Conformational preferences and energetics of N–O heterolyses in aryl nitrenium ion precursors: ab initio and semiempirical molecular orbital calculations

1991 ◽  
pp. 607-616 ◽  
Author(s):  
George P. Ford ◽  
P. S. Herman
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Nitrenium Ion ◽  
Conformational Preferences ◽  
Semiempirical Molecular Orbital

CNDO/2 Calculations for Organohalides

1986 ◽  
Vol 39 (2) ◽  
pp. 233 ◽  
Author(s):  
TH Spurling ◽  
DA Winkler
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Organic Molecules ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital

A CNDO/2 parameterization for performing semiempirical molecular orbital calculations for organic molecules containing bromine and iodine is presented; the results are superior to those from other parameterizations, and generally agree with ab initio calculations and experiment.

Conformational preferences and barriers to internal rotation in fluorothioanisoles from long-range spin–spin couplings, photoelectron spectroscopy, and semiempirical molecular orbital calculations

1993 ◽  
Vol 71 (10) ◽  
pp. 1741-1750 ◽  
Author(s):  
Dietmar Chmielewski ◽  
Nick Henry Werstiuk ◽  
Timothy A. Wildman
Keyword(s):  
Internal Rotation ◽  
Molecular Orbital ◽  
Long Range ◽  
Photoelectron Spectra ◽  
Semiempirical Methods ◽  
Molecular Orbital Calculations ◽  
Methyl Carbon ◽  
Conformational Preferences ◽  
Barriers To Internal Rotation ◽  
Semiempirical Molecular Orbital

The conformational preferences and barriers to internal rotation about the S—C(phenyl) bond have been investigated for thioanisole and its 2-fluoro, 2,6- and 3,5-difluoro, and 2,3,5,6-tetrafluoro derivatives. Measurements of long-range spin–spin couplings between the methyl carbon and the para ring proton indicate that the 2-fluoro and 3,5-difluoro compounds prefer conformations with all heavy atoms coplanar. The 2,6-difluoro and 2,3,5,6-tetrafluoro compounds prefer conformations in which the methyl carbon lies in or near the plane perpendicular to the aromatic ring. Semiempirical molecular orbital calculations with the MNDO method indicate that all of the molecules prefer perpendicular conformations while similar calculations with AM1 indicate that all prefer planar conformations. Apparently the conformational behaviour can be quite sensitive to subtle changes in intramolecular interactions, which may indicate improvements to these semiempirical methods. The NMR results have been used to derive an internally consistent set of rotational potentials. Synthetic photoelectron spectra derived from these potentials and the AM1 orbital energies are in good agreement with the experimental spectra.

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