Gas and solution phase NMR studies of N-ethylmorpholine intra- and intermolecular effects on ring inversion rate constants

Semiquinones of 6,7-dihydroxy- 1,2,3,4-tetrahydroisoquinolines and -naphthalenes are investigated by ESR-spectroscopy in the presence of diorganothalliumhydroxide. The ESR-spectra show a significant temperature dependence of the coupling constants of the β-methylene protons due to ring inversion of the partially hydrogenated ring. Computer simulation of the spectra gave the rate constants and the activation parameters for this ring inversion process. The heterocyclic compounds show considerably lower rate constants due to implication of N-inversion. In comparison to analogous cyclohexene-semidione systems, our systems showed rate constants about 10 times higher than those of their monocyclic counterparts.

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Pressure- and temperature-dependent proton NMR studies of N-methylpiperidine ring inversion in the gas phase

The Journal of Physical Chemistry ◽

10.1021/j100204a021 ◽

1992 ◽

Vol 96 (25) ◽

pp. 10201-10205 ◽

Cited By ~ 15

Author(s):

Mohsen Tafazzoli ◽

Cristina Suarez ◽

Nancy S. True ◽

Clifford B. LeMaster ◽

Carole L. LeMaster

Keyword(s):

Gas Phase ◽

Proton Nmr ◽

Temperature Dependent ◽

Nmr Studies ◽

Ring Inversion

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Pressure-dependent gas-phase proton NMR studies of tetrahydropyran ring inversion

The Journal of Physical Chemistry ◽

10.1021/j100258a038 ◽

1985 ◽

Vol 89 (12) ◽

pp. 2625-2630 ◽

Cited By ~ 13

Author(s):

Pak Sin Chu ◽

Nancy S. True

Keyword(s):

Gas Phase ◽

Proton Nmr ◽

Nmr Studies ◽

Ring Inversion

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Complexes of hybrid ligands. Comparative studies on two cationic Pt2+ complexes of a fluorinated alkoxy-thioether ligand: solid-state structures and evidence for coupled ring-thioether inversion in solution

Canadian Journal of Chemistry ◽

10.1139/v86-243 ◽

1986 ◽

Vol 64 (8) ◽

pp. 1474-1481 ◽

Cited By ~ 6

Author(s):

René T. Boeré ◽

Nicholas C. Payne ◽

Christopher J. Willis

Keyword(s):

Chelate Ring ◽

Careful Consideration ◽

Shielding Effect ◽

Orthorhombic Space Group ◽

Nmr Studies ◽

Ring Inversion ◽

Nmr Data ◽

Hybrid Ligands ◽

Solid State Structures ◽

Ring Conformations

Complete structural determinations are reported for two cationic platinum(II) complexes of the chelating, hybrid, alkoxythioether ligand CH3SCH2O(CF3)2O− with phosphine coligands and BF4− counterions. Complex 1, [Pt(PPh3)2{CH3SCH2C(CF3)2O}]BF4, C42H37BCl2F10OP2PtS (CH2Cl2 solvate) is monoclinic, space groupP21/c, with a = 12.2534(9), b = 18.584(2), c = 19.612(3) Å, β = 97.36(1)°, V = 4466(1) Å3, Z = 4. Complex 2, [Pt(PPh2Me)2{CH3SCH2C(CF3)2O}]BF4, C31H31BF10OP2PtS, is orthorhombic, space group Pna21, with a = 23.093(4), b = 11.362(3), c = 12.880(2) Å, V = 3379(2) Å3, Z = 4. The structures show the five-membered chelate ring to have similar conformations in the two complexes, the CH3S and axial CF3 groups being in an anti conformation.The structural results are discussed in relation to previous nmr studies on these and related complexes. It is concluded that an anisotropic shielding effect on the CH3S and CF3 resonances is present in both complexes, but that it is significantly greater in 1, where PPh3 is the coligand, and anomalies in the 19F nmr spectra are explained on this basis. A careful consideration of the nmr data, in light of the crystal structures, demonstrates the persistence of preferred chelate ring conformations in solution. Thioether inversion induces ring inversion in these complexes.

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