Question

In H2O, the 31P NMR spectrum of the compound gives 2 lines shifted from each other by about 1ppm, corresponding to the hydrate and ketone in the ratio of 60:40.

You want to measure the rates of interconversion between them in the range of 0.1-3.0 per second using a cross relaxation method. Both the hydrate and ketone have T1's of 5.0 second and linewidths, delta v1/2 of 2 hz. The experiments are performed in a field such that the 31P resonant frequency is 125.000 Mhz.

a.) How will the system respond to a non selective inversion recovery sequence?

b.) How can you generate a state in which the hydrate line has been inverted and the ketone line has been de-excited using 2 non-selective pulses similar to those used for jump-return water supression?

c.) How will the system recover if you impose the conditions of b. on the system at t=0.

d.) Describe how you will measure the chemical interconversion rate from the data in c.

Answer 1

Instantaneous selectivity is the production rate of one component per production rate of another component.

For overall selectivity the same problem of the conflicting definitions exists. Generally, it is defined as the number of moles of desired product per the number of moles of undesired product. However, the definitions of the total amount of reactant to form a product per total amount of reactant consumed is used as well as the total amount of desired product formed per total amount of limiting reactant consumed.