Infra-Red Absorption Spectra of Chlorophylls and Derivatives.

We have measured the infra-red absorption spectra of chlorophyll and some of its derivatives in order to obtain information useful for eventual understanding of reversible transformations of this pigment. Such transformations are (a) Moliseh phase test, (b) bleaching by FeCl3, and (c) photochemical reduction by ascorbic acid-"Krasnovsky reaction" (10, 13, 16). Only in the case of the phase test is there evidence of the specific group involved (the cyclopentanone ring). Whether this ring is involved in the other reactions is not known. However, if the C=O bands in the spectrum of the parent substance are correctly assigned, any change in this ring should be apparent from the infra-red spectrum of the intermediate. To obtain unequivocal assignments of the C=O stretching bands we prepared and studied appropriate derivatives. In addition we studied the influence of solvent on the spectrum and found strong effects in the C=O region. These solvent effects were not studied by earlier investigators (18, 19). The complexity of the spectra below 1600 cm-' is so great that we have not attempted to assign the bands. Spectra are presented from 650 to 3800 cm-1 in order to make the data available for future comparisons (except in cases of chlorophyll a in ethyl ether and ethyl pheophorbide a-oxime in CHCl3).