hypervalent N

Marvin 14.9.15.0. When I draw ON(O)=O, the N is given an extra H, and no valence error is reported. This is incorrect. N does not make five bonds except in very rare cases like NCl5. In ON(O)=O, the N should have a valence error.

No comment?

This is allowed because MDL in the old days allowed the drawing of structures like c1ccccn1=O and CN(=O)=O and users changing to ChemAxon from MDL wanted to continue the use this traditional way of molecule drawing. There is an API method to mark structures like these with valence error, but as far as I know it's can't be set for GUI usage at the moment. We use the more strict calculation for resonance structure calculation.

It's not likely for us to change the default behaviour as most of our users are like the current setup.  However we may introduce the setting of this as a parameter for Marvin.

Please do add that option. The way it is now teaches students bad habits.

Hi Bob,

Peter created a ticket into our issue tracking system, currently we can not promise anything on the timing, but we will notify you in this topic when the feature is ready.

Regards,
Istvan 

So why does MarvinSketch highlight as having an invalid valence the central N in CN=[N]#N?

Dear Bob,

   As Experts here explained me, it is only allowed to mark a 5 valance Nitrogen without charge, if it has an Oxygen connected to it with a double bond. I was told, it has a traditional reason.

Regards:
Balázs 

Well, that's just silly. Either you should accept pentavalent N as an alternative for N ylides, or you shouldn't.

Dear Bob,

   I told the experts your opinion. They agree, but they will keep this behavior due to traditional reasons. 

I am sorry:
Balázs