The Conformational Equilibrium of 1,2,3-Tribromopropane in Solution

1973 ◽  
Vol 51 (4) ◽  
pp. 565-572 ◽  
Author(s):  
L. Ernst ◽  
T. Schaefer
Keyword(s):  
Conformational Equilibrium ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Minor Role ◽  
Nonpolar Solvents ◽  
Spin Coupling Constants ◽  
A Minor ◽  
Spin Spin Coupling ◽  
Rule Out

The p.m.r. spectra of dilute solutions of 1,2,3-tribromopropane in carbon tetrachloride, acetonitrile, and dimethylsulfoxide as well as of the neat compound are examined. From the three- and four-bond spin–spin coupling constants and from a comparison between observed and calculated dipole moments it is concluded that in nonpolar solvents the title compound exists preferably in the enantiomeric conformations a and i. In polar solvents other rotamers contribute to the equilibrium but still seem to play only a minor role. Semiempirical calculations of conformational energies rule out contributions to the conformational equilibrium from rotamers having (1:3) bromine–bromine interactions, but otherwise are only in moderate agreement with experiment.

Proton Magnetic Resonance Study of Conformational Equilibria of the Pyridinealdehydes in Solution. Comparison with Other Methods

1974 ◽  
Vol 52 (23) ◽  
pp. 3986-3995 ◽  
Author(s):  
Werner Danchura ◽  
Ted Schaefer ◽  
J. Brian Rowbotham ◽  
Donald J. Wood
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Trans Form ◽  
Nonpolar Solvents ◽  
Conformational Equilibria ◽  
Proton Magnetic Resonance Study ◽  
Precise Measure ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Solvation Theory

A p.m.r. study of the pyridinealdehydes shows that accurate spectral analysis yields long-range spin–spin coupling constants which are a precise measure of the conformational equilibria in solution. Thus, in CS2 solution the ON-trans form of 2-pyridinealdehyde is more stable than the ON-cis form by at least 2.3 kcal/mol, while in acetone solution it is 1.6 kcal/mol more stable than the cis form. Classical solvation theory allows the conclusion that in the gas phase the trans form is more stable than the cis form by about 7 kcal/mol, in contradiction to the predictions of approximate MO theory at the INDO level. The trans form of 3-pyridinealdehyde is also more stable than the cis form in polar and in nonpolar solvents. The results are compared with those of other experiments on these equilibria.

scholarly journals Proton Magnetic Resonance Spectra, Conformational Preferences, and Approximate Molecular Orbital Calculations for the syn and anti 2-Furanaldoximes

1972 ◽  
Vol 50 (2) ◽  
pp. 274-280 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Dipole Moments ◽  
Intramolecular Hydrogen Bonding ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Intramolecular Hydrogen ◽  
Spin Spin Coupling

Evidence is adduced, mainly from proton chemical shift and long-range coupling constant data, that the anti isomer of 2-furanaldoxime exists almost exclusively in the s-cis form in solution, independently of the type of intermolecular association that occurs. Intramolecular hydrogen bonding apparently is absent in this isomer. Similarly, the syn isomer exists in roughly equal mixtures of s-cis and s-trans forms in solvents of widely different polarities. A variety of nuclear spin–spin coupling constants are calculated via the INDO and CNDO molecular orbital approximations, as are the dipole moments and conformational energies, for 2-furanaldehyde and its oximes. On the whole the experimental trends are well reproduced by the computations.

INDO- and CNDO-Approximated Molecular Orbital Calculations on the Spin-Spin Coupling Constants in Some 2-Substituted Oxetanes

1974 ◽  
Vol 29 (12) ◽  
pp. 1907-1913 ◽  
Author(s):  
Jukka Jokisaari
Keyword(s):  
Dipole Moments ◽  
High Energy ◽  
Methine Proton ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
High Energy Barrier ◽  
Spin Coupling Constants ◽  
Oxetane Ring ◽  
Spin Spin Coupling

Spin-spin coupling constants between the methine proton in the oxetane ring and the phenyl protons and carbon nuclei have been calculated in different conformations in the INDO approximation for 2-phenyloxetane and 2-(4-fluorophenyl) oxetane, and in the CNDO approximation for 2-(2- chlorophenyl) oxetane and 2-(3-chlorophenyl) oxetane. In each case the finite perturbation method has been used. In the case of 2-(2-chlorophenyl) oxetane a fairly high energy barrier for the rotation around the C-C bond between the rings is obtained, while in the other three cases the barrier is much lower. The calculations predict an equilibrium conformation in which the oxygen atom lies almost in the plane of the aromatic ring. The calculated dipole moments of 2-(2-chlorophenyl) oxetane and 2-(3-chlorophenyl) oxetane vary significantly with conformation.

Vibrational and thermal averaging of the indirect nuclear spin-spin coupling constants of CH4, SiH4, GeH4 and SnH4

1997 ◽  
Vol 91 (5) ◽  
pp. 897-907 ◽  
Author(s):  
SHEELA KIRPEKAR ◽  
THOMAS ENEVOLDSEN ◽  
JENS ODDERSHEDE ◽  
WILLIAM RAYNES
Keyword(s):  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

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