pierre laszlo

L'analyse chimique comme dématérialisation

L'analyse chimique est prise comme exemple, dans l'activité réelle d'un laboratoire d'aujourd'hui. La matière y est tenue à distance, mise entre parenthèses. Elle est certes indispensable, mais à titre de matière première pour la prduction d'information. L'analyse chimique traduit des messages instrumentalisés en des modules informationnels. Nous sommes redevables de cette révolution conceptuelle aux grands chimistes, Justus von Liebig, Auguste Laurent, Jean-Baptiste Dumas et autres qui, au milieu du XIXe siècle, ont bâti l'audacieuse théorie des radicaux. Depuis lors, la chimie moléculaire est devenue combinatoire de ces modules idéaux, groupes d'atomes n'ayant d'existence que fictive, qui sont pour la chimie ce que les phonèmes sont pour la parole.

The nomadic state

Intellectual nomadism and its virtues

Scientific discovery can thrive on lack of familiarity. Often, an outsider to a field will rejuvenate it and render it fertile. 1 Cross-disciplinary research is fecund. But how to encourage it? How does one go across scientific boundaries? Where obtain the "road maps" and the guides for venturing into unknown territories?

An obvious answer is multidisciplinary teams, small enough that conversation will ensue and that a "trading zone" 2 will start to exist. One ought to encourage also (bureaucracies running science as a district administration by their very existence discourage it) a spirit of intellectual nomadism. Nomadic tribes, nomadic people, nomadic nations have enriched history. Remember some of their epics: the Jewish diaspora; the Westward move from the Gobi Desert to Central Europe and to Scandinavia of Magyars and Finns; the Turkish migration from the shores of the Pacific to present-day Turkey; the tribulations of the Mongols from Central Asia to set-up empires in India and China; the Indo-European migration into Western Europe, the Gypsies embodying its lingering trace; closer to us, in the nineteenth century, the Western expansion of the United States. Such moves of populations are emblematic of a free-roving spirit of enquiry across disciplinary boundaries. A living example is Paul C. Lauterbur, a pioneer in many areas within nuclear magnetic resonance (nmr). Two of those areas he explored and put on the map almost single-handedly are carbon-13 nmr and magnetic resonance imaging (mri). His motto, borrowed from the US military during the Vietnam War, is "search and destroy," with the meaning of forays into unknown territory for "quick and dirty" (another American phrase) sizing-up the riches.

Michelet vulgarisateur


Pourquoi Pasteur s'est-il livré à l'attaque publique de Michelet? La réponse à cette question se trouve du côté de la jalousie d'auteur: Pasteur ambitionne la gloire littéraire, celle du génial vulgarisateur que Michelet est devenu.

L'a-t-il fait, comme Pasteur l'insinue, au détriment de l'exactitude scientifique? S'il est permis de généraliser à partir d'une citation de L'Insecte, il semblerait plutôt que Michelet présente une information tout-à-fait fiable; davantage, qu'il fut un précurseur, annonçant et anticipant certaines des percées de la science du XXe siècle.

Mais l'exposé, loin de verser dans l'hagiographie, nous montrera aussi un autre aspect de Michelet vulgarisateur, celui de l'habile plagiaire. L'analyse d'une page célèbre de La Mer nous le fera voir dans cet autre rôle.

The say of things

by Roald Hoffmann and Pierre Laszlo

In search of a chemical conversation we are on a farm in Uniow, a little Ukrainian village in Austro-Hungarian Galicia, just before the onset of World War I. In the farm yard we see a big, steaming lead-lined iron pot. The men have mixed some potash in it (no, not the pure chemical with composition KOH from a chemical supply company, but the real ash from burning good poplar) and quicklime, to a thickness that an egg ÿ plenty of eggs here, judging from the roaming chickens ÿ floats on it.

Elsewhere in the yard, women are straining kitchen grease, suet, pig bones, rancid butter, the poor parts skimmed off the goose fat (the best of which had been set to cool, cracklings and all). This mix doesn’t smell good; they would rather toss the kitchen leavings and bones into the great iron pot, but the fat must be free of meat, bones, and solids for the process to work.

