In an evangelical spirit, three vignettes will be presented that have the character of molecular parables: stories with lessons that transcend the specific details. (1) How knowledge of the orientation of a methyl group with respect to a neighboring double bond, obtained from thermodynamics and microwave spectroscopy, enabled chemists to synthesize the single biologically active form of a molecule that has 5 x 1021 different structural isomers. (2) The lack of a single methyl group on a particular amino acid among billions in each DNA molecule on the Y chromosome of a human fetus is found to result in an infertile female rather than a male. This mutation is rare, of frequency ~ 10-5. Consider how different human society would be if it were to become dominant! (3) Remarkable feats, such as synthesis of Indigo, a highly prized dye for many centuries, were achieved in the 19th century. Nothing was yet known about atomic structure and experimental tools were very modest; substances could be characterized just by measuring weights, melting and boiling temperatures, observing colors, odors, and tastes. The key guiding concept, which proved amazingly powerful, was simply that all substances are composed of definite proportions of various chemical elements.
D. Herschbach, Chemistry: Blithe Sibling of Physics, Physics Today 50, 11 (April, 1997).
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