It's between rounds in one of the longest-lasting and most impassioned battles in contemporary chemistry: the fight over where the positive charge lies on a certain seven-carbon ion, or charged molecule. In one corner stand the vast majority of participants in the fight, who believe that the positive charge simultaneously over, or shared by, several atoms of that molecule. Having just dealt a few sizable blows, this group says the fight now should be called in its favor. In the other corner stand the mere handful of remaining participants, who either cling to the notion that the positive charge behaves more conventionally, belonging to only one atom at a time, or at least insist that there not yet enough evidence to support the idea. Though it the general consensus of the community that this minority opinion has been scientifically pummeled, its most vociferous proponent, a Nobel-Prize winning chemist, shows no signs of throwing in the towel. While there have been several other chemistry controversies that also ... were carried forth because virtually only one of their participants would not give up, says one observer, there really have been no others quite like this debate over the positively charged molecule, or cation, called the 2-norbornyl cation (n6r-b6r'-n'l kat'i-an). In some ways, it ranks among the worst of debates: Its strained, often brutal discourse, for example, led at least one prominent chemist early on to quit doing research related to the issue because he didn't like the stress involved. But in other ways, it ranks among the best: It has depended on-and in some cases, redefined the state of the art in several research fields. In addition, the heart of the issue how the positive charge distributed on the 2-norbornyl cation is not a negligible question, says George A. Olah, champion of the smeared theory. The skeletal norbornyl structure is found in many of nature's terpenes [chemicals found in plant oils], Olah says. Moreover, the norbornyl cation an ionic intermediate-a charged link between the neutral starting materials and neutral end products of various chemical reactions; and some of its chemical cousins are ionic intermediates in major petrochemical reactions, says Olah, of the University of Southern California in Los Angeles. Understanding the precise behavior of the 2-norbornyl cation eventually could have implications for research on both terpenes and major industrial processes. The attempt to understand the precise behavior of the 2-norbornyl cation can be traced back to work reported in 1949 by the late Saul Winstein of the University of California at Los Angeles. Winstein was studying a chemical reaction that can start with either of two versions of the same compound: One, called the exo-norbornyl starting material, has a group of atoms (labeled A in the diagram on p. 107) substituted for a hydrogen at the carbon-2 position of norbornane in such a manner that it lies slightly above the plane formed by carbons 2, 3, 5 and 6. The other version, called the endo-starting material, also has