Copyright 2000 Southam Inc.

The Gazette (Montreal)

November 19, 2000 Sunday FINAL EDITION

SECTION: MAGAZINE, Pg. C4 The Right Chemistry

LENGTH: 1274 words

HEADLINE: Organics? Elementary...: Wait! Do you know how 'animal' and 'vegetable' are different from 'mineral'?

BYLINE: JOE SCHWARCZ

SOURCE: The Gazette

BODY:

The St. Louis World's Fair of 1904 featured a most unusual exhibit. A bright spotlight illuminated a small vial that contained some nondescript white crystals. But these were no ordinary crystals. They were crystals of synthetic urea, crystals that had changed the course of chemical history. Organic chemistry is a most wondrous endeavour. Imagine creating a new painkiller, a novel anti-cancer drug or a revolutionary plastic by manipulatingsubstances too small to be seen. These invisible building blocks of matter, these "molecules," govern every aspect of our life, yet few people have a grasp of whatthey really are.

Of course, one does not have to understand molecules in order to manipulate them. Through most of history, people made soap from animal fat, smelted metals from ores, brewed alcohol from grapes and extracted dyestuffs from plants without knowing anything about molecules. It really wasn't until the 19th century that a comprehensive picture of the fundamental substances that constitute matter began to emerge. Antoine-Laurent Lavoisier had laid the foundation with his description of how elements combined to form compounds, and John Dalton had introduced the idea that the elements themselveswere composed of little particles he called atoms. But there was a complication in the quest to explain the properties of matter in terms of atoms. Substances derived from living organisms were somehow very different from those found in non-living matter. They were more complex, more difficult to separate and were usually destroyed by heat. A green ore could ooze metallic copper when heated, but a flower would be quickly converted to a piece of useless charred matter.

Clearly these natural materials required specialized study. "Organic chemistry" was the term suggested in 1808 by the Swedish chemist Joens Jacob Berzelius for the new discipline that would be dedicated to the study of substances from living organisms. And a difficult discipline it turned out to be. Although most organic materials were found to contain only carbon, oxygen, hydrogen and nitrogen, attempts to synthesize them from these elements always failed. Some scientists, including Berzelius, suggested that a "vital force" was inherent to organic substances, a forcethat could only be produced by living things. There was no point in trying to make quinine in the laboratory because the "vital force" that gave this substance itsproperties could only be infused into it by the living cinchona tree.

Organic chemistry seemed to some frustrated scientists like a maze. But there was a way out. And it was Friedrich Wohler who found it. He had originally trained as a physician, and had isolated urea during an investigation of the waste products found in urine. This captured his imagination, and he decided to focus on chemistry instead of medicine. He traveled to Sweden to study under Berzelius. Here Wohler heard about the impassable gulf that separated organic substances from inorganics. Wohler went on to become professor of chemistry at Gottingen, where he became interested in substances that could release cyanide when heated. One day in1828, he heated up some ammonium cyanate, expecting to liberate some cyanide. None was released. But his original crystals had taken on a new form. Their weight had not changed, but these crystals had a different melting point and a different appearance from his starting material. What could have happened? When Wohler examined the crystals, he realized that their shape seemed familiar. Where had he seen them before? His mind darted back to his medical-school daysand then he knew: he was looking at crystals of urea!

Wohler excitedly wrote to Berzelius: "I must tell you that I can prepare urea without requiring a kidney of an animal, either man or dog." He somewhatremorsefully added that he had witnessed "the great tragedy of science, the slaying of a beautiful hypothesis by an ugly fact."

Indeed, he had. On that day in 1828, the "vital force" theory was mortally wounded, although it would linger for a few more years. Wohler had made an "organic"substance in the laboratory from an "inorganic" one. Clearly, in his attempts to make novel substances, man would be limited not by any vital force, but by his ingenuity. Although Wohler had shown that there was nothing mystical about organic materials, neither he nor his contemporaries could explain why they behaved differentlyfrom inorganic substances. It had something to do with their chemical makeup, but what? Wohler's previous exploits provided a clue. While studying with Berzelius, he had analyzed silver cyanate and found it to be composed of silver, oxygen, nitrogenand carbon. But another German chemist, Justus von Liebig, had just published an analysis of silver fulminate, a completely different substance, which was madeup of the same elements in exactly the same weight ratio as Wohler's compound. Liebig called Wohler an incompetent, claiming that his analysis must be wrong. But when the two met and went over their data, they agreed that both were correct.How could this be? Berzelius stepped in and suggested that both substances could be made of the same elements, yet still be different if their atoms were joined together in a differentway. Eureka!

Now Wohler's urea experiment also made sense. Why did the original ammonium cyanate and the final urea weigh the same? Because the only difference was thearrangement of their atoms. It was now becoming clear that the properties of materials reflected not only what kinds of atoms they were made of but how theseatoms were arranged. The complexity of organic chemistry lay in the fact that atoms of hydrogen, oxygen, carbon and nitrogen could combine in numerous ways to generate a myriad "molecules." Liebig and Wohler couldn't even dream of how these atoms united to form molecules. Luckily, though, August Wilhelm Kekule, who had devoted himself tosolving the mysteries of atoms and molecules, could. The revelation supposedly came in a dream. Kekule had been riding a London omnibus when he dozed off. He later described how "atoms began to gambol infront of his eyes and suddenly one latched on to another, then another and quickly a chain of atoms was formed!" At this moment he was roused by the cry of"Clapham Rd.," but the basics of molecular structure had been forged in his mind.

The reason organic compounds were so complex and of such great diversity was that carbon atoms were able form bonds to each other, creating an almost infinite array of patterns. In order to rationalize the ratios of the weights of elements in organic compounds, Kekule had even postulated that each carbon atom could form four such bonds. A Scot, Archibald Couper, put the finishing touches to this theory of molecular structure by drawing the first molecular diagrams in which the atoms were represented by their letter symbols and bonds by straight lines. Organic chemistry was now seen not as a study of substances from living sources but as the study of the compounds of carbon. The field was thrown open. Organic chemists now knew what molecules were and soon found ways to make them. And make them they did. By the millions. Drugs, dyes, plastics andcosmetics soon burst from their test tubes. Although molecules as complex as DNA can now be synthesized, organic chemists still have a special appreciation for urea. Indeed, an American chemist remarked on seeing Wohler's original urea sample at the St. Louis World's Fair that he felt like a pilgrim "who has just seen a piece of the true cross."