Dynamic Nuclear Polarization in Phosphorus Compounds with Perchlorotriphenylmethyl and Other Radicals

Publisher Website
Google Scholar
Abstract
Dynamic nuclear polarization has been examined in liquid solutions containing the radical perchlorotriphenylmethyl and 14 different phosphorus compounds. In addition, the radicals bisdiphenylenephenylallyl, tri‐t‐butylphenoxyl, and diphenylpicrylhydrazyl have been examined with five phosphorus compounds. The chlorocarbon radical shows on the average the least scalar coupling of the four. This is in accord with the well‐shielded spin distribution on this radical and the great chemical stability of aromatic chlorocarbons. PCTM is found to be almost completely inert, both electronically and chemically, toward phosphines and phosphites. Exceptional cases of high coupling were observed with PCTM and dimethylphosphite, triphenylphosphine oxide, and hexamethylphosphoramide. The first case appears to be due to a transient hydrogen bond Cl···H–P, the second due to an exposed polarizable orbital system, and the last due to an obscure chemical complexation tendency. Exceptional cases with the other radicals serve to illustrate further stereospecific molecular couplings between sites of active chemical or electronic attraction for each other.