Should carbonyl oxygens be considered unsaturated?

[rogersayle]

The (admittedly dubious) name "4,O4-dihydro-uridine" generates the error message "hydrogen addition at locant: O4 was requested, but this atom is not unsaturated", which (pedantically) isn't entirely correct. My current work-around is to use (the acceptable to OPSIN) "3,4-dihydro-4-deamino-4-hydroxy-cytidine", but I thought I'd suggest this feature as a possible enhancement request. Thanks in advance, Roger

[dan2097]

The error is technically misworded, and probably should be more like the error you get from say "dihydroethene", which focuses on there being no applicable cyclic atoms. No cases immediately come to my mind where the hydro prefix applies to acyclic atoms.

3,4-dihydro-4-deamino-4-hydroxy-cytidine doesn't seem an unreasonable name, and probably better shows the relationship to cytidine than a more systematic name like 4-Hydroxy-1-(β-D-Ribofuranosyl)-3,4-dihydro-2(1H)-pyrimidinone