Revista CENIC. Ciencias Químicas ISSN: 1015-8553 [email protected] Centro Nacional de Investigaciones Científicas Cuba

Wisniak, Jaime Joseph Achille Le Bel. His Life and Works Revista CENIC. Ciencias Químicas, vol. 33, núm. 1, enero-abril, 2002, pp. 35-43 Centro Nacional de Investigaciones Científicas La Habana, Cuba

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RESEÑA BIOGRAFICA

Joseph Achille Le Bel. His Life and Works

Jaime Wisniak

Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84105. [email protected].

Recibido: 26 de abril del 2001. Aceptado: 22 de mayo del 2001.

Palabras clave: Le Bel, Química, estereoquímica, actividad óptica, cosmogonia Key words: Le Bel, Chemistry, stereoquímica, optical activity, cosmogony.

RESUMEN. Joseph Achille Le Bel es un ejemplo de científicos como Réaumur The same year his father passed que investigaron muchÍsimos temas, pero solo son recordados por uno. Le Bel away and his two sisters, Marie and es un nombre bien conocido por los estudiantes de Química en general, y Emma, took charge of the family in- estereoquímica en particular. El nos dejo los principios básicos que determinan dustry and in this way allowed Le las condiciones geométricas que un compuesto de carbón debe satisfacer para Bel to continue chemical studies. He que presente actividad óptica. Aparte de esto, desarrolló una teoría curiosa res- was appointed préparateur (respon- pecto al origen del Universo. sible for preparing the apparatus needed in lecture demonstrations) to ABSTRACT. Joseph Achille Le Bel is an example of scientists like Réaumur the General Chemistry chair held by who researched in many subjects but is remembered by only one. Le Bel is a Liés Bodart at the University of well-known name to students of Chemistry in general, and stereochemistry in Strasbourg but after a short time he particular. He left us with basic principles that determine the geometrical con- ditions that must be satisfied by a carbon compound in order to have optical left to take a similar position with activity. In addition, he developed an unusual theory regarding the origin of the Antoine-Jérôme Balard (1802-1876, Universe. the discoverer of bromine) at the Collège de France, with an annual remuneration of 1 500 francs. In 1873 he moved to Paris to work in the INTRODUCTION his scientific achievements, and, in laboratory of Charles-Adolphe Würtz Joseph Achille Le Bel is an ex- particular, how his concepts about (1817-1884), at the École de Médecine ample of scientists, like Réaumur, stereochemistry set the basis to this in Paris. After Würtz death, his suc- who did research in many subjects important branch of organic chem- cessor Armand Gautier (1837-1920) but is remembered by only one. Le istry. continued to employ Le Bel as an Bel is a well-known name to stu- assistant. 1-3 dents of chemistry in general, and LIFE AND CAREER Simultaneously to his work with stereochemistry in particular. He Joseph Achille Le Bel was born Würtz he took an active role in the left us with basic principles that de- on January 21, 1847, at Péchelbronn, management of the family business, termine the geometrical conditions Alsace, the youngest of the four chil- doing research in the area of petro- that must be satisfied by a carbon dren of Louis-Frédéric-Achille Le leum and its chemistry. His results compound in order to have optical Bel. From the side of his father he led him to adopt Dimitri Mende- activity. In addition, he developed an was a nephew of Jean-Baptiste leev’s (1834-1907) view that petro- unusual theory regarding the origin Dieudonné Boussingault (1802-1887) leum deposits resulted from the ac- of the Universe. an experimental agricultural chem- tion of steam on metallic carbides at Chemists and chemical engi- ist who also managed the Lobsann volcanic temperatures. In 1879 he neers are familiar with Le Bel petroleum field. Le Bel came from a introduced in Péchelbronn the through the theory that carries his wealthy family that controlled a bi- Fauvelle well-perforation method name, a theory related to asymmet- tuminous sand and asphalt process- that led to the production of new ric carbon and optical rotary power. ing plant at Péchelbronn and he per- subproducts and the discovery of They are generally unaware that he sonally managed it between 1882 fields of light oil and gas. In 1885 Le also contributed to other scientific and 1889. Le Bel started his high Bel installed vertical stills that al- areas such as the chemistry of pe- school studies at the Collège d’Ha- lowed him to quadruplicate the pro- troleum, stereochemistry of nitro- guenau and completed them in duction of the factory and to obtain gen, crystallography, fermentation, Paris. In 1865, at the age of eighteen, head products of distillation lamp cosmogony and prehistory. Here we he entered the École Polytechnique oil. In addition he installed dewaxing describe his personal life and career, from where he graduated in 1867. units for separating the liquid oil 35 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002.

