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Author Topic: Stable and radioactive Isotope Labelling  (Read 388 times)

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veroconnan

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Stable and radioactive Isotope Labelling
« on: April 25, 2017, 05:00:30 AM »

I'm confused about carbon numbering with isotopes:

[1-13C] Phenylalanine is labelled at the carboxyl end (carbon #1)
http://www.sigmaaldrich.com/catalog/product/aldrich/490091?lang=en&region=US

The radioactive [4-3H] Phenylalanine is tritiated on the phenyl ring (which I would have thought would be carbon #7, not carbon #4...) 
http://www.chemicalbook.com/ProductChemicalPropertiesCB4372040_EN.htm

Why aren't the carbons numbered the same way between these two phenylalanine forms? 
For one, the carbon numbering begins at the carboxyl end and for the other, it begins where the ring connects.

Am I going crazy?!
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