Location of the proton in the very strong OHO hydrogen bonds in 2-(N,N-diethylamino-N-oxymethyl)-4,6-dichlorophenol. A single crystal neutron diffraction study

The crystal structure of 2-(N,N-diethylamino-N-oxymethyl)-4,6-dichlorophenol contains two slightly different molecules A and B, both with very strong intramolecular O … H … O hydrogen bonds, with O–O distances 2.423(4) Å and 2.400(5) Å, respectively, and with no crystallographic symmetry. The bridging oxygen atoms are also chemically different, O1 is bonded to carbon and O2 to nitrogen. The single crystal neutron diffraction study shows quite unambiguously that the proton in both cases is located slightly off-centred. In the A molecule O1–H = 1.167(6) Å, H–O2 = 1.258(6) Å and the angle O–H–O = 175.8(5)°; in the B molecule O1–H = 1.186(7) Å, H–O2 = 1.214(7) Å and the angle O–H–O = 176.5(5)°. As expected the proton is thus closer to the centre in the slightly shorter hydrogen bond.