from the materials that solidified at also appointed honorary President expected celebrated French dishes room temperature. All these im- of the Societé Préhistorique Fran- Le Bel drew out of his pocket a small provements should be considered çaise. paper package, out of which he ex- against the background that at that According to Pope2 ‘’Le Bel did erted pieces of cold meat he had time Alsace was under German not publish a great amount of experi- brought with him from Paris. This domination and France had no pe- mental work probably because he was the Spartan way of life of a man, troleum sources of her own. held no academic post and found so who was known as possessing many In 1889 the Le Bel family trans- few collaborators. His writings cover millions, but whose pleasant manner ferred the Péchelbronn factory to a wide range of subjects and are per- made one forget the insufficient group of Alsacien investors, and meated by quite uncommon philo- material pleasures offered in his moved Paris. The Péchelbronn sophic spirit. He was an individual- house. works were severely damaged dur- ist and mixed little with his scien- Le Bel was a complete ing the Second World War; on August tific colleagues; he was intolerant of autodidact, and hardly ever made 4, 1944, a total of 1 350 bombs was officialdom in any of its aspects, and any attempts to join the academy, dropped on it, destroying it almost was wont to express his contempt of being a stranger to any form of van- completely.1 bureaucracy with some vigor. His ity. Even though he published Le Bel was appointed member of originality of thought, his outspo- little, it would be a mistake to sup- the Societé Chimique in 1869. He kenness, and his unconventionality, pose that after his significant suc- became its Vice President in 1890 indeed bohemianism, made his cess in stereochemistry −he was and President in 1892. Afterwards, somewhat difficult of access, but in hardly 30 years old then− he stopped he served in different committees of congenial society he was a delight- his scientific work. During ten years the same and made many cash con- ful companion, full of knowledge of he tried to establish a connection be- tributions to it. In April 1930, he of- the world and sparkling with anec- tween the crystal forms of chemical fered a money prize of 50 000 francs dote and caustic wit.’’ compounds, but he rejected all at- for the rediscovery of a microscopic Wedekind3 gives another view of tempts of his friends to publish the green alga, found and lost by him, Le Bel’s personality: ‘’My stay in results of his work, saying that his which had the power of converting Paris, where I was studying and observations were of no significance atmospheric nitrogen into ammonia. working in the laboratory of Henri and fell short of the goals he had Le Bel passed away in Paris on Moissan, led to our personal meet- envisioned for himself. He had a 45 m August 6, 1930, and was buried at the ing, which gave me an opportunity deep shaft constructed, so that he Bagneux cemetery. Although in his to get to know this very special, lov- would be able to perform certain ex- testament he donated all his fortune able person closer. We would often periments under constant tempera- (about 4 million francs) to the Societé meet in the café ‘’Pantheon’’ on Bou- ture. Chimique. Delépine1 comments that levard St. Michel. Our conversations He treated his plants and flow- this generous gift was reduced to revolved almost exclusively around ers with great love. These grew first nothing by the economic and social questions related to stereochemis- in the garden of his laboratory in measures of the French govern- try, while we would construct ex- Rue Amyot, but as he moved to an- ments that followed Le Bel’s death. planatory models from toothpicks. other house, they had to be brought Le Bel never held an academic Le Bel, who was known as being ex- to a terrace, which soon became appointment nor he ever had any traordinarily rich since he inherited reminiscent of a hanging botanical students. In 1881, when Le Bel was the ‘’Péchelbronner’’ petroleum garden.’’ thirty-four years old, the Académie works, had three homes in his pos- An interesting point is that on des Sciences awarded him the Jecker session: a ‘hotel’ in the beautiful the occasion of Le Bel’s 80th birth- prize. In 1924, on the occasion of the neighborhood Passy, a laboratory day a medal was issued in his honor. fiftieth anniversary of the asymmet- with residential facilities in the old- In it, next to his great discoveries of ric carbon theory it awarded him a est part of Paris in Rue Amyot, and carbon asymmetry (1874) and nitro- gold medal bearing Lavoisier’s ef- finally a beautifully located castle gen asymmetry (1894), are engraved figy. In 1888 he stood up for the first outside of the city. Le Bel was a bach- his researches on the catathermic time as candidate for membership in elor and hardly ever used his ‘’ho- phenomenon (1918) and rational cos- the Académie des Sciences; his per- tel’’, he would normally sleep in his mology (1911). sonality lead to conflict with mem- laboratory, surrounded by a little gar- bers of the Académie delaying his den. He would occasionally invite a SCIENTIFIC ACTIVITIES membership until 1929, replacing small circle of friends to his castle Some of Le Bel’s most relevant the marshal Ferdinand Foch (1851- in the country. One took a train first contributions to the chemistry of 1929). The vote took place on June 3; and was then brought by a car to the petroleum, stereochemistry, crystal- Le Bel obtained 39 votes against castle located on a height, around lography, fermentation, cosmogony Armand de Gramony with 8, Jacques which there was a completely wild and prehistory, will be discussed Cavalier with 4, and Louis Martin garden. In this park all kinds of ani- now, with particularly emphasis on with 1 vote. In the same year Le Bel mals moved with a paradise sense of his work on the asymmetry of car- was appointed Commandeur de la freedom, among them a lama, who bon. Légion d’Honneur. He was elected could even approach the guests. an honorary fellow of the Societé Only the dining room was somehow 1. Petroleum and hydrocarbons Chimique in 1908 and a foreign suitable for taking meals. Instead of The first scientific publication of member of the Royal Society in 1913; a door bell there was a shell, in which Le Bel appeared in 1872, was done in 1893 both he and Jacobus Henri- the master of the castle blew, calling at Würtz’s laboratory and was de- cus van’t Hoff (1852-1911) became for the hospitable spirit of the house. voted to discussing the properties of Humphry Davy medallists of the First, a simple soup was served, then the bitumen present in the fields lo- Royal Society. In 1911 Le Bel was there was a pause, and instead of the cated in Schwabwiller, Péchelbronn, 36 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002. and Lobsann (Lower Rhine).4 This rate isomeric olefins like isobutylene ride was slightly levo while amyl bro- work is historically interesting be- (2-methylpropene) and 2-butene. mide and iodide were strongly dex- cause it signals Le Bel’s first ac- Le Bel with his collaborators tro. The three chemicals were pre- quaintance with amyl alcohol, a sub- studied the reaction of several pared by substitution of the OH stance he would investigate thor- alcohols, according to the method group in the alcohol, they contained oughly. proposed by Étard, in which an al- the same number of molecules In this publication Le Bel cohol, dripped slowly over molten grouped in the same manner, but showed that the most volatile frac- zinc chloride, was reduced to an ole- nevertheless light rotation had tion of these bitumens contained fin. In this manner he prepared CH3- changed direction significantly. Le pentane, hexane, and unsaturated CH=CH-CH3 from butanol and pro- Bel reasoned that the only possible components. The latter were easily pylene from propanol. An unusual explanation was the different man- converted into their chlorides and result was obtained with methanol, ner in which the three halides were iodides, particularly amyl iodide, Le Bel expected that the dehydra- prepared: amyl bromide and amyl and then into an amyl alcohol mix- tion of the alcohol would give place iodide were obtained by the action ture boiling in the range 118 to 121 oC . to several olefins of the ethylene se- of phosphorus iodide or bromide on His amyl iodide had a boiling point ries, instead he found that the reac- the alcohol, while the chloride was similar to that of the ethyl allyl io- tion yielded hexamethylbenzene, a prepared by distilling the alcohol in dide, synthesized previously by crystalline laminar solid that melted the presence of hydrogen chloride. Würtz. Treatment of the amyl iodide at 160 oC and boiled at 259 oC . The He proved his hypothesis by prepar- with silver oxide produced a mixture elemental analysis was the same as ing the chloride by two different pro- of isoamyl alcohol (today 3-methyl- a sample of hexamethylbenzene pro- cedures, one distilling the alcohol in 1-butanol) and isoamyl ether, while vided to Le Bel by Charles Friedel the presence of aqueous HCl, and treatment with silver acetate yielded (1832-1899, codiscoverer of the the other heating to 110 oC amyl al- pure isoamyl acetate. Friedel-Craft reaction). cohol saturated with gaseous hydro- In a following memory Le Bel5 A subject that interested Le Bel chloric acid, followed by treatment gave full experimental details about in particular was the origin of petro- with phosphorus pentachloride. The his procedure for separating the leum. In papers published in 1885 second procedure yielded dextro volatile components of petroleum and 19287,8 he discussed the follow- amyl chloride.9,10 and the preparation of several de- ing three possible sources of the ori- In a following publication11 rivatives, for example, isoamyl and gin of petroleum (a) fermentation of found that the optical activity of ac- isohexyl alcohols, and the identifi- animal or vegetable matter, as illus- tive amyl alcohol disappeared if two cation of two isomers of the same. trated by the gas produced in of its radicals were made identical or His considered his procedure so marshes, (b) decomposition of soft one of them was transformed into simple that he added the comment coal under the simultaneous action the unsaturated form. Thus, treating that if a commercial use was found of the heat from the Earth’s core and active amyl iodide with methyl io- for these compounds it would be the pressure of the surrounding lay- dide in the presence of sodium very easy to prepare them in large ers, the resulting products being yielded C2H5-CH(CH3)-C2H5 while amounts. petroleum and anthracite, and (c) treatment with potassium ethoxide

