Subject: Drawing Lewis structures

From: "Gurp, Ron van" <[email-masked]>
Date: Wed, 3 Feb 1999 09:41:29 +0100

Dear netters,

We are looking for software (Linux/Windows95/98 or NT) that can draw Lewis
structures of organic molecules, depicting all electron lone  pairs as well
as bonding pairs. Is there any computer program  available that generates
such structures semi-automatically? 

I appreciate all your answers and I will summarize.

Kind Regards, 

Ron A. Rumley- Van Gurp, M.Sc. 
TNO Prins Maurits Laboratory
Chemical Toxicology
E-mail: [email-masked]

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From: Allen Adler <[email-masked]>
Date: Wed, 3 Feb 1999 09:41:18 -0600 (CST)

Disclaimer: I am a mathematician, not a chemist.

>such structures semi-automatically? 

I asked about this several years ago. At the time, people referred
me to ChemTeX, which draws chemical formulas, but it doesn't seem
to handle Lewis structures. In Latex, one could probably use the
resident graphics capabilities to write macros or enhance the ones
that come with ChemTeX. If I were to do it, I would probably write
some programs directly in PostScript, but that is a matter of taste
and endurance.

Does "semi-automatically" imply that the program will figure out the
Lewis structure as well as draw it? The problem with that, in
my perception, is that, at least as it is described in textbooks,
the procedures for determining Lewis structures are not consistent.
There is an exception in the case of books which dumb down the rules
to apply only to a small class of examples (the "This is a course on
how to pass this course" approach), but let's not even mention that.

People have been complaining about this all the way back to Lewis, who
never intended that his innovation should be used to prop up the same
kind of arbitrary rule-based pedagogy about bonding that he himself had
to go through and which he had hoped to dispel by inventing Lewis structures.
I have a list somewhere, guaranteed not to be complete, which I compiled
when I was thinking of writing an article about how screwed up pedagogy
seems to be on this point. I abandoned the project when I realized that
people have long complained about this in print and it has had no effect
whatsoever on pedagogical practice.

Apart from such inconsistencies, different authors try to do different
things with Lewis structures. For example, Wheland's book on resonance
has much fancier versions of Lewis structures with different kinds of
electrons, and if I remember correctly he refers to other literature
that I was unable to obtain that takes it even further. At any rate,
there seem to be a lot of versions of "Lewis structures" in the literature.

Allan Adler
[email-masked]