Pyryliumverbindungen, XXV. Quantenchemische Berechnungen zur Valenzisomerisierung von 2‐Amino‐2H‐pyran und ‐thiopyran

Publisher Website
Google Scholar
Abstract
Pyrylium Compounds. XXV. Quantum Chemical Calculations Concerning the Valence Isomerization of 2‐Amino‐2H‐pyran and ‐thiopyranThe equilibrium 2‐amino‐2H‐pyran6⇌ 5‐amino‐2,4‐dien‐1‐one7was investigated using the semi‐empirical MINDO/3 and MNDO methods. In accordance with experimental findings for the substituted derivatives1/2a–d, the introduction of a methyl group into the position 3 of6or the exchange of oxygen by sulfur shifts the equilibrium towards the cyclic structures8and10, respectively. Polar solvents, the influence of which was estimated applying the reaction field approach as well as the solvaton theory, and entropy effects are calculated to favour the ring‐open valence isomer7. These results also correspond to experimental results.