3H-1,3,4-oxadiazolin-2-one gives error: hydrogen addition at locant: 3 was requested, but this atom is not unsaturated

[IngvarLa]

Opsin gives 1,3,4-oxadiazolin-2-one as:
O1C(N=NC1)=O

For every atom that I try to specify as having an extra hydrogen I get the error: hydrogen addition at locant: # was requested, but this atom is not unsaturated.

In particular I try to find which name to give:
O1C(NN=C1)=O
I thought 3H-1,3,4-oxadiazolin-2-one would resolve to this

Am I missing something here.

[dan2097]

The suffix oline implies a double bond cf. rule 1.2: https://www.acdlabs.com/iupac/nomenclature/79/r79_702.htm
You can use locants to move this around e.g. 2-azoline vs 3-azoline

I think 4-1,3,4-oxadiazolin-2-one might be valid (or at least OPSIN will accept it), but it's definitely clunky!

I think the typical way of naming this would be:
1,3,4-oxadiazol-2(3H)-one or by analogy to the name you gave 3H-1,3,4-oxadiazol-2-one

[IngvarLa]

OK - that works fine, allowing 3H in either place would be useful.
Same issue for oxazolin-2-one which would usually be 4-oxazolin-2-one