Glycerine, Glucose, and Archibald Couper

Frame 23: Glycerine and Glyceric Acid

Archibald Couper was able to deduce with his newly-acquired empirical expertise with chemistry that Carbon is tetravalent, bonds with other Carbons, and comes in "pairs" that are essentially one (we now know they really are one); that Oxygen also comes in such "pairs"; and that Hydrogen "has no affinity for itself when united to another element." With this knowledge, Couper devised surprisingly accurate structures for molecules made up of these three elements. He knew the "skeleton" would have to be made of the self-linking Carbons, and the other atoms should be distributed according to the rules above.

Thus, in 1858, he composed a structural formula for glycerine that is much like the one we use now that has been confirmed experimentally. Couper wrote CH(OH)2-CH2-CH2OH; the actual formula is CH2OH-CHOH-CH2OH.

He was similarly close for glyceric acid, a product of the oxidation of glycerine. Instead of having two OH groups attached to the top carbon as Couper postulated, one of the OH groups is bonded to the top carbon and the other to the middle carbon (for both glycerine and glyceric acid). This achievement is quite impressive seeing that it came from very indirect evidence concerning the behavior of C, H, and O, incorrect atomic weights for two of these, and a prevalent Type theory that did not agree well with Couper.

Frames 24-25: Glucose

While his structural formulae for glycerine were quite amazing, and rather a novelty at the time, Couper's work on glucose really propelled both chemical notation and theory. Firstly, Couper's prediction of the structure of glucose was entirely correct! (Not counting the fact that he included as part of the molecular structure an extra water molecule that is omitted nowadays.) In the first drawing of the glucose molecule, the bonds between the carbons of the chain are not drawn, but are understood to be there. Secondly, in the French version of his paper, he started using lines for bonds and brackets to indicate a single molecule's structure. While borrowing notation (like brackets) from Type theory, Couper also emphasized C-C bonds. This type of structures had a large influence on future chemists, including Kekulé and Lewis. He had the correct structure if hydrated; the aldehyde had added water.

Frame 26: Honoring Couper

Couper was born almost a century after Lavoisier, and, like "father," like "son," never got the chance to complete his groundbreaking work. Apparently outfoxed by Kekulé and angrily fired by Wurtz, Couper was as good as guillotined. (Note also that he experienced a mental breakdown and severe sunstroke). This slide shows the picture of his grave in Kirkintilloch, Scotland with flowers and our thank you note attached to it to honor his significant contributions to organic chemistry. Now our thank you note is less than ten feet away from one of the greatest chemists of the 19th century. He died on March 11 1892, 4 days before the Liverpool football club was founded in England.

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