Representative IR spectra are shown in Figure . The anhydride is detected through the absorbance (A) of the peak at 1793 cm -1 , associated with the symmetric stretch of the anhydride and well-separated from the rest of the spectrum. On our instruments, there is significant drift in the baseline throughout the experiment. We found it helpful to reference the absorbance data to the absorbance at 1650 cm -1 , where the spectrum is unchanging (i.e., ∆A = A 1793 -A 1650 ). Plotting ln ∆A against time allows k for the hydrolysis to be determined. For us, the data tends to be a bit noisier than that from the NMR experiments, but still yields a good linear fit.