Chemical shift nonequivalence in prochiral groups

Jennings, W. Brian

doi:10.1021/cr60295a003

Cited by 260 publications

(73 citation statements)

References 40 publications

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“…Two of these radicals showed magnetic inequivalence of their p-CH2 protons due to the presence of a nonadjacent P-chiral carbon, an EPR phenomenon that has received little attention (3-7) and, in the case of acyclic C-centered radicals, no systematic study (5)(6)(7). Similar long-range effects of molecular asymmetry are numerous in the NMR literature (8)(9)(10)(11)(12), and the adjacent chiral effect, namely, magnetic inequivalence of p-CH2 protons adjacent to a y-C chiral center or of y-CH2 protons adjacent to a p-C chiral center, is common in EPR spectroscopy (1 3-23).…”

Section: Introductionmentioning

confidence: 70%

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

Smith¹,

Donovan²

1988

Can. J. Chem.

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PETER S M~T Hand W~L L~A M HARLEY DONOVAN. Can. J. Chem. 66, 2304 (1988.Using aqueous TiC1,-based continuous-flow, radical-generating methods at 25°C we have carried out a comprehensive EPR study o f . hydroxyl-and aminyl-radical addition to eight alkene substrates that yielded radicals of general formula XCH~-CY-C*HR'R~, where C* is a chiral center, to investigate the magnetic inequivalence of p-CH2 protons arising from a nonadjacent p-C chiral center. We attribute the observed nonequivalence to the long-range influence of the chiral center in these radicals, and note that our results are consistent with the reasonable expectation that the presence of bulky groups in the radicals is likely to favor particular conformations, leading to more easily observed inequivalence of the p-CH2 proton splittings. Operant a25"C et utilisant des mCthodes de production de radicaux basCes sur des Ccoulements continus de solutions aqueuses de TiCl,, on a rCalisC une ttude rpe dCtaillCe d'additions des radicaux hydroxyle et aminyle sur huit alcenes conduisant des radicaux de formule gCnCrale X C H~--C Y -C * H R ' R '~~~S lesquels C* est un centre chiral; ces expkriences ont CtC rCalisCes afin d'ivaluer si les protons CH2 en p , qui sont sournis a l'influence d'un centre chiral qui n'est pas adjacent, sont equivalents. On a observt qu'ils ne sont pas Cquivalents et on attribue ce resultat a l'influence longue distance du centre chiral present dans ces radicaux; de plus, on note que nos rCsultats sont en accord avec les attentes qu'on peut raisonnablement avoir si on adrnet que la prCsence de groupements volumineux dans les radicaux devrait favoriser des conformations particulikres et ainsi conduire a une inequivalence plus facilernent observable des couplages des protons CH2 en p.[Traduit par la revue] IntroductionRecently (I), we presented the results of an EPR study of three XCH~-CH-CH(OH)CH~X radicals, with -X = -CN, -COOH, and -OH, formed from symmetrical 1,2-disubstituted alkenes in aqueous solution at ca. 25°C with use of the TiC13-H202, continuous-flow, radical-generating method (2). Two of these radicals showed magnetic inequivalence of their p-CH2 protons due to the presence of a nonadjacent P-chiral carbon, an EPR phenomenon that has received little attention (3-7) and, in the case of acyclic C-centered radicals, no systematic study (5-7). Similar long-range effects of molecular asymmetry are numerous in the NMR literature (8-12), and the adjacent chiral effect, namely, magnetic inequivalence of p-CH2 protons adjacent to a y-C chiral center or of y-CH2 protons adjacent to a p-C chiral center, is common in EPR spectroscopy (1 3-23).Previously (I), we stressed the importance to spectral interpretation of recognizing the possibility of there-being inequivalent p-CH2 protons in radicals with a nonadjacent chiral center. The present investigation successfully extends our previous study ofthe nonadjacent chiral effect; specifically, to determine how often inequivalence of p-CH2 protons can occur in radicals of general structu...

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Section: Introductionmentioning

confidence: 70%

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

Smith¹,

Donovan²

1988

Can. J. Chem.

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“…The transmission of chirality effects through sulfenyl sulfur as evidenced by the appearance of methylene AB quartets in 3 is noteworthy. This type of observation is precedented, albeit uncommonly (14).…”

Section: Nuclear Magnetic Resonance Spectramentioning

confidence: 91%

A novel synthesis of 2,4,6-trithiaheptane and its conversion into 2,6-bis(methylthio)thiane. Spectral properties of some thiaalkanes

Grossert¹,

Hooper²,

Neaves³

1981

Can. J. Chem.

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2,4,6-Trithiaheptane (1a) has been prepared by lithium tetrahydridoaluminate reduction of the methiodide of 1,3,5-trithiane (2). Treatment of 1a with strong bases permitted formation of 3-alkylated derivatives (3) which could in turn be converted into diastereomeric mixtures of 3,5-dialkyl derivatives (4). A two-step alkylation of 1a with 1-bromo-3-chloropropane led to the formation of 2,6-bis(methylthio)thiane (5). Proton and 13C nmr spectral studies on these compounds, including the measurement of long-range carbon–proton coupling constants, are described; their mass spectra showed elimination of methanethiol as a characteristic major fragmentation pathway.

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“…Es fällt jedoch auf, daß nur eine 'H -Resonanz für die NCH-Gruppierung auftritt, obwohl der Strukturvorschlag die unterschiedliche Koordination der Stickstoffatome fordert. Ferner sollten bei fixierter Struktur von ( l b ) 2 im 'H -N M R -Spektrum insgesamt vier Dubletts anstelle der beobachteten zwei Dubletts für die M e thylgruppen in den N'Pr-Resten auftreten (als Folge der unterschiedlichen Umgebung der Stickstoff atom e und der D iastereotopie [7] dieser M ethylgrup pen). A ndererseits zeigt das 'H-NM R-Spektrum von und im 'H-NM R-Spektrum (300 MHz) fallen zwei der vier Dubletts zusammen, so daß drei D ubletts im Verhältnis 2:1:1 resultieren.…”

Section: Ergebnisse Und Diskussionunclassified

Dynamisches Verhalten dimerer 1,3,2,4λ²-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ²-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study

Wrackmeyer

Horchler

Zhou

et al. 1989

Zeitschrift Für Naturforschung B

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Chemical shift nonequivalence in prochiral groups

Cited by 260 publications

References 40 publications

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

A novel synthesis of 2,4,6-trithiaheptane and its conversion into 2,6-bis(methylthio)thiane. Spectral properties of some thiaalkanes

Dynamisches Verhalten dimerer 1,3,2,4λ²-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ²-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study

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Chemical shift nonequivalence in prochiral groups

Cited by 260 publications

References 40 publications

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons

A novel synthesis of 2,4,6-trithiaheptane and its conversion into 2,6-bis(methylthio)thiane. Spectral properties of some thiaalkanes

Dynamisches Verhalten dimerer 1,3,2,4λ2-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ2-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study

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Dynamisches Verhalten dimerer 1,3,2,4λ²-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ²-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study