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An 1 H‐NMR. Spectroscopic Study of Alloxazines and Isoalloxazines
Author(s) -
Grande Hans J.,
Van Schagen Cees G.,
Jarbandhan Tjan,
Müller Franz
Publication year - 1977
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19770600207
Subject(s) - chemistry , chemical shift , coupling constant , resonance (particle physics) , benzene , molecule , cationic polymerization , ring (chemistry) , spectral line , nmr spectra database , stereochemistry , nuclear magnetic resonance , computational chemistry , crystallography , organic chemistry , atomic physics , physics , particle physics , astronomy
1 H‐NMR.‐spectra of a series of alloxazines and isoalloxazines and certain cationic derivatives were investigated (Tab. 2 and 5). Unequivocal assignment of all resonance signals was achieved in some compounds by selective deuteriation also by double resonance technique. The coupling constants were verified by computer simulation. Considerable enhancement of the signals due to H‐C(9) and H‐C(6) is found on decoupling of H 3 C‐C(7), H 3 C‐C(8) and H 3 C‐N(10), resp. These results are compared with those obtained with FAD. The methyl resonance signal of the H 3 C‐C(7) compounds give doublets due to coupling with H‐C(6). The difference in chemical shifts observed upon successive formal introduction of methyl groups into the benzene nucleus of (iso)alloxazines indicates that the molecule becomes less planar thereby. The pyrimidine ring of (iso)alloxazines does not contribute to the ring current except by indirect effects via the carbonyl groups. The experimental data are compared with published MO calculations and discussed.