ASSIGNMENT OF C-13 RESONANCES IN THE PHENCYCLONE-NORBORNADIENE ADDUCT VIA 2D NMR - C-13 EVIDENCE FOR HINDERED ROTATION OF UNSUBSTITUTED BRIDGEHEAD PHENYL RINGS

C-13 NMR chemical shift assignments were obtained for the Diels-Alder adduct of phencyclone with norbornadiene in CD2Cl2 and in CDCl3 solution. The C-13 spectrum at 50.3 MHz, as well as the H-1 spectrum at 200.1 MHz, show evidence for hindered rotation of the two unsubstituted bridgehead phenyl rings of the adduct at ambient temperatures. In CD2Cl2 solution, all 19 of the unique C-13 nuclei of this molecule give rise to individual C-13 resonances. The H-1 assignments which were made earlier, together with one-bond and long-range 2D heteronuclear correlation experiments, allowed the assignment of all C-13 chemical shifts in the molecule.