13 C and 31 P NMR spectra of 1‐adamantylphosphoryl derivatives

The 13 C and 31 P NMR data of 26 bridgehead phosphorylated adamantanes, adamantyl‐P(O)XY, are reported. The 13 C chemical shifts of the α‐carbons are dependent on the X and/or Y group electronegativities, and can be interpreted by assuming p π d π electron back‐donation from X/Y to P. As expected, 31 P chemical shifts cannot be rationalized simply in similar terms. There is an extraordinarily good correlation between α‐carbon chemical shifts and the corresponding 1 J (CP) values. A tentative interpretation, based on the proportions of s and p character in phosphorus bond orbitals, is presented. Surprisingly large 4 J (PP) values were observed for two bis‐1,3‐dihalophosphophoryladamantanes.