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Chemical Eye on a DC Substitution Reaction
by Preston MacDougall


October 07, 2007

In the timeless American film "Mr. Smith Goes to Washington", the political machine lost its rhythm after a Western state's Senator kicked the can. In the current upper house drama, Idaho Senator Larry Craig played some footsie while on the can, but the only thing that died was his credibility.

Still, the political machine is churning as if he had died, and I wouldn't be surprised if a Republican Party loyalist in Idaho was secretly picking out drapes.

Why Republican? Because that's the way the machines work. When a Senate seat is vacated mid-term, the Constitution allows for that state's governor to appoint someone to fill the seat until the next general election. Since both Senator Craig and the current Idaho governor are members of the Republican Party, everyone expects this DC substitution reaction to proceed with retention of political configuration.

In the more common SN2 reaction mechanism - bimolecular nucleophilic substitution - there is a forced inversion of configuration.
Credit: Creon Levit, NASA Ames Research Center.

According to the system of classifying the reaction mechanisms of organic chemistry, which was developed by the late British chemist Sir Christopher Ingold, this would be analogous to a SE2 reaction - bimolecular electrophilic substitution - where one group replaces another without inverting the original molecular configuration. In the more common SN2 reaction mechanism - bimolecular nucleophilic substitution - there is a forced inversion of configuration.

Things don't always play out according to the script, however. In the movie, the unnamed political machine had all the cards, but didn't get its way. In Idaho, the Senator announced that he intends to resign, but only if he has to. And he has since taken steps so that he doesn't have to, such as appealing his guilty plea to a public sex sting in a Minneapolis airport.

Even if he gets forced out, like the Senate tried to do to Mr. Smith, there is no guarantee that Idaho governor C. L. "Butch" Otter will play the role of party hack. He may have something up his sleeve. He could have something in his back pocket, but that's unlikely. People have been watching his back pocket since it was revealed that he once won a tight jeans contest. So that's the last place he would hide something from the Republican machine, none of whom are gay.

Another odd thing, that you would have to file under "not even Frank Capra could invent this stuff", is the disagreement between the testimonies of Senator Craig and the arresting police officer, over which hand Senator Craig used immediately after playing footsie.

jpg left and right gloves

Left and right gloves with a natural container of only left-handed amino acids.

According to Senator Craig, he used his right hand to pick up toilet paper that was to his right and on the bathroom floor. According to the policeman, who was in the stall to the right, Senator Craig used his left hand to rub the bottom of the divider between them.

Both of these actions are unusual, and probably unhygienic, but neither is illegal as far as I know. They do, however, remind me of the stereochemistry of organic molecules, such as amino acids. If a carbon atom has four different bonds to it, then there are two different ways that they can be arranged, and they are mirror images of one another.

The direct conversion of one form into the other is possible, but there is a high energy barrier to overcome during this contortion of the molecule. Inversion is usually achieved by breaking old bonds and forming new ones, as in the substitution reactions mentioned earlier.

Assuming you have all of your fingers, your right and left hands are similarly related to these molecules. And when chemists refer to right- and left-handed stereoisomers of an organic compound, they are referring the direction - to the right or to the left - that solutions containing these compounds will rotate so-called "plane-polarized light". The details are not important - unless you're on the jury of a trial of a pharmacist arrested for selling cheap, and possibly dangerous, right- and left-handed mixtures of a drug that has only been tested in one form, such as thalidomide.

Except for glycine, all amino acids have at least one carbon with four different bonds to it, and only "left-handed amino acids" are found in nature. This is not a "vast left-wing political conspiracy", but rather a result of the fact that amino acids are made by, and do biochemical business with, enzymes that discriminate between left and right symmetry much the same way your gloves discriminate between your right and left hands.

Laevus levus is Latin for "left side", as well as "unlucky". So the L in L-asparagine - a common amino acid first isolated from asparagus - stands for laevorotatory. This is not to be confused with lavatory rotation, which was implied by Senator Craig's arresting officer.

And finally, while party machineries will surely attack Senator Craig with disparaging comments, you won't find any D-asparagine molecules in your asparagus - that's not the way biomolecular machines (enzymes) work.


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Chemical Eye On... Columns by Preston MacDougall

Preston MacDougall is a chemistry professor at Middle Tennessee State University. His "Chemical Eye" commentaries are featured in the Arts and Public Affairs portion of the Nashville/Murfreesboro NPR station WMOT (

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Ketchikan, Alaska