In his investigation about petro- reactions of water with the Earth yielded C2H5-C(CH3)=CH2; in both leum sources containing large per- molten core (theory maintained by cases the loss of carbon asymmetry centages of volatile (olefinic) compo- Mendeleev). He rejected the first meant the loss of optical activity. nents, Le Bel found that the amount hypothesis because it assumed that Similarly, active amyl alcohol be- of volatiles decreased if the oil was the petroleum formed was capable comes racemic after treatment with kept for a long time in contact with of stopping the fermentation pro- sodium amylate. water. He believed that these cess and killing the microorganism Le Bel used the results of his volatiles reacted with water and that responsible. The other two seemed work on amyl alcohol to justify the the resulting derivatives were both reasonable, Le Bel preferred main consequences of his theory soluble in water and in the oil; ole- the one postulated by Mendeleev, about carbon asymmetry: racemiza- fins from heptene on produced hy- although it was at odds with the fact tion, resolution by yeasts, disappear- drate crystals that were soluble in that optical rotatory power had been ance of the required asymmetry, etc. both phases and decomposed easily detected in some petroleums. Ac- In particular, Le Bel showed that the on heating. Le Bel used these find- cording to Le Bel the second theory resolution of inactive amyl alcohol ings to substantiate his explanation explained well the presence of opti- demonstrated that its structure nec- that petroleum deposits that were in cal isomers but was unable to justify essarily contained four different contact in water (like the ones in the presence in petroleum of asphal- groups and that it should be consid- American oil fields) contained only tenes and metals like iron, silicium, ered a mixture of the dextro and levo saturated hydrocarbons. manganese, copper, and silver. forms. In a study related to the reaction Mendeleev’s theory did not require between hydrochloric acid and ole- the presence of natural fuels because 3. Crystallography fins in general6 Le Bel developed a it was based of the reaction between Le Bel did extensive work on the simple procedure for separating ole- water and metals present in the study of the crystals formed by the fins. He found that olefins having ferrisphere. chloroplatinates of a large number the general structure CH2=CRR’ and of amines with the purpose of learn- CHR=CR’R” reacted with a cold 2. Amyl alcohol ing the influence of their composi- aqueous solution of saturated HCl In 1873 Le Bel become inter- tion on the crystalline form. It was while those with general formula ested on why different halo deriva- well known that the chloroplatinate

CH2=CHR and CHR=CHR’ did not. tives of amyl alcohol presented op- of ammonium was isomorphic with This procedure allowed him to sepa- posite optical activities; amyl chlo- that of potassium, which was regu- 37 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002.

lar, and that the regularity was also action was fast as long as every day lengthy memory published in the valid for three of its relatives that is, Le Bel would neutralize the alkalin- Journal de Chimie Physique15 Le Bel

for M3, M4, and E4 (where M is me- ity with sulfuric acid; in about a few presented his theories regarding the thyl and E is ethyl). Le Bel’s results weeks the gelatin was totally con- origin of the Universe stating from indicated that this was also true for sumed. The fermentation process the beginning that his was a ratio-

the octahedral salts ME3, EM3, and was finished when no more ammo- nal approach in that it assumed that

M3P (where P is propyl). Salts like nia was produced and addition of a the forces present in the cosmos had

PE3 and EP2 deviated from the cu- small amount of acid turned the liq- been able to maintain its existence

bic structure while salts like MP2, uid acid. The product of the fermen- in the past, they did it in the present,

EP2, and EMP that presented the tation process had an important and would continue doing it in the particular characteristic of having characteristic: addition of a cord of future. He was not trying to justify their optical axes almost superim- gut and a cord of hemp caused the the existence of the Universe during

posed. Salts like P2 and P3 were char- total dissolution of the first while the a given period of time, no matter acterized by having their axes per- second was left untouched. From how long. It was necessary to find pendicular one to the other. Accord- these results Le Bel concluded that the causes able to maintain an in- ing to Le Bel, the crystal form of all the bacillus thus cultivated was ca- definite cycle. He indicated that his these salts derived from an equilat- pable of attacking the walls of the discussion did not include super- eral pyramid having the four hydro- intestine and should certainly be natural phenomena, without negat- gen of the ammonium group at the considered one of the causes of acute ing the existence of a superior intel- four summits.12 enteritis, which at the time was ligent force. As we will see, the ar- Le Bel also prepared a large treated with bacillus bifidus or the guments presented in this paper are number of double salts formed by lactic ferment. circular and somewhat unclear. They the chloroplatinate of ammonium Le Bel analyzed the products of can be debated on the same basis he bases, some of them were unable to the fermentation of gelatin and rejected the theories opposing his combine between them but pairs like found them to contain ammonium tenets. the chloroplatinates of tripropyl and carbonate and several low fatty ac- The idea that the Universe was triethylamine, dimethyl and methyl- ids up to and including valeric acid. turning along the same circle was propylamine, and dimethyl and On the other hand, the fermentation very old and the ancient philoso- dipropylamine, were able to do so on of a sugar produced higher alcohols phers had characterized it by a snake

