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Quantitative analysis of Earth's field NMR spectra of strongly-coupled heteronuclear systems.
- Source :
-
Journal of magnetic resonance (San Diego, Calif. : 1997) [J Magn Reson] 2009 Sep; Vol. 200 (1), pp. 88-94. Date of Electronic Publication: 2009 Jun 18. - Publication Year :
- 2009
-
Abstract
- In the Earth's magnetic field, it is possible to observe spin systems consisting of unlike spins that exhibit strongly coupled second-order NMR spectra. Such spectra result when the J-coupling between two unlike spins is of the same order of magnitude as the difference in their Larmor precession frequencies. Although the analysis of second-order spectra involving only spin-(1/2) nuclei has been discussed since the early days of NMR spectroscopy, NMR spectra involving spin-(1/2) nuclei and quadrupolar (I>(1/2)) nuclei have rarely been treated. Two examples are presented here, the tetrahydroborate anion, BH4-, and the ammonium cation, NH4+. For the tetrahydroborate anion, (1)J((11)B,(1)H)=80.9Hz, and in an Earth's field of 53.3microT, nu((1)H)=2269Hz and nu((11)B)=728Hz. The (1)H NMR spectra exhibit features that both first- and second-order perturbation theory are unable to reproduce. On the other hand, second-order perturbation theory adequately describes (1)H NMR spectra of the ammonium anion, (14)NH4+, where (1)J((14)N,(1)H)=52.75Hz when nu((1)H)=2269Hz and nu((14)N)=164Hz. Contrary to an early report, we find that the (1)H NMR spectra are independent of the sign of (1)J((14)N,(1)H). Exact analysis of two-spin systems consisting of quadrupolar nuclei and spin-(1/2) nuclei are also discussed.
Details
- Language :
- English
- ISSN :
- 1096-0856
- Volume :
- 200
- Issue :
- 1
- Database :
- MEDLINE
- Journal :
- Journal of magnetic resonance (San Diego, Calif. : 1997)
- Publication Type :
- Academic Journal
- Accession number :
- 19596600
- Full Text :
- https://doi.org/10.1016/j.jmr.2009.06.012