E.S.R. spectra of X-irradiated methylene diphosphonic acid

X-irradiation of single crystals of methylene diphosphonic acid gives rise to E.S.R. spectra which have been assigned to (OH)2(O)P-ĊH2 and The former species is the more abundant of the two and the methylene group undergoes rapid re-orientation about a two-fold axis at room temperature but is stationary at 77 K. The 1H and 31P coupling constants in this radical are very similar to those in Ph3P+CH2, and support the previous conclusions [1] that there is little delocalization of the unpaired electron to the phosphorus atom.