Two groups of protons have 8 = 4.0 and 8 = 5.2 and are interconverted by a conformational change of a fluxional molecule. In a 60 MHz spectrometer, the spectrum collapsed into a single line at 280 K but at 300 MHz the collapse did not occur until the temperature had been raised to 300 K. Calculate the exchange rate constant at the two temperatures and hence find the activation energy of the interconversion