The conformers of a nitrosamine and a carboxamide: Comparison of NMR line shape and equilibration methods

Jaeschke, A.; Muensch, Helmut; Schmid, H.; Friebolin, H.; Mannschreck, Albrecht

doi:10.1016/0022-2852(69)90336-1

Cited by 96 publications

(17 citation statements)

References 25 publications

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“…We calculated the inversion barrier according to the method of Friebolin and Mannschreck. [25,26] With T c 35.1 AE 2 8C, the following DG = values for the reversible inversions were obtained. DG A3B = 65.81 AE 0.4 kJ mol À1 DG B3A = 65.14 AE 0.4 kJ mol À1 Usually the DG = values of the inversion barriers of alkylphosphanes, arylphosphanes, and alkylarylphosphanes are % 130 ± 140 kJ mol À1 .…”

Section: Resultsmentioning

confidence: 99%

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Polyphospha[m]cyclo[n]carbons (m+n=15, 20, 25, 30, 40)

et al. 2000

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The Eglinton reaction of diethynyl(2,4,6-tri-tert-butylphenyl)phosphane (7a), that is, the oxidative coupling of 3, 4, 5, or 6 of these phosphane units, affords a mixture of the 15-, 20-, 25-, and 30-membered macrocycles 8, 9, 10, and 11. Pure triphosphacyclopentadecahexayne 8 and pentaphosphacyclopentacosadecayne 10 were isolated by HPLC, while the mixture of 9 and 11 could not be separated. Multistep syntheses of open-chain polyphosphapolyynes are described, whose intra- or intermolecular coupling yields the phosphamacrocycles 8, 9, and 11. Eglinton coupling of bis(ethynylphosphanyl)butadiyne (17) gave a mixture of the 20-membered tetraphosphacycloicosaoctayne 9, the 30-membered hexaphosphacyclotriacontadodecayne 11, and the 40-membered octaphosphacyclotetracontahexadecayne 23 as result of a di-, tri-, and tetramerization, respectively. Intramolecular coupling of bis[(ethynylphosphanyl)butadiynyl]phosphane 25a gave 8, while intermolecular coupling gave 11; these two compounds were isolated by chromatography to give yields of 70 and 5%, respectively. The open-chain tetraphosphaeikosaoctayne 28 couples intramolecularly to give 9 and intermolecularly to give the 40-membered octaphosphacyclotetracontahexadecayne 23, which was isolated in the pure form. Octaphosphatetracontahexadecayne 32 cyclized to give 23, exclusively. The temperature-dependent 1H and 31P NMR spectra of the open-chain and cyclic ethynylphosphanes indicated a lowering of the inversion barrier of the tertiary phosphanes from the usual 130-140 kJ mol(-1) to 65-75 kJ mol(-1). Ab initio calculations proved that the dramatic reduction of the inversion barriers results from the interaction of the lone pair on phosphorus with the pi orbitals of the triple bonds in the planar transition state during inversion. The situation is comparable with the dramatic reduction of the P inversion barrier in phospholes, because of the planar, aromatic transition state. The polyphospha[m]cyclo[n]carbons may be considered as precursors to cyclic PmCn systems.

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Section: Resultsmentioning

confidence: 99%

“…The Gibbs DG = values have been calculated according to the method of Friebolin and Mannschreck [26] :…”

Section: Resultsmentioning

confidence: 99%

Polyphospha[m]cyclo[n]carbons (m+n=15, 20, 25, 30, 40)

et al. 2000

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“…the line-shape function is given by while that of the undistorted signal (W, = 0) is At the centre of the spectrum, where v = 0, the ratio of the latter equations becomes (9) The same kind of expression is valid for the reference signal (10) Dividing Eqn. This shows that one can eliminate the effects of inhomogeneity broadening by always taking the ratio of the signal amplitude at the centre of the spectrum and the amplitude of the reference signal.…”

Section: Appendixmentioning

confidence: 93%

Dynamic NMR: A single operational parameter approach for evaluation of lifetime in an uncoupled, equally populated AB system

Dimitrov

1974

Org. Magn. Reson.

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“…The barriers were calculated using the coalescence method, in which the NMR shift difference ∆ν c is extrapolated to the coalescence temperature, using correction for the bandwidth of the signals and the equilibrium constant. For an uncoupled AB: with and K; [25] for a coupled AB: with and . [26] The 1 H NMR spectrum of the naphthalene H atoms was simulated with the program LAME.…”

Section: Methodsmentioning

confidence: 99%

Correlated Rotations and Unusual Fluorescence Properties ofperi-Substituted, Axially Chiral Naphthyl Ketones

Kiefl

2000

Eur. J. Org. Chem.

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The dynamics of the two rotors in 8-(dimethylamino)naphthyl ketones possessing a tetrahedral amino group and a trigonal planar carbonyl group has been investigated by 1 H NMR spectroscopy. The dynamic system is described by an aryl−nitrogen and an aryl−carbonyl rotation and a possible amine inversion. As the two rotors, which are twisted in the ground state, are tightly interlocked, the question arises of how strongly the processes might be correlated and how strongly the electrostatic interactions would influence the barriers. In the case of the isopropyl, tert-butyl, and benzyl ketones, the rotors are coupled sufficiently strongly that correlated rotations become energetically preferred over independent rotations of the individual groups. For the methyl and trimethoxyphenyl ketone, the Ar−N and Ar−C barriers could be distinguished because of the lesser degree of inter-

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The conformers of a nitrosamine and a carboxamide: Comparison of NMR line shape and equilibration methods

Cited by 96 publications

References 25 publications

Polyphospha[m]cyclo[n]carbons (m+n=15, 20, 25, 30, 40)

Polyphospha[m]cyclo[n]carbons (m+n=15, 20, 25, 30, 40)

Dynamic NMR: A single operational parameter approach for evaluation of lifetime in an uncoupled, equally populated AB system

Correlated Rotations and Unusual Fluorescence Properties ofperi-Substituted, Axially Chiral Naphthyl Ketones

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