Pyryliumverbindungen. XXII. 1H‐NMR‐ und UV‐spektroskopische Untersuchungen zur Isomerisierung von Pseudobasen unsymmetrisch substituierter 2, 4, 6‐Triarylpyryliumsalze

Publisher Website
Google Scholar
Abstract
Pyrylium Compounds. XXII. 1H‐N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6‐Triarylpyrylium SaltsThe kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5‐diones 2 and 3, were studied by 1H‐n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2⇄3 proved to be a base‐catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσp. The results obtained suggest resonance‐stabilized anions of type4 as intermediates. ‐ Pseudobases of 3‐alkyl‐2, 4, 6‐triarylsubstituted pyrylium salts do not undergo a reversible isomerization.