They are making soap. Not that we had to go that far, near where one of us was born, for soap was prepared in this way on farms since medieval times well into this century. Fat was boiled up with lye (what the potash and quicklime made). The reaction was slow ÿ days of heating and stirring until the lye was used up, and a chicken feather would no longer dissolve in the brew. One learned not to get the lye on one's hands. The product of a simple chemical reaction was then left in the sun for a week, stirred until a paste formed. Then it was shaped into blocks and set out on wood to dry.

And inside the steaming pot, deep inside, where the fat and the lye are reacting? There is the conversation we are after, a hellishly animated molecular conversation. The lye that formed was an alkaline mixture of KOH, Ca(OH)2 and NaOH. In the vat one had hydroxide (OH-) ions, and K+ , Ca2+ , Na+ all surrounded in dynamic array and disarray by water molecules. Contaminants aside, the fat molecules are compounds called esters, in which an organic base, glycerol, combines with three long-chain hydrocarbon chains. A typical one is stearate:

If we just call this ion Rÿ, then the formula for a fat is roughly

Rose ou Noir?


Le dernier demi-siècle arbora, pour la chimie, les couleurs de la science: on y compte plus de chercheurs que leur nombre cumulé sur toutes les périodes passées; on y répertorie de multiples applications, prises comme locomotives es économies de pays qui sont déjà les plus riches; et on y constate la fascination du public pour des domaines comme l'astronomie ou la paléontologie. Néanmoins, si l'avancement du savoir est venu remplir des cases de la science chimique restées longtemps désespérement vides (structure des protéines, synthèse organique nantiosélective, ou reconnaissance moléculaire, pour ne citer que ces trois cas), la véritable création fut souvent eléguée dans les coulisses de la recherche d'imitation, et contrainte de jouer les utilités.

In any form or shape?


This study places the history of stereochemistry into its rightful time span of the longue durée., To do so, it has been necessary to do three things.
First, I draw attention to Wollaston's and Ampère's contributions dealing with molecular geometry, and why they have been neglected. Second, I single out Ampère's paper for fleshing out Haüy's crystallographic ideas. Those ideas underline the geometric understanding of molecular structure. With their Pythagorean make-up, not only do they bridge a succession of visionary scientists across the centuries, from Kepler and Robert Hooke to Alfred Werner and others; they also attempt to link chemical structure to the incisive mathematical physics introduced by Galileo and Descartes. Finally, I shall also counter two misleading constructions: ascribing the birth of stereochemistry uniquely to Le Bel's and van't Hoff's announcement of the tetrahedral carbon atom; and the glib, hasty dismissal as "Whig" of the in-depth reworking of the historical narrative made necessary by more recent developments.

Conventionalities in formula writing


Chemical formulas, those small icons which chemists are wont to scribble in their notebooks and in odd places, such as the back of an envelope, and which to the general public have become emblems of their profession, are an excellent topic for history. These artefacts remain today tools for communication within the community of chemists. They continue serving as didactic instruments in teaching. The establishment of an individual formula for a chemical compound or a substance chronicles the laboratory methods, both routine and specific, which came into play in order for it to be written down and to assume the status of the analog of a word, to be stored within the growing lexicon of chemistry.

When addressing this topic, the historical narrative, besides its usual needs for accuracy and for an unerring sense of the strange and original taste of the bygone, demands the twin crutches of philosophical and linguistic inquiries. I wish to provide these complements if not in full, at least in a manner suggestive of some of the main issues.

I shall concern myself with the period of consolidation, when formulas entered the language of organic chemistry and started becoming sterotyped, the approximate period 1865-1905. 1 Why choose such a periodization? Because it brackets, approximately, the birth of the modern chemistry journal, JACS was started in 1879, and that of the modern comprehensive repertory of new chemical compounds, Chemical Abstracts were launched in 1907. Kekulé announced in 1865 his cyclic structure of benzene. The Chemical Society published in London, in 1882, Nomenclature and Notation, the first guidelines for establishing systematic and uniform practice. And the American Chemical Society followed suit in 1884 by establishing its Committee on Nomenclature and Notation. The international conference convened in Geneva in 1892 established norms for chemical nomenclature. 2 And Alfred Werner, in 1895, gave a systematic nomenclature for coordination complexes. Key milestones in the history of molecular formulas - so-called "structural formulas"; I favor the adjective "molecular" since the meaning of "structural" has changed considerably over the twentieth century - include the serendipitous synthesis of mauveine (1857), the first synthesis of alizarin (1868) and the identification of ibogaine (1905); Gomberg first free radical appeared in print in 1900. The forty years 1865-1905 were thus for molecular formulas of organic compounds those of the rise in their practical use, of their standardization and also of the first challenges to the rules governing them.

