Field of Science

Gernot Frenking is not happy...not at all

Stable is simply "able" with a "st"

Wow. This is a first for me. Three of the heavyweights in theoretical and computational chemistry have published a set of prescriptions in Angewandte Chemie for theoretical chemists claiming to have discovered new, "stable" molecules. In response, Gernot Frenking who is a well-known chemist himself has not just published a piercing and trenchant critique in reply to this article, but they actually seem to have reproduced the text of his referee's comments as a reply. This is a lively and extremely readable debate.

In an article asking for more "realism" from theory, the three heavyweights- Roald Hoffmann, Paul von Schleyer and Henry Shaefer III- have basically come up with a roster of suggestions in response to what they see as the rather flippant declarations by theoretical chemists of molecules as "stable". One of the annoying things about theoreticians is that they regularly analyze molecules and proclaim them as stable. Experimentalists then have to sweat it out for years to actually try to make these molecules. Frequently such molecules are stable under rather extreme conditions, for example in gas phase at 4 degrees kelvin. To address the animosity that experimentalists feel against such carefree theoretical predictions, the three chemists have come up with suggestions for publication.

They make some interesting points about criteria that should be satisfied when declaring molecules as stable. In fact they think that one must do away with the word "stable" and replace it by the words "viable" and "fleeting". For example for "viable" molecules, one has to be clear about the difference between thermodynamic and kinetic stability. Molecules described as viable by theoreticians must have half lives of about a day, must be isolable in condensed phases at room temperature and pressure, and must not react easily with oxygen, nitrogen and ozone (?). Molecules with more than +1 positive or negative charge must also be included with "realistic" counterions. Molecules must even be stable under conditions of some humidity. The authors then also make suggestions about reporting accuracy and precision, and about the well-known fact that theoretically reported precision cannot be more than experimentally measured precision.

If theoreticians think these suggestions are asking for too much, they have a friend in Gernot Frenking.

Frenking batters these suggestions down by basically launching two criticisms:
1. The suggestions are too obvious and well-known to be published in Angewandte Chemie
2. The suggestions are heavily biased towards experimentalists' preferences
As Frenking puts it, he expected to walk into a "gourmet restaurant", and was served a "thin soup" instead. Ouch.

I have to say that while the suggestions made by the three prominent scientists are quite sound, Frenking's points are also well-taken. He lambasts the suggestions that realistic counterions should be included in the calculation of a molecule with multiple charges; there are already molecules with multiple charges predicted to be theoretically stable which were then isolated by experiment. Ionic molecules with charges more than + or -1 are easily isolated in condensed phases. And one of the central questions Frenking asks is; why does a molecule need to be so experimentally stable in order to justify the publication of its theoretical existence. After all there are many molecules present in interstellar space which cannot be isolated under average Joe lab conditions. Under these circumstances, Frenking is of the opinion that the distinction between "viable" and "fleeting" is "eyewash" (it's the European way of euphemism)

I resoundingly agree especially with this contention, harsh as it sounds. Why should experimentalists get an easy pass? The whole point of theory is to push the boundaries of what's experimentally possible. To suggest that one should only publish a theoretical prediction if it can easily be verified by experiment is to do disservice to the frontiers of science. While I can understand the angst that an experimentalist may feel when he sees an unusual molecule stable only under extreme conditions declared by a theoretician as "stable", that's exactly the challenge experimentalists should be up to, to devise conditions under which they can observe these short-lived molecules. If they do this they are the ones who carry the day. Since stability as is well-known is a relative term anyway, why insist on calling something "stable" only if it satisfies the everyday lab conditions of the experimentalist. I believe that it is precisely by testing the extreme frontiers of stability that chemistry progresses. And this can be done only by making things hard for experimentalists, not easy. Theoreticians pushing experimentalists and vice versa is how science itself progresses, and there is no reason for either one of them to quit questioning the boundaries of the others' domain.

There are other points and criticisms worth reading, include other referee comments which endorse the article and are also quite interesting. In the end however, I cannot answer Frenking's central question; should this article have been published in Angewandte Chemie? We should leave it for readers to judge.

Roald Hoffmann, Paul von Ragué Schleyer, Henry F. Schaefer III (2008). Predicting Molecules - More Realism, Please! Angewandte Chemie International Edition, 47 (38), 7164-7167 DOI: 10.1002/anie.200801206

Gernot Frenking (2008). No Important Suggestions Angewandte Chemie International Edition, 47 (38), 7168-7169 DOI: 10.1002/anie.200802500


  1. The suggestions are heavily biased towards experimentalists' preferences

    May it ever be so, or they can stop calling themselves theoretical chemists and pitch their tents with physicists! Frenking is getting a little uppity!

    All kidding aside, I hope that chemistry never degenerates to the point that physics has, where an experimentalist can too easily become a data-monkey for theorists. Chemistry need not be easy, not at all, and clearly, it isn't. But part of the charm of chemistry is that it is mostly about stuff that you can experience.

    Qualitative and semi-quantitative models are both necessary (because of complexity) and sufficient (because more decimal places doesn't necessarily yield insight). There are oddballs that violate simple models that have a lot to teach us, and very delicate compounds well worth making to ascertain that we are, in fact, on solid ground theoretically. But I will not cede chemistry to theorists. No way.

    I know several theorists, admire and love their work (as I do Frenking's from what I have read), but in chemistry, they are helpful peers and not masters, and I'll not sit still for theorists trying to run things. I'll make stuff, and they can explain why it does what it does, but they only get to do that if I can't do it first!

    I started life as a physics major, and postdoc'd at a physics lab. I love them, too, and am fine with the way physics is driven by theorists. But boy, I would sure hate to see chemistry go that way.

  2. Who is talking about "ceding" to theorists? But the history of science makes it clear that theorists have as much claim to prediction that experimentalists have to then validate, as experimentalists have claim in producing stellar results which theorists have to explain. To say that theorists have to predict things which experimentalists can make or observe easily is in my opinion as much of an insult to experimentalists as it is to theorists. You are right that chemistry is mostly about things that we can experience, but as Carl Sagan said sometime, scientific experiences can have their own "variety"


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