A Simple Method for Measuring Long-Range1H−13C Coupling Constants in Organic Molecules

Tweezer-type binding cavity formed by the helical folding of a carbazole-pyridine oligomer

We have synthesised a new aromatic foldamer based on the carbazole-pyridine oligomers that adopt helical conformations via dipole-dipole interactions and π-stacking between two ethynyl bond-linked monomers. This foldamer scaffold has been further modified into a synthetic receptor with a tweezer-type binding cavity outside the helical backbone upon folding, in contrast to most aromatic foldamers with internal binding cavities. The tweezer-type cavity is composed of two parallel pyrenyl planes, allowing for the intercalation of a naphthalenediimide guest via π-stacking and CH⋯O interactions, as demonstrated using its ¹H NMR spectra and X-ray crystal structure.

Pure shift NMR approach for fast and accurate extraction of heteronuclear couplings

An NMR experiment for the direct determination of heteronuclear couplings from the severely overlapped ¹H NMR spectrum.

Long-range proton-carbon coupling constants: NMR methods and applications

A general review of novel NMR methods to measure heteronuclear long-range proton-carbon coupling constants ((n)JCH; n>1) in small molecules is made. NMR experiments are classified in terms of NMR pulse scheme and cross-peak nature. A discussion about simplicity, general applicability and accuracy for each particular NMR experiment is presented and exemplified. Important aspects such as the sign determination and measurement of very small coupling values involving protonated and non-protonated carbons as well as the complementarity between different experiments are also discussed. Finally, a compilation of applications in structural and conformational analysis of different types of molecules since 2000 is surveyed.

Measurement of long-range proton-carbon coupling constants from pure in-phase 1D multiplets

The SELective INverse detection of carbon-proton CORrelation pulse sequence that yields a 1D spectrum of a proton directly bonded to a selected carbon resonance has been converted into a proton and carbon double-selective variant that provides a (1)H spectrum of a selected proton that is long-range coupled to a specific carbon resonance. The resulting 1D proton multiplet exhibits a pure absorptive in-phase lineshape for precise measurement of specific long-range proton-carbon coupling constants in small organic molecules at natural abundance.

Improved NMR methods for the direct 13C-satellite-selective excitation in overlapped 1H-NMR spectra

Improved pulsed-field gradient echo methods are presented and discussed for the direct selective excitation of the (13)C-satellite lines in overcrowded (1)H NMR spectra of small molecules. Sensitivity enhancements in (13)C spin-state selection can be achieved by combining multiple-proton-frequency excitation and Hadamard phase encoding. Several satellite-selective (SATSEL) NMR experiments are proposed and exemplified by measuring the sign and the magnitude of small, long-range proton-carbon coupling constants for (1)H resonances showing several levels of signal overlapping.