Conformational analysis of small organic molecules using NOE and RDC data: A discussion of strychnine and a-methylene-y-butyrolactone

To understand the properties and/or reactivity of an organic molecule, an understanding of its three-dimensional structure is necessary. Simultaneous determination of configuration and conformation often poses a daunting challenge. Thus, the more information accessible for a given molecule, the better. Additionally to (3)J-couplings, two sources of information, quantitative NOE and more recently also RDCs, are used for conformational analysis by NMR spectroscopy. In this paper, we compare these sources of conformational information in two molecules: the configurationally well-characterized strychnine 1, and the only recently configurationally and conformationally characterized ?-methylene-?-butyrolactone 2. We discuss possible sources of error in the measurement and analysis process, and how to exclude them. By this means, we are able to bolster the previously proposed flexibility for these two molecules

"Perfecting" pure shift HSQC: full homodecoupling for accurate and precise determination of heteronuclear couplings

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Aufklärung von Struktur-Reaktivitäts-Beziehungen komplexer organischer Moleküle mit moderner NMR-Spektroskopie

Die vorliegende Dissertation leistet Beiträge zum Verständnis verschiedener Reaktionen komplexer organischer Moleküle mit moderner NMR-Spektroskopie. Dazu wird an verschiedenen Beispielen gezeigt, welchen Einfluss die molekulare Flexibilität auf die Wahl der passenden Methode oder Methodenkombination besitzt. Im Rahmen dieser Dissertation konnten mehrere Erfolge erzielt werden. Erstens konnte die Genauigkeit und Anwendbarkeit der NOE- und RDC-Analyse deutlich verbessert werden. Zweitens gelang es, die Komplementarität der NOE- und RDC-Analyse an verschiedenen Beispielen zu demonstrieren. Drittens konnten dadurch verschiedene komplizierte Strukturaufklärungsprobleme gelöst werden, wodurch verschiedene Struktur-Reaktivitäts-Beziehungen aufgeklärt werden konnten. Die untersuchten Beispiele umfassten dabei drei Klassen der organischen Synthese: Photoreaktionen, katalysierte Reaktionen und Syntheseprodukte

Accurate determination of one-bond heteronuclear coupling constants with "pure shift" broadband proton-decoupled CLIP/CLAP-HSQC experiments

AbstractWe report broadband proton-decoupled CLIP/CLAP-HSQC experiments for the accurate determination of one-bond heteronuclear couplings and, by extension, for the reliable measurement of small residual dipolar coupling constants. The combination of an isotope-selective BIRD(d) filter module with a non-selective 1H inversion pulse is employed to refocus proton–proton coupling evolution prior to the acquisition of brief chunks of free induction decay that are subsequently assembled to reconstruct the fully-decoupled signal evolution. As a result, the cross-peaks obtained are split only by the heteronuclear one-bond coupling along the F2 dimension, allowing coupling constants to be extracted by measuring simple frequency differences between singlet maxima. The proton decoupling scheme presented has also been utilized in standard HSQC experiments, resulting in a fully-decoupled pure shift correlation map with significantly improved resolution