Chirality of α-Nitronyl Nitroxide Radicals in the Solid State

Minguet, María; Amabilino, David B.; Wurst, Klaus; Veciana, Jaume

doi:10.1006/jssc.2001.9175

Cited by 14 publications

(5 citation statements)

References 98 publications

(7 reference statements)

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“…CIS calculations on 33 and on appropriately modified geometries demonstrated that the sign of the two bands is dictated by two distinct conformational parameters, that is, the helicity of the 5‐membered ring and the twist angle between the planes of phenyl and ONCNO moiety 181. In a second article, such a piece of information was employed to interpret solid‐state CD spectra of a series of crystalline α‐nitronyl nitroxide radicals 182…”

Section: Examples Of Applicationmentioning

confidence: 99%

Absolute structural elucidation of natural products—A focus on quantum‐mechanical calculations of solid‐state CD spectra

et al. 2009

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In this review article we examine state-of-the-art techniques for the structural elucidation of organic compounds isolated from natural sources. In particular, we focus on the determination of absolute configuration (AC), perhaps the most challenging but inevitable step in the whole process, especially when newly isolated compounds are screened for biological activity. Among the many methods employed for AC assignment that we review, special attention is paid to electronic circular dichroism (CD) and to the modern tools available for quantum-mechanics CD predictions, including TDDFT. In this context, we stress that conformational flexibility often poses a limit to practical CD calculations of solution CD spectra. Many crystalline natural products suitable for X-ray analysis do not contain heavy atoms for a confidential AC assignment by resonant scattering. However, their CD spectra can be recorded in the solid state, for example with the KCl pellet technique, and analyzed possibly by nonempirical means to provide stereochemical information. In particular, solid-state CD spectra can be compared with those calculated with TDDFT or other high-level methods, using the X-ray geometry as input. The solid-state CD/TDDFT approach, described in detail, represents a quick and reliable tool for AC assignment of natural products.

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Section: Examples Of Applicationmentioning

confidence: 99%

Absolute structural elucidation of natural products—A focus on quantum‐mechanical calculations of solid‐state CD spectra

et al. 2009

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“…The conformation of the lactate groups in this crystal structure is comparable to those of other phenyl derivatives. [13][14][15][16] The acid OH group of each molecule is associated with the SO group of the nearest solvent molecule by strong hydrogen-bond (O2ÁÁÁO9 2.567 and O6ÁÁÁO10 2.549). The polar layer is reinforced by weak hydrogen-bonds (CH 3 ÁÁÁO) between the À ÀCH 3 and both the SO of DMSO molecules and the CO of the acid group of (S)-1.…”

Section: Results and Discussion Synthesis And X-ray Structurementioning

confidence: 99%

Organization of the enantiomeric and racemic forms of an amphiphilic resorcinol derivative at the air–water and graphite–1‐phenyloctane interfaces

Iavicoli

Keszthelyi

et al. 2011

Chirality

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This article describes a study of the outcome of racemate condensation in different types of monolayers. The study was performed on a resorcinol surfactant bearing an octadecyl chain and a lactate group which formed a monolayer at the interface of graphite and 1-phenyloctane as well as a Langmuir film at the air-water interface. Control experiments with the enantiopure materials provided the characteristics of the chiral organizations. The results obtained on the racemate show that on graphite the molecule forms chiral domains, indicating that spontaneous resolution takes place at the surface, a phenomenon that has been rationalized using molecular modeling. The X-ray crystal structure of the DMSO solvate of one of the enantiomers shows a similar type of packing to this monolayer. On the other hand, in the Langmuir layer it appears that the formation of a racemic compound is favoured, as it is in the solid state in three dimensions. The work shows how the symmetry restrictions in different environments can have a critical influence on the outcome of racemate organization, and underline the tendency of graphite to favour symmetry breaking in monolayers formed at its surface.

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“…Other principal characteristics of the n-OH(OMe)PhNN group of molecules are the two angles, the deformation angle of the imidazolyl ring denoted ∠C 1 N 2 C 3 C 2 in Table 1 and the twist angle 50 between the hydroxyphenyl and NCN elements of the imidazolyl ring (not presented in Table 1). Investigations of the crystal structure indicate that combinations of these two angles into enantiomeric or pseudoeclipsed conformations are preferred 51 for all members of the n-OH(OMe)PhNNs group of molecules. Our optimized structures have an organization of angles that exactly corresponds to the crystallographic data.…”

Section: Resultsmentioning

confidence: 99%

Influence of Hydrogen Bonding in the Paramagnetic NMR Shieldings of Nitronylnitroxide Derivative Molecules

et al. 2003

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We apply our recently developed methodology for first-principles computations of paramagnetic NMR shieldings and explore the shieldings in a selected set of radicals that form core units in molecular magnets. The influence on these parameters of hydrogen bonding, that corresponds to the crystal environment, is the prime objective of the study. Nitronylnitroxide radicals with the hydroxyphenyl group in the ortho, meta, and para positions, as well as p-methoxyphenyl derivatives, are chosen for this purpose. The strong NO‚‚‚HO hydrogen bonding in the real crystal structure has been simulated by adding water molecules in the twelve molecular complexes investigated. Comparison of calculated and experimental data is made by taking the special features of the solid state and solution environments into account. The observed change in the shielding constant due to hydrogen bonding is explained by the spin delocalization picture; the dominating contribution is the temperature-dependent contact shielding containing the isotropic hyperfine coupling constant.

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Chirality of α-Nitronyl Nitroxide Radicals in the Solid State

Cited by 14 publications

References 98 publications

Absolute structural elucidation of natural products—A focus on quantum‐mechanical calculations of solid‐state CD spectra

Absolute structural elucidation of natural products—A focus on quantum‐mechanical calculations of solid‐state CD spectra

Organization of the enantiomeric and racemic forms of an amphiphilic resorcinol derivative at the air–water and graphite–1‐phenyloctane interfaces

Influence of Hydrogen Bonding in the Paramagnetic NMR Shieldings of Nitronylnitroxide Derivative Molecules

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