Is there a way to change the spectrometer frequency used in the ChemNMR estimation?
Yes, you can change the frequency (in MHz) for the 1H NMR in ChemDraw 8 and above. Select the structure, and hold down the Alt key (Option key on the Mac), then click and hold on the Structure menu and choose the Predict 1H NMR Shifts command. This will bring up a dialog box that allows you to change the frequency from the 300 MHz default. Now when you choose the 1H command again, the prediction will be done at the new frequency.