Recent Advances in Stereodynamics and Conformational Analysis by Dynamic NMR and Theoretical Calculations

Abstract

Dynamic NMR spectroscopy can determine energy barriers due to internal motion over the range of about 4.5-23 kcal mol -1 . Conformational analysis of the frozen conformations can be simulated and interpreted by reliable theoretical calculations based mainly on density functional theory (DFT). The same calculations can identify transition states

Atropisomerism of 2,2′‐Diaryl‐1,1′‐binaphthalenes Containing Three Stereo­genic Axes: Experimental and Computational Study

“…[7] Dianisyl and dianilinyl derivatives 1 and 2, respectively, each exhibited four signals for methyl group protons in their 1 H NMR spectra at lower temperatures: one signal for each of the u,u and l,l isomers, and two signals of equal integral intensity for the l,u isomer (one signal for each of its methyl groups). In the case of ditolyl derivative 3, only three signals for methyl group protons were observed, due to the absence of the minor l,l atropisomer.…”

“…Rotation around aryl-aryl bonds in sterically congested oligoaryl systems is not only a widely studied phenomenon, [1] but it is important for applications such as axially chiral catalysts in stereoselective synthesis [2] and chemosensors in enantioselective recognition.…”

Dynamic NMR study of cyclic derivatives of pyridoxine

“…NMR has been proven to be a powerful tool for conformational analysis and the investigation of stereodynamic processes . Seven‐membered heterocycles are interesting compounds for nuclear magnetic resonance studies because of the wide range of different structural types of these molecules.…”

Dynamic NMR of low‐sensitivity fast‐relaxing nuclei: 17O NMR and DFT study of acetoxysilanes

“…Dynamic NMR (DNMR) is a long‐time established and very useful experimental technique for studying intermolecular or intramolecular dynamic processes, and density functional theory (DFT) calculations have proven to be of considerable value in mechanistic investigations. Advances in stereodynamics and conformational analysis by DNMR and by theoretical calculations have been reviewed recently . Typically, DNMR studies of organic compounds rely on the detection of slowly relaxing spin‐1/2 nuclei, mainly 1 H or 13 C, because (i) the natural linewidth is usually negligible and (ii) there is no serious experimental difficulty in obtaining spectra over a wide range of temperatures, comprising those near coalescence for which the shape of the NMR signals is the most sensitive to the exchange kinetics.…”

“…Typically, DNMR studies of organic compounds rely on the detection of slowly relaxing spin‐1/2 nuclei, mainly 1 H or 13 C, because (i) the natural linewidth is usually negligible and (ii) there is no serious experimental difficulty in obtaining spectra over a wide range of temperatures, comprising those near coalescence for which the shape of the NMR signals is the most sensitive to the exchange kinetics. Therefore, rate constants and activation parameters characterizing the dynamic process can be obtained with a rather good accuracy . In contrast, DNMR of low‐sensitivity and fast‐relaxing nuclei, among which are 17 O and other quadrupolar nuclei, is definitely more challenging.…”