In order to understand magnetic interaction pathways, an experimental electron density distribution was determined in a purely organic free radical, m-(ethynyl)pyridyl nitronyl nitroxide, using accurate X-ray diffraction measurements. The intermolecular contacts were characterized by a topological analysis of the experimental electron density. Hydrogen bonds involving the O-N-C-N-O fragment reveal a 3D character. Atomic charges obtained by integration over the topological atomic basins indicate a charge transfer from the two oxygen atoms to the C=C triple bond by electron conjugation through the molecular skeleton, but also possibly through a short hydrogen bond. The X-ray results are compared to theoretical DFT calculations and to experimental spin densities obtained by polarized neutron diffraction.