Trans effect of the good .sigma. donor ligands dimethyl phosphate, methyl phenyl phosphonate, and diphenylphosphinate. Evidence for complete bond breaking in the transition state of SN1lim reactions of dimethylphosphonatocobaloxime and methylcobaloxime complexes

1974 ◽  
Vol 96 (11) ◽  
pp. 3697-3699 ◽  
Author(s):  
William C. Trogler ◽  
Robert Charles Stewart ◽  
Luigi G. Marzilli
Keyword(s):  
Transition State ◽  
Donor Ligands ◽  
Bond Breaking ◽  
Trans Effect ◽  
Dimethyl Phosphate ◽  
Methyl Phenyl

Berechnung kinetischer Isotopeneffekte für die Reaktion von Methyljodid mit Cyanid-Ion

1966 ◽  
Vol 21 (9) ◽  
pp. 1377-1384
Author(s):  
A. V. Willi
Keyword(s):  
Transition State ◽  
Secular Equation ◽  
Isotope Effects ◽  
Force Constants ◽  
Bond Breaking ◽  
Bending Force ◽  
A Value ◽  
Order Of Magnitude ◽  
Deuterium Isotope Effects ◽  
The Difference

Kinetic carbon-13 and deuterium isotope effects are calculated for the SN2 reaction of CH3I with CN-. The normal vibrational frequencies of CH3I, the transition state I · · · CH3 · · · CN, and the corresponding isotope substituted reactants and transition states are evaluated from the force constants by solving the secular equation on an IBM 7094 computer.Values for 7 force constants of the planar CH3 moiety in the transition state (with an sp2 C atom) are obtained by comparison with suitable stable molecules. The stretching force constants related to the bonds being broken or newly formed (fCC, fCC and the interaction between these two stretches, /12) are chosen in such a way that either a zero or imaginary value for νʟ≠ will result. Agreement between calculated and experimental methyl-C13 isotope effects (k12/ k13) can be obtained only in sample calculations with sufficiently large values of f12 which lead to imaginary νʟ≠ values. Furthermore, the difference between fCI and fCC must be small (in the order of 1 mdyn/Å). The bending force constants, fHCI and fHCC, exert relatively little influence on k12/k13. They are important for the D isotope effect, however. As soon as experimental data on kH/kD are available it will be possible to derive a value for fHCC in the transition state if fHCI is kept constant at 0.205 mdynA, and if fCI, fCC and f12 are held in a reasonable order of magnitude. There is no agreement between experimental and calculated cyanide-C13 isotope effects. Possible explanations are discussed. — Since fCI and fCC cannot differ much it must be concluded that the transition state is relatively “symmetric”, with approximately equal amounts of bond making and bond breaking.

scholarly journals Transition between [R]- and [S]-Stereoisomers without Bond Breaking

2020 ◽  
Author(s):  
Shampa Raghunathan ◽  
Komal Yadav ◽  
V. C. Rojisha ◽  
Tanashree Jaganade ◽  
V. Prathyusha ◽  
...  
Keyword(s):  
Transition State ◽  
Theoretical Calculations ◽  
Bond Breaking ◽  
Kinetic Properties ◽  
Intermediate Structure ◽  
Structure Dynamic ◽  
Planar Transition ◽  
First Time

We for the first time shown that transition between (R) and (S) stereoisomers via a planar transition state or an intermediate structure without having to break a bond is possible. Rigorous theoretical calculations have been used to study this novel phenomenon and to characterize the energetic, structure, dynamic and kinetic properties.

Pyrazolines IX. Chemistry of some 3-cyano-3-carbomethoxy-1-pyrazolines

1969 ◽  
Vol 47 (21) ◽  
pp. 3965-3973 ◽  
Author(s):  
Donald E. McGreer ◽  
Y. Y. Wigfield
Keyword(s):  
Transition State ◽  
Kinetic Studies ◽  
Product Distribution ◽  
Bond Breaking ◽  
State Structure ◽  
Transition State Structure ◽  
Aryl Group

Product and kinetic studies have been made on the pyrolysis of a series of 3-cyano-3-carbomethoxy-1-pyrazolines substituted at C-4 with a methyl and an aryl group (phenyl, p-methoxyphenyl, and p-nitrophenyl). Evidence is presented supporting a transition state structure in which little progress to bond breaking of the C-5 to N bond has taken place at the transition state. The product distribution is largely dependent on the stereochemistry of the initial pyrazoline and to a lesser degree on the nature of the aryl group at C-4. The cis pyrazolines gave products resulting primarily from aryl migration while the trans pyrazolines gave products predominantly from methyl migration.

scholarly journals Ab initio Study of Nucleophilic Aromatic Substitution of Polyfluorobenzene

1999 ◽  
Vol 23 (9) ◽  
pp. 528-529
Author(s):  
Kiyoshi Tanaka ◽  
Makoto Deguchi ◽  
Satoru Iwata
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Transition States ◽  
Nucleophilic Aromatic Substitution ◽  
Bond Breaking ◽  
Aromatic Substitution ◽  
Ab Initio Study ◽  
Rate Determining Step ◽  
Elimination Mechanism ◽  
The Stability

Calculations at ab initio levels of theory of the nucleophilic aromatic substitution of pentafluoronitrobenzene with amines demonstrate an addition–elimination mechanism (SNAr), with the rate-determining step at the second transition state involving C–F bond breaking, and support the ortho-selectivity of the reactions based on the stability of the second transition states.

Transition between [R]- and [S]-Stereoisomers without Bond Breaking

2020 ◽  
Author(s):  
Shampa Raghunathan ◽  
Komal Yadav ◽  
V. C. Rojisha ◽  
Tanashree Jaganade ◽  
V. Prathyusha ◽  
...  
Keyword(s):  
Transition State ◽  
Theoretical Calculations ◽  
Bond Breaking ◽  
Kinetic Properties ◽  
Intermediate Structure ◽  
Structure Dynamic ◽  
Planar Transition ◽  
First Time

We for the first time shown that transition between (R) and (S) stereoisomers via a planar transition state or an intermediate structure without having to break a bond is possible. Rigorous theoretical calculations have been used to study this novel phenomenon and to characterize the energetic, structure, dynamic and kinetic properties.

Transition State Geometry and Solvent Effects in the Enantioselective Oxidation of Sulfides to Chiral Sulfoxides by Oxaziridines

1995 ◽  
Vol 50 (9) ◽  
pp. 1396-1403
Author(s):  
Andreas Pointner ◽  
Rudolf Herrmann
Keyword(s):  
Transition State ◽  
Enantioselective Oxidation ◽  
Phenyl Sulfide ◽  
Methyl Phenyl Sulfide ◽  
Chiral Sulfoxides ◽  
Solvent Dependence ◽  
Transition State Geometry ◽  
Planar Transition ◽  
Better Than ◽  
Methyl Phenyl

AbstractFor the enantioselective oxidation of methyl phenyl sulfide and tert-butyl methyl sulfide to the corresponding chiral sulfoxides by 3,3-dibromo-(camphorsulfonyl)oxaziridine, semiempirical calculations (MNDO, AMI, PM3) concerning transition state geometries were performed. The results show that only PM3 is able to localize a transition state. For methyl phenyl sulfide, a spiro arrangement of the oxaziridine ring and the sulfur atom explains the observed direction of the selectivity better than a planar transition state. The solvent dependence of the observed enantioselectivity is related to the calculated dipole moment of the transition state by the Kirkwood-Onsager model. In THF as solvent, its direct participation in the transition state has to be considered

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