on the occasion of his 65th birthday
The reaction mechanism is the detailed, step-by-step description of a chemical reaction. Most chemical reactions take place through a complex sequence of steps via reactive intermediates. The most important reactive intermediates in organic chemical reactions in solution are carbocations, carbanions, carbenes, and radicals. Of course, chemists have been able to detect these intermediates indirectly by chemical and physical methods, and spectroscopic methods are available to study them directly and in detail. [1] For example, Olah investigated carbocations in ™magic acid∫ solutions under nonreaction conditions. [2] Transient carbocations that contained an appropriate chromophore were studied by using UV spectroscopy. [3,4] Radicals were explored by ESR spectroscopy and in appropriate cases by CIDNP (chemically induced dynamic nuclear polarization), and UV spectroscopy. [5,6] However, it seems to be most remarkable that these methods (there may be some exceptions) are not generally suited to detect and to study these reactive intermediates directly in reaction solutions, for example, of a radical chain reaction. Furthermore, substrates, intermediates, and final products cannot be monitored by using these methods. Additional measurements have to be applied to do so. Clearly, it would be of great importance to have a simple method available to study a reaction by monitoring substrates and all intermediates and final products formed, and especially to detect and characterize simultaneously and directly the reactive intermediates. Such a method could give new and important insights in our understanding of reactions and their mechanisms. Furthermore, the method should be applicable to micro amounts of substrates and should allow a high throughput, thus contributing to a sustainable development. [7] Recently, electrospray ionization mass spectrometry (ESIMS) [8] has been successfully applied to the investigation of some chemical reactions in solution. The investigations were mostly performed offline, for example, with the oxidation of tetrahydropterins to radical cations, [9] homogeneously catalyzed reactions such as the Suzuki reaction, [10] and the