Abstract
THE thirty-third Bedson Lecture was delivered on February 21 at Armstrong College, Newcastle-on-Tyne, by J. D. Bernal, assistant director of research in the Crystallographic Laboratory, Cambridge, who took as his subject “Modern Crystallography and Organic Chemistry”. Mr. Bernal gave practical details of the method of X-ray examination of organic substances, which he explained constitutes an indirect method of seeing molecular structures. A pencil of X-rays is diffracted by all possible internal planes of regularity of a crystal to a series of points which can be photographed; the intensities and angles of deviation of these diffracted rays constitute the observed data which will unequivocally characterise a substance. It is also relatively easy to determine the symmetry of the molecule, which in some cases identifies an isomeride as cis or trans, and to determine the size of the unit cell of the crystal from which, knowing the density, the molecular weight can be found, and also the shape of the molecule, which has been of value in sterol chemistry. The complete interpretation of X-ray diagrams to yield the position of each atom in the unit cell and the electron density in each part of the molecule is much more laborious and has only recently been achieved. Besides confirming the classical organic structures, this method gives direct information of the distortion of valency angles in such cases as durene, and of the semi-aromatic nature of the bonds in benzoquinone and dinitrobenzene.
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X-Ray Studies of Molecular Structure. Nature 137, 391 (1936). https://doi.org/10.1038/137391b0
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DOI: https://doi.org/10.1038/137391b0