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Core CIF Dictionary version 2.3



'_geom_torsion_atom_site_label_1' '_geom_torsion_atom_site_label_2' '_geom_torsion_atom_site_label_3' '_geom_torsion_atom_site_label_4'

Category: geom_torsion

Data type: char

Must appear in a looped list
Must match a value of '_atom_site_label'


   The labels of the four atom sites which define the torsion angle
   specified by _geom_torsion. These must match codes specified as
   _atom_site_label in the atom list. The torsion angle definition
   should be that of Klyne and Prelog. The vector direction
   *_label_2 to *_label_3 is the viewing direction, and the torsion
   angle is the angle of twist required to superimpose the
   projection of the vector site2-site1 onto the projection of the
   vector site3-site4. Clockwise torsions are positive,
   anticlockwise torsions are negative.

   Ref: Klyne, W. & Prelog, V. (1960). Experientia, 16, 521-523.

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