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Natural abundance 17 O NMR spectroscopy of heteroaromatic Nitro compounds
Author(s) -
Balakrishnan Pattabiraman,
Boykin David W.
Publication year - 1986
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570230140
Subject(s) - chemistry , chemical shift , lone pair , nitro , ring (chemistry) , stereochemistry , nucleus , medicinal chemistry , molecule , organic chemistry , alkyl , biology , microbiology and biotechnology
Abstract The 17 O chemical shift data, at natural abundance, for selected nitroquinolines, nitroindoles, nitroindazoles and nitrothiophenes are reported. In the absence of a peri or a lone‐pair repulsion effect, the nitroquinolines' chemical shifts differ little from those of their carbocyclic analogs. However, the signal for 5‐nitroquinoline, 2 , is deshielded by 25 ppm compared to 6‐nitroquinoline, 1 , and the 17 O nucleus in 8‐nitroquinoline, 3 , is deshielded by 49 ppm compared to that in 1 . Both these shifts are attributed to rotation of the nitro group from the plane of the heteroaromatic ring arising from peri hydrogen interaction and lone pair repulsion, respectively. The signals for nitro groups on electron excessive ring systems ( e.g. , indoles and thiophenes) are shielded relative to corresponding ones in electron deficient heterocyclic ring system analogs. The chemical shifts for the π‐excessive systems are interpreted in terms of electronic effects.