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I'm so confused. I used to think Xanthosine is Xanthine with a ribose instead of H but it appears to me as if it isn't. If you look at the picture in top-right of its wikipedia page you will see that the Imidazole is reversed from the picture in here also the picture in the bottom of this page in additional images section is like the second one. I'm sorry if didn't use the right chemical terms! I'm no chemist. Also I while I was searching I saw different images for Adenine and Guanine where the Imidazole loop was reversed in some by reversed I mean like the position of NH and N was reversed with respect to the Benzene loop!

P.S. It would be great if you could also teach me the correct way to ask this question by means of the chemical terms I should use.

P.S.S I hope it is not a wikipedia problem!

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  • $\begingroup$ All they’ve done is flip the picture… $\endgroup$ – canadianer Nov 2 '17 at 16:23
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    $\begingroup$ They are the same. The purine imidazole can exist in two tautomeric forms. $\endgroup$ – canadianer Nov 2 '17 at 17:11
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    $\begingroup$ 9H-xanthine (ebi.ac.uk/chebi/searchId.do?chebiId=17712) is a tautomer of 7H-xanthine (ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:48517) $\endgroup$ – gilleain Nov 2 '17 at 17:54
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    $\begingroup$ I guess it depends on your definition of "same". Tautomers are often considered to be the same compound even though they are constitutional isomers. $\endgroup$ – canadianer Nov 2 '17 at 17:54
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    $\begingroup$ On the question "Is PubChem/Wikipedia/etc completely reliable?" the answer is "not completely!". It is very hard to get all chemical data 100% correct, but there are efforts to cross-check and validate such data with experts... $\endgroup$ – gilleain Nov 2 '17 at 18:02
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The two structures are tautomers of one another:

enter image description here

Tautomers are often considered the same compound even though they are really constitutional isomers. Technically they are called 7H-xanthine and 9H-xanthine, respectively (thanks to gilleain for the links).

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