a one to one mole ratio. The up to C5, their quantity was larger if eating its tail. In modern times, it chloroplatinate of dimethylamine the substrate contained nitrogenous had been supported by Georges was particularly interesting for the components. From this he deduced Louis Leclerc Buffon (1707-1780) large number of double salts it that these alcohols were derived and Emmanuel Kant (1724-1804), but formed. Its double salts with another from the nitrogenous substance. Fer- it had lost credibility after geology amine having two identical radical mentation of the nitrogenous sub- had shown that life seemed to have groups (like, for example, dipropyl- stance alone gave a series of low fatty appeared on Earth, after an incan- amine) were remarkably crystal- acids up to and including valeric descence period, in the form of lower lized. Dimethylamine presented also acid. Le Bel explained the apparent species that had evolved in time. the phenomenon of dimorphism, the absence of hexyl alcohols by assum- Le Bel went on to describe the ordinary stable form was reddish in ing that distillation was unable to different theories about the origin of color, had a density of 2.27, and its separate them from the pertinent the Universe, in order to justify his crystalline axis were in the ratio a:b:c fatty acids. Another finding was that ideas on the subject. He claimed the = 0.993:1:0.997; the unstable form bacillus lactis and others resisted best explanation was to be the one crystallized as yellow needles that the action of the light of a mercury that the required the fewer hypoth- were stable at 100 oC, had a density quartz lamp. According to Le Bel, eses. of 2.12, and its crystalline axis were the resistance to this light was sim- According to Pierre-Simon in the ratio a:b:c = 0.621:1:0.890. ply another confirmation of Svante Laplace (1749-1827), the Universe Both crystals had an orthorhombic Arrhenius’ (1859-1927; 1903 Nobel was originally composed of matter structure.13 Prize in Chemistry) panspermiste distributed everywhere. Eventually, theory that the light pressure of so- this matter had begun to concen- 4. Fermentation and microorga- lar radiation could transport very trate very slowly giving place to the nisms small germs. These germs had a long stars and planets. The discovery of Le Bel investigated the fermen- longevity, particularly in interstellar the conversion of kinetic energy into tation of several substances, gelatin space, and thus could be easily trans- heat explained the thermal energy among them, as part of his work on ported by a comet or an meteorite present in these bodies. It was as- the production of alcohols and fatty from one planetary system to an- sumed that life had appeared spon- acids. Of particular interest is his other. Again, the required energy taneously and Jean-Baptiste La- paper on the fermentation of gela- had to come from the ether and marck (1744-1829) and Charles Rob- tin14 where he discussed the origin could be explained by the catather- ert Darwin’s (1809-1882) theories jus- of the alcohols and fatty acids pro- mic radiation Le Bel claimed to have tified the further evolution of living duced. Le Bel obtained the ferment discovered (see below). entities. According to Le Bel, al- (bacteria) of gelatin by seeding a 2 % though this hypothesis was very at- aqueous solution of gelatin with fe- 5. Cosmogony tractive it was basically wrong be- cal matter, at 38 to 40 oC and gentle Besides his interest in petro- cause it did not provide an explana- agitation. The resulting liquor be- leum and chemistry, Le Bel become tion for the indefinite existence of came very alkaline and took a brown interested in many philosophical the Universe. Not only that, Gustave color. It was then used to seed 50 L subjects, particularly those related Adolph Hirn (1815-1890) and Johann of the same gelatin solution, the re- to the creation of the Universe. In a Wilhelm Ritter (1776-1810) had cal- 38 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002. culated that according to Laplace’s a perfect mirror, with the difference tually become part of magnesium theory it would have taken less than that this mirror did not send the and calcium salts that in the end twelve million years to create the primitive ray but a radiation. Le Bel would settle in the bottom of the seas Sun, a number well below the one- substantiated his arguments by say- and become unavailable for recircu- hundred million years that the gla- ing that Gavriil Adrianovich Tikhov lation. The second argument cial age had lasted. In addition, the (1875-1960) and Charles Nordmann claimed that in the heat period cor- matter that had formed the Sun had already demonstrated that ether responding to lunar volcanoes, life could not have come from every- influenced light in a similar way as should have disappeared completely where in the Universe, after a cer- material bodies, that is, the velocity but no fossils had been found in tain distance it would have gone into of light depended on the wave- primitive rocks proving that they forming other stars. Hence Laplace’s length. had existed. Spontaneous genera- theory could not explain the perma- According to Le Bel, Tissot’s tion was unattainable but we had nence of the solar system in the past theory implied that the heat recov- proofs of a creation followed by de- and in the future and it was contrary ered by a star like the Sun, was com- struction. According to Le Bel, these to the idea of a cyclic system or of posed of three elements: (a) the one arguments were easily discarded. an equilibrium state. that came from the star itself and First of all, he had proven that a It was possible to extend Marie was returned by the surrounding warm period fitted better a cyclic Curie’s (1867-1934; 1903 Nobel Prize celestial space, (b) the heat that came theory than the one proposed by in Physics) discoveries to assume directly or indirectly from other Laplace. Not only that, the passing that part of the matter constituting stars in the Milky Way, and (c) the of the Sun through the central parts the stars had the property of decom- one received from stars located out- of the galaxy implied an increase in posing, as radium did, and thus had side the galaxy. The last contribution temperature but this did not mean provided during the Azoic and Pa- was probably negligible due to the that the planets had became incan- leozoic era the energy lost by the enormous distance between the gal- descent. It was possible that the high stars. Nevertheless, this fact could axies and was also independent of temperatures achieved in the equa- not be used to justify a cyclic theory the position of the Sun in the Milky torial area could have killed tall ani- because the mass of every star was Way. mals and plants, but inferior forms limited and if the mass regenerated The immediate consequence of life would have certainly survived over the same star it would require was that the hottest stars should be in the poles and their spores would the same amount of energy that had located in the central part of the have been easily transported by the been released previously. The same Milky Way. This consequence was winds from one pole to the other. In arguments were to be used to reject substantiated by the known fact that addition, the high temperatures a theory based on radioactive mate- stars close to the Sun also possessed would have increased substantially rials since they constituted a very a metallic spectrum, hotter stars had volcanic action and the water’s tem- small fraction of the total mass. a protometallic spectrum, while gas- perature, resulting in the transfor- According to Charles Joseph eous stars had temperatures in the mation of sedimentary rocks into Tissot (1828-1884), stars recovered range of 20 000 to 25 000 oC . crystalline forms, thus destroying the heat they were losing by absorb- Le Bel went on to say that the the fossil record. ing radiation emitted by the ether, Sun was traveling from a region poor Le Bel pointed out that Arrhe- which originated from the transfor- in stars towards a point called the nius had already raised the possibil- mation of the heat and light emitted solar apex, located near the Hercules ity that germs could be transported by the stars (Le Bel called this radia- constellation, rich in stars. That is, from one planet to another and that tion cathathermic). Tissot’s hypoth- our system was leaving a cold region this transport could have been ef- esis had been rejected because it (period) and approaching a hotter fected by the action of the pressure seemed to contradict Carnot’s prin- one. This was not surprising since it of light upon the spores. The same ciple: If the ether was at temperature was known that our world was leav- spores could also have been carried

