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I have been studying organic chemistry for years, and I do not remember the spotting double bond represented with crossed lines, except maybe one ore two more times in addition to the following one

enter image description here

which is taken from the Aescin Wikipedia graphics here.

I guess it is a drawing or rendering mistake, or a representation of unspecific E/Z configuration. If the latter is true, where can I find more info on usage of this symbol?

UPDATE:

A comment by gilleain leads to GRAPHICAL REPRESENTATION OF STEREOCHEMICAL CONFIGURATION (IUPAC Recommendations 2006). Relevant paragraph is:

...
The most common convention for depicting double bonds with unspecified configuration in molecules of all sizes uses a wavy bond.
...
A crossed double bond has sometimes been used to indicate unspecified double bond configuration or a mixture of configurations. This type of bond is not considered acceptable for general use, although it may still be required by some computer software.

There's still missing piece of information about which software and by what means it "requires" this representation.

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It is, for example, used by Marvin JS -- one of the editors in the GUI of Reaxys by Elsevier to query the database for structures, where you do not impose either (E)-, nor (Z)-configuration of the double bond. Below an example if you were looking for both isomers of stilbene:

enter image description here

(demo version here).

Beside ChemDraw, ChemDoodle's sketcher (here) and PubChem's sketcher are other examples of "some software" equally allowing such a representation, too. I speculate it has something to do how databases (like ISISBase, Beilstein/Reaxys, Scifinder, for example) traditionally store(d) chemical structures and reaction schemes in a machine-readable format.

One may, for example, draw (cis)-stilbene with ChemDoodle "in the standard way" and save it as *.mol format and set this file in comparsion with the result of an undefined double bond with the using the wavy bond towards one of the phenyl rings. In the chemical table, there is no significant difference spot:

enter image description here

If the "standard (cis) *.mol" file is compared with the one where the double bond is crossed -- as in the OP figure -- there is a difference on line #26 (fourth column now reads a three, instead of a zero), while maintaining the other entries:

enter image description here

This picture, naturally, differs from the *.mol files of classically specified (cis) and (trans) configuration:

enter image description here

used structures:

enter image description here

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