As always in history of science, the risk of Whig history lurks at every corner of the retrodictive narrative. The danger is to read into the structural formulas, as they were used at the end of the nineteenth-beginning of the twentieth century, meanings which they had yet to acquire in the post-Gilbert N. Lewis and post-Linus C. Pauling eras. Examples of such potential anachronisms are: (i.) viewing benzene rings as ipso facto synonyms of "aromaticity;" (ii.) reading double bonds as implying shorter and stronger interatomic linkages; (iii.) interpreting loss of a water molecule in a dehydration process as a thermodynamic driving force for the observed conversion. The eerie superficial similarity of these late nineteenth formulas to our early twenty-first century formulas can easily become misleading.



Pierre Laszlo and Roald Hoffmann

A critical stance is essential to science. Proving other people wrong is a favorite private and public satisfaction -- there is nothing some people like better. But, excess zeal discounted, doubt serves as a powerful impulse to the advancement of knowledge. We document it here with the discovery of the structure of ferrocene, a story which also plays up the virtue of the spoken word. [1] We base it on various published (and most fragmentary) accounts, supplemented with some very helpful correspondence from colleagues.

Diborane story

Just as with ferrocene, 1 the formula first written for diborane B2H6 was orthodox, in conformity with the usual paradigmatic rules regarding molecular structure. And it was wrong. Correcting the mistake showed an extremely unusual bonding picture for the molecule. Just as in the ferrocene case, it opened up a whole new chapter of chemistry, later recognized with the award of a Nobel prize to William N. Lipscomb in 1976 for "his studies on the structure of boranes illuminating problems of chemical bonding."

I shall highlight here only a few episodes from the diborane story. In 1937, a former student of Linus Pauling, Simon H. Bauer - incidentally he is still active in research at Cornell, at the age of 88 - applied the technique of electron diffraction, a tool which he had learned to use at Caltech with Pauling, to diborane. He found and he reported a structure analogous to that of ethane, which therefore he wrote as H3B-BH3. 2 In 1942, Bauer reiterated his contention of the ethane-like structure for diborane. 3 At the same time of the early 1940s, H.I. Schlesinger, a chemistry professor at the University of Chicago, was also working on boron compounds. One of the reasons was his involvement in the Manhattan Project: it was thought that an isotope separation could be devised for uranium using such derivatives. In any case, Schlesinger was very much interested in the structure of diborane.

Science often advances upon willful transgression of a seeming interdiction. Examples which leap to a chemist's mind are noble gas compounds, strained hydrocarbons such as tetrahedrane, activation (by organometallics) of even methane, and, to mention just one brilliant, more recent achievement, inclusion of an allene within the confines of a six-membered ring while preventing its conversion into a benzenoid. Such feats put all the cunning of a scientist into coaxing and, yes, coercing the system at hand to obey instructions from one's daring imagination. As always, it is hard. Not for nothing is our playroom called a laboratory. And when the task is done and the time arrives to convey to others (who might not be privy to the anguish of the work) all that struggle and the majesty of the achievement, the scientist quite naturally lapses into metaphor. One such, founded in male 19th century language as much as in history, is some more or less prurient variant of "Unveiling the Secrets of Nature." Another, evoking the thorny, twisted path to understanding and the long hours of toil in the laboratory, is "Wrestling with Nature."
Circulation of concepts


A major obstacle to chemistry being a deductive science is that its core concepts very often are defined in circular manner: it is impossible to explain what an acid is without reference to the complementary concept of a base. There are many such dual pairs among the core concepts of chemistry. Such circulation of concepts, rather than an infirmity chemistry is beset with, is seen as a source of vitality and dynamism.