Pyrrole studies. IV. The electronic spectra of alkyl- and ethoxycarbonyldipyrromethenes

Abstract

The NH stretching frequency and the electronic spectra of 8 alkyl- and 12 ethoxycarbonyl-dipyrromethenes have been measured and the results correlated with the electronic and steric effects of the substituents. It is postulated that there is steric interaction between the two ethoxycarbonyl groups of 3,3'-diethoxycarbonyl. 4,5,4',5'-tetramethyldipyrromethene. The electronic effect of substituents in the 4,4'-positions of 3,5,3',5'-tetramethyldipyrromethenes is discussed.