The Windshield Wiper Effect

Schleyer and co-workers have shown that the ions formed from 2-p-anisyl- and l,2-di-p-anisyl-endo-2-norbornanols have the same ultraviolet spectra (HjSOJ which they believe to speak in favour of the rapid equilibration of classical cations / // if the developing ion had a nonclassical structure III then both aromatic 

Schleyer s data cannot convince of the rapid equilibrium of classical 2-nor-bomyl ions. The tertiary carbocation having a p-anisyl group as a substituent can be assumed to be classical however, the data reported do not preclude a nonclassical structure either. 

Corey and co-workers have shown that solvolysis of optically active 2-exo-norbornyl m-carboxybenzenesulphonate yields a racemic product. If the reaction proceeded via a classical ion, then since the interaction between the carbocation and the carboxylate-anion must be high compared with the Wagner-Meerwein rearrangement (this is not always true, see ), some optical activity would be retained. But the solvolysis via a classical ion implies such a fast interconversion of classical ions that Corey, for chemical purposes, takes the ion as symmetrical. 

If a reaction, as pointed out by Bethel and Gold proceeds via a classical 2-norbornyl ion, then the rate of conversion of the initially formed ion into an enantiomer must exceed the rate of its interaction with the solvent by more than 2000. The latter interaction is characterized by a constant of alxiut 10 -10 see hence the interaction rate o nstant of classical ions must he of the order of 10 sec . Such a rate constant can only belong to reactions wh free activation energy is close to zero. 

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An apparatus for studying this effect in more detail was described by Roberts and Tabor in 1971, as shown in Fig. 6.5. They had been particularly interested in the effect of lubricant films under car tires or beneath windshield wipers. Previously, Blok had tried to study these thick contaminant layers by placing a smooth plastic sheet on the tire rubber surface. But Roberts showed that this was unnecessary. If the rubber was molded against an optical glass surface, then the rubber itself acted as a mirror and enabled Newton s rings to be... 

Man-made contaminants come primarily from the combustion of hydrocarbons and the aforementioned impurities in the hydrocarbons that cause fuel-side contaminants. The combustion of hydrocarbons, such as coal in power plants or gasoline in cars, produces SO, and NO, emissions in the atmosphere. SO, and NO, are two important airborne contaminants that are the subject of many studies (Gould et al., 2009 Nagahara et al, 2008). Other man-made contaminants include road de-icers, such as MgCl2, which can have similar effects as sea salt, and the methanol in windshield wiper fluid. Man-made battlefield contaminants can lead to permanent performance losses in PEMFCs (Moore et al., 2000). Their sources include the combustion products of heavy fuels, explosive products, and chemical agents. 

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