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a. Uses of cell dimensions and refractive indices

In the early 1930s, before any but the simplest structure analyses were possible, the X-ray crystallographers assisted the chemists by demonstrating that the formula derived for steroids by Wieland and Windaus in 1928 could not be correct since the molecule could not be fit into the unit cell for which dimensions were determined crystallographically . Not only did Bernal, Crowfoot and Fankuchen show that the steroid molecule must be longer and thinner than the formula indicated, but, by considering the maximum and minimum directions of refractive indices, they showed exactly how the steroid molecule must lie in the unit cell, and from this where the functional groups for hydrogen bonding were located in the molecule. Since that time the structures of hundreds of steroids have been determined, verifying these early structural deductions.

References

1. Crowfoot, D., Harris, R. S. and Thimann, K. V. (eds.), Vitamins and Hormones , Vol. II, p. 409, New York, Academic Press, Inc. (1944).

2. Duax, W. L. and D. A. Norton, Atlas of Steroid Structure , Vol. 1, New York, Washington, London, Plenum (1975).


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Next: b. Determination of chemical formulae Up: 7. Small Structures in Biology Previous: 7. Small Structures in Biology

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