T and the star at temperature T0, ing a glacial epoch. The Sun was not within a meteorite and survived the then the efficiency of the heat re- following a linear or regular trajec- conditions in space. These were rare covery process should be less than tory because it was forced to travel phenomena but certainly possible

(T - T0)/T, in other words, the radia- through a network of stars, being when considering the infinite life of tion proposed by Tissot was unable rejected, every time, towards a far- the Universe. to provide all the thermal energy re- ther away position farther way that Le Bel concluded that there was quired. Le Bel rejected this argu- would lead to a new period of cold. an absolute need for a cycle and that ment saying that to assume that the These periods would be extreme ev- the Universe had functioned and ether followed the same laws as ma- ery time the Sun would locate itself continued to function by its own terial bodies was to accept not only in the external part of the ring form- means. The heat lost by the stars re- that it had a temperature, it must ing our galaxy. Thus, the existence turned to them by means of a mate- also have a specific heat. Or, if the of ancient glacial periods on the rial substance or by the vibrational temperature of the ether was defined Earth was simply a consequence of movement of the ether or other fluid. on the basis of the energy content Tissot’s theory. Both mechanisms had to originate per unit volume, this energy would Le Bel indicated that two argu- in the celestial space in order to pick be zero resulting in a value of unity ments had been given against the up the energy required. These two for Carnot’s efficiency. In other cyclic planetary theory: One indicat- hypotheses had the same difference words, there was no contradiction ing that CO2 would eventually be- as the one between the matter and between Tissot’s hypothesis and the come unavailable because it would wave theories of light. The latter thermodynamic principle regulating be absorbed by the alkali generated theory was the one we were used to the behavior of material bodies. Sim- from the decomposition of granite and thus he was tempted to think ply, the celestial space behaved like rock. These carbonates would even- that energy recovery was due more 39 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002.

