The successful identification of hydrogen positions unambiguously confirmed the presence of the expected 7H tautomer. This tautomer is formed upon deamination of guanine and generally predominates over the 9H form of xanthine . Figure shows a Fourier electron potential map in which the hydrogen positions can be clearly recognised. The unrestrained N-H and C-H bond lengths were found to vary between 1.06(4) and 1.16(4) Å (Table .3). It is notable that these bond lengths are longer than the corresponding distances found using X-ray crystallography, particularly since the latter are often used by default for kinematically refined 3D-ED structures where hydrogen positions cannot be resolved. Locating the position of hydrogen atoms from X-ray data can be complicated by their low atomic number, low scattering power, and variability due to thermal motion (characterised by atomic displacement factors) . In addition, by virtue of having only one electron, a hydrogen atom's entire electron density is always involved with bonding, resulting in a measured shift of the hydrogen atom towards the atom to which it is bonded using X-ray diffraction data . It has previously been possible to determine and dynamically refine hydrogen positions with electron diffraction data in which average C-H bond lengths were found to be 1.15 Å by Palatinus et al. . The elongated N-H and C-H distances (in comparison to X-ray distances) discovered here are consistent with trends in this previous work. This observed difference in distances between electron and X-ray diffraction data is likely due to the fundamentally different nature of their interactions, where electrons interact with the crystal potential whilst X-rays interact with the electron density.