N-Methylpicramide–methoxide ion interactions: proton abstraction versus σ-complex formation

1980 ◽  
Vol 58 (16) ◽  
pp. 1615-1620 ◽  
Author(s):  
Erwin Buncel ◽  
Masashi Hamaguchi ◽  
Albert R. Norris
Keyword(s):  
Complex Formation ◽  
Hydrogen Ion ◽  
Proton Abstraction ◽  
Ring Carbon ◽  
Bearing Ring ◽  
Ion Interactions ◽  
Methoxide Ion ◽  
First Time ◽  
Conjugate Base ◽  
Sole Product

The interactions of N-methylpicramide (NMP) with methoxide ion in dimethylsulfoxide–methanol media and with 1,4-diazabicyclooctane in dimethylsulfoxide have been investigated spectrophotometrically at 25.0 °C. Dimethylsulfoxide has been found to stabilize the conjugate base of NMP, formed via loss of hydrogen ion from the methylamino group, with respect to the anionic σ-complex generated via addition of methoxide ion to a ring carbon position. As a result, methanol–dimethylsulfoxide solutions rich in dimethylsulfoxide (i.e., 95/5, v/v, DMSO/MeOH) contain the conjugate base of NMP as the sole product of the 1:1 interaction of NMP and methoxide ion. At mole ratios of methoxide ion to NMP > 1 a second interaction results, yielding a dianion formed via addition of methoxide ion to one of the H-bearing ring carbon atoms of the conjugate base. Values of absorption maxima and molar absorptivities at the absorption maxima for the conjugate base of NMP and the dianion are reported here for the first time.

N,N-Dimethylpicramide–methoxide ion interactions: 1:1 and 2:1 σ-complex formation

1980 ◽  
Vol 58 (16) ◽  
pp. 1609-1614 ◽  
Author(s):  
Erwin Buncel ◽  
Masashi Hamaguchi ◽  
Albert R. Norris
Keyword(s):  
Complex Formation ◽  
Reaction Conditions ◽  
Ion Interactions ◽  
Methanol Solutions ◽  
Methoxide Ion ◽  
First Time

The interactions of N,N-dimethylpicramide (DMP) with methoxide ion in dimethylsulfoxide–methanol media have been investigated spectrophotometrically at 25.0 °C. Both the 1:1 and 2:1 σ-complexes of DMP and methoxide ion have been observed under the various reaction conditions employed. However, dimethylsulfoxide has been found to preferentially stabilize the 1:1 σ-complex relative to the 2:1 σ-complex. As a consequence, at low base concentrations in dimethylsulfoxide–methanol solutions rich in dimethylsulfoxide (i.e. 95/5, v/v, DMSO/MeOH), the 1:1 σ-complex can be formed in the absence of any 2:1 σ-complex. This observation has been used to obtain, for the first time, values of the absorption maxima and molar absorptivities at the absorption maxima of both the 1:1 and 2:1 σ-complexes.

N-Picrylethylenediamine – methoxide ion interactions: N-deprotonation and σ-complex formation reactions

1981 ◽  
Vol 59 (5) ◽  
pp. 795-801 ◽  
Author(s):  
Erwin Buncel ◽  
Masashi Hamaguchi ◽  
Albert R. Norris
Keyword(s):  
Carbon Atom ◽  
Dimethyl Sulfoxide ◽  
Solvent Mixtures ◽  
Absorption Properties ◽  
Visible Absorption ◽  
Ring Carbon ◽  
Ion Interactions ◽  
Uv Visible ◽  
Methoxide Ion ◽  
Ring Carbon Atom

The interactions of N-picrylethylenediamine as the HCl salt (PED) with methoxide ion in dimethyl sulfoxide – methanol (DMSO/MeOH) media and with 1,4-diazabicyclooctane in dimethyl sulfoxide have been investigated spectrophotometrically at 25.0 °C. Evidence is presented to show that, in solvent mixtures rich in dimethyl sulfoxide (e.g. 95/5, V/V, DMSO/MeOH), deprotonation reactions at the nitrogen centres on the ethylenediamine occur in preference to reactions in which σ-complexes are formed via addition of CH3O− to one or more ring carbon atoms. The initial 1:1 interaction of CH3O− and PED results in the rapid, reversible deprotonation of the NH centre while the 2:1 interaction is associated with rapid, reversible abstraction of H+ from the NH3+ centre. At mole ratios of CH3O− to PED > 3 a σ-complex is formed as a result of the addition of CH3O− ion to a C-3 ring carbon atom of the di-deprotonated PED. The uv–visible absorption properties of these various species are reported and compared to the properties of corresponding species formed in related systems.

Formation and Trapping of the Thermodynamically Unfavoured Inverted-Hemicucurbit[6]uril

2019 ◽  
Author(s):  
Elena Prigorchenko ◽  
Sandra Kaabel ◽  
Triin Narva ◽  
Anastassia Baškir ◽  
Maria Fomitšenko ◽  
...  
Keyword(s):  
Complex Formation ◽  
Combinatorial Chemistry ◽  
Trifluoroacetic Acid ◽  
Chloride Anion ◽  
Binding Affinities ◽  
Dynamic Covalent Chemistry ◽  
Reaction Selectivity ◽  
Low Concentration ◽  
Dynamic Combinatorial Chemistry ◽  
First Time

Amplification of a thermodynamically unfavoured macrocyclic product through the directed shift of the equilibrium between dynamic covalent chemistry library members is difficult to achieve. We show for the first time that during condensation of formaldehyde and <i>cis</i>-<i>N,N'</i>-cyclohexa-1,2-diylurea formation of <i>inverted-cis</i>-cyclohexanohemicucurbit[6]uril (<i>i-cis</i>-cycHC[6]) can be induced at the expense of thermodynamically favoured <i>cis</i>-cyclohexanohemicucurbit[6]uril (<i>cis</i>-cycHC[6]). The formation of <i>i-cis-</i>cycHC[6] is enhanced in low concentration of the templating chloride anion and suppressed in excess of this template. We found that reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous removal of the formed cycHC[6] macrocycles from the equilibrating solution by precipitation. Notably, the <i>i-cis</i>-cycHC[6] was isolated with 33% yield. Different binding affinities of three diastereomeric <i>i-cis</i>-, <i>cis</i>-cycHC[6] and their chiral isomer (<i>R,R</i>)-cycHC[6] for trifluoroacetic acid demonstrate the influence of macrocycle geometry on complex formation.

Mechanistic Information from the Effect of Pressure on the Kinetics of Hydrolysis of Iodopentaaquochromium(III) Ion

1975 ◽  
Vol 53 (24) ◽  
pp. 3697-3701 ◽  
Author(s):  
Milton Cornelius Weekes ◽  
Thomas Wilson Swaddle
Keyword(s):  
Ionic Strength ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Aqueous Hclo ◽  
Conjugate Base

The rate of hydrolysis of iodopentaaquochromium(III) ion has been measured as a function of pressure (0.1 to 250 MPa) and hydrogen ion concentration (0.1 to 1.0 mol kg−1) at 298.2 K and ionic strength 1.0 mol kg−1 (aqueous HClO4–LiClO4). The volumes of activation for the acid independent and inversely acid dependent hydrolysis pathways are −5.4 ± 0.5 and −1.6 ± 0.3 cm3 mol−1 respectively, and are not detectably pressure-dependent. Consideration of these values, together with the molar volume change of −3.3 ± 0.3 cm3 mol−1 determined dilatometrically for the completed hydrolysis reaction, indicates that the mechanisms of the two pathways are associative interchange (Ia) and dissociative conjugate base (Dcb) respectively.

scholarly journals KINETIC STUDY ON ANIONIC σ-COMPLEX FORMATION BETWEEN 2,4,6-TRINITROANISOLE AND METHOXIDE ION BY HIGH PRESSURE STOPPED-FLOW METHOD

1979 ◽  
Vol 8 (6) ◽  
pp. 671-674 ◽  
Author(s):  
Noboru Takisawa ◽  
Muneo Sasaki ◽  
Fujitsugu Amita ◽  
Jiro Osugi
Keyword(s):  
High Pressure ◽  
Complex Formation ◽  
Kinetic Study ◽  
Stopped Flow ◽  
Flow Method ◽  
Methoxide Ion

Mechanism of Sulfonation of 4-Hydroxyazobenzene

1971 ◽  
Vol 49 (1) ◽  
pp. 152-156 ◽  
Author(s):  
E. Buncel ◽  
W. M. J. Strachan ◽  
H. Cerfontain
Keyword(s):  
Sulfuric Acid ◽  
Complex Formation ◽  
Sulfonic Acid ◽  
Acid Media ◽  
Proton Abstraction ◽  
Rate Determining Step ◽  
Concentrated Sulfuric Acid

The mechanism of sulfonation of 4-hydroxyazobenzene and of 4-hydroxyazobenzene-4′-sulfonic acid in concentrated sulfuric acid media is examined through rate correlations and comparison is drawn with sulfonation of alkyl- and halogenobenzenes by means of [Formula: see text] plots. It is concluded that several mechanisms are operative in the hydroxyazobenzene system and that the curvature of the plot is the result of a change in rate-determining step from σ-complex formation to proton abstraction.

scholarly journals Spectrophotometric investigations of the reaction between gold(III) and potassium iodide

2000 ◽  
Vol 65 (5-6) ◽  
pp. 345-352 ◽  
Author(s):  
Vesna Vasic ◽  
Suzana Premovic ◽  
Mira Cakar ◽  
Bojan Radak ◽  
Gordana Milovanovic
Keyword(s):  
Complex Formation ◽  
Aqueous Solutions ◽  
Absorption Spectra ◽  
Potassium Iodide ◽  
Equilibrium Constants ◽  
Hydrogen Ion

The equilibria of the complex formation between AuCl4-n(OH)n - and I- was studied spectrophotometrically in aqueous solutions containing KI:Au(III)?2 in the acidity range from 1 M HCl to pH 7 at 25?C. From the hydrogen ion and Cl-ion dependence of the absorption spectra, it was found that AuCl2I2 - and Au(OH)2I2 - complexes were formed. The equilibrium constants of complex formation were determined.

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