A ¹³C‐NMR. Study of <i>cis‐trans</i> Isomeric Vitamins A, Carotenoids and Related Compounds

Abstract

Abstract The 1 H‐decoupled 13 C‐NMR. spectra of 35 all‐ trans , 17 mono‐cis vitamin A compounds (acetates, alcohols, aldehydes, acids and esters) and of one 11, 13‐di‐cis compound (11, 13‐di‐cis retinol) are reported. Included in this investigation are desmethyl‐, desmethylethyl, and aryl‐vitamin A analogues and others as well as 30 reference compounds of smaller molecular weight. Furthermore, the 13 C‐NMR. spectra of 23 β‐apo‐ and other carotenoids were studied. A complete assignment of the signals of all 106 compounds to the specific carbon atoms was achieved by extensive application of lanthanide shift reagents, mainly Yb(dpm) 3 , by CW‐offset and selective 1 H‐decoupling experiments, by comparison of the shifts of related compounds, and in three cases by utilization of specifically deuteriated compounds (11, 12‐D 2 ‐retinol and retinyl acetate, 15, 15′‐D 2 ‐β‐carotene). The chemical shift differences between the cis ‐ and trans ‐vitamin A compounds and the applicability of the shift reagents for the assignment of the 13 C‐NMR. spectra are discussed.