Using different versions of ChemDraw, I get different results for molecular weight.
ChemDraw uses the latest version of Standard Atomic Weights published by IUPAC, which can differ slightly from NIST.
- For version 18.0 and earlier, we used the average mass values from ATOMIC WEIGHTS OF THE ELEMENTS 2009 (https://iupac.qmul.ac.uk/AtWt/AtWt09.html).
- For versions going from 18.1 and up to version 20.1, we used the atomic weights from this table: ATOMIC WEIGHTS OF THE ELEMENTS 2015 (https://www.qmul.ac.uk/sbcs/iupac/AtWt/AtWt15.html).
- For version 21.0, the average mass values used in the Molecular Weight calculation are from ATOMIC WEIGHTS OF THE ELEMENTS 2019 (https://www.qmul.ac.uk/sbcs/iupac/AtWt/).
As of version 21.0, this information is reflected on the "CS Isotopes Table.txt" file located on your ChemDraw Items folder. This location for version 21.0 is C:\ProgramData\PerkinElmerInformatics\ChemOffice2021\ChemDraw\ChemDraw Items