Abstract
Neutron diffraction can provide very precise stereochemical information about hydrogen bonds and other features involving hydrogen atoms in crystals. This is because, unlike for x rays, the hydrogen atom has a significant scattering amplitude for neutrons relative to other atoms. Highβprecision studies of a class of molecules, like those on Ξ±βamino acids carried out at Brookhaven and Trombay, can provide important information on systematics of the structure, conformation, and hydrogen bonding parameters. Some attempts have also been made to extend these singleβcrystal studies to some proteins like myoglobin, lysozyme, and trypsin. The large anomalous scattering amplitudes for some stable isotopes like ^113^Cd and ^149^Sm and the easy variability of neutron wavelength also provides, in principle, a method for solving the phase problem without crystallizing too many heavy atom derivatives. The combination of neutron and xβray diffraction data, now being used to study charge density distributions in organic molecules and hydrogen bonds, may be extended in the future to larger molecules of biological importance. The smallβangle scattering of neutrons is also a powerful technique for studying large biological particles in solution at low resolution to obtain information about sizes, shapes and distribution of constituents.