to vibrational effects than to the fall ones called stag horns, very slim the configuration is defined as Z of material particles upon the stars. with their branches forming perfect (from the German, zusammen, to- Along with to these philosophi- half-circles. According to Le Bel, gether) and when the two groups of cal speculations, Le Bel dedicated these formations were extremely the higher priority are on opposite time to investigate what he called rare because the air in the caves was sides of the double bond then the catathermic radiation, that is, a ra- normally very dry. configuration is defined as E (from diation that originated in the inte- the German, entgegen, across) rior of a body heated nonuniformly 7. Stereochemistry of carbon Dextro and levo optical isomers and that reflected, in a smaller scale, First of all, some words about the are known as optical antipodes or the radiation that Tissot claimed was concept of stereochemistry and enantiomorphs (from the Greek, emitted by the ether (for example, isomerization. It has been known for enantios, opposite, and morphe, references 16, 17). more than 150 years that asymmet- form). They differ in the direction in A curious fact about Le Bel’s ric crystals of certain minerals, such which they rotate the plane of polar- speculations about the Universe is as tourmaline (a borosilicate mineral ized light; the difference, however, that he made no mention of the Prin- of complex and variable composi- is in direction only, for the specific ciple of Entropy Growth, although it tion) and quartz, rotate the plane of rotations of the two isomers are nu- was well known in his time. Accord- polarized light and that the rotatory merically equal. ing to Le Bel ether did not have power of these minerals is lost if the Enantiomorphs usually differ mass, nevertheless, his reasoning crystals are melted or dissolved. In markedly in their optical activity, implied that it was able to create other words, the asymmetry of the biological behavior, and their reac- energy without leaving traces (per- mineral resides only in the crystal- tions with chiral reagents, but are petual motion engine of the first line form. Certain carbon com- very similar in ordinary physical and class). His catathermic radiation had pounds, however, rotate the plane of chemical properties; they have the the same characteristic. Another polarized light in solution (for ex- same melting points, boiling points, curious fact is that Lépine, in his ample, cane sugar solutions) or even solubilities, dipole moments, and book about the life and works of Le in the gaseous state (turpentine, for other such physical properties. Op- Bel,1 mentions his theories but does example). In these cases, optical ac- tical antipodes show identical chem- not say a word about how they were tivity is a property of the molecules ical behavior in most of their reac- received and to what criticism they themselves. The crystals of optically tions. For example, the reactions of were subjected (Lépine wrote his active minerals are asymmetric and l-lactic acid are exactly those of d- book while he was President of the it is equally certain that the mol- lactic acid. Both acids form salts, Societé de Chimique). ecules of active carbon compounds esters, and other acid derivatives in are also asymmetric. Solutions of the regular manner. Furthermore, 6. Prehistory compounds described as optically there is no difference in the rate of In two communications to the active rotate the plane of polarized such reactions. There is a difference, Societé de Chemie Le Bel reported light either to the right (dextrogyres) however, in the rates of reaction at that in Eysies, Dordogne, he had or to the left (levogyres). which optically active compounds found a cave where the stalactites Stereoisomers are molecules that react with other optically active sub- presented some interesting mineral- contain the same functional groups stances in the formation of diaste- ogical characteristics.18,19 They were and have the same structure but dif- reoisomers. covered by a calcareous vegetation fer in the spatial arrangement of the Unlike enantiomers, diastereoi- going in every direction although component atoms. Stereoisomers somers differ in their physical and directed upwards. The water did not may be configurational or conforma- chemical properties, allowing their seem to ascend by capillarity but by tional; configurational isomers are separation by fractional crystalliza- a small internal channel. When hit interconverted by the breakage and tion or chromatography. by a pickaxe they gave sparks, which reformation of a bond while confor- Before discussing Le Bel’s con- Le Bel assumed to be due to silica mational are interconverted by ro- tribution to this area, let us look first crystals or flint inserted between the tation about a single bond. Diastere- at the history of the knowledge on other crystals. He took a sample to oisomers are stereoisomers that do optical activity. In 1815 Jean-Baptis- his laboratory and to his surprise not have a mirror image relationship te Biot (1774-1862) discovered the when digested with HCl it yielded between them and this definition presence of rotary power in certain only a very small amount of jelly includes isomerism owing to the natural organic substances such as silica. Le Bel found that this phe- presence of a double bond. Tradi- sugar, gum, dextrin, camphor, and nomena was uncommon, it existed tionally, the term geometrical isom- turpentine. These findings came af- in only few caves, usually character- erism has been used to describe this ter his research on the rotation of ized by being very old. Analysis of type of stereoisomerism. polarized light in quartz, following samples that came from other caves The terms cis and trans are usu- the discovery of the same by that presented the same character- ally used to describe the diastereoi- François Arago (1785-1853), in 1811. istic (Han-sur-Lesse, Belgium; La someric forms of simple alkanes. His discoveries were followed by the Cave, Rocamadour) yielded again a However, their use is not always inferences of René Just Haüy (1743- very small amount of silica. Le Bel ambiguous and recently, to avoid 1822) and John Herschel (1792-1891) attributed the phenomena to tribolu- ambiguities that may arise, the so- about the sense of rotation in quartz minescence. called sequence rules have been and certain facets of the crystal. The stalactites in Eyzies had also employed to assign the configura- From the very beginning, Biot real- the characteristic of being generally tion of an alkene. When the two ized that the rotatory power of the inclined and taking bush-like shapes groups of higher priority from each organic substances depended on the called coral bushes. Anyhow, the end of the double bond are on the constitution of the substance and most curious formation were the same side of the double bond then could take place in the solid, liquid, 40 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002. and gaseous phases. The property isomers and in the study of bacteria metries, which might arrive from the was lost only when the substances and other microorganisms, which spatial arrangement of the atoms decomposed. In 1843 Apollinaire often produced such substances and and monatomic radicals, that is, he Bouchardat (1806-1886) reported left the theoretical explanation of considered them to be spheres or that the same phenomena was the molecular structure to others. material points, which would be present in alkaloids and glucosides. Pasteur’s ideas were not extended to identical if these elements were The real cause of the optical phe- molecular structures even after equal, or different if they were dif- nomena remained unknown until Kekulé had explained the structures ferent. He justified these assump- Louis Pasteur’s (1822-1895) pioneer- of organic compounds in terms of tions on the basis that all the cases ing research. In 1848 Pasteur discov- the tetravalence of carbon. of isomerism observed thus far ered that the crystals of the sodium The year 1874 signaled the ini- could be accounted for without as- ammonium salt of tartaric acid, a tiation of stereochemistry as we suming a particular spatial arrange- dextrorotatory optically active sub- know it today. Le Bel, starting from ment. He then went on to state the stance, exhibited hemihedral facets, the views of Pasteur, and van’t Hoff, following two principles: that is, one half of all the faces de- starting from the more rigid ideas of First general principle. Replace- veloped unequally. Observation of August Kekulé (1829-1896), arrived ment of three of the A’s by simple or many other crystal forms of tartaric independently at the theory that complex univalent radicals, differ- acid led him to believe that the phe- when the four substituents around ing from one another and from M, nomena of hemihedry and optical a carbon atom are different, that is, will yield a dissymmetric molecule rotation were interrelated. the carbon compound is asymmet- that will have rotatory power. If we Pasteur found further that the ric, molecular images must exist and assimilate the three radicals (R, R’, crystals of paratartrate (racemic tar- they must show opposite optical ac- and R’’) and A to material points, taric acid) also exhibited hemihedral tivities. Both Le Bel and van’t Hoff they will form a structure that is not facets but that the hemihedry some- used this idea to explain many cases superimposable on its image and the times faced to the right, and some- in which such isomers did or did not residue M will be unable to reestab- times to the left, that is, the racemate occur. lish symmetry. crystals were specimens of two Le Bel started from a different This principle had two clear ex- asymmetric types, one the mirror of considerations than van’t Hoff, ceptions: (a) if the original molecule image of the other.20 Pasteur summa- they were not based on graphs, there had a symmetry plane containing rized his findings in the three follow- were more abstract but also more the four atoms A then the substitu- ing rules general. As indicated by the title of tion product would be unable to (a) When the elementary atoms his paper Le Bel was intent in find- change the original symmetry and of organic products were arranged ing the rules that allowed prediction all the set of possible derivatives asymmetrically, then the crystalline of the existence of rotatory power. would be inactive; (b) if the last radi- form reflected this asymmetry by Le Bel started his paper21 by stat- cal substituted for A had the same non-superimposable hemihedry. ing that there was no known method atomic composition as the rest of the (b) The existence of molecular to predict if the solution of a sub- group into which it entered, then the dissymmetry was reflected by the stance had rotatory power. Although net optical effect would result in the existence of rotatory power. the derivatives of an active sub- canceling or strengthening the origi- (c) If the non-superimposable stance were generally active, never- nal one. In the first case the final molecular asymmetry occurred in theless it would be found often that effect would be zero optical activity. opposite directions (like it existed in this property would disappear in the For example, if in MR1R2R3R4, the levo and dextro tartaric acids, as well most near derivatives and would last radical was substituted by the as in their derivatives) then these persist in very remote derivatives. grouping MR1R2R3, the two groups bodies had identical chemical prop- He went on to state that based on would neutralize or synergize one erties. geometrical considerations alone he another. Pasteur succeeded in obtaining had been able to derive some gen- Le Bel illustrated this first ex- two forms of tartaric acid, one of eral rules that would allow answer- ception with tartaric and erythric which one rotated the plane of po- ing the following question: Given a acids, which also represents one of larized light to the right (dextro tar- molecule having the formula MA4, the exceptions cited by van’t Hoff’s taric acid), the other to the left (levo composed of a simple or complex paper. tartaric acid). The question arose radical M, how will it combine with In his first principle Le Bel ana- immediately about the arrange- four univalent atoms or radicals (A) lyzed the case of three substitutions ments of the atoms in the molecules and become optically active? in compounds of structure MA4, he of these substances. In 1860 Pasteur Pasteur had already found that then went on to discuss what hap- asked. ‘’Are the atoms of the right molecular asymmetry and rotatory pened when only two new radicals acid grouped on the spirals of a power were closely associated. If were introduced. dextrogyrate helix, or place at the asymmetry existed only in the crys- Second general principle. If, in summits of an irregular tetrahedron, talline molecule, then the crystal our fundamental molecule only two or disposed according to some par- would be active, but if the asymme- radicals were substituted (R and R’), ticular asymmetric grouping or try belonged to the molecule, then it was possible to have and not have other? We cannot answer these ques- its solution would also show rotatory symmetry according to the structure tions. But it cannot be a subject of power. The crystal may also show of the original molecule MA4. If the doubt that there exists an arrange- this property of its structure allowed original molecule had a symmetry ment of the atoms in an asymmetric perceiving it, like in the case of strych- plane passing through the two atoms order, having a non-superimposable nine sulfate of amyl amine alum. A that were replaced by R and R’, image.20 Pasteur was interested Le Bel stated then that his rea- then this plane would remain a plane chiefly in the separation of optical soning ignored the possible asym- of symmetry after the substitution 41 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002.

