Search

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.

In this chapter a summary is given of the different ways in which spectroscopy at radio and microwave frequencies can be applied to obtain information of various kinds, and correlated with other branches of research in physics and chemistry. Some of the applications have already become clear in the preceding chapters, especially those associated with the evaluation of fundamental physical and chemical data, such as the determination of nuclear spins or moments, and chemical bond lengths or angles. Other applications have been mentioned in passing, such as the possibility of extremely precise frequency standards in the microwave region, and the very accurate determination of magnetic field strengths; whereas other problems, that can also be attacked by these techniques, have not been considered at all as yet—e.g. the detection of very small amounts of paramagnetic impurities, the study of photo-chemical reactions involving free-radicals, and several others.