Proton Double Quantum and Relayed Proton Double Quantum Coherence Two-Dimensional NMR Mapping of Proton-Proton Connectivity Networks in Natural Products: a Model Study of Strychnine

Toward the Complete Prediction of the 1H and 13C NMR Spectra of Complex Organic Molecules by DFT Methods: Application to Natural Substances

“…Most experimental JA C H T U N G T R E N N U N G (H,H) couplings [33,34,37] have been recently corrected and agree better with our calculated values: thus, 2 J(H-17a,H17b) was reported [34] to be 15.5 Hz and was revised to 10.3 Hz; [38] (calcd À11. .…”

A Spin-Echo Technique for Separation of Multiplets in Crowded Spectra

“…At the expense of some loss of intensity, this generates very clean subspectra in the form of two anti-phase multiplets. Figure 1 illustrates the TSETSE-2 effect for protons 8, 16, 23a, 23b, and 12 of strychnine (12,13), inverted by a soft Gaussian pulse (7) with an excitation bandwidth that covers all five protons. The signals from the scalar-coupled protons 23a and 23b gradually change from an in-phase to an anti-phase (dispersive) configuration, and progress to inverted in-phase absorption signals as the interval t is further increased.…”

A Homonuclear Equivalent of the INEPT Experiment. Simplification of Crowded Proton Spectra and Measurement of Unresolved Couplings

“…Consequently, we may safely ignore chemicalshift effects and concentrate on the evolution through spinAn alternative approach is to simplify the spectra through double-resonance methods such as selective decoupling (2), spin coupling, which persists during the soft pulses. Then, if the t interval fulfills the approximate relation cross relaxation (3), or Hartmann-Hahn coherence transfer (4,5). We report here a proton-proton polarization-transfer The 90Њ hard pulse causes the magnetization transfer.…”