Current transition state hypothesis

This is in agreement with a transition state in which the C—H bond is at least partially broken. The current transition state hypothesis for the C—H insertion with a rhodium nitrene species involves an asynchronous-concerted pathway, in which the C—H—N angle is smaller than 180° (Figure 5.3). 

A useful way to do this is to use the transition state theory of chemical reaction rates (e.g., see Glasstone, Laidler, and Eyring [55] also, for a current review, sec Laidler [56]). This is based on the hypothesis that all elementary reactions proceed through an activated complex ... 

The current mechanistic hypothesis for hydroboration, a concerted, one-step syn addition to alkenes in which the two new bonds are partially formed to different extents in the transition state, nicely rationalizes all the experimental data. A mechanism involving formation of an open cation followed by hydride transfer fails to account for the observed syn stereochemistry of addition, which is demanded by the one-step mechanism. 

The spectral analysis of fluctuations yields also valuable information, and it can be used to test the validity of kinetic schemes describing the transitions between different channel states. In Ranvier nodes the component of the sodium current fluctuations which corresponds to the sodium inactivation process observed in voltage-clamp experiments is much larger than expected from a simple Hodgkin-Huxley scheme with statistically independent activation and inactivation processes. This finding provides a strong argument in favour of the hypothesis that the inactivation process is at least partially sequential to the activation process. 

---