Elektronenverdeling in cyanuurzuur

Bond lengths and angles obtained from X-ray diffraction are an important source of information about the nature of the chemical bond. X-ray diffraction may,in addition, yield even more detailed information on the chemical bond because, in principle, the distribution of the valence electrons in the molecule can be deduced from the diffraction data by a Fourier synthesis. The first attempts to determine the distribution of valence electrons by X-ray methods have been made around 1939 for diamond, rock salt and hexamethylenetetramine. From these and more recent investigations it. was concluded that accurate diffraction intensities and a very careful interpretation of the resul ts are required. It was our objective to find out, using the example of cyanuric acid, whether the recent improvements in both experimental and theoretical X-ray diffraction techniques may make it possible to test approximate wave functions by means of X~ray diffraction. The structure of cyanuric acid was (re)determined at room temperature (Ch. 2) and at 100 oK. The intensities at 100 0 K were measured accurately (4.3.4) on a three circle diffractometer constructed in the workshop of the chemistry department of the University of Groningen. Use was made of molybdenum radiation and balanced filters, the w scan method was applied and a scintillation counter with pulse height discrimination was used as detector. Attenuation filters were used to reduce the errors due to non-linearity to 1%. ... Zie: Summary