ORGLIST: Elemental analysis

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From: Jonas Nilsson (jonni$##$ifm.liu.se)
Date: Tue Feb 15 2000 - 03:13:34 EST

Hello

I'm having some trouble with my elemental analysis of some of my
compounds. The ones which gives me trouble are all aromatic amidines
Ar-C(=NH)-NH2. This is an example of how it works out:

Theory:Given
C:65.3%:54.0%
H:6.4%:5.6%
N:14.2%:12.0%
O:14.2%:12.4%

Total:100%:84.0%

The compound is purified on HPLC (C18-column, MeOH/H2O/CH3COOH), there
should be no other elements than C,H,N and O. The isolated compound is
an acetate salt of the amidine. The NMR looks very pure. The sample is
dried overnight at 80 deg. centigrade, 5 mTorr (0,005 mm Hg) before
elemental analysis is run.

The other functionalities in the compound are another aromatic system,
and a diamide:
Ar-NH-CO-C-C-CO-NH-CH2-Ar

As you all can see all percentages are much to low.
Now, what is the 16% which is not C,H,N,O? And how can the C analysis be
11% low?! I have 8 other samples all containing the amidine which gives
me similar results.

Please advice. I cannot publish this until i get it right, and I know
the compounds are pure. (There are at least not 10-20% impurities).
/jN 

--
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|   Jonas Nilsson     |   |                     |
|Linkoping University |   |      Telephone      |
|       IFM           |   |      ---------      |
| Dept. of Chemistry  |   | work: +46-13-285690 |
|  581 83 Linkoping   |   | fax:  +46-13-281399 |
|      Sweden         |   | home: +46-13-130294 |
|_____________________|   |_____________________|

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