Solvent effect in β-phosphorylated nitroxides. Part 4: detection of traces of water by electron paramagnetic resonance

Abstract

For decades, the nitrogene hyperfine coupling constant a_N of nitroxides has been applied to probe their environment using EPR. However, the small changes observed (≈2 G from n-pentane to water) with the solvent polarity allow only a qualitative discussion. A stable β-phosphorylated nitroxide exhibiting a small change in a_N (≈3 G from n-pentane to water) and a striking change (≈25 G from n-pentane to water) in phosphorus hyperfine coupling constant a_P with the polarity of solvent was prepared and used to develop the first procedure for the titration of water in THF by EPR, down to 0.1% v/v.