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  • Title: Long-range heteronuclear coupling constants in 2,6-disubstituted purine derivatives.
    Author: Procházková E, Cechová L, Jansa P, Dračínský M.
    Journal: Magn Reson Chem; 2012 Apr; 50(4):295-8. PubMed ID: 22467566.
    Abstract:
    Four- and five-bond heteronuclear J-couplings between the hydrogen H-8 and carbons C-6 and C-2 in a series of 7- and 9-benzyl substituted purine derivaties with variuous substituents in positions 2 and 6 were studied by coupled (13)  C NMR and H,C-HMBC experiments and by DFT calculations. We have found that for some of the derivatives, the five-bond coupling H8-C2 is higher than the four-bond H8-C6 coupling, which is also evidenced by a stronger crosspeak in the HMBC. This finding contradicts the generally accepted opinion that only strong three-bond crosspeaks and one weak four-bond H8-C6 crosspeak can be observed in the HMBC spectra of purine derivatives. The misinterpretation of HMBC spectra may lead to an incorrect determination of the purine derivatives' structure.
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