TY - JOUR
T1 - Quantitative analysis of Earth's field NMR spectra of strongly-coupled heteronuclear systems
AU - Halse, M.E.
AU - Callaghan, P.T.
AU - Feland, B.C.
AU - Wasylishen, R.E.
PY - 2009/9/1
Y1 - 2009/9/1
N2 - 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, BH , and the ammonium cation, NH . For the tetrahydroborate anion, J( B, H) = 80.9 Hz, and in an Earth's field of 53.3 μT, ν( H) = 2269 Hz and ν( B) = 728 Hz. The 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 H NMR spectra of the ammonium anion, NH , where J( N, H) = 52.75 Hz when ν( H) = 2269 Hz and ν( N) = 164 Hz. Contrary to an early report, we find that the H NMR spectra are independent of the sign of J( N, H). Exact analysis of two-spin systems consisting of quadrupolar nuclei and spin-1/2 nuclei are also discussed.
AB - 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, BH , and the ammonium cation, NH . For the tetrahydroborate anion, J( B, H) = 80.9 Hz, and in an Earth's field of 53.3 μT, ν( H) = 2269 Hz and ν( B) = 728 Hz. The 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 H NMR spectra of the ammonium anion, NH , where J( N, H) = 52.75 Hz when ν( H) = 2269 Hz and ν( N) = 164 Hz. Contrary to an early report, we find that the H NMR spectra are independent of the sign of J( N, H). Exact analysis of two-spin systems consisting of quadrupolar nuclei and spin-1/2 nuclei are also discussed.
UR - http://www.scopus.com/inward/record.url?scp=68049105102&partnerID=8YFLogxK
U2 - 10.1016/j.jmr.2009.06.012
DO - 10.1016/j.jmr.2009.06.012
M3 - Article
AN - SCOPUS:68049105102
SN - 1090-7807
VL - 200
SP - 88
EP - 94
JO - Journal of Magnetic Resonance
JF - Journal of Magnetic Resonance
IS - 1
ER -