Abstract P-Vinylbenzylphosphonic acid (2) was synthesized and crystallized in two phases A and B. The latter phase was easily converted into the former. Both phases were investigated by IR and solid-state 31 P and 1 H NMR spectroscopy, and X-ray crystallography. The use of recently developed NMR methods has enabled us to increase the usually poor resolution of solid-state 1 H spectra. This gave additional insights on the proton environments. In ...