Conformational conversion and chemical exchange

We need to understand how to analyze spectra to determine rates of dynamical events of biological importance, such as conformational changes and proton exchange between molecules. 

The NO group in N,JV-dimethylnitrosamine, (CHjijN-NO, rotates about the N-N bond and, as a result, the magnetic environments of the two CH3 groups are interchanged. The two CH3 resonances are separated by 390 Hz in a 600 MHz spectrometer. At what rate of interconversion will the resonance collapse to a single line  

Strategy Use eqn 13.21 for the average lifetimes of the conformations. The rate of interconversion is the inverse of their lifetime. 

It follows that the signal will collapse to a single line when the interconversion rate exceeds about 830 s . 

19 The interactions between the a and p states of a proton and an external magnetic field may be visualized as the precession of the vectors representing the angular momentum. 

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