and the resulting compound would and yielded an active compound, as excellent example of this situation: be inactive. had been demonstrated by Johannes it always produced dextro and levo Le Bel went on to state that if a Wislecenus (1835-1932). Similarly, acids (racemic acid) in the same pro- single substitution furnished but malic acid presented the similar portion. one derivative, but also if two and structure: As we have seen, Le Bel’s paper three substitutions gave only one is largely concerned with the rela- H and the same chemical isomer, then tionship between molecular dissym- we were forced to admit that the four HO.OCCH C CO.OH metry and optical rotation and only atoms of A occupied the vertices of 2 once does he mention the tetrahe- a regular tetrahedron. The symme- OH dral carbon atom. A curious fact is try planes of the latter were identi- that van’t Hoff was also working with

cal to those of the original MA4 mol- that was optically active as were its Würtz and he and Le Bel announced ecule. In this case no bisusbstituted derivatives asparagine (by substitu- the same theory almost simulta- 23 product would possess optical rotary tion of the two OH by NH2) and as- neously. van’t Hoff’s paper ap- power. partic acid (by substitution of the peared in Dutch in September 1874,

Although Le Bel did not give an central OH by NH2). and Le Bel’s was published in example for the second exception, it In the case of sugars the situa- French in November of the same is clear that it would be applicable to tion was similar but more compli- year, however, there is not evidence combinations of bivalent platinum cated. The general composition of that either was influenced by the

such as [PtABCD]X2, [PtA2X2], etc. sugars was known but not their ex- other. Each arrived at his conclusion From the above principles it can act formulas. Many times sugars independently at this time probably be seen that the concept of tetrahe- were found that had a carbon atom because organic chemistry had dral carbon was a result of symme- united to a hydrogen, a hydroxyl, reached a point at which such a try arguments and no more. Actu- and two different radicals; these sug- theory had become essential to fur- ally, in a later publication Le Bel ars would generally be active. Sug- ther progress. The structural theory, stated clearly that he was not the ars derive from hexatomic alcohols, which had so well explained many originator of the tetrahedron such as mannose and glucose. In- types of isomerism, had failed to ac- theory.22 spection of normal hexanol (Fig. 1) count for optical isomers. Le Bel applied then his prin- indicated that each of its four cen- Although the names of the two ciples to saturated compounds of the tral carbons had potential rotatory are linked together in the develop- fatty series, noting that all of them power. If the only cause for the dis- ment of the theory of the tetrahedral derived from methane by substitu- symmetry of the above molecules arrangement of the carbon valences, tion of one or more hydrogen atoms related to the manner in which the the question of the relative impor- by various radicals. Since optically radicals surrounded one of these tance of their contribution to the active trisubstituted derivatives four carbons, we would then have a development of stereochemistry re- were available it was clear that the levogyre or dextrogyre substance mains unsettled. According to four hydrogens did not lie on the only, but since its four carbons had Snelders24 ‘’it is evident that the same plane and thus his first prin- this property then a large number of 1874-ideas of van’t Hoff rather than ciple was applicable. Not only that, isomers was possible. Nevertheless, those of Le Bel must be considered since methane gave only one deriva- since the four carbons had similar as the foundation of the stereochem- tive when two or three substitutions structures, it could be well that some istry of organic carbon compounds”. were performed, then the second were levo and others dextro, result- On the other hand, Grossman principle was also applicable and ing in a molecule that had very little states25 that ‘’it was van’t Hoff’s sys- hence, any member of the fatty acid rotatory power, as was the case for tem that was adopted by chemists; that had a carbon atom combined mannitol, dulcitol, and their nitric the symmetry considerations of Le with two hydrogens or two identical and acetic derivatives. Bel, although often cited as being radicals, would not show optical ac- Le Bel concluded his paper by among the founding ideas of stere- tivity. Le Bel went on to discuss the stating the following theorem: When ochemistry, were usually pushed members of the fatty series, which an asymmetric body is formed in a into the background.’’ Grossman ex- were active (derivatives belonging to reaction where only asymmetric plains this attitude on the fact that the groups lactic, malic, tartaric, bodies are present, then the two iso- van’t Hoff’s concepts were easier to amylic, sugars, unsaturated fatty mers of inverse symmetry will be assimilate than Le Bel’s abstract acids, and aromatic compounds), formed in the same amount. He ones. In addition, van’t Hoff made without using the concept of asym- based this conclusion by consider- significant contributions to other metric carbon. For example, lactic ing two independent events having fields, such as kinetics and physical acid was derived from methane by equal probabilities m and m’; in this chemistry. Grossman speculates substitution of three hydrogen at- case the ratio m/m’ would tend to one that had Le Bel had been a profes- oms by the groups HO, CO.OH and if the sum (m + m’) approached in- sor at a major German university his

CH3, yielding (as in Le Bel’s pape): finity (that is, if the event was re- contribution to stereochemistry peated an infinite number of times). would have been given much more H The synthesis of tartaric acid was an weight.

H 3 C C CO.OH H

CCH.O H OH HO.H 2 C CH.OHCH.OH CH.OH 2

The central carbon satisfied the OH requirements of the first principle Fig. 1. Hexanol normal. 42 Revista CENIC Ciencias Químicas, Vol. 33, No. 1, 2002.

