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.

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.

scholarly journals The para substituent dependence of the internal rotational barrier in benzenethiol

1977 ◽  
Vol 55 (3) ◽  
pp. 552-556 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Molecular Orbital ◽  
Rotational Barrier ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

On the basis of the observed spin–spin coupling constants between the sulfhydryl and ring protons and a hindered rotor treatment of the twofold barrier to internal rotation in a series of para substituted benzenethiol derivatives, it is argued that V2 is essentially zero in p-amino-benzenethiol and is 2.5 ± 0.2 kcal/mol in p-nitrobenzenethiol; having intermediate values for the methoxy, fluoro, methyl, and bromo derivatives in solution. The results are based on an assumed relationship between the four-bond and the fictitious six-bond couplings to the sulfhydryl proton. The conclusions are consistent with the observed magnitudes of the couplings over six and seven bonds, respectively, between the sulfhydryl proton and the fluorine nucleus and the methyl protons in the appropriate derivatives; as well as with the coupling between the sulfhydryl and methyl protons in 4-bromo-3-methylbenzenethiol. The experimental barriers are compared with ab initio molecular orbital calculations of their substituent dependence.

Long-range 13C,1H and 13C,19F coupling constants as indicators of the conformational properties of 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole

1984 ◽  
Vol 62 (8) ◽  
pp. 1592-1597 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen ◽  
Timothy A. Wildman ◽  
James Peeling ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Long Range ◽  
Methoxy Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dynamic Nmr ◽  
Methyl Group ◽  
Conformational Properties ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Rotor Model

Long-range spin–spin coupling constants over six bonds between 13C nuclei in the methyl group and ring protons or 19F nuclei in the para position are reported for 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole in solution. The couplings are σ–π electron mediated, as indicated by INDO MO FPT computations and by measurements on anisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-dibromo-4-fluoroanisole, and 2,6-dibromo-4-methylanisole. On the basis of the measured coupling magnitudes and a hindered rotor model, it is concluded that the barrier to internal rotation about the [Formula: see text] bond in 4-fluoroanisole lies near 6 kcal/mol, is nearly zero in the tetrafluoroanisole, and is somewhat less than 1 kcal/mol in the pentafluoroanisole. In the latter, the preferred conformation is that in which the methoxy group lies in a plane perpendicular to the pentafluorophenyl plane. Some inconclusive dynamic nmr experiments on anisole, including T1ρ measurements, are briefly discussed.

The internal barriers to rotation about the carbon–carbon bond in 3,5-dichlorobenzyl alcohol and selenol by the J method

1978 ◽  
Vol 56 (13) ◽  
pp. 1721-1723 ◽  
Author(s):  
Ted Schaefer ◽  
Werner Danchura ◽  
Walter Niemczura ◽  
William J. E. Parr
Keyword(s):  
Internal Rotation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Carbon Carbon Bond ◽  
Carbon Carbon Bonds ◽  
Spin Coupling Constants ◽  
Internal Barriers ◽  
Spin Spin Coupling

The J method, depending on a comparison between observed spin–spin coupling constants over six bonds between protons on a side chain and para ring protons and those calculated by a hindered rotor treatment, is applied to the determination of the twofold barrier to internal rotation about the carbon–carbon bonds in 3,5-dichlorobenzyl alcohol and selenol. In the alcohol, the C—O bond prefers the benzene plane by 0.3 ± 0.2 kcal/mol whereas, in the selenol, the C—Se bond prefers a plane perpendicular to the benzene ring by 3.8 ± 0.7 kcal/mol. Comparison with the thiol suggests that a major component of the barrier arises from repulsive interactions, increasing as the size of the XH (X = O, S, Se) group increases.

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.

Proton spin–spin coupling constants and intramolecular hydrogen bonding in bromine derivatives of 1,3-dihydroxybenzene

1976 ◽  
Vol 54 (14) ◽  
pp. 2228-2230 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The conformational preferences in CCl4 solution at 32 °C of the hydroxyl groups in bromine derivatives of 1,3-dihydroxybenzene are deduced from the long-range spin–spin coupling constants between hydroxyl protons and ring protons over five bonds. Two hydroxyl groups hydrogen bond to the same bromine substituent in 2-bromo-1,3-dihydroxybenzene but prefer to hydrogen bond to different bromine substituents when available, as in 2,4-dibromo-1,3-dihydroxybenzene. When the OH groups can each choose between two ortho bromine atoms, as in 2,4,6-tribromoresorcinol, they apparently do so in a very nearly statistical manner except that they avoid hydrogen bonding to the common bromine atom.

One-bond CC spin—spin coupling constants in derivatives of benzene. Non-linearity of 1J(CC) vs substituent electronegativity

1993 ◽  
Vol 49 (11) ◽  
pp. 1613-1619 ◽  
Author(s):  
Krystyna Kamieńska-Trela ◽  
Andrzej Dabrowski ◽  
Henryk Januszewski
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of
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