The crystal structure of alpha-glycylglycine

The cystal structure of the α crystal form of glycylglyeine, -CO 2 CH 2 NHCOCH 2 NH 3 + , has been investigted. The cell dimensions are a = 7·70, b = 9·57, c = 9·48 A β = 124°35'. The space group is P2 1 /a with four molecules per cell. Mo kα rays were used. The trial structure was derived by use of part-cell Patterson methods and modlfied Banerjee equations. Final refinement was by block-diagnol anisotropic least-squares adjustment to an R of 12·3 and yielded standard deviations of about 0·007A in bond lengths.The intramolecular chemical bond lengths and interbond angles agree well with those found for the same molecule in the previously reported β crystal form but the configuration of the molecule is somewhat different. There is an angle of about 22·4° between the plane of the amide group and that of the carboxyl group. In the β crystal these group were coplanar within experimental error. Since the α form is probably the stable form, this distortion presumbly permits better molecular packing with stronger hydrogen bonds and van Waals interactions.