High-Resolution Zero-Field NMR J-Spectroscopy of Aromatic Compounds

Abstract

ABSTRACT:We report the acquisition and interpretation of nuclear magnetic resonance (NMR) J-spectra at zero magnetic field for a series of benzene derivatives, demonstrating the analytical capabilities of zero-field NMR. The zeroth-order spectral patterns do not overlap, which allows for straightforward determination of the spin interactions of substituent functional groups. Higher-order effects cause additional line splittings, revealing additional molecular information. We demonstrate resonance linewidths as narrow as 11 mHz, permitting resolution of minute frequency differences and precise determination of long-range J-couplings. The measurement of J-couplings with the high precision offered by zero-field NMR may allow further refinements in the determination of molecular structure and conformation.

Zero-field nuclear magnetic resonance spectroscopy of viscous liquids

“…In contrast to the thermal variation, an offset linewidth of 0.3 Hz (the left vertical axis) remains in the scaling relation, presumably due to the effect of water protons in the infinite-dilution limit. This linewidth is substantially greater than would be attributed to magnetic field inhomogeneity or temperature gradients (approximately 0.01 Hz) [14][15][16], and should be primarily representative of the intrinsic spin-spin relaxation time. A detailed understanding of the shifts towards higher frequencies observed both with increasing temperature and dilution with water would require an accurate description of the conformers' populations.…”

“…Until now, investigations of ZULF-NMR with atomic magnetometers have focused on low-viscosity liquids with simple molecular structures and weak intermolecular interactions [5][6][7], achieving half width at half maximum as low as %0.01 Hz [14][15][16] comparable to that of advanced high-field (HF) NMR. Many materials of practical interest -polymers or proteins, for example, feature significant van der Waals interactions and hydrogen bonds.…”

Nuclear magnetic resonance at millitesla fields using a zero-field spectrometer

“…[1,2,3,4,5,6,7] This approach to NMR, instrumentally considerably less demanding than traditional high-field NMR with superconducting magnets, has the potential to be analytically useful for many of the experiments carried out on small to medium sized molecules. [8,9] Examples of experiments on a variety of aromatic molecules demonstrated compelling spectral detail that differentiated between the compounds.…”

“…[8,9] Examples of experiments on a variety of aromatic molecules demonstrated compelling spectral detail that differentiated between the compounds. [1] Zero-field spectroscopy is therefore a route to chemically informative NMR signals.…”

Milli-tesla NMR and spectrophotometry of liquids hyperpolarized by dissolution dynamic nuclear polarization

“…Line widths typically are narrower than at higher field, which enables resolving J-couplings when they are otherwise unobservable [8,9]. J-spectroscopy even at zero-field has been shown to contain chemical information alternative to the traditional spectra based on chemical shifts at high fields [10,11].…”