Louis Pasteur's momentous discovery of the enantiomers of sodium ammonium paratartrate in 1848 was published roughly a decade before the tetravalence of carbon was firmly established and structural formulas similar to modern ones were published. His intuition suggested the abstract possibilities of distorted tetrahedra or helical molecular structures. Although the concept of isomers was known as early as 1824 to be the result of different arrangements of the same atoms, specifics were unknown. For example, a textbook representation of isomeric monoterpenes in the 1850s pictured these simply as attractively-symmetric different arrangements of the constituent carbon and hydrogen atoms. As a result there were significant confusions and surprises in understanding chemical relationships among series of synthetically-related organic molecules. An example would be the series: asparagine, aspartic acid, malic acid, tartaric acid, maleic acid and fumaric acid. The first four are capable of enantiomerism while the last two are not. How could optically-active molecules be synthesized from molecules which could never be optically active? This talk will also describe Pasteur's discovery and exploration of <i>chemical</i> means for separation of a racemic mixture into enantiomers.

More stereochemical discoveries by Pasteur ahead of organic structural formulas

256th National Meeting (2018)

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