Commentary: Wonders - The Left and the Right; August 1998; Scientific American Magazine; by Morrison, Morrison; 2 Page(s)

In 1848 the king of France abdicated his constitutional post--not that he was the only king in Europe to be replaced by republics in those times. Yet the older regime came back; even emperors remained through World War I. That same spring of 1848 an eloquent and enduring pamphlet appeared, the Communist Manifesto of Karl Marx and Friedrich Engels. Its radical appeal would sound throughout the entire 20th century; its critique still defines political Right from Left, even though the demise it prophesied seems farther off than ever after 150 years. The metaphor of right and left is powerful among us still, but at the molecular level, that literal distinction is a rigorous and subtle property of three-dimensional space. And it was in 1848 that its consequences for matter first became clear.

No familiar molecular formula that accounts for the kinds and numbers of atoms present, such as H2O, is enough to fix its shape fully. All atom-to-atom links must be described geometrically. In a plane that is easy, but in real 3-D it is trickier. A right glove is so similar to the left glove of its pair that a basic description often fits both, although we know that the two gloves cannot equally fit either hand. Each glove matches exactly the image of its partner in an ideal mirror. Mirror-image molecular pairs possess what we call handedness; the chemists term them enantiomers, from the Greek for "opposites."