Hydrogen helicoidal structure

The chains of isotactic polymers (in which the dimensions of R are much greater than those of the hydrogen atom) have the tendency to assume a helicoidal configuration with a pitch which depends on the dimensions of the R group. There is evidence that a helicoidal structure has the tendency to exist also (at least partially) in the amorphous state. It is detectable. 

Cense, J.M., Agafonov, V., Ceolin, R., Ladure, P., and Rodier, N. (1994) Crystal and molecular structure analysis of flutamide. Bifurcated helicoidal C H- -O hydrogen bonds. Struct. Chem. 5, 79-84. 

Although the base sequence of DNA remains to be elucidated, Watson and Crick [90, 91] proposed a model for its tridimensional structure. Several models had been proposed prior to that enounced by Watson and Crick, but they were all discarded because they were not compatible with the established physical and chemical properties of the DNA molecule. Modern concepts of the tridimensional structure of the DNA molecule are based on four different sources of factual information (1) the base composition of the DNA molecule, (2) the physicochemical information suggesting the existence of hydrogen bonds (3) the electron microscopy data, which indicates that the molecule is a long, extended structure about 30,000 A long and 30 A wide and (4) X-ray diffraction studies of crystalline and paracrystalline DNA molecules from which the molecule is known to have a helicoidal shape. (The term spiral should not be used to describe DNA. A spiral winds around a cone and a helix winds around a cylinder.)... 

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