O-17 NMR spectra of some Meisenheimer adducts

Citation
V. Machacek et al., O-17 NMR spectra of some Meisenheimer adducts, MAGN RES CH, 38(12), 2000, pp. 1001-1004
Citations number
16
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
MAGNETIC RESONANCE IN CHEMISTRY
ISSN journal
07491581 → ACNP
Volume
38
Issue
12
Year of publication
2000
Pages
1001 - 1004
Database
ISI
SICI code
0749-1581(200012)38:12<1001:ONSOSM>2.0.ZU;2-O
Abstract
The O-17 NMR spectra of O-17 isotope-enriched 1,3,5-trinitrobenzene and its Meisenheimer adducts with hydride ion (1), acetone anion (2) and methoxide ion (3) were measured. The adducts 1-3 show O-17 signals shifted upheld co mpared with those of 1,3,5-trinitrobenzene. A higher upheld shift is exhibi ted by the oxygen atoms of the 4-nitro group (similar to 90 ppm) and a lowe r shift by those of the 2- and 6-nitro groups (similar to 40 ppm). The shif t is practically independent of the structure or bulkiness of the nucleophi le bound at the tetrahedral centre C-1 in the adduct and also, within an ex perimental error, of the counter ion and solvent (acetonitrile or a mixture of DMSO-d(6) and methanol). The measured delta(O-17) values indicate that in the Meisenheimer adducts the negative charge at the oxygen atoms is larg er in 4-NO2 than in 2- and 6-NO2 groups. Copyright (C) 2000 John Wiley & So ns, Ltd.