Pyrolysis of Aryl Azides. XIII. Conformational Effects on the Ability of Carbonyl as a Neighbouring Group

1996 ◽  
Vol 49 (11) ◽  
pp. 1197 ◽  
Author(s):  
LK Dyall ◽  
JA Ferguson ◽  
TB Jarman
Keyword(s):  
Transition State ◽  
Carbonyl Group ◽  
Electronic Effects ◽  
Aryl Azides ◽  
Conformational Effects ◽  
Acetyl Group ◽  
Previous Claim

Our previous claim, that locking an ortho carbonyl group into a favourable conformation causes very large increases in the rate of thermolysis of aryl azides , has been reexamined. In 8-azido-5-methoxy-1-tetralone the rate advantage over an azide with a rotatable ortho acetyl group is estimated to be only 18-fold. Nevertheless, this factor is large enough to invalidate attempts to explain relative neighbouring group abilities on simple electronic effects alone. The very large rate increases we reported previously for 1-azidoacridin-g(10H)-one and 1-azidoanthracene-9,10-dione are partly due to favourable retention of conjugation in the transition state.

Pyrolysis of aryl azides. III. Steric and electronic effects upon reaction rate

1975 ◽  
Vol 28 (10) ◽  
pp. 2147 ◽  
Author(s):  
LK Dyall
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effects ◽  
Electronic Effects ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Methyl Group ◽  
First Order ◽  
Ortho Substituent

First-order rate constants have been measured for the pyrolysis of 15 phenyl azides in decalin solution. The rate for phenyl azide is increased only slightly by all para and many ortho substituents; in these cases Eact and ΔSact values are related linearly. ��� The very large rate increases when the ortho substituent is phenylazo, nitro, acetyl or benzoyl cannot be from steric or normal electronic effects and therefore identify a specific involvement of these groups in the transition state. This rate enhancement is reduced to scarcely significant levels by a 6-chloro or 6-methyl group in 2- nitrophenyl azide, but not by a 6-nitro group. These results raise doubts about recent claims1 to establish mechanism by measuring polar effects on rates of pyrolysis of azides in which steric effects might also operate.

On the regioselectivity of the condensation of stabilized phosphoylids with 3-substituted phthalic anhydrides

1989 ◽  
Vol 67 (4) ◽  
pp. 569-573 ◽  
Author(s):  
Livain Breau ◽  
Margaret M. Kayser
Keyword(s):  
Oxygen Atom ◽  
Transition State ◽  
Carbonyl Group ◽  
Lewis Base ◽  
Carbonyl Function ◽  
Deficient Phosphorus ◽  
Phthalic Anhydrides

Condensations of stabilized phosphorane 1 with 3-substituted phthalic anhydrides were investigated. The importance of various effects influencing regio- and stereoselectivity of these reactions is discussed. It is proposed that the oxygen atom on the substituents in position 3 can act as a Lewis base toward the electron-deficient phosphorus of the ylid. The resulting complexation stabilizes the transition state for the reaction at the ortho carbonyl group, thus offsetting the usual steric and "push" effects, which favour attack at the meta carbonyl function. Keywords: Wittig condensations, phthalic anhydrides, regioselectivity, stereoselectivity.

scholarly journals Separating Electronic from Steric Effects in Ethene/α-Olefin Copolymerization: A Case Study on Octahedral [ONNO] Zr-Catalysts

Processes ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 384 ◽  
Author(s):  
Francesco Zaccaria ◽  
Roberta Cipullo ◽  
Andrea Correa ◽  
Peter H. M. Budzelaar ◽  
Vincenzo Busico ◽  
...  
Keyword(s):  
Transition State ◽  
Electronic Properties ◽  
Polymerization Kinetics ◽  
Relative Reactivity ◽  
Steric Effects ◽  
Reactivity Ratios ◽  
Ancillary Ligand ◽  
Electronic Effects ◽  
Dft Modeling

Four Cl/Me substituted [ONNO] Zr-catalysts have been tested in ethene/α-olefin polymerization. Replacing electron-donating methyl with isosteric but electron-withdrawing chlorine substituents results in a significant increase of comonomer incorporation. Exploration of steric and electronic properties of the ancillary ligand by DFT confirm that relative reactivity ratios are mainly determined by the electrophilicity of the metal center. Furthermore, quantitative DFT modeling of propagation barriers that determine polymerization kinetics reveals that electronic effects observed in these catalysts affect relative barriers for insertion and a capture-like transition state (TS).

Sur l'aptitude à l'extension du noyau pipéridique en fonction de la substitution de l'atome d'azote: réaction du diazométhane avec quelques pipéridones-4 et désamination nitreuse des aminométhyl-alcools correspondants

1971 ◽  
Vol 49 (19) ◽  
pp. 3075-3085 ◽  
Author(s):  
H. Favre ◽  
Z. Hamlet ◽  
R. Lanthier ◽  
M. Ménard
Keyword(s):  
Nitrogen Atom ◽  
Carbonyl Group ◽  
Nitrous Acid ◽  
Ring Expansion ◽  
Nucleophilic Attack ◽  
Electronic Effects ◽  
Field Effects ◽  
Benzoyl Group ◽  
La Substitution

Aptitude to ring expansion in the piperidine series, measured by the ratio of ring expanded ketone to epoxide, varies considerably according to the nitrogen atom substituent. This ratio is essentially the same in the case of the reaction of diazomethane on 4-piperidones and the nitrous acid deamination of the corresponding aminoalcohols. The values of the ratio are 0.01–0.1 for a phenylsulfonyl group, of the order 0.3–0.6 for a benzoyl group and slightly greater than 1 for a benzyl group. Electronic effects (inductive and field effects) are the cause of these differences. Parallels between the two reactions indicate that nucleophilic attack of diazomethane on the carbonyl group can lead to the ring expanded ketone and the epoxide.

scholarly journals Theoretical Study of the Electronic Effects in the Intramolecular Ketene-Styrene [2+2] Cycloaddition

2019 ◽  
Vol 54 (4) ◽  
Author(s):  
Manuel Fernando Rubio ◽  
Federico Jiménez-Cruz ◽  
Guillermo Ramírez-Galicia
Keyword(s):  
Transition State ◽  
Theoretical Study ◽  
Positive Charge ◽  
Ring Structure ◽  
Experimental Results ◽  
Electronic Effects ◽  
Hartree Fock ◽  
Reaction Constant ◽  
Remote Substituent

DFT (B3LYP/6-31+G*) and post-Hartree-Fock (MP2/6-31+G*//B3LYP/6-31G*) calculations were carried out in order to explain the effect of a remote substituent in the intramolecular ketene-styrene [2+2] cycloaddition of p-substituted 2-methyl-7-arylhepta- 1,6-dien-1-one which produces the bicycle[3.1.1] or the bicycle [3.2.0] heptanones according to Bèlanger experimental results. The transition state geometries were found as an asynchronous process with a three-member ring structure and an incipient positive charge development. Kinetic and thermodynamic controls were proposed at B3LYP/6-31+G* to determine which product is most likely to form in a competence reaction. In addition, the value of the ρ experimental reaction constant was reproduced, ρ ~ -1.34.

scholarly journals Binding energy and catalysis. Fluorinated and deoxygenated glycosides as mechanistic probes of Escherichia coli (lacZ) β-galactosidase

1992 ◽  
Vol 286 (3) ◽  
pp. 721-727 ◽  
Author(s):  
J D McCarter ◽  
M J Adam ◽  
S G Withers
Keyword(s):  
Escherichia Coli ◽  
Transition State ◽  
Kinetic Parameters ◽  
Parent Compound ◽  
Order Rate Constant ◽  
Linear Free Energy Relationship ◽  
Electronic Effects ◽  
Linear Free Energy ◽  
Covalent Intermediate ◽  
Hydrolysis Of

Kinetic parameters for the hydrolysis of a series of deoxy and deoxyfluoro analogues of 2′,4′-dinitrophenyl beta-D-galactopyranoside by Escherichia coli (lacZ) beta-galactosidase have been determined and rates found to be two to nine orders of magnitude lower than that for the parent compound. These large rate reductions result primarily from the loss of transition-state binding interactions due to the replacement of sugar hydroxy groups, and such interactions are estimated to contribute at least 16.7 kJ (4 kcal).mol-1 to binding at the 3, 4 and 6 positions and more than 33.5 kJ (8 kcal).mol-1 at the 2 position. The existence of a linear free-energy relationship between log(kcat./Km) for these compounds and the logarithm of the first-order rate constant for their spontaneous hydrolysis demonstrates that electronic effects are also important and provides direct evidence for oxocarbonium ion character in the enzymic transition state. A covalent intermediate which turns over only extremely slowly (t1/2 = 45 h) accumulates during hydrolysis of the 2-deoxyfluorogalactoside, and kinetic parameters for its formation have been determined. This intermediate is nonetheless catalytically competent, since it re-activates much more rapidly in the presence of the transglycosylation acceptors methanol or glucose, thereby providing support for the notion of a covalent intermediate during hydrolysis of the parent substrates.

Reactions of 1,3-diacylthioureas with methoxide ion and with amines

1987 ◽  
Vol 52 (1) ◽  
pp. 120-131 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Jirman ◽  
Vojeslav Štěrba
Keyword(s):  
Carbonyl Group ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Order Of Magnitude ◽  
Acetyl Group ◽  
Methoxide Ion ◽  
Rate Limiting

Rate constants of base-catalyzed methanolysis and dissociation constants in methanol have been determined for benzoylthiourea (II), 1,3-diacetylthiourea (III), 1,3-dibenzoylthiourea (IV), and 1-acetyl-3-benzoylthiourea (V). With the diacyl derivatives III and IV, the reaction of methoxide ion with the neutral substrate is accompanied by that of methoxide with the substrate anion (at higher alkoxide concentrations). Above 0.1 mol l-1 CH3O(-), the rate constants are also affected by medium. The rate of the reaction of neutral diacyl derivative is decreased, and that of the reaction of methoxide with the substrate anion is rapidly increased. The dissociation constant of II is higher than that of acetylthiourea (I) by about one order of magnitude, but the attack of methoxide on the carbonyl group of II is about three times slower than that in I. The benzoyl group at the N1 nitrogen exhibits a greater activating influence (in both the rate and the equilibrium constants) on the other NHCOR group than the acetyl group does. With V the ratio of methanolysis rate constants is 9 : 1 in favour of the acetyl group. The reaction of diacetyl derivative III with 1-butanamine has been followed in butanamine buffers. At the lowest butanamine concentrations, the reaction is second order in the amine, and the rate-limiting step is the proton transfer from the intermediate to the second amine molecule. At the highest butanamine concentrations the reaction becomes first order in the amine, and the rate-limiting step changes to the attack of butanamine on the carbonyl group of diacetyl derivative III.

THE TRANSMISSION OF THE POLAR EFFECTS OF SUBSTITUENTS IN AROMATIC AND ARYLALIPHATIC CARBOXYLIC ACIDS: REACTIONS OF THE ACIDS WITH DIAZODIPHENYLMETHANE IN ETHANOL

1964 ◽  
Vol 42 (8) ◽  
pp. 1979-1983 ◽  
Author(s):  
K. Bowden ◽  
N. B. Chapman ◽  
J. Shorter
Keyword(s):  
Carboxylic Acids ◽  
Carbonyl Group ◽  
Cinnamic Acid ◽  
Field Effect ◽  
Rate Coefficients ◽  
Side Chain ◽  
Side Chains ◽  
Electronic Effects ◽  
Electron Effect

Rate coefficients have been determined for the reactions in ethanol at 30° of diazodiphenylmethane with several groups of carboxylic acids. Each group included the parent acid and three nuclear substituted acids. The parent acids were: benzoic, phenylacetic, β-phenylpropionic, phenoxyacetic, and trans-cinnamic acid. The reactions of 3-fluoro- (or chloro-) or 4-methyl-biphenyl-4′-carboxylic, and of 9-X-10-anthroic acids (X = Me, Cl, or Br) were also studied similarly. The Hammett polar susceptibility constant, ρ, has been calculated for each set of reactions. The values of ρ are discussed in terms of transmission of electronic effects through the side-chain by a field effect, and for side-chains conjugated with the ring, by a π-electron effect, both of which are inversely proportional to the first power of the distance of the carbonyl group from the ring.

Synthesis and thermolysis rate constants of diastereomeric oxadiazoline sources of acetoxy(methoxy)carbene — Reaction of acetoxy(methoxy)carbene with isocyanates

2006 ◽  
Vol 84 (7) ◽  
pp. 927-933 ◽  
Author(s):  
Wojciech Sokol ◽  
John Warkentin
Keyword(s):  
Acetic Acid ◽  
Ethyl Acetate ◽  
Carbonyl Group ◽  
Rate Constants ◽  
Acid Catalysis ◽  
Major Product ◽  
Acetyl Group ◽  
Methyl Pyruvate ◽  
Acetyl Transfer ◽  
Cis And Trans

Oxidation of the methoxycarbonylhydrazone of p-methoxyacetophenone affords both the cis- and trans-2-acetoxy-2-methoxy-5-(p-methoxyphenyl)-5-methyl-Δ3-1,3,4-oxadiazolines (also known as corresponding 2,5-dihydro-1,3,4-oxadiazoles) as well as methyl 1-acetoxy-1-(p-methoxyphenylethyl)diazenecarboxylate. The three isomers were separated and identified by spectroscopic means. Methyl 1-acetoxy-1-(p-methoxyphenylethyl)diazenecarboxylate is the major product from oxidation in dichloromethane. Oxidation in acetic acid did not afford the oxadiazolines but gave the diazenecarboxylate and, in addition, 1-(p-methoxyphenyl)ethyl acetate. Attempts to isomerize the diazenecar boxylate to the oxadiazolines by acid catalysis were not successful. Thermolysis of the oxadiazolines at 50.4 °C occurred with approximately the same rate constant (ca. 3.6 × 10–5 s–1) to afford acetoxy(methoxy)carbene, which rearranges to methyl pyruvate by acetyl transfer. The carbene, which reacts with relatively unhindered isocyanates to transfer the methoxy carbonyl group to carbon and the acetyl group to nitrogen, can be considered an acyl anion equivalent in that reaction.Key words: acetoxy(methoxy)carbene, diazene, oxadiazoline, isocyanate, (acetylamino)oxoacetate.

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