The remarkable effect of 7-amino substituents on the reactivity of 4-nitrobenzofurazans with nucleophiles

2005 ◽  
Vol 83 (9) ◽  
pp. 1222-1227 ◽  
Author(s):  
Michael R Crampton ◽  
Chukwuemeka Isanbor ◽  
Thomas C Willett
Keyword(s):  
Nucleophilic Substitution ◽  
Key Words ◽  
Alkaline Solution ◽  
Equilibrium Constants ◽  
Remarkable Effect ◽  
Iminium Ion ◽  
Nucleophilic Reactivity ◽  
Conjugate Bases ◽  
Sulfite Ions

The reactions of four 4-nitrobenzofurazans (4a–4d) substituted at the 7 position with (a) N-ethyl, (b) N-butyl, (c) piperidino, or (d) pyrrolidino groups have been examined with sulfite ions and with hydroxide ions in water–DMSO (80:20, v/v). Addition of sulfite at the 5 position gives σ adducts with equilibrium constants ca. 105 lower than that for the formation of the corresponding adduct from 4-nitrobenzofurazan. These reductions are attributed to the stabilization of the parent molecules 4a–4d by conjugative interaction between the 4 and 7 substituents. In alkaline solution, 4a and 4b yield the conjugate bases while 4c and 4d suffer nucleophilic substitution to give 7-hydroxy-4-nitrobenzofurazan. Reactivity here is relatively high because of the iminium ion character of the substrates. Key words: benzofurazans, σ adducts, nucleophilic reactivity, substitution.

β-Substitution de la méso-tétraphénylporphyrine de zinc par voie électrochimique

1991 ◽  
Vol 69 (7) ◽  
pp. 1161-1165 ◽  
Author(s):  
Alain Giraudeau ◽  
Lana El Kahef
Keyword(s):  
Carbon Atom ◽  
Nucleophilic Substitution ◽  
Key Words ◽  
Electrochemical Oxidation ◽  
Electrochemical Reactions

The electrochemical oxidation of the zinc tetraphenylporphyrin complex in a mixed acetonitrile–dichloroethane solution in the presence of nucleophiles (Py, 3-Pic, [Formula: see text], SCN−) leads to the formation of the corresponding monosubstituted metalloporphyrin. For each of these nucleophiles the substitution occurs at a pyrrole carbon atom (β-substitution). The electrochemical conditions of these substitutions are discussed and an overall reaction is proposed. Key words: porphyrins, electrochemical reactions, nucleophilic substitution.

Absolute gas-phase acidities of CH3NH2, C2H5NH2, (CH3)2 NH, and (CH3)3N

1976 ◽  
Vol 54 (10) ◽  
pp. 1624-1642 ◽  
Author(s):  
Gervase I. Mackay ◽  
Ronald S. Hemsworth ◽  
Diethard K. Bohme
Keyword(s):  
Equilibrium Constant ◽  
Gas Phase ◽  
Equilibrium Constants ◽  
Heats Of Formation ◽  
Molecular Orbital Calculations ◽  
Electron Affinities ◽  
Flowing Afterglow ◽  
Experimental Assessment ◽  
Gas Phase Acidity ◽  
Conjugate Bases

The flowing afterglow technique has been employed in measurements of the rate and equilibrium constants at 296 ± 2 K for reactions of the type[Formula: see text]and[Formula: see text]where R1 and R2 may be H, CH3, or C2H5. The equilibrium constant measurements provided absolute values for the intrinsic (gas-phase) acidities of the Brønsted acids CH3NH2, C2H5NH2, (CH3)2NH, and (CH3)3N, the heats of formation of their conjugate bases, and the electron affinities of the corresponding radicals R1R2N. Proton removal energies, ΔG0298/(kcal mol−1), were determined to be 395.7 ± 0.7 for [Formula: see text] 391.7 ± 0.7 for [Formula: see text] 389.2 ± 0.6 for [Formula: see text] and > 396 for [Formula: see text] Heats of formation, ΔH0f.,298, were determined to be 30.5 ± 1.5 for CH3NH−, 21.2 ± 1.5 for C2H5NH−, and 24.7 ± 1.4 for (CH3)2N−. Electron affinities (in kcal mol−1) were determined to be 13.1 ± 3.5 for CH3NH, 17 ± 4 for C2H5NH, and 14.3 ± 3.4 for (CH3)2N. These results quantify earlier conclusions regarding the intrinsic effects of substituents on the gas-phase acidity of amines and provide an experimental assessment of recent molecular orbital calculations of proton removal energies for alkylamines.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

Ligand scrambling reactions of cyano(thione)gold(I) complexes and determination of their equilibrium constants

2002 ◽  
Vol 80 (10) ◽  
pp. 1279-1284 ◽  
Author(s):  
Saeed Ahmad ◽  
Anvarhusein A Isab ◽  
Herman P Perzanowski
Keyword(s):  
Ionic Strength ◽  
Nmr Spectroscopy ◽  
Key Words ◽  
Equilibrium Constants ◽  
Solvent Polarity ◽  
Approach To Equilibrium ◽  
Initial Concentration ◽  
C Nmr

Ligand scrambling reactions in cyano(thione)gold(I) complexes ([>C=S-Au-CN]) to form [Au(>C=S)2]+ and [Au(CN)2]– species have been investigated for a series of thiones in DMSO using 13C and 15N NMR spectroscopy. Rapid approach to equilibrium occurred and resulted in distinct signals for the [>C=S-Au-CN] and [Au(CN)2]– complexes, both in 13C and 15N NMR. Equilibrium constants (Keq) were determined for scrambling of all the complexes by integrating the CN resonances in the 13C NMR recorded at 298 K. The influence of various factors (initial concentration, ionic strength, temperature, and solvent polarity) on the Keq value was examined for a representative complex (ImtAuCN (Imt = Imidazolidine-2-thione)).Key words: cyanogold(I) complexes, thiones, ligand scrambling, NMR, Keq.

Comparison of the nucleophilicities of alcohols and alkoxides

2005 ◽  
Vol 83 (9) ◽  
pp. 1554-1560 ◽  
Author(s):  
Thanh Binh Phan ◽  
Herbert Mayr
Keyword(s):  
Free Energy ◽  
Key Words ◽  
Rate Constants ◽  
Correlation Equation ◽  
Linear Free Energy Relationship ◽  
Hydroxide Solution ◽  
Linear Free Energy ◽  
S Parameters ◽  
Nucleophilic Reactivity ◽  
Kinetics Of

The kinetics of the reactions of benzhydrylium ions with some alcohols and alkoxides dissolved in the corresponding alcohols were photometrically investigated. Using the correlation equation log k (20 °C) = s(E + N), the N and s parameters of methoxide, ethoxide, n-propoxide, and isopropoxide in alcohol–acetonitrile (91:9, v/v) were determined. The cosolvent acetonitrile has only a little influence on the rate constants of the reactions of alcohols and alkoxides. The order of N values (OH– << MeO– < EtO– < n-PrO– < i-PrO–) shows that alkoxides differ only moderately in reactivity but are considerably more nucleophilic than hydroxide. As a consequence, the nucleophilic reactivity of a 0.5 mmol/L aqueous hydroxide solution increases by a factor of 13 when 10% (v/v) methanol is added. In 1–10 mmol/L alkoxide solutions in alcohols, weak electrophiles react considerably faster with alkoxides than with the corresponding alcohols. With increasing electrophilicity, the preference for alkoxides decreases, and electrophiles of –3 < E < 3 react with alkoxides (1–10 mmol/L) and alcohols with comparable rates. Stronger electrophiles will react with alcohols exclusively when alkoxides are present in concentrations ≤10 mmol/L. Key words: kinetics, alcohol, alkoxide, linear free energy relationship, nucleophilicity.<

scholarly journals 4,6-Dichloro-5-Nitrobenzofuroxan: Different Polymorphisms and DFT Investigation of Its Reactivity with Nucleophiles

2021 ◽  
Vol 22 (24) ◽  
pp. 13460
Author(s):  
Elena Chugunova ◽  
Nurgali Akylbekov ◽  
Alexey Dobrynin ◽  
Alexander Burilov ◽  
Carla Boga ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Nucleophilic Substitution ◽  
Nitro Group ◽  
Kinetic Data ◽  
Aromatic Nucleophilic Substitution ◽  
X Ray ◽  
Nucleophilic Reactivity ◽  
Amino Derivatives ◽  
Torsional Angles

This research focuses on the X-ray structure of 4,6-dichloro-5-nitrobenzofuroxan 1 and of some of its amino derivatives (4a, 4e, 4g, and 4l) and on DFT calculations concerning the nucleophilic reactivity of 1. We have found that by changing the solvent used for crystallization, it is possible to obtain 4,6-dichloro-5-nitrobenzofuroxan (1) in different polymorphic structures. Moreover, the different torsional angles observed for the nitro group in 1 and in its amino derivatives (4a, 4e, 4g, and 4l) are strictly dependent on the steric hindrance of the substituent at C-4. DFT calculations on the course of the nucleophilic substitution confirm the role of the condensed furoxan ring in altering the aromaticity of the carbocyclic frame, while chlorine atoms strongly influence the dihedral angle and the rotational barrier of the nitro group. These results corroborate previous observations based on experimental kinetic data and give a deep picture of the reaction with amines, which proceeds via a “non-aromatic” nucleophilic substitution.

The aldol condensation of acetone with acetophenone

1992 ◽  
Vol 70 (4) ◽  
pp. 1055-1068 ◽  
Author(s):  
J. Peter Guthrie ◽  
Xiao-Ping Wang
Keyword(s):  
Kinetic Model ◽  
Alkaline Solution ◽  
Aldol Condensation ◽  
Equilibrium Constants ◽  
Analytical Data ◽  
Initial Compound ◽  
Aqueous Alkaline Solution ◽  
First Order ◽  
Carbon Acid ◽  
Best Fit

The kinetics and equilibria involved in the aldol condensation of acetone, acting as carbon acid, and acetophenone have been studied in aqueous alkaline solution. The enone isolated is the E isomer. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for E-enone as initial compound) of: k12 = (5.55 ± 0.17) × 10−6 M−1 s−1, k21 = (8.00 ± 0.40) × 10−6 M−1 s−1, K21 = (1.44 ± 0.55) (ketol to E-enone), K24 = 0.160 ± 0.033 (ketol to Z-enone), K32 = (1.89 ± 0.26) × 10−3 M−1 (acetone plus acetophenone to ketol), k23 = 0.180 ± 0.005 M−1 s−1, k32 = (3.41 ± 0.49) × 10−4 M−2 s−1. There is an equilibration of the two enones in base that is faster than hydration to the ketol: k14 = (3.14 ± 0.84) × 10−5 M−1 s−1; k41 = (2.81 ± 0.61) × 10−4 M−1 s−1; K14 = 0.112 ± 0.019. To analyze the behavior of the enone:ketol equililbrium system in acid we simultaneously fitted analytical data for all three species (E-enone, Z-enone, and ketol) to a kinetic model, so that the rate constants were determined by the best fit to all of the data for an experiment.

2-Azabuta-1,3-diene-4-carbonitriles: stereoselective synthesis and nucleophilic substitution at the carbon–nitrogen double bond

1996 ◽  
Vol 74 (3) ◽  
pp. 287-294 ◽  
Author(s):  
Antonio Lorente ◽  
Marta Casillas ◽  
Pilar Gomez-Sal ◽  
Antonio Manzanero
Keyword(s):  
Double Bond ◽  
Nucleophilic Substitution ◽  
Key Words ◽  
Sodium Methoxide ◽  
Stereoselective Synthesis ◽  
X Ray Diffraction ◽  
Key Words 2 ◽  
X Ray ◽  
Nitrogen Double Bond

The synthesis of (E)-1-methoxy-2-azabuta-1,3-diene-4-carbonitriles was performed by methylation of N-alkenylamides 9 and 11. The Z isomers were obtained by treatment of (E)-1-methylthio-2-azabuta-1,3-diene-4,4-dicarbonitriles with sodium methoxide in methanol. We also describe the reactions of (E)-1-methylthio-2-azabuta-1,3-diene-4,4-dicarbonitriles with pyrrolidine, which afforded 1-(1-pyrrolidinyl) derivatives 20, 21, and 23. X-ray crystallographic analyses of 21 and 23 established the E stereochemistry of the C—N double bond. Key words: 2-azabuta-1,3-diene-4-carbonitriles: stereoselective synthesis, nucleophilic substitution and X-ray diffraction; N-alkenylamides: methylation.

The aldol condensation of acetophenone with acetone

1991 ◽  
Vol 69 (2) ◽  
pp. 339-344 ◽  
Author(s):  
J. Peter Guthrie ◽  
Xiao-Ping Wang
Keyword(s):  
Alkaline Solution ◽  
Aldol Condensation ◽  
Equilibrium Constants ◽  
Mesityl Oxide ◽  
Initial Compound ◽  
Aqueous Alkaline Solution ◽  
First Order ◽  
Related Series ◽  
Carbon Acid ◽  
Condensation Of Acetophenone

The kinetics and equilibria involved in the aldol condensation of acetophenone, acting as carbon acid, and acetone have been studied in aqueous alkaline solution. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for enone as initial compound) of: k12 = 3.3 × 10−4 M−1 s−1, k21 = 3.2 × 10−5 M−1 s−1K12 = 10.2, k23 = 8.0 × 10−2 M−1 s−1, k32 = 3.3 × 10−4 M−2 s−1, K32 = 4.1 × 10−3 M−1. The series methylbutenal, mesityl oxide, and 3-methyl-1-phenyl-2-buten-1-one can now be compared with regard to regularities and deviations from regularity. The related series cinnamaldehyde, benzalacetone, and chalcone also provides insights into the behaviour of this system. Key words: aldol, dehydration, equilibrium, acetophenone, acetone.

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