Indirect Nuclear Spin-Spin Coupling Constants 1J(17O,11B). First Observation And Calculation Using Density Functional Theory (Dft)

2006 ◽  
Vol 61 (8) ◽  
pp. 949-955 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Oleg L. Tok
Keyword(s):  
Density Functional ◽  
Reasonable Agreement ◽  
Bond Angle ◽  
Calculated Data ◽  
Molecular Structures ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Coupling constants 1J(17O,11B) of borates, borane adducts and boranes with boron-oxygen bonds have been calculated on the basis of optimised molecular structures using the B3LYP/6-311+G(d,p) level of theory. This indicates that such coupling constants can be of either sign and that their magnitudes can be rather small. Since both 11B and 17O are quadrupole nuclei, it is therefore difficult to measure representative data. In the cases of trimethoxyborane and tetraethyldiboroxanes, it proved possible to obtain experimental data 1J(17O,11B) (22 and 18 Hz) by measurement of 17O NMR spectra at high temperature (120 °C and 160 °C) respectively. The magnitude of these coupling constants is in reasonable agreement with calculated data. In the case of the diboroxane, this points towards a bond angle B-O-B more close to 180◦ than to 140°

Hyperconjugation In Trialkylboranes Shown By Indirect Nuclear Spin-Spin Coupling Constants. Experimental Data And Density Functional Theory (Dft) Calculations

2005 ◽  
Vol 60 (3) ◽  
pp. 259-264 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Oleg L. Tok
Keyword(s):  
Experimental Data ◽  
Dft Calculations ◽  
Density Functional ◽  
Calculated Data ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
C Nmr

Trimethylborane (1), triethylborane (2), 1,3-dimethyl-1-boracyclopentane (3), 1-methyl-1- boracyclohexane (4), 9-methyl- and 9-ethyl-9-borabicyclo[3.1.1]nonane [5(Me) and 5(Et)], and 1- boraadamantane (6) were studied by 11B and 13C NMR spectroscopy with respect to coupling constants 1J(13C,11B) and 1J(13C,13C). Results of DFT calculations at the B3LYP/6-311+g(d,p) level of theory show satisfactory agreement with the experimental data. Hyperconjugation arising from C-C σ bonds adjacent to the tricoordinate boron atom is indicated, in particular for 1-boraadamantane (6), by the optimised calculated structures, and by the experimental and calculated data 1J(13C,13C). The calculated magnitude of 1J(13C,1H) for carbon atoms adjacent to boron becomes significantly smaller if the optimised structures suggest hyperconjugative effects arising from these C-H bonds

Prediction of spin-spin coupling constants in solution based on combined density functional theory/molecular mechanics

2009 ◽  
Vol 130 (13) ◽  
pp. 134508 ◽  
Author(s):  
Andreas Møgelhøj ◽  
Kestutis Aidas ◽  
Kurt V. Mikkelsen ◽  
Stephan P. A. Sauer ◽  
Jacob Kongsted
Keyword(s):  
Density Functional Theory ◽  
Molecular Mechanics ◽  
Density Functional ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Density Functional Theory (DFT) Calculations of Indirect Nuclear Spin-Spin Coupling Constants 1J(31P, 13C) in λ3-Phosphaalkynes

2003 ◽  
Vol 58 (11) ◽  
pp. 1041-1044 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Strong Dependence ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Positive Sign ◽  
Spin Orbital ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of the spin-spin coupling constants 1J(31P,≡13C) of λ3-1-phosphaalkynes P≡C-R (R = H, Me, tBu, Ph, SiMe3 and NMe2) using density functional theory (DFT) have revealed a positive sign of this coupling constant in agreement with the experiment for P≡C-tBu. The calculations have shown that the Fermi contact (FC) contribution to this coupling is negative [in contrast to FC for 1J(14N,≡13C) in the corresponding nitriles], and that the positive sign of 1J(31P,≡13C) is the result of significant contributions arising from spin-dipole (SD) and paramagnetic spin-orbital (PSO) terms. Coupling constants were also calculated for some representative λ3-phosphorus compounds containing two- and three-coordinate phosphorus, indicating the strong dependence of the FC term on the geometry at the phosphorus atom.

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