8. Stereochemistry of nitrogen forming isomers. If the four radicals 10. Le Bel J.A. Procédé Pour Préparer Le Bel’s brilliant work in the do- were different the material would l’Alcohol Inactif. Bull. Soc. Chim., main of carbon asymmetry led him present optical activity and if two of 21, 542-544, 1874. to believe that pentavalent nitrogen the radicals were identical then two 11. Le Bel J.A. Sur l’Amylène et Quelques Autres Dérivés de l’Alcohol could exhibit the same phenom- isomers were possible, one optically Amylique Actif. Bull. Soc. Chim., 25, enon. Before considering his results active and the other inactive. The 545-547, 1876. we must realize that at the time they preferred form was the inactive one. 12. Le Bel J.A. Étude de la Forme were done nitrogen was assumed to In the same paper Le Bel prepared Cristalline des Chloroplatinates de la be pentavalent and that the ammo- salts of methylethylpropylisobutyl Série des Ammoniaques Composées. nium radical had a substitution ammonium and described how he Bull. Soc. Chim., 2, 642, 1889. value of the same order as that of the obtained a solution exhibiting a 13. Le Bel J.A. Sur la Forme Cristalli- four substituent radicals. For ex- small rotatory power from the cor- ne des Chloroplatinates de Di- ample, some chemists considered responding chloride by the action of amines. Compt. Rendu, 125, 35- 353, 1897. the chloride of ammonia to be am- Penicillum glaucum. Le Bel attrib- 14. Le Bel J.A. Sur le Ferment de la monium chloride while others de- uted the optical activity to the asym- Gélatine. Bull. Soc. Chim., 47, 380- scribed it as nitrogen pentahydride metry of pentavalent nitrogen. 382, 1930. chloride. In the latter the five atoms Later, other researchers were unable 15. Le Bel J.A. Essai de Cosmologie attached to hydrogen had an identi- to confirm this result, for example, Rationnelle. J. Chim. Phys., 9, 559- cal role (all five valences were Pope and Read2 [prepared the same 568, 1911. equivalent). A third group thought compound from ethylpropylisobutyl 16. Le Bel J.A. Sur le Rayon Catather- that its structure was NH .HCl. iodide and methyl iodide and found mique. Compt. Rendu, 157, 201-202, 3 1913. These ideas were discarded after that its behavior was the same as 17. Le Bel J.A. Phénomènes Catather- development of the octet theory and claimed by others, but different from miques à 1 000 oC . Compt. Rendu, that nitrogen was quadricoor- the compound prepared by Le Bel. 166, 1047-1048, 1918. dinating. As we will see below, al- Pope and Read28 claimed that Le Bel 18. Le Bel J.A. Sur les Stalactites. though Le Bel’s arguments were not had not obtained methylethylpro- Compt. Rendu, 186, 1306, 1928. according to modern ideas, his find- pylisobutyl ammonium iodide, that 19. Le Bel J.A. Sur les Étincelles que ings represented a significant is, the optical activity his product Jaillissent des Stalactites Frap- progress in stereochemistry when could not be associated with the pées Violemment Avec un Outil d’Acier. Compt. Rendu, 189, 890, showing that nitrogen could cer- presence of an asymmetric quin- 1929. tainly be a pivot for an asymmetry quevalent nitrogen atom. 20. Pasteur L. Recherches sur la Dis- that reflected in the existence of ro- symétrie Moléculaire des Produits tatory power. ACKNOWLEDGMENT Organique Naturels. Lib. Hachette: The first question raised was the The help of Mrs. Karine Barker, Paris, 1860. possibility that the order of introduc- Librarian, Document Supply De- 21. Le Bel J.A. Sur les Relations qui tion of the substituents may give partment, Radcliffe Science Library, Existent Entre les Formules place to the production of isomers. Oxford, in providing copies of hard- Atomiques des Corps Organiques et le Pouvoir Rotatoire de Leurs Le Bel stated that it was well possible to-get documents is gratefully ac- Dissolutions. Bull. Soc. Chim., 22, that radicals that were heavy (mo- knowledged. 337-347, 1874. lecular weight) and bulky would not 22. Le Bel J.A., Sur les Conditions change their location in the mol- BIBLIOGRAPHY d’Équilibre des Composés Saturés du ecule as easily as hydrogen and me- 1. Delépine M. Vie et Oeuvres de Joseph- Carbone. Bull. Soc. Chim., 3, 788-789, thyl. According to Le Bel, in a gross Achille Le Bel, Masson Éditeurs, Paris, 1890. manner it was possible to think of 1949. 23. Van’t Hoff J.H., Woorstell tot the molecule NRR’ Cl as having its 2. Pope W.J. Joseph Achille Le Bel. J. Uitbreding der Structuurformules in 3 Chem. Soc., 2789-2791, 1930. de Ruimte, J. Greven, 1874. five substituents located on a 3. Wedekind, E., From the History of Ste- 24. Snelders H.A.M., J. A. Le Bel’s Ste- sphere; either their location was not reochemistry; a Word to Commemo- reochemical Ideas Compared with fixed and hence no isomers were rate the Death of J.A. Le Bel. Z. Angew. Those of J. H. Van’t Hoff (1874). ACS possible, or the five radicals were Chem., 43, 45-46, 1930. Symposium Series #12, American located in fixed positions. In the lat- 4. Le Bel J.A. Sur les Pétroles du Bas- Chemical Society, Washington, D.C. ter case it would be impossible to Rhin. Compt. Rendu, 73, 499-450, 1871. 66-75, 1975. distribute the five points on a 5. Le Bel J.A. Sur les Huiles Pyrogénés 25. Grossman R.B. Van’t Hoff, Le Bel, regular fashion on a sphere and de Péchelbronn. Bull. Soc. Chim., 18, and the Development of Stereochem- 164-167, 1872. istry: A Reassessment. J. Chem. Edu- there would be at least two deriva- 6. Le Bel J.A. Réaction de l’Acide cation, 66, 30-33, 1989. tives having the same global for- Chlorhydrique sur Deux Butylènes 26. Le Bel J.A., Sur les Dérivés de Sub- mula. Isomériques et sur les Oléfins en stitution du Chlorure Ammonique. In two papers related to the sub- Général. Bull. Soc. Chim., 28, 460-461, Compt. Rendu, 110, 144-146, 1890. stitution derivatives of ammonium 1877. 27. Le Bel J.A., Sur la Dyssymétrie et la 26,27 7. Le Bel J.A. Notice Sur le Gisement de Création du Pouvoir Rotatoire dans chloride, NH4Cl, Le Bel claimed that if less than four of the hydro- Pétrole à Péchelbronn, Bull. Soc. les Dérivés Alcooliques du Chlorure gen atoms was substituted by radi- d’Hist. Nat. de Colmar, 15 pages, d’Ammonium Compt. Rendu, 112, Imprimerie Decker, Colmar, 1885. 724-726, 1891. cals no isomers were possible. In- 8. Le Bel J.A. Sur l’Origine du Pétrole. 28. Pope W.J., Read J., Asymmetric creasing the number of substituents Bull. Soc. Soc. Chim., 43, 653-656, 1928. Quinvalent Nitrogen Compounds of to four and their size increased the 9. Le Bel J.A. Procédé Pour Préparer Simple Molecular Constitution. possibility of their attaining fixed l’Alcohol Amylique Actif. Compt. Journal of Chem. Soc., 101, 519- positions and thus their capability of Rendu, 77, 1021-1023, 1873. 529, 1912.

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