Organic / Inorganic
Name: doug happ
I teach sophomores an introductory biology course. When I cover
the biochemistry section the terms organic and inorganic come up.
I am not satisfied with the simplistic statement that organic
chemicals are ones that contain carbon since it does not account
for carbon dioxide being an inorganic.
Is there a definition of 'organic chemical' which accounts for all
or most molecules?
Given the existence of hemoglobin, "zinc fingers" in some
enzymes, and buckyballs, I'd guess not.
Considering the number of carbon containing molecules that ARE considered
to be organic relative to the number that are NOT, the rule that an
organic molecule is one that contains carbon, works VERY well.
The "exceptions" might serve as a lead-in to a discussion of the
use of rules, such as classifying molecules as organic or inorganic, as
a contrived convenience. They are helpful for most cases. In the cases
where the rules don't work well we have to be able to turn to other tools,
such as an understanding of chemical bonds or molecular orbitals so we
can concentrate on the characteristic of interest -- which is very rarely
whether the molecule is organic or more often things like reactivity.
You're at the leading edge of helping these students think for themselves
in a field where they probably feel unsure of themselves!
It sounds like you have some inquiring students there and some active
discussions. May you have many more!
An interesting question.
I believe that "organic" vs. "inorganic" originally stemmed
from the ancient idea that compounds could be divided
into two categories; those isolated from plants and animals
(organic) and those extracted from minerals and ores (inorganic).
[source: Bodner and Pardue, Chemistry: An Experimental Science, 1993].
As a working definition, now we think of organic chemistry as
primarily being the chemistry of carbon-containing compounds.
Most carbon-containing compounds have one or more of the
following: H,N,O,S,P. Some authors describe organic chemistry
as the study of compounds that contain carbon and hydrogen.
By this definition, CO2 would be "inorganic." But I would
like to stress that in fact there is no general agreement
on such semantics, and I'd bet that a lot of chemists
consider CO2 to be "organic" because it contains C and O.
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Update: June 2012