Substituent effects on stability of oxiranes, oxirenes, and dioxiranes

2000 ◽  
Vol 78 (5) ◽  
pp. 562-567 ◽  
Author(s):  
Kuangsen Sung
Keyword(s):  
Substituent Effect ◽  
Transition States ◽  
Substituent Effects ◽  
Stabilization Energies ◽  
Homodesmotic Reaction

Homodesmotic reactions were designed to study substituent effects on stability of oxiranes, oxirenes, and dioxiranes. Good or fair correlation between their homodesmotic stabilization energies and Taft's dual-substituent-parameters has been found. Oxiranes are stabilized by σ-donating and π-donating substituents but destabilized by σ-accepting and π-accepting substituents. The π-effects on oxiranes are comparable to σ-effects for π-acceptor substituents and are much stronger than σ-effects for π-donor substituents. Oxirenes are stabilized by σ-donating, π-donating, and π-accepting substituents but destabilized by σ-accepting substituents. The π-effects on oxirenes are stronger than σ-effects. Oxirenes with strong π-donor substituents such as F, OH, and NH2, or strong σ-donor substituents such as Li and Na are neither real molecules nor transition states. Dioxiranes are stabilized by σ-donating and π-donating substituents but destabilized by σ-accepting and π-accepting substituents. The π-effects on dioxiranes are stronger than σ-effects for π-donor substituents, but weaker than σ-effects for π-acceptor substituentsKey words: oxirane, oxirene, dioxirane, homodesmotic reaction, substituent effect.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

Substituent effects of rate constants for thermal [4π + 2π] cycloreversion of spiro-fused β-lactam oxadiazolines

1993 ◽  
Vol 71 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Michel Zoghbi ◽  
John Warkentin
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Substituent Effects ◽  
Ground States ◽  
Phenyl Substituent ◽  
First Order ◽  
Average Value ◽  
Carbonyl Ylide

Twelve Δ3-1,3,4-oxadiazolines in which C-2 is also C-4 of a β-lactam moiety (spiro-fused β-lactam oxadiazoline system) were thermolyzed as solutions in benzene. Substituents in the β-lactam portion affect the rate constant for thermal decomposition of the oxadiazolines to N2, acetone, and a β-lactam-4-ylidene. The total spread of first-order rate constants at 100 °C was 47-fold and the average value was 6.7 × 10−4 s−1. A phenyl substituent at N-1 or at C-3 was found to be rate enhancing, relative to methyl. At C-3, H and Cl were also rate enhancing, relative to methyl. The data are interpreted in terms of the differential effects of substituents on the stabilities of the ground states, and on the stabilities of corresponding transition states for concerted, suprafacial, [4π + 2π] cycloreversion. The first products, presumably formed irreversibly, are N2 and a carbonyl ylide. The latter subsequently fragments to form acetone (quantitative) and a β-lactam-4-ylidene.

The log kexovs. log kendo correlation as a mechanistic criterion; on the mechanisms of solvolysis of norbornyl derivatives and base-catalyzed isotope exchange of norbornanones

1976 ◽  
Vol 54 (5) ◽  
pp. 678-684 ◽  
Author(s):  
Sujit Banerjee ◽  
Nick Henry Werstiuk
Keyword(s):  
Transition State ◽  
Exchange Rates ◽  
Isotope Exchange ◽  
Transition States ◽  
Substituent Effects ◽  
Proton Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Rate Data ◽  
Hydrogen Deuterium ◽  
The Difference

Rate data for the acetolysis of exo-norbornyl-sulfonates have been correlated with those for the corresponding endo isomers. It is shown that the slopes of the log kexovs. log kendo plots reflect the difference in delocalization between the transition states derived from the exo and endo isomers, respectively. The log kexovs. log kendo plot, which is comprised of the parent norbornyl sufonate and its derivatives substituted at the 5, 6, and 7 positions, has a slope of 1.11 ± 0.08, which establishes that σ bridging is absent in the transition state obtained from the exo isomer. A similar analysis of base-catalyzed hydrogen–deuterium exchange rates of norbornanones reveals that exo proton exchange is more sensitive to substituent effects than the corresponding endo process.

ChemInform Abstract: CAPTO-DATIVE SUBSTITUENT EFFECTS. PART 11. CAPTO-DATIVE SUBSTITUENT EFFECT ON N THE CIS-TRANS ISOMERIZATION OF CYCLOPROPANES

1982 ◽  
Vol 13 (38) ◽  
Author(s):  
A. DE MESMAEKER ◽  
L. VERTOMMEN ◽  
R. MERENYI ◽  
H. G. VIEHE
Keyword(s):  
Substituent Effect ◽  
Substituent Effects ◽  
Trans Isomerization

ChemInform Abstract: Captodative Substituent Effects. Part 44. Captodative Substituent Effect in Synthesis

ChemInform ◽  
1990 ◽  
Vol 21 (12) ◽  
Author(s):  
H. G. VIEHE ◽  
Z. JANOUSEK ◽  
R. MERENYI
Keyword(s):  
Substituent Effect ◽  
Substituent Effects

Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids

1975 ◽  
Vol 53 (23) ◽  
pp. 3622-3633 ◽  
Author(s):  
T. M. Krygowski ◽  
W. R. Fawcett
Keyword(s):  
Substituent Effect ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Point Of View ◽  
Aromatic Acids ◽  
Resonance Effects ◽  
Equation Analysis ◽  
Reaction Constant ◽  
Enthalpy And Entropy Changes ◽  
Substituent Constants

Separation of the substituent effect ρσ into entropie ρSσS and enthalpic ρHσH contributions is presented within the framework of the general Hammett equation. Analysis of the experimental data for aromatic acids shows that, in general, entropie effects are the major contribution to the total substituent effect, the entropic reaction constant being approximately equal to the normal Hammett ρ A comparison of the present results with those based on a separation of inductive and resonance effects shows that the entropie and inductive effects are directly related. On the other hand, strongly resonance interacting substituents were found to be enthalpy controlled. The substituent effect on enthalpy and entropy changes is discussed from a molecular point of view and related to inductive and resonance effects. A list of 16 enthalpic (σH) and entropie (σS) substituent constants are presented.

SUBSTITUENT EFFECT ON TWO-PHOTON ABSORPTION PROPERTIES OF FLUORENE DERIVATIVES

2004 ◽  
Vol 13 (03n04) ◽  
pp. 475-479 ◽  
Author(s):  
JUN KAWAMATA ◽  
MASAHARU AKIBA ◽  
YOSHIO INAGAKI ◽  
TAKEHARU TANI ◽  
AKINORI HARADA
Keyword(s):  
Cross Sections ◽  
Substituent Effect ◽  
Femtosecond Pulse ◽  
Substituent Effects ◽  
Photon Absorption ◽  
Absorption Properties ◽  
Two Photon Absorption ◽  
Ti:Sapphire Laser ◽  
Two Photon ◽  
The Relationship

Two novel fluorene derivatives having cationic substituents were synthesized. Two-photon absorption (TPA) properties of the derivatives were evaluated using the fluorescence-based technique with a femtosecond pulse emitted from a Ti:sapphire laser. Maximum TPA cross-sections of the compounds were estimated from the TPA spectra. Based on the results, the relationship between the TPA cross-sections and the substituent effects of the derivatives were discussed.

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