The synthesis of retinals enriched with 13C at positions 11, 13, 14, 15, 12&20, 13&14, and 14&15 in high isomeric purity is reported. The importance of these retinals in studying the structure and properties of rhodopsin and bacteriorhodopsin by 13C NMR spectroscopy is briefly described. Copyright © 1985 John Wiley & Sons, Ltd.
