two-electron electron-flow arrow from bond to atom

Hi,

It makes no chemical sense for a two-electron electron-flow arrow to point from a bond to an atom that is not participating in that bond (see pictures below), but it is difficult for students to understand and keep in mind the difference between an electron-flow arrow pointing directly to an atom versus one pointing to between two atoms. I think it would be helpful to make it impossible to draw a two-electron arrow from a bond to an atom that is not participating in the bond, unless you can think of a good reason to allow it.

-- Bob

Hi Bob,

I have to check this with other users. However, I do not think that it is so bad to allow  the users drawing what they want, and I trust in them that they draw chemically correct  structures (except if you want to emphasize that something is not correct). For example: I like your first picture, it could be a nice figure in a book illustrating the theoretically possible /impossible electron movements. I would rather allow you  drawing this picture in Marvin and hope that it helps the student to understand the meaning of it.

Best regards,

Efi

ehoffmann wrote:

I trust in them that they draw chemically correct  structures.

Clearly, you do not work with undergraduates!

MarvinSketch already disallows certain illegal electron-flow arrow starting and ending points. The problem with the ones I have shown is that they look legal even though they are illegal. One of the nice things about Marvin is that it has chemical intelligence and alerts you when you do something that makes no sense chemically. This is something that makes no sense chemically, but Marvin allows it anyway.

How about at least highlighting the arrow in red when the user draws an electron-flow arrow from a bond to an unattached atom? It would be analogous to underlinging in red an atom with an illegal valence.

I have been thinking what would be the best solution in this case. 

I think  you should develop Structure checker option for it a https://docs.chemaxon.com/display/structurechecker/Structure+Checker+Developer%27s+Guide

We implemented a parameter which allows you to turn on the checker by default. (autoCheckStructure: https://docs.chemaxon.com/display/marvinsketch/Other+parameters)

Please let me know whether it could be a solution for you.

Best regards,

Efi

Hi Efi, I don't know about Structure Checker, but I can definitely screen the students' responses for a bond-to-atom electron-flow arrow and give an error message if the atom is not one of the bond atoms. (I can't correct the structure automatically, because there would be no way to know which of the bond atoms should be making the new bond to the atom.) Thanks for the suggestion.

No, I do not mean to correct the structure it automatically (the students should do that), just show the red patch automatically if the electron flow is not correct. I believe that you can do it with structure checker. Than you can run the Checker automatically.

Efi