Zur Kenntnis der Sesquiterpene und Azulene. 118. Mitteilung. Über die drei isomeren Benz‐azulene: II. Die basischen Eigenschaften der Benz‐azulene

Abstract

The uv. absorption spectra of the conjugate acids of the three isomers 1, 2‐benzoazulene (II), 4,5‐benzoazulene (III), 5,6‐benzoazulene (IV) and of azulene (I) have been determined, as well as the relative basicity of I, II, III and IV. Correlation of these experimental data with predictions based on zeroth order MO theory supports the proposed formulation of the conjugate acids of I and II as derivatives of the tropylium cation and of III and IV of the benzotropylium cation from a qualitative point of view.

Pyridylazulenes: Synthesis, Color Changes, and Structure of the Colored Product

“…We studied changes in the spectral properties and colors of 1 − 9 upon addition of a moderately strong organic acid, trifluoroacetic acid (p K a 0.3). Under these conditions, protonation of the pyridine moiety was expected to enhance its electron-withdrawing ability and influence the π-conjugate system of azulene . For 1-pyridylazulenes 1 and 3 , and 1,3-dipyridylazulenes 7 and 9 (which contain either the 2-pyridyl or the 4-pyridyl group), the addition of trifluoroacetic acid gradually produced a color change from blue to red.…”