Synthese von 2.4.6‐Tri‐tert.‐butyl‐phenoxyl‐[1‐<sup>13</sup>C]

Rieker, Anton; Scheffler, Klaus; Müller, Eugen

doi:10.1002/jlac.19636700104

Cited by 37 publications

(12 citation statements)

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“…Ethyl [1-13 C]acetate was prepared as described previously 32 and used as the carbon-13 containing building block. Application of the method described by Cannone et al [35][36][37] involved the cyclocondensation of this ester with 3-methyl-1,5-bis(bromomagnesio)hexane in THF and produced a mixture of the diastereomeric 1,4-dimethyl-[1-…”

Section: Resultsmentioning

confidence: 99%

“…34,39,40 Dehydrogenation using an industrial catalyst (Pt or Pd on asbestos) at 4508C was reported to lead to partial disproportionation. 31,32 Therefore, we decided to use palladium on charcoal as the catalyst in the presence of maleic acid as a hydrogen acceptor, analogous to a procedure described by Robertson and Djerassi. 33 However, GC-MS analysis of the product indicated the…”

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confidence: 99%

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Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene

Mormann

Kuck

2002

Labelled Comp Radiopharmac

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene

Mormann

Kuck

2002

Labelled Comp Radiopharmac

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“…We decided to prepare monolabeled phenol from sodium 1-[ 13 C]acetate (EURISOTOP, 99 % 13 C), following the seven-step synthesis of Rieker et al [51] An overall yield of 70 % 1-[ 13 C]phenol with respect to the educt could be gained (lit. : 67 %).…”

Section: Discussionmentioning

confidence: 99%

A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials

Sehnert

Senker

2007

Chemistry A European J

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We present the successful application of a concerted approach for the investigation of the local environment in ordered and disordered phases in the solid state. In this approach we combined isotope labeling with computational methods and different solid-state NMR techniques. We chose triphenylphosphite (TPP) as an interesting example of our investigations because TPP exhibits two crystalline modifications and two different amorphous phases one of which is highly correlated. In particular we analyzed the conformational distribution in three of these phases. A sample of triply labeled 1-[13C]TPP was prepared and 1D MAS as well as wide-line 13C NMR spectra were measured. Furthermore we acquired 2D 13C wide-line exchange spectra and used this method to derive highly detailed information about the phenyl orientation in the investigated TPP phases. For linkage with a structure model a DFT analysis of the TPP molecule and its immediate environment was carried out. The ab initio calculations of the 13C chemical shift tensor in three- and six-spin systems served as a base for the calculation of 1D and 2D spectra. By comparing these simulations to the experiment an explicit picture of all phases could be drawn on a molecular level. Our results therefore reveal the high potential of the presented approach for detailed studies of the mesoscopic environment even in the challenging case of amorphous materials.

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“…To account for the effect of solvation of phenoxyl in water and 2,4,6-tri-t-butylphenoxyl in benzene, the value of h was varied between 1.1 and 1.9 and then between 1.59 and 1.55. The best agreement with the experimental spin concentration in the 3-and 5-positions (0.067) and with the experimental 13C-coupling constant for C-1 (9.6 gauss [41] was obtained at h = 1.56. The spin densities are then as follows: po = 0.261, p l = 0.127, p2,6 = 0.247, p3,s = 0.067, and p4 = 0.253.…”

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confidence: 89%

Spin Density Distribution in 2,4,6‐Triphenylphenoxyl

Dimroth

Berndt

Bär

et al. 1967

Angew. Chem. Int. Ed. Engl.

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The distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6-triphenylphenoxy radical was determined by electron spin resonance spectroscopy andquantum-mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum-mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with 13C in positions I , 2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the 1 7 0 -coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.The dehydrogenation of 2,4,6-triphenylphenoI 111 and many other 2,4,6-triarylphenols[zl in an alkaline or a neutral medium leads to phenoxy radicals, which are unusually stable: they do not react with oxygen and, despite their high oxidation potentials 131, they can be kept in organic solvents for a long time without any change. As in the case of 2,4,6-tri-t-butylphenoxyl[41, blocking of the reactive 2, 4, and 6 positions with aryl groups suppresses the susceptibility of the ring to further addition and substitution. Since the steric hindrance with phenyl groups is less than with t-butyl groupsanother factor must be present in 2,4,6-triphenylphenoxyl to compensate for the decrease in steric hindrance. This effect is due to the participation of the phenyl groups in the 7c-electron system thus enabling the unpaired electron to occupy 25 positions, as compared to only seven in phenoxyl or trialkylphenoxyls.The distribution of the unpaired electrons over the various atoms can be determined from the ESR spectra[sl, and in particular from the resulting coupling constants and empirical relations between the latter and the spin densities. The ESR spectra with proton hyperfine structure can be used to determine the spin densities only on carbon atoms carrying hydrogens, and, for the other ("blind" [71) atoms, one can use quantum-mechanical approximations in such a way that the calculated results agree with the experimental values for the hydrogen-carrying carbons. However, it has been shown on p-benzosemiquinone [71, that this technique may lead to incorrect values for the blind atoms. We have therefore checked the calculated spin densities of the blind atoms with triphenylphenoxyl labeled in known positions with 13C. From the experimental spin density distribution and the 170-coupling constant 181, we could make an inference concerning the connection between the 170-coupling constant and the spin density on oxygen.

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Synthese von 2.4.6‐Tri‐tert.‐butyl‐phenoxyl‐[1‐¹³C]

Cited by 37 publications

References 8 publications

Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene

Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene

A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials

Spin Density Distribution in 2,4,6‐Triphenylphenoxyl

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Synthese von 2.4.6‐Tri‐tert.‐butyl‐phenoxyl‐[1‐13C]

Cited by 37 publications

References 8 publications

Synthesis of [1‐13C]‐para‐xylene and [2‐13C]‐para‐xylene

Synthesis of [1‐13C]‐para‐xylene and [2‐13C]‐para‐xylene

A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials

Spin Density Distribution in 2,4,6‐Triphenylphenoxyl

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Product

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Synthese von 2.4.6‐Tri‐tert.‐butyl‐phenoxyl‐[1‐¹³C]

Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene

Synthesis of [1‐¹³C]‐para‐xylene and [2‐¹³C]‐para‐xylene