A neutron diffraction study of the crystal of benzoic acid from 6 to 293 K and a macroscopic-scale quantum theory of the lattice of hydrogen-bonded dimers

•Proton transfer and tautomerism are revisited from quantum viewpoint.•Neutron-diffraction gives evidence for long-range correlations for protons.•We introduce a decoherence-free macroscopic-scale crystal-state.•All observations accord with the principle of complementarity.•Computational-chemistry models are inappropriate.