Even MORE intellectual

Stereochemistry: An Heuristically
Systematized Polysyllabic Excursion
Illustrating The Influence Of
Greek And Latin On The Sciences

by SmartAZ
December, 1997

Louie Pasteur discovered something, studying grains of crystal.
He saw left and right enantiomorphs, and Louie said "Now this'll
Change our conception of molecular construction. Images nonsuperimposible
Have inverse arrangements. Dextro and levo constructions are supposible."

This helped to explain Biot's observation of optical activity
Where polarized light gets twisted around, an interesting proclivity.
The construction is called "chirality", which is Greek for "handedness".
(We like to use Greek and Latin words, because of their splendidness. )

"Rectus" and "sinister" refer to construction, when discussing chirality.
"Dextro" and "levo" mean polarized light gets twisted in that locality.
Rectus and sinister are determined by substituents, so they can be predicted,
But dextro and levo are experimental, so our knowledge is still restricted.

Stereoisomers look different, that's all. Mirror images are called enantiomers.
If they're not mirror images we need a new term: how about "diastereomers"?
If you think it's hard to remember these words, wait till you see a projection;
You'll wish again for the good old days when all you needed was recollection!

Fischer projections can help understanding when figuring these things out:
You draw your molecule flat on a page, and pretend it's sticking out.
Two lines stick up and two stick down, a passable representation.
Well, at least it's better than the alternative: fatiguing your imagination!

Sometimes construction is chiral but there's a plane of symmetry,
Then mirror images look identical with perfect mimicry.
So then we call it "meso", and perhaps you begin to see
That things are not always what they seem when you run into chirality.

Consider for instance L-Dopa, a medicine for Parkinson's disease:
It's mirror image is D-Dopa, with no bioactivities.
Likewise the antibiotic that we know as penicillin:
The mirror image is totally worthless for treating your sick chillun.

Then there's one called plus caravone; in caraway seeds it's found.
It gives the seeds their unique odor. But the other way around,
It has the odor of spearmint. Now doesn't that seem dumb?
On the one hand it smells like bread, on the other like a stick of gum!

And if you buy ibuprofen you're sure to get R and S mixed
Because that's the only way the drug can be economically fixed.
The rectus interferes with the sinister and makes its action anemic.
When R and S types are mixed this way, the mixture is called "racemic".

Racemic products can be produced even if you don't expect it.
An achiral reagent gives chiral products, if there's nothing to protect it.
But if two substituents are the same, you know, an identical pair,
You don't need to worry at all 'cause there's no stereogenic center there.

Many organic reactions yield products with stereogenic centers.
In addition of HBr to alkenes, it depends on how the Br enters.
A secondary carbocation is SP2 hybridized
And mashed out planar so either side is easily reactionized.

The bromine approaches, this way or that, and does its little dance.
Transition states have equal energies, so it's just a matter of chance.
The products form at identical rates, they're equally likely to be,
But one of them will pay the bills and the other is just debris.

So if carefully integrated theoretical models suggest a chiral result,
Consider innovative transitional scenarios to minimize undesireable tumult.
Compatible functional capabilities necessitate flexible management objectives
And synchronized logistical contingencies can forestall unpleasant invectives.

Parallel development of empirical procedures to separate rectus from sinister
May require prohibitive investments, or be excessively difficult to administer.
Responsible engineering mobility coupled with reciprocal systematic projections
Might indicate asymmetric synthesis is needed to avoid expensive corrections.

So study your Latin and Greek real well, and master chirality.
Then you too can be an expert, and speak with finality
On subjects impressively erudite, with multisyllabic words.
And people will be impressed, and call you "One of those chemistry nerds".