An Ab Initio Molecular Orbital Study of Sulfur-Substituted Carbanions: Toward an Understanding of Regiochemistry in the Chlorination of Unsymmetrical Sulfides

1997 ◽  
Vol 50 (6) ◽  
pp. 517 ◽  
Author(s):  
Jack Leon Ginsburg ◽  
Katherine Valenta Darvesh ◽  
Patricia Axworthy ◽  
Richard Francis Langler
Keyword(s):  
Free Radicals ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Dimethyl Sulfide ◽  
Experimental Results ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Carbonium Ions ◽  
Moller Plesset ◽  
Better Than

Moller-Plesset molecular orbital calculations at the 6-31+G(d) level have been completed on substituted dimethyl sulfide-derived carbanions. The results are applied to the prediction of regiochemistry for chlorination of unsymmetrical sulfides. Notwithstanding the need for future improvements, regiochemical predictions based on stabilities of sulfur-substituted carbanions match experimental results better than earlier predictions based on stabilities of sulfur-substituted carbonium ions or sulfur-substituted free radicals. The present results suggest that the mechanism for the elimination step in the Pummerer rearrangement of a chlorosulfonium cation is an E 1cb-like process.

Ab initio molecular orbital study of simple 1,3-dipolar reactions

1976 ◽  
Vol 29 (3) ◽  
pp. 465 ◽  
Author(s):  
D Poppinger
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Transition States ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Orbital Study ◽  
Extended Basis ◽  
Optimized Geometries

Ab initio molecular orbital calculations with minimal and extended basis sets have been carried out for the 1,3-dipolar addition of fulminic acid to acetylene, ethylene, ethynamine and propynenitrile. Optimized geometries are reported for the transition states HCNO+C2H2, HCNO+C2H4, HCNO+ C2HNH2, for the adducts isoxazole and 2-isoxazoline, and for nitrosocyclopropene as a possible intermediate. The calculations indicate that (a) these 1,3-dipolar reactions are synchronous processes, (b) the geometry of the transition state is insensitive to substitution and (c) of the isomeric substituted adducts, 5-aminoisoxazole and isoxazole-4-carbonitrile should be formed preferentially.

Singlet and Triplet States of Aminonitrenes: An Ab Initio Molecular Orbital Study

1973 ◽  
Vol 51 (20) ◽  
pp. 3303-3308 ◽  
Author(s):  
N. C. Baird ◽  
R. F. Barr
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Triplet States ◽  
Density Distributions ◽  
Molecular Orbital Study ◽  
Triplet Splitting ◽  
Optimum Geometry ◽  
Singlet And Triplet States ◽  
Carbonyl Substitution

Ab initio STO-3G molecular orbital calculations are reported for the lowest singlet and the lowest triplet state of the aminonitrenes H2NN, CH3(H)NN, F(H)NN, and HCO(H)NN. The optimum geometry calculated for the H2NN triplet is nonplanar (Cs symmetry), with N—N and N—H bond distances of 1.436 and 1.034 Å, and HNN and HNH angles both of 107.5°. The optimum singlet is predicted to be planar (C2v symmetry), with N—N and N—H distances of 1.276 and 1.041 Å respectively, and an HNN angle of 124°. An analysis of the calculated geometries and electron density distributions indicates that the "idealized" representations 3 and 5 are adequate to explain the bonding in the triplet and singlet respectively. The effects of methyl, fluoro, and carbonyl substitution upon the singlet–triplet splitting and upon the charge distribution are discussed. The optimum-geometry triplet is predicted to be slightly more stable than the optimum-geometry singlet in all cases.

An ab initio Molecular Orbital Study of Bonding in Fluorocarbonium Ions

1971 ◽  
Vol 49 (22) ◽  
pp. 3708-3713 ◽  
Author(s):  
N. C. Baird ◽  
R. K. Datta
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Minimal Basis ◽  
Fluorine Substitution ◽  
Abstraction Reaction ◽  
Carbonium Ions ◽  
Hydride Abstraction ◽  
Resonance Stabilization

Ab initio molecular orbital calculations are reported for the series of carbonium ions (CH3)+, (FCH2)+, and (F2CH)+ and for their neutral molecule counterparts CH4, CH3F, and CH2F2. The energies and wavefunctions for the carbonium ions have been calculated both with and without including the carbon 2pπ orbital in the minimal basis set in order to unravel the inductive destabilization and resonance stabilization due to fluorine substitution. The increase in bonding energy with multiple fluorine substitution is less than linear, due primarily to nonadditivity in the dative carbon–fluorine π bonding. The "saturation" effect noted previously for the hydride abstraction reaction enthalpies is shown to be due primarily to stability effects in the neutral molecules themselves rather than to energetic effects of the carbonium ions.

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.

Ab initio molecular orbital calculations on the water-carbon dioxide system: Molecular complexes

1975 ◽  
Vol 30 (1) ◽  
pp. 58-59 ◽  
Author(s):  
B. Jönsson ◽  
G. Karlström ◽  
H. Wennerström
Keyword(s):  
Carbon Dioxide ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Molecular Complexes ◽  
Molecular Orbital Calculations
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