Drawing /incorrect/ structures: writing exams

The "Chemically Intelligent" feature is nice, but it prevents me from drawing


an /incorrect/ Lewis structure. When writing exams, it is necessary to make


sketches of molecules that cannot exist. For instance:





Which resonance structure has a lower energy, and why?





O=C=O (with all the lone pairs, etc) or O-C(triple-bond)O (etc.)





Obviously, I don't want to display charges on the oxygen atoms; that's what the question is about.





I am sure you can imagine plenty of other oddball structures that an instructor would like to create - and even some fairly routine things. I cannot seem to draw an ozone molecule without having charge labels on the atoms.





It should be very easy to add an option (call it "expert mode" or "free draw" mode or something) that turns off all of the checking and allows the user to place as many bonds, electron pairs, wrong charge symbols, etc. as they want. Your product comes closest of all that I have tried in the last week, and generates the best images. But I have still had to export an image and touch it up in a drawing program in many cases.

Maybe the solution we discussed in the other topic (http://www.chemaxon.com/forum/viewtopic.php?t=3309) also helps here.





I attached the O-C#O structure using aliases. To display it correctly, make sure that the View > Misc > Lone Pairs option is switched on.

Close! The O with the single bond is missing a lone pair, because it thinks it should be an OH group (implicit H). I should have attached my "best effort" to my first post so you see what I mean. View what I have attached with view->misc->lone pairs enabled and view->misc->implicit hydrogens->on all both enabled to see what I'm getting at.





It seems that with the alias trick, I can get very close to drawing whatever I want, with the limitation that MarvinSketch displays charges on atoms. I suppose I can always just go erase the charge symbols in gimp or something, but that is an extra step I would like to avoid. Can you turn off the display of charges? With that option and some fooling around, I should be all set.





It also occurs to me that I am asking MSketch to do something for which it may not have been designed. But there just are not many chemical drawing programs that let you drop electron pairs wherever you want, and for GeneralChemistry educational material from homework up to textbooks, that's what I want.





Thanks for all your help.





Justin

Actually, there are several problems here.


- you want to correctly display lone pairs and radical electrons without the correct display of charges: it is not possible in Marvin


- you want to be able to assign the charge to the bracket instead of an atom inside: this feature will be implemented in Marvin 5.2


- in NO2 the oxidation state of Nitrogen is 4: it is not supported in Marvin yet (because it is not usual in organic compounds); we will fix it


- I don't really understand your request related to lone pairs on terminal hydrogens, but if you want to represent Hydrogen-bonds this way, that is not possible with Marvin

We also had some situations in which the chemical intelligence of MarvinSketch prevented us (or students) from drawing erroneous structures. We solved the problem by writing our own applet, which we call LewisSketch. We've incorporated it into ACE Organic. LewisSketch allows the user to add up to 16 lone pairs per atom, up to +/-8 charges, and as few or as many bonds to each atom as the user likes. Depending on what you are using it for, we might make it available to you for free. Contact me directly if you are interested.