Internal Rotation of 1-Aryl-3,3-dialkyltriazenes. Comparison of Semiempirical Molecular Orbital Calculations with Far Infrared, Raman, and NMR Spectroscopic Results

1994 ◽  
Vol 98 (35) ◽  
pp. 8817-8822 ◽  
Author(s):  
J.-C. Panitz ◽  
T. Lippert ◽  
A. Wokaun
Keyword(s):  
Internal Rotation ◽  
Molecular Orbital ◽  
Far Infrared ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital

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.

Conformational analysis of aminovinylpyrazine by semiempirical molecular orbital calculations

1997 ◽  
Vol 33 (1) ◽  
pp. 33-39 ◽  
Author(s):  
Hisayoshi Shiozaki ◽  
Atsushi Oshida ◽  
Dongfeng Hou ◽  
Masaru Matsuoka
Keyword(s):  
Conformational Analysis ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital
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