ChemNMR options do not appear in the Structure menu.
First, make sure that you are launching ChemDraw Ultra, and not a Pro, Std, or Net version of ChemDraw. You can determine this by launching ChemDraw, going to the Help menu and choosing the About option.
If you are launching the Ultra version, you may need to reset your Preferences. Go to the File menu (ChemDraw menu for MacOS X users) and choose Preferences. Click on the Directories tab and confirm that the path at the top of the "ChemDraw Items Location Search Priority" list is the one pointing to the correct ChemDraw Items folder. For example, in ChemDraw 9, the default path should be: C:\Program Files\CambridgeSoft\ChemOffice2005\ChemDraw\ChemDraw Items
In ChemDraw 8, there is no Directories tab. The ChemDraw Items path is defined in the Open/Save tab. Click on the Open/Save tab and reset the ChemDraw Items folder location by using the Browse button (even if the location looks correct).