Structure and Dynamic Properties of Solid l -Tyrosine-Ethylester as Seen by 13C MAS NMR

13 C MAS NMR experiments on solid l -tyrosine-ethylester with 13 C in low natural abundance and in fully 13 C enriched form are reported. The phenyl rings are found to undergo π flips with a rather low activation energy E a = 50 ± 12 kJ mol -1 . In addition, the ester groups are afflicted by dynamic disorder at all temperatures accessible to MAS NMR experiments. Zero-quantum homonuclear 13 C recoupling experiments on fully 13 C enriched l -tyrosine-ethylester were carried out at low temperature. These experiments faithfully reproduce those molecular structural features, known from single-crystal X-ray diffraction, that are defined by short-range 13 C− 13 C interactions but fail to uniquely characterize the complete molecular conformation defined by intermediate-range 13 C− 13 C interactions.