Intramolecular Hydrogen Bond Reverting the Solvent Effect on Phosphorus Hyperfine Coupling Constants of β‐Phosphorylated Nitroxides

Recently, we reported a dramatic solvent effect on the phosphorus hyperfine coupling constant a(P) of beta-phosphorylated six-membered ring nitroxides, that is, a(P)proximately 25G of difference in a(P) from n-hexane to water (Org. Biomol. Chem. 2016, 14, -1228-1292). In this article, we report on the effect of intramolecular hydrogen bonding (IHB) in three nitroxides exhibiting IHB between the hydroxyl and diethylphosphoryl groups and one exhibiting IHB between the hydroxyl group and the nitroxyl moiety. It is observed that for the first three nitroxides, a(P) increases with increasing polarity/polarizability and hydrogen bond donor (HBD) properties of the solvent (pi* and alpha, respectively)-in sharp contrast to the data reported in the literature-and for the last nitroxide, a(P) decreases with pi* and alpha. In fact, the occurrence of IHB induces a large strain, its suppression by hydrogen bond acceptor (HBA) solvents affords an increase in a(P).