Infrared spectroscopy of retinoids

The Fourier transform infrared spectra of 15 purified retinoids were compared. Retinoids with conjugated C = O groups revealed the presence of a band between 1730 and 1630 cm-1 X A characteristic of retinoids is the presence of a band between 1650 and 1620 cm-1 due to C = C stretching where three to four conjugated C = O and C = C bonds were present or between 1610 and 1555 cm-1 where more conjugated unsaturations were present. The presence of cis double bonds was confirmed by a band at 1380 cm-1 while unsubstituted trans double bonds gave absorbances at 990 to 955 cm-1. Epoxy rings, which are present in some retinoids, resulted in bands at 1250, 880, and 790 cm-1 while a furan structure was confirmed by bands at 1175, 1083, and 1065 cm-1.