Application of 59Co NMR to the investigation of interactions between cobalt sepulchrate and various counterions

1991 ◽  
Vol 69 (3) ◽  
pp. 567-569 ◽  
Author(s):  
João Sotomayor ◽  
Helena Santos ◽  
Fernando Pina
Keyword(s):  
Quantum Yield ◽  
Association Constant ◽  
Chemical Shifts ◽  
Cobalt Complex ◽  
Ion Pairs ◽  
Formation Constants ◽  
Ion Pair ◽  
Association Constants ◽  
Quantum Yields ◽  
True Quantum

Association constants for the ion pairs formed between [Co(Sep)]3+ and the anions fluoride, chloride, bromide, iodide, perchlorate, and oxalate were obtained from the chemical shifts of the 59Co resonance that occur upon addition of such anions to solutions of the cobalt complex. The usefulness of 59Co NMR to obtain formation constants, in order to calculate the "true" quantum yields for the ion pairs, is discussed. Key words: association constant, cobalt sepulchrate, ion pair, 59Co NMR, quantum yield.

Octahedral cobalt(III) complexes in dipolar aprotic solvents. II. Association between cis- and trans-dichlorobisethylenediamine cobalt(III) cations,[Co en2 Cl2]+, and chloride and bromide ions in the solvents NN-dimethylformamide, dimethyl sulphoxide, and LVN-dimethylacetamide

1966 ◽  
Vol 19 (1) ◽  
pp. 43 ◽  
Author(s):  
WA Millen ◽  
DW Watts
Keyword(s):  
Spectrophotometric Method ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Dimethyl Sulphoxide ◽  
Aprotic Solvents ◽  
Ion Association Constants ◽  
Cis And Trans ◽  
Dipolar Aprotic Solvents

Ion association constants at 30� have been determined for the cis-[Co en, Cl2]+Cl- ion pair in NN-dimethylformamide (DMF), NN-dimethylacetamide (DMA), and at 20.0�, 25.0�, and 30.0� in dimethyl sulphoxide (DMSO), by a spectrophotometric method. Association constants for the cis-[Co en2 Cl2]+Br- and the trans- [Co en2 Cl2]+Cl- ion pairs have also been determined in DMF at 30�.

scholarly journals When spectroscopy fails: The measurement of ion pairing

2006 ◽  
Vol 78 (8) ◽  
pp. 1571-1586 ◽  
Author(s):  
Glenn Hefter
Keyword(s):  
Metal Ion ◽  
Chemical Speciation ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Spectroscopic Techniques ◽  
Association Equilibria ◽  
Solvent Molecules ◽  
Contact Ion Pairs

Spectroscopic techniques such as UV/vis, NMR, and Raman are powerful tools for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Specifically, spectroscopic measurements do not in general produce thermodynamically meaningful association constants for non-contact ion pairs, where the ions are separated by one or more solvent molecules. Such systems can only be properly quantified by techniques such as dielectric or ultrasonic relaxation, which can detect all ion-pair types (or equilibria), or by traditional thermodynamic methods, which detect the overall level of association. Various types of quantitative data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve solvent-separated ion pairs. The implications for ion association equilibria in general are briefly discussed.

The limiting conductivity of the borate ion and its ion-pair formation constants with sodium and potassium under hydrothermal conditions

2016 ◽  
Vol 18 (34) ◽  
pp. 24081-24094 ◽  
Author(s):  
H. Arcis ◽  
J. P. Ferguson ◽  
G. H. Zimmerman ◽  
P. R. Tremaine
Keyword(s):  
High Precision ◽  
Ac Conductivity ◽  
Formation Constants ◽  
Ion Pair ◽  
Pair Formation ◽  
Association Constants ◽  
Potassium Ions ◽  
Hydrothermal Conditions ◽  
Sodium And Potassium ◽  
Limiting Conductivity

The limiting conductivity of borate and its association constants with sodium and potassium ions have been determined from T = 298 K to T = 623 K at p = 20 MPa, using a high-precision flow AC conductivity instrument.

Effects of substituents on ion-association properties. II. 1H N.M.R. studies of substituted pyridinium and tetraalkylammonium Bis(4-methylbenzene-1,2-dithiolato)cobaltate(III) in non-aqueous solvents

1981 ◽  
Vol 34 (11) ◽  
pp. 2321 ◽  
Author(s):  
N Tsao ◽  
Y Lim
Keyword(s):  
Dielectric Constant ◽  
Complex Anion ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Ionic Clusters ◽  
Isotropic Shift ◽  
Large Size ◽  
Pyridinium Cations

A series of nine compounds containing quaternary ammonium and substituted pyridinium cations and the bis(4-methylbenzene-1,2-dithiolato)cobaltate(III) complex anion have been prepared andtheir ion-pair properties studied by lH n.m.r. spectroscopy. Their concentration association constants in nitrobenzene at 307 K range from 9 to 20. In the pyridinium series of ion pairs, it is concludedfrom the measured isotropic shift ratios that methyl substituents at the meta and para positions favour a geometry where the anion is tilted towards the ring of the cation but the ortho substituents push the anion away from the ring. In the methyltrioctylammonium ion pair, there is linear correlation between the observed isotropic shift of the N-methyl or the N-methylene protons and the dielectric constant of the solvents (E) from 4.56 to 12.3 for the 0.06, 0.09 and 0.12 M solutions. Its implication is discussed in terms of the formation of the ionic clusters of sufficiently large size.

Influence of cyclodextrins on the photo-Fries rearrangement of acetanilide

1988 ◽  
Vol 66 (11) ◽  
pp. 2794-2798 ◽  
Author(s):  
Mirtha Nassetta ◽  
Rita H. De Rossi ◽  
Juan J. Cosa
Keyword(s):  
Quantum Yield ◽  
Association Constants ◽  
Para Position ◽  
Quantum Yields ◽  
Fries Rearrangement

The effect of α-, β-, and -γ-cyclodextrins on the quantum yield for the formