Ab initio and DFT studies on the mechanism of ring-opening reactions of 4H-1-benzopyran-4-one with hydroxide ion†

摘要: The mechanism of the first steps degradation 4H-1-benzopyran-4-one in alkaline media, i.e., nucleophilic addition hydroxide ion at C2 carbon followed by ring-opening, is investigated ab initio [HF/6-31+G(d) and MP2/6-31+G(d)] density functional theory [B3LYP/6-31+G(d)] methods. In addition, bulk solvent effects are estimated polarised continuum (overlapping spheres) model (PCM) polarizable conductor PCM (CosmoPCM). Depending on level used three reaction coordinates found: path A (1→TS1→2→TS2A→3A), B (1→TS1→2→TS2B→3B) C (1→TS1→2→TS2A→3C). ring-opening step passing through TS2B has a lower activation energy than proceeding TS2A. These second barriers higher compared with barrier step. Therefore fission γ-pyrone ring (2→TS2B→3B) seems to be rate-determining gas phase. Contrary these phase results, (reactants→TS1→2) for aqueous solution, agreement experimental results.