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Chapter 2 - Distances


“Organic chemistry! Puzzle chemistry! Stink chemistry! Drugstore chemistry! … organic chemistry, that is a trade for pot-washers.”

[from Sinclair Lewis’ “Arrowsmith”, The Modern Library, NY, 1933]

One of the true marvels of science is that 19th chemists were able to deduce molecular structures long before 20th century chemists learned to “look inside” molecules and measure atom positions. Perhaps a greater marvel is the fact that we still make routine use of their ideas about structure and bonding.

Nevertheless, chemistry has witnessed great changes in the way chemists think about structure. Once upon a time, it may have been enough to know which atom was bonded to which, but today’s chemists need more information than that. The design of modern medicines, fuels, and so on, relies heavily on quantitative knowledge of molecular geometries. Consequently, the 19th century caricature of an organic chemist as a mixer of “potions” and “stinks”, is rapidly being replaced by one in which the chemist is a “designer”, “architect”, “sculptor”, and “builder” of molecules.

This chapter gives you a brief taste of one aspect of molecular geometry, interatomic distance. As you will see, the distance between two atoms depends on the presence of a chemical bond between the atoms. Distance data can be used to locate bonds within molecules, identify the type of bond, and even characterize forces between different molecules.

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