From: Stefan K. <ste...@un...> - 2005-12-16 09:58:23
|
Hi all, I am still struggling with molecular masses. The problem seems to be the = exact=20 mass of atomic mixtures. For example from isotopes.xml we get a mass for = C of=20 12.011036563427163, which should be 12.011 according to mainstream period= ic=20 systems. For a molecule with formula C8H10O2Cl2 we get mass of=20 209.0720977783203 - it should be 209.0718. What do the chemists say about this? Stefan --=20 Stefan Kuhn M. A. Cologne University BioInformatics Center (http://www.cubic.uni-koeln.de) Z=C3=BClpicher Str. 47, 50674 Cologne Tel: +49(0)221-470-7428 Fax: +49 (0) 221-470-7786 My public PGP key is available at http://pgp.mit.edu |
From: Egon W. <e.w...@sc...> - 2005-12-16 10:28:14
|
On Friday 16 December 2005 11:29, Stefan Kuhn wrote: > I am still struggling with molecular masses. The problem seems to be the > exact mass of atomic mixtures. For example from isotopes.xml we get a mass > for C of 12.011036563427163, which should be 12.011 according to mainstream > periodic systems. So, mainstream in not precise enough in it's data. > For a molecule with formula C8H10O2Cl2 we get mass of > 209.0720977783203 - it should be 209.0718. > What do the chemists say about this? That's a clear propogation of rounding error, caused by mainstream doing rounding at an too early stage. Egon -- Egon Willighagen http://chem-bla-ics.blogspot.com/ |