Spin density distribution and stereochemistry of triphenylmethyl radical in solution

Schreiner, Kurt; Berndt, A.; Baer, F.

doi:10.1080/00268977300102181

Cited by 32 publications

(18 citation statements)

References 33 publications

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“…These radicals, initially developed by Nycomed Innovation to be used as hyperpolarizing agents for Overhauser magnetic resonance imaging (OMRI), [1] possess exceptional properties. This conformation was suggested by Lewis et al in 1944 based on UV spectra [12] and confirmed later by other techniques (X-ray diffraction, [13] EPR spectrsoscopy, [14] etc.). As a result, the sensitivity of detection is very high, because the signal intensity is inversely proportional to the square of the linewidth.…”

Section: Introductionsupporting

confidence: 54%

Configurationally Stable Tris(tetrathioaryl)methyl Molecular Propellers

et al. 2012

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Tris(tetrathioaryl)methanols and tris(tetrathioaryl)methanes are direct precursors and metabolites, respectively, of tris(tetrathioaryl)methyl radicals, which are very attractive paramagnetic spin probes for many magnetic resonance applications. Due to steric hindrance, these propeller‐shaped molecules display slow interconversion between their two enantiomeric conformations (right‐handed and left‐handed propeller conformations). Syntheses and HPLC resolutions carried out on a chiral stationary phase have been achieved. The influence of the hybridization of the central carbon atom as well as the para substitutient on the conformational stability were experimentally and theoretically studied. Depending on their particular structure, the free activation energy for the isomerization process determined by kinetics of racemization varies from 24.4 to 26.4 kcal mol–1 and corresponds to racemization half‐lives of 12 and 343 h, respectively. Computational and NOESY/exchange spectroscopy (EXSY) studies are consistent with a two‐ring flip mechanism for the isomerization process of tris(tetrathioaryl)methanols, radicals and tris(tetrathioaryl)methanes.

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Section: Introductionsupporting

confidence: 54%

Configurationally Stable Tris(tetrathioaryl)methyl Molecular Propellers

et al. 2012

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“…On the one hand, these additional lines can arise from weak exchange interactions between spin labels; on the other, they can originate from 13 C satellites. The values of 13 C hyperfine interaction (HFI) constants are known for simple TAMs already since 60s of the past century [43,44]. However, in case of a family of Finland TAMs synthesized relatively recently, measurements of 13 C HFI constants were only performed for the core Finland trityl ( FH ) [45].…”

Section: Introductionmentioning

confidence: 99%

Triarylmethyl Radicals: An EPR Study of ¹³C Hyperfine Coupling Constants

Kuzhelev

Tormyshev

Rogozhnikova

et al. 2016

Zeitschrift Für Physikalische Chemie

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Triarylmethyl (TAM) radicals are widely used in Electron Paramagnetic Resonance (EPR) spectroscopy as spin labels and in EPR imaging as spin probes for in vivo oxymetry. One of the key advantages of TAMs is extremely narrow EPR line, especially in case of deuterated analogues (~5 μT). Another advantage is their slow spin relaxation even at physiological temperatures allowing, in particular, application of pulsed dipolar EPR methods for distance measurements in biomolecules. In this paper a large series of TAM radicals and their deuterated analogues is synthesized, and corresponding spectroscopic parameters including 13C hyperfine constants are obtained for the first time. The negligible dependence of 13C hyperfine constants on solvent, as well as on structure and number of substituents at para-C atoms of aromatic rings, has been found. In addition, we have demonstrated that 13C signals at natural abundance can be employed for successful room-temperature distance measurements using Pulsed Electron Double Resonance (PELDOR or DEER).

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“…4,5 The previously reported introduction of t Bu groups onto the trityl radical H- 1· yielded tris(3,5-di- tert -butylphenyl)methyl ( t Bu- 1· ) that was found to be monomeric in benzene 19 and Rieker concluded that […] steric hindering of formation of the Jacobson–Nauta structure [R- 2 ] by incorporation of bulky groups [in meta and/or para positions], [R- 1· ] must then either be persistent as the monomer—or dimerize to [R- 1 2 ]. 4,5 Indeed, “poor, colourless crystals” could be grown from the orange cyclohexane solution consisting of the first unbridged HPE derivative 1,1,1,2,2,2-hexakis(2,6-di- tert -butyl-[1,1′-biphenyl]-4-yl)ethane ( t Bu- 4 2 ).…”

mentioning

confidence: 99%

“…The sample gave an EPR signal featuring the known spin pattern. 19,24 This, together with the known NMR lifetime broadening of organic radicals 25 as well as the r –6 line width dependence of the NMR signal with respect to the radical centroid in the molecule, 26 made it possible to identify the broad peak as the tert -butyl group hydrogen resonance of t Bu- 1· .…”

mentioning

confidence: 99%