A proton magnetic resonance determination of the rotational barrier in benzyl chloride and of the low energy conformations in benzyl bromide and iodide derivatives based on motionally averaged spin–spin interactions

1976 ◽  
Vol 54 (20) ◽  
pp. 3210-3215 ◽  
Author(s):  
Ted Schaefer ◽  
Leonard J. Kruczynski ◽  
William J. E. Parr
Keyword(s):  
Long Range ◽  
Benzyl Chloride ◽  
Benzyl Bromide ◽  
Low Energy ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Ambient Temperatures ◽  
Low Energy Conformations

The long-range spin–spin coupling constants over six bonds between side-chain and ring protons in benzyl chloride derivatives are combined with solutions to the hindered rotor problem to demonstrate that the twofold barrier to internal rotation in benzyl chloride is 2.1 ± 0.4 kcal/mol. The low energy conformation is that in which the C—Cl bond lies in a plane perpendicular to the aromatic plane. Molecular orbital calculations at the MINDO/3 and STO-3G levels indicate that the conformation in which the C—Cl bond lies in a plane having an angle of 60° to the aromatic plane has a higher energy; comparable to kT at ambient temperatures. The geometry-optimized STO-3G results agree quantitatively with the derived barrier for benzyl chloride. A semiempirical relationship between the long-range couplings over four bonds and the internal barrier for a number of benzyl compounds indicates a barrier of 3.1 kcal/mol for benzyl bromide and of 3.6 kcal/mol for benzyl iodide, these values being lower limits. The observed coupling constants are only consistent with low-energy conformations analogous to that for benzyl chloride, so that they contrast with the low-energy conformation for benzyl fluoride in which the C—F bond lies in the aromatic plane. The present method for the determination of twofold barriers in benzyl derivatives is useful in the range from about 0.2 to 2 kcal/mol.

A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes

1977 ◽  
Vol 55 (3) ◽  
pp. 557-561 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Low Energy Conformations

The long-range spin–spin coupling constants between protons bonded to silicon and ring protons in C6H5SiH3, C6H5SiH2Cl, C6H5SiH2CH3, C6H5SiHCl2, and C6H5SiH(CH3)2 are determined from the proton magnetic resonance spectra of benzene solutions. A hindered rotor treatment of the barrier to internal rotation about the C—Si bond, in conjunction with the coupling constants over six bonds, allows the deduction of the low-energy conformations for C6H5SiH(CH3)2 and for C6H5SiHCl2, as well as of barriers of 1.0 ± 0.2 kcal/mol. The approach becomes less reliable for C6H5SiH2CH3 and for C6H5SiH2Cl and, particularly for the latter compound, the derived barrier is very likely an upper limit only. Ab initio molecular orbital calculations of the conformational energies are reported for C6H5SiH3, C6H5SiH2Cl, and for C6H5SiHCl2.

Molecular orbital computations and 1H nuclear magnetic resonance measurements of the bending motion of xanthene in the gas and in solution

1990 ◽  
Vol 68 (9) ◽  
pp. 1548-1552 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ambient Temperatures ◽  
Folding Angle ◽  
Analytical Functions ◽  
Planar Molecule ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

STO-3G and 4-31G MO computations are reported for a range of values of the folding angle in xanthene, the dihedral angle between the benzene planes. Unlike 9,10-dihydroanthracene but like dibenzo-p-dioxin, its "parent" molecules, the inversion or puckering potential for xanthene is calculated to be rather flat. The molecular energies between a folding angle of 180° (planar molecule) and 120° are reproduced by analytical functions of [Formula: see text], θ being the folding angle. The long-range spin–spin coupling constants between the methylene protons and the aromatic protons at 300 K are reported for xanthene dissolved in a CS2/C6D12 solvent mixture and in acetone-d6 solution. These conformationally sensitive coupling constants are consistent with the theoretical puckering potentials and therefore with substantial "butterfly" motion at ambient temperatures. The computed geometries of xanthene are also given and briefly discussed. Keywords: xanthene, MO computations on inversion; xanthene, long-range spin–spin coupling constants; xanthene, internal motion; xanthene, inversion potentials.

scholarly journals Proton Magnetic Resonance Spectrum of 1-Penten-3-yne. INDO and CNDO/2 Molecular Orbital Calculations on Long-Range Spin–Spin Coupling Constants in Enynes

1972 ◽  
Vol 50 (12) ◽  
pp. 1863-1867 ◽  
Author(s):  
L. Ernst ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Benzene Solution ◽  
Parent Compound ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The high resolution p.m.r. spectra of 1-penten-3-yne in carbon disulfide and in benzene solution are analyzed. Long-range spin–spin coupling constants are discussed in terms of σ and π electron contributions. Comparisons are made with the isomeric 2-methyl-1-buten-3-yne and the parent compound, vinylacetylene. The results of INDO and CNDO/2 molecular orbital calculations are compared to the experimental coupling constants. It is concluded that the π electron contribution to 5J in enyne systems is +0.6 to 0.7 Hz and that σ electron contributions are rather small, the transoid ("pseudo-zig–zag") being larger than the cisoid one. Observed allylic coupling constants in the propene derivative are compared with the calculated values, including those for propene and 2-cyanopropene, available in the literature.

scholarly journals Long-range proton–carbon coupling constants for the determination of the stereochemical structure of organic compounds.

2021 ◽  
pp. 125-131
Author(s):  
Anwar, E. M. Noreljaleel
Keyword(s):  
Nmr Spectroscopy ◽  
Organic Compounds ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectroscopy Method ◽  
Stereochemical Structure ◽  
New Methods ◽  
Spin Coupling Constants

A new methods for elucidating stereochemistry of organic compounds was developed on the basis of long-range proton–carbon coupling constants (2,3JC,H) and interpreting spin-coupling constants (3JH,H). Reaction of compound containing pyrin ring with nucleophile reagent was done to open the ring. HSQC-TOCSY experiments one of the new NMR spectroscopy method used to measure this values of spin-coupling constants and elucidating the stereochemistry of the product.

Determination of Absolute Signs of 119Sn-117Sn Spin-Spin Coupling Constants

1994 ◽  
Vol 49 (10) ◽  
pp. 1407-1409 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Gerald Kehr
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Two Dimensional ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
First Time

AbstractIf for a given system two-dimensional (2D) 119Sn/1H heteronuclear shift correlations can be established for long range coupling constants nJ(119Sn,1H) (n = 4, 6), absolute signs of coupling constants J(Sn,Sn) are accessible by this technique for the first time. This has been demonstrated for tetrakis(trimethylstannyl)allene (1) with 2J(119Sn,117Sn) (>0) and 4J(Sn. 117Sn) (<0) and for tris(trimethylstannyl)phosphane (2) and bis(trimethvlstannyl)- sulfane (3) with 2J(119Sn,117Sn) (<0).

The internal rotational potential in benzyl chloride

1986 ◽  
Vol 64 (7) ◽  
pp. 1322-1325
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Internal Rotation ◽  
Long Range ◽  
Nmr Spectra ◽  
Benzyl Chloride ◽  
Polar Solvent ◽  
Low Energy ◽  
Coupling Constants ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
H Nmr

The 1H nmr spectra of benzyl chloride in dilute CS2 and acetone-d6 solutions are analyzed. The long-range coupling constants are consistent only with a low-energy conformation in which the C—Cl bond lies in a plane perpendicular to the benzene plane. Geometry optimized computations at the STO 3G level of molecular orbital theory agree with this conclusion and yield a nearly pure twofold barrier to internal rotation of 8.6 kJ/mol. In CS2 solution the long-range couplings yield 8.8 kJ/mol, rising to 11.2 kJ/mol in acetone solution. This increase in the internal barrier in a polar solvent is similar to that found for benzyl fluoride, but in the latter the barrier itself is very much smaller than in benzyl chloride.

Long-range Spin–Spin Coupling Constants from Amino Protons and 15N to Ring Protons in Aniline-15N and Some Derivatives. INDO Molecular Orbital Calculations

1972 ◽  
Vol 50 (16) ◽  
pp. 2575-2585 ◽  
Author(s):  
R. Wasylishen ◽  
J. B. Rowbotham ◽  
L. Ernst ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Complete Analysis ◽  
Molecular Orbital Calculations ◽  
Orbital Theory ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

A complete analysis (8-spins) is given of the p.m.r. spectrum of aniline-15N, of the spectra of some haloanilines-15N and of 2-aminoacetophenone-15N. Intermolecular exchange of the amino protons is slow enough for observation of their spin–spin coupling to the ring protons. The magnitudes of the coupling constants between amino protons and 15N or ring protons are a measure of the geometry of the amino group. This is not true of the couplings between 15N and the ring protons. Long-range couplings computed in the CNDO/2 and INDO approximations of molecular orbital theory show points of agreement with experiment. For example, their signs and magnitudes are consistent with a nonplanar but not with a planar conformation of aniline. Couplings from 15N to ring protons are also computed for nitrobenzene.

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