Electron Density Studies of Methyl Cellobioside

Experimental X-ray diffraction crystallography determines the variations in electron density that result from the periodic array of atoms in a crystal. Normally, the positions and type of atom are determined from the electron density based on an approximation that the atoms are spherical. However, the atoms can also be refined based on a multipole approximation that permits the electron density to show a more resolved picture. For example, the lone pairs of electrons become visible, and the characteristics of the electron density between atoms can indicate when bonding is occurring. Even rather weak interactions, such as hydrogen bonds, can be resolved with this technique. Comparable information can be obtained from theoretical electronic structure theory calculations, and the two methods can work together to gain added insight. Methyl cellobioside has structural similarities to cellulose III which results from ammonia mercerization of cotton, but unlike the cellulose polymorph, provides sufficiently high quality crystals for these determinations.