Stereodynamics of 1-tert-butyl-8-fluoronaphthalene. Restricted tert-butyl rotation about an sp3-sp2 carbon-carbon bond. An unusually high barrier to isolated methyl rotation. Through-space-spin-spin coupling to fluorine

1993 ◽  
Vol 58 (6) ◽  
pp. 1631-1634 ◽  
Author(s):  
Gordon W. Gribble ◽  
Erik R. Olson ◽  
Jay H. Brown ◽  
C. Hackett Bushweller
Keyword(s):  
Spin Coupling ◽  
Carbon Bond ◽  
Tert Butyl ◽  
Carbon Carbon Bond ◽  
Methyl Rotation ◽  
Spin Spin Coupling

The preferred conformations in solution and rotational barriers of the phenyl moiety in 3,5-dichlorobenzyl derivatives of ammonia, dimethylamine, and dimethylarsine

1978 ◽  
Vol 56 (17) ◽  
pp. 2229-2232 ◽  
Author(s):  
Ted Schaefer ◽  
Werner Danchura ◽  
Walter Niemczura
Keyword(s):  
Long Range ◽  
Phenyl Ring ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Carbon Bond ◽  
Carbon Carbon Bond ◽  
Spin Coupling Constants ◽  
Internal Barriers ◽  
Spin Spin Coupling ◽  
Derivatives Of

The long-range spin–spin coupling constants between methylene protons and ring protons are measured in 3,5-dichlorobenzylamine, 3,5-dichlorobenzyldimethylamine, and in 3,5-dichlorobenzyldimethylarsine. The couplings over six bonds are used to derive internal barriers to rotation about the carbon–carbon bond to the phenyl ring. In the above order, they are 0.3 ± 0.3, 0.8 ± 0.2, and 3.0 ± 0.5 kcal/mol. The conformation of lowest energy in the arsine is that in which the CH2—X bond lies in a plane perpendicular to the benzene plane.

The spin–spin coupling mechanism for 5J(C-4, CHα) in toluene derivatives and its conformational applications

1983 ◽  
Vol 61 (12) ◽  
pp. 2773-2776 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Glenn H. Penner
Keyword(s):  
Internal Rotation ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Carbon Nucleus ◽  
Conformational Preference ◽  
Carbon Bond ◽  
Carbon Carbon Bond ◽  
Spin Spin Coupling

It is shown that the spin–spin coupling over five formal bonds between carbon 4 and the α protons in toluene and its ring or sidechain substituted derivatives is transmitted by a σ–π mechanism. As such it varies as sin2 θ, where θ is the angle by which the α C—H bond twists out of the benzene plane, and can be used to determine the conformational preference and the barrier to internal rotation about the exocyclic sp2–sp3 carbon–carbon bond. The coupling is remarkably insensitive to ring substituents, even to those at carbon 4. Two measurements suggest that the coupling over six formal bonds between a β carbon nucleus and apara proton also represents a σ–π interaction

Internal barriers to rotation in 2,6-difluoroisopropyl and 2,6-difluoroethylbenzenes. Overlap of dynamic nuclear magnetic resonance (DNMR) and the J method

1982 ◽  
Vol 60 (20) ◽  
pp. 2611-2616 ◽  
Author(s):  
Ted Schaefer ◽  
Richard P. Veregin ◽  
Reino Laatikainen ◽  
Rudy Sebastian ◽  
Kirk Marat ◽  
...  
Keyword(s):  
Internal Rotation ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Carbon Carbon Bond ◽  
Barrier Region ◽  
Yield Formula ◽  
Internal Barriers ◽  
Dynamic Nuclear Magnetic Resonance ◽  
Spin Spin Coupling

The temperature-dependent 19F nmr spectra of 2,6-difluoroisopropylbenzene yield [Formula: see text], ΔH≠, and ΔS≠ as 6.93 (5) kcal/mol, 6.1(1) kcal/mol, and −5.0(8) cal/mol K, respectively, for the internal rotation of the isopropyl group about the sp2–sp3 carbon–carbon bond. The long-range spin–spin coupling constant over six bonds, 6JpH,CH, combined with the J method gives a twofold internal potential barrier of 5.0 ± 1.6 kcal/mol at 305 K. Although in this barrier range the J method suffers from large errors, the two methods yield comparable values for the barrier height. The lineshape method is inapplicable to 2,6-difluoroefhylbenzene. The J method finds the preferred conformation and a twofold barrier of 6.0 ± 2 kcal/mol, again in a barrier region where this method is inaccurate. Relative to hydrogen, the fluorine substituents cause substantial increases in the barriers to internal rotation. Signs of the stereospecific couplings, 4JoF,CH, are determined.

scholarly journals Concerning in 2-methylphenol and its derivatives. A proximate coupling

1985 ◽  
Vol 63 (3) ◽  
pp. 773-776 ◽  
Author(s):  
Ted Schaefer ◽  
Timothy A. Wildman ◽  
Rudy Sebastian
Keyword(s):  
Spin Coupling ◽  
Hydroxyl Group ◽  
Methyl Group ◽  
Proximate Mechanism ◽  
Tert Butyl ◽  
Vinyl Group ◽  
Spin Spin Coupling ◽  
Derivatives Of

In 2-chloro-6-methylphenol in CCl4 solution, [Formula: see text] the spin–spin coupling between the hydroxyl and methyl protons, is + 68(3) mHz. In this compound, the hydroxyl group lies trans to the methyl group. If the coupling becomes −120 ± 60 mHz in a cis orientation of these two groups, then the apparent vanishing of [Formula: see text] in some derivatives of 2-methylphenol is understandable, as well as its presence in other derivatives. Computations of this coupling imply its proximate mechanism and can rationalize its value of −220 ± 20 mHz in 2-tert-butyl-6-methylphenol. Analogies are noted with [Formula: see text] in 2-trifluoromethyl phenol and with a coupling in styrene, which also appears to vanish in certain orientations of the vinyl group.

69/71Ga and 115In NMR Spectroscopy of Lithium Tetra(tert-butyl)gallate and -indate: Spin-Spin Coupling Constants 1J(69/71Ga,13C) and 1J(115In,13C)

2009 ◽  
Vol 64 (1) ◽  
pp. 41-46
Author(s):  
Bernd Wrackmeyer ◽  
Elena V. Klimkina
Keyword(s):  
Nmr Spectroscopy ◽  
Dft Calculations ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Tert Butyl ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
First Time

The 13C, 69/71Ga and 115In NMR spectra of lithium tetra(tert-butyl)gallate and -indate were measured under various conditions. It proved possible to determine for the first time the coupling constants 1J(69/71Ga,13C) = 182 Hz/232 Hz and 1J(115In,13C) = 310±10 Hz for these metallates under conditions for solvent-separated ions. DFT calculations [B3LYP/6-311+G(d,p)] were carried out for organogallium compounds such as tri(tert-butyl)gallium, trimethylgallium and tetramethylgallate in order to predict and confirm coupling constants 1J(Ga,13C).

scholarly journals Sign-Determination of Spin-Spin Coupling Constants in tert-Butylphosphaalkyne

1992 ◽  
Vol 47 (3) ◽  
pp. 437-438
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Positive Sign ◽  
Two Dimensional ◽  
Tert Butyl ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Sign Determination

The signs o f the coupling constants 1J(31P≡13C) ( > O ) , J(31P13C) ( > O ) , 3J(31P13C) ( > O ) and 4J(31P1H) ( > O ) in tert-butyl-phosphaalkyne (1) were determined by selective 1H {31P} NMR experiments and two-dimensional (2 D ) 13C/1H heteronuclear shift correlations based on nJ(13C1H ) (n = 1,2,3), confirming the previously assumed positive sign of 1J( 31P≡13C) in phosphaalkynes.

The conformational behaviour of 2-fluoro and of 2,6-difluoroacetophenone implied by proximate spin–spin coupling constants and MO calculations

1985 ◽  
Vol 63 (8) ◽  
pp. 2256-2260 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Timothy A. Wildman ◽  
James Peeling
Keyword(s):  
Temperature Dependence ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Population Distributions ◽  
Carbon Carbon Bond ◽  
Acetyl Group ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The temperature dependence of [Formula: see text], the nuclear spin–spin coupling constant over five formal bonds between the methyl protons and the 19F nucleus in 2-fluoroacetophenone and 2,6-difluoroacetophenone, is modelled on the assumption that 5J is a proximate coupling and that the STO 3G MO potential functions describe the population distributions of the rotamers defined by rotation about the exocyclic sp2–sp2 carbon–carbon bond. It is assumed that 5J has a cos4 θ dependence between 0 and 90°, where θ is the angle by which the acetyl group twists out of the plane of the benzene plane. The potential function is obtained from extensive geometry optimization procedures for a range of θ values. At 305 K, nonplanar conformations are substantially populated in 2-fluoroacetophenone, according to this model, which is also consistent with the idea that the 2,6-difluoro derivative has a markedly nonplanar ground state. The model reproduces the large 5J in the monofluoro relative to the difluoro compound, as well as the much larger temperature dependence in the former.

Derivatives of diphenylmethane. Preferred conformations and barriers to internal rotation by the J method

1979 ◽  
Vol 57 (14) ◽  
pp. 1881-1886 ◽  
Author(s):  
Ted Schaefer ◽  
Walter Niemczura ◽  
Werner Danchura ◽  
Timothy A. Wildman
Keyword(s):  
Internal Rotation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Carbon Carbon Bond ◽  
Conformational Properties ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Rotor Model

The long-range spin–spin coupling constants over six bonds, 6JpH,CH, in 3,5-dibromodiphenylmethane and 4,4′-difluorodiphenylmethane, respectively, imply that the ground state conformations of these molecules have C2v symmetry (gable conformations). In terms of a hindered rotor model which assumes a twofold barrier to internal rotation about the exocyclic carbon–carbon bond, the barrier in the dibromo derivatives is 1.1 ± 0.3 kcal/mol. A satisfactory fit to the temperature dependence of 6JpF,CH is found for a gable conformation. If the conformational properties of these molecules and of diphenylmethane are determined mainly by steric interactions between ortho C—H bonds on neighbouring phenyl groups, it seems likely that the results above are a first approximation to the conformational behaviour of diphenylmethane. Some molecular orbital calculations are in semiquantitative agreement with the conclusions based on coupling constants.

Spin-Spin Coupling Constants 1J(27Al,13C) and 1J(13C,11B) in Comparable Organoaluminum and -boron Compounds. NMR Spectroscopy of Lithium Tetra(tert-butyl)alanate

2008 ◽  
Vol 63 (8) ◽  
pp. 923-928 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Elena V. Klimkina
Keyword(s):  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Set ◽  
Relaxation Rates ◽  
Dft Methods ◽  
Tert Butyl ◽  
Pair Separation ◽  
Spin Spin Coupling ◽  
Ion Pair Separation

The 13C, 27Al and 11B NMR spectra of tri(tert-butyl)alane, AlBut3, and of the corresponding borane, BBut3, respectively, were examined in order to determine the magnitude of the coupling constants 1J(27Al,13C) = 94±5 Hz and 1J(13C,11B) = 52±2 Hz by measurement of the line widths of the 13C NMR signals and of the relaxation rates of the quadrupolar 27Al and 11B nuclei. This is the first example of 1J(27Al,13C) determined for a monomeric trialkylalane. In addition, the coupling constants were calculated by DFT methods (B3LYP) using the 6-311+G(d,p) basis set. The 1H, 13C and 27Al NMR spectra of lithium tetra(tert-butyl)alanate, Li[AlBut4], were measured under various conditions. Ion-pair separation in THF revealed the expected patterns for 27Al-13C spin-spin coupling across one and two bonds as well as for the three-bond 27Al-1H spin-spin coupling.

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