Computational study on fused five membered heterocyclic compounds containing tertiary oxygen

The structure, stability and electronic properties of two fused five membered heterocyclic compounds containing tertiary oxygen have been investigated with quantum chemistry computation. The results show that 3H-4λ3-furo[1,2-a]furan (M1) and 2a1λ4-oxacyclopenta[cd]pentalene (M2) both own three CO bonds and especially in M2 the three CO bonds and angles are approximately identical. The two compounds are comparatively stable and M2 with three pentacycles is more stable than compound M1 according to the CO bond lengths, bond orders, Egap, electronegativity (χ), hardness (η), electrophilicity (ω), and aromaticity indexes. The aromaticity indexes such as NICS(0), NICS(1) and NICS(1)zz show that they both have strong aromaticity. The natural bonding orbital (NBO) analysis shows that oxygen atom takes hybrid orbitals composed of s and p orbital components to form σ(CO) bonds in compounds M1 and M2. The second order perturbation analysis shows that the occurrence of intramolecular charge transfer within the molecule exists in compound M1.