Choosing Models of Reactive Intermediates

In later chapters we will consider in more detail the energies and structures of reactants, transition states, intermediates, and products. It will be important to remember that the environment and lifetime of a reactive intermediate in a spectroscopic study, such as a carbocation in a frozen matrix or superacid solution at low temperature, are quite different from those of the 

The electrochemistry of carbanions was discussed by Fox, M. A. in Bimcel, E. Durst, T., Eds. Comprehensive Carbanion Chemistry. Part C. Ground and Excited State Reactivity Elsevier Amsterdam, 1987 pp. 93-174. 

Diradicals 97 and 98 show rather different properties. Structure 97 shows predominantly singlet character at low temperature, although triplet character becomes evident at higher temperature. On the other hand, 98 displays predominantly triplet character under all conditions. Rationalize these results. 

The EPR spectrum of the benzyl radical in solution shows a values for the a, ortho, meta, and para protons of 16.4 G, 5.17 G, 1.77 G, and 6.19 G, resp ectively. Interpret these results in terms of the relative impaired electron density at each of these four positions. How do the results compare with the predictions of HMO theory or simple resonance theory from Chapter 4  

In the NMR spectrum of the isopropyl cation, the coupling constant between C2 and the hydrogen bonded to it is 169 Hz. Based on the relationship between 

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