH): DFT calculations

Aromatic character is not a directly measurable or computable quantity. Aromatic character is generally evaluated on the basis of energetic, geometric, and magnetic criteria [1-6]. There is some procedure for the estimation of aromatic stabilization energies (ASE) and/or homo-aromatic stabilization energies (HASE) from various isodesmic reactions [7]. These usually require comparisons the non-aromatic model compounds respect to aromatic model compound. Isodesmic reaction schemes insist only equal numbers of formal single and double bonds in products and reactants. Systems with negative SE are aromatic, while those with positive ASE are antiaromatic.