a. The term organic given to the chemistry of carbon, in fact, is based on the 18th century notion that only live organisms could produce its compounds.

b. The absolute configuration of organic compounds is obtained by the "sequence rule": (I) rank the four substituents of C* (see Fig. 7.1.d) by their atomic numbers (lowest number, lowest rank); (II) figuratively orient the chiral molecule in space so as to look down the C bond with the smallest rank (you will see the remaining three substituents radiating like spokes from the asymmetric C); (III) now if you can connect from the top through the middle to the lowest rank substituents with a counterclockwise (left, sinister) route the molecule is S; if the route is clockwise (right, rectus), it is R.

c. The carbon atom next to a carboxylic (COOH) acid function is slightly acidic, because of electron withdrawal by the nearby oxygen atoms and tends to loose a H+ in water. The ion that forms can then re-acquire an H, a process that may result in a change ofconfiguration. With time and appropriate conditions, this process will lead to racemic mixtures.


Further Readings

The following references are quoted in the text to provide further reading in the subjects indicated in their title as well as specific references to analytical papers to be found in the literature.

1. Geison GL. The private science of Louis Pasteur. Princeton University Press, Princeton, New Jersey, 1995.

2. Cronin JR, Reisse J. Chirality and the origin of homochirality. In: Gar-gaud, M. ed. Lectures in Astrobiology. Vol. 1; Berlin: Springer-Verlag, 2005:473-514.

3. Bonner WA. The origin and amplification of biomolecular chirality. Origin Life Evol Biosphere 1991; 21:59-111.

4. Hegstrom RA, Kondepudi DK. The handedness of the universe. Scientific American 1990:108-115.

5. The web-site: from "The Encyclopedia of Astrobiology, Astronomy and Spaceflight" offers a descriptive entry on the subject of Panspermia.

Specific References

6. Nielsen PE. Peptide-Nucleic Acid (PNA)-A model structure for the primordial genetic code. Origins Life Evol Biosphere 1993; 23:323-327.

7. Kondepudi DL, Kaufman RJ, Singh N. Chiral symmetry breaking in sodium chlorate crystallization. Science 1990; 250:975-976.

d. The interpretation of a difference in energy between enantiomers (referred to as parity-violating energy difference or PVE) derives from a theory of physics that unifies the electro magnetic and weak forces. The force resulting from this theory will be able to interact with both nucleus and electron and distinguish between "left" and "right".4

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