Why Cant We See Molecules Some General Considerations of Diffraction and Spectroscopic Techniques

9-3 WHY CANT WE SEE MOLECULES SOME GENERAL CONSIDERATIONS OF DIFFRACTION AND SPECTROSCOPIC TECHNIQUES 

Virtually all parts of the spectrum of electromagnetic radiation, from x rays to radio waves, have some practical application for the study of organic molecules. The use of x-ray diffraction for determination of the structures of 

Other diffraction methods include electron diffraction, which may be used to determine the structures of gases or of volatile liquid substances that cannot be obtained as crystals suitable for x-ray diffraction, and neutron diffraction, which has special application for crystals in which the exact location of hydrogens is desired. Hydrogen does not have sufficient scattering power for x rays to be located precisely by x-ray diffraction. 

The major kinds of spectroscopy used for structural analysis of organic compounds are listed in Table 9-1. The range of frequencies of the absorbed radiation are shown, as well as the effect produced by the radiation and specific kind of information that is utilized in structural analysis. After a brief account of the principles of spectroscopy, we will describe the methods that are of greatest utility to practical laboratory work. Nonetheless, it is very important to be aware of the other, less routine, methods that can be used to solve special problems, and some of these are discussed in this and in Chapters 19 and 27. 

3A useful description of how molecular structures can be determined by x-ray vision is given in Chapter XI of Organic Molecules in Action by M. Goodman and F. Morehouse, Gordon and Breach, New York, 1973. 

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