in-out isomerism

https://doi.org/10.1351/goldbook.I03055
@I03294@ found in bicyclic systems having long enough bridges to allow the @B00736@ exocyclic bond or lone pair of electrons to point either inside the structure or outside.
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Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2210 [Terms] [Paper]