Molecular orbital calculations and carbon-13 NMR studies to explain a regiospecific demethylation of 3-alkyl-1,2-dimethoxybenzenes

1984 ◽  
Vol 49 (12) ◽  
pp. 2130-2135 ◽  
Author(s):  
Phillip W. Jardon ◽  
Euin H. Vickery ◽  
Leon F. Pahler ◽  
Naser Pourahmady ◽  
Gilbert J. Mains ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Nmr Studies

Long-range proton coupling constants and molecular orbital calculations as indicators of conformational populations of benzene-1,2- and -1,3-dicarbaldehydes

1986 ◽  
Vol 64 (1) ◽  
pp. 158-163 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Rudy Sebastian ◽  
Craig S. Takeuchi
Keyword(s):  
Dipole Moment ◽  
Carbon Tetrachloride ◽  
Molecular Orbital ◽  
Long Range ◽  
Benzene Solution ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Trans Form ◽  
Nmr Studies

The 1H nmr spectra of the benzene-1,2- and -1,3-dicarbaldehydes in carbon tetrachloride, benzene-d6, and acetone-d6 solutions at 300 K are analyzed. The stereospecific long-range couplings over five formal bonds between the sidechain and ring protons show that the 1,2 isomer exists as an 87:13 mixture of the cis–trans and trans–trans conformers in carbon tetrachloride. These populations are insensitive to solvent. Molecular orbital calculations utilizing extensive geometry optimization procedures imply that the cis–cis form, with proximate C=O bonds, is indeed of negligible significance as assumed in obtaining the populations of the other forms. Further calculations define a pathway of relatively low energy for interconversion of the two abundant forms, in agreement with dynamic nmr studies. For the 1,3 isomer the long-range couplings provide a check of the conformer populations deduced from dipole moment and 13C nmr studies. For example, if the cis–trans form is 70% abundant, as deduced from the dipole moment in benzene solution, then the long-range couplings imply that the population of the cis–cis conformer is insignificant.

Interactions between Methylene Blue and Pullulan According to Molecular Orbital Calculations

2020 ◽  
Vol 140 (11) ◽  
pp. 529-533
Author(s):  
Pasika Temeepresertkij ◽  
Saranya Yenchit ◽  
Michio Iwaoka ◽  
Satoru Iwamori
Keyword(s):  
Methylene Blue ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

ChemInform Abstract: MOLECULAR ORBITAL CALCULATIONS ON THE C2H4SH+ CATION

1976 ◽  
Vol 7 (10) ◽  
pp. no-no
Author(s):  
JAMES W. GORDON ◽  
GEORGE H. SCHMID ◽  
IMRE G. CSIZMADIA
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations
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