Pyrazolonderivate. V [1]. UV‐spektroskopisches und photochemisches Verhalten von N‐mono‐ und N,N‐disubstituierten 4‐Aminomethylen‐Δ²‐pyrazolinonen‐(5)

Abstract

Pyrazolone Derivatives. V. U.V.‐Spectroscopical and Photochemical Behaviour of N‐mono and N,N‐disubstituted 4‐Aminomethylene‐Δ2‐pyrazolinones‐(5) U.V.‐spectra of N‐mono and N,N‐disubstituted 4‐Aminomethylene‐Δ2‐pyrazolinones‐(5) 1a–j and their dependence on solvent and temperature are discussed. N,N‐disubstituted and N‐monosubstituted 4‐aminomethylene‐3‐methyl‐1‐phenyl‐Δ2‐pyrazolinones‐(5) show a Z‐/E‐isomerization of the exocyclic CC‐double bond at low temperatures. Compared to the N‐monosubstituted compounds the compound 1j exhibits a strong interaction in the E‐configuration between the aminomethylene‐substituent and the methyl‐group at the parazolone‐ring. The Z‐/E‐isomerization depends on solvent polarity. With increasing solvent polarity the energy of activation of thermic E‐/Z‐isomerization is decreased. A low temperature cell is described.