How does ChemDraw calculate the exact mass?
The exact molecular mass of the structure is where atomic masses of each atom are based on the most common isotope for the element. The "CS Isotopes Table.txt" (or "isotopes.txt" for old Windows versions or "Isotopes Table" for Mac users) file stored in your ChemDraw Items folder (or CD_Items for old Windows versions or "ChemDraw Folder" for old Mac versions) is the resource ChemDraw uses to help calculate the exact mass. Open this file in a text editor for further details. The CS Isotopes Table.txt is located at the following location of Windows 7 machine. C:\ProgramData\PerkinElmerInformatics\ChemOffice2016\ChemDraw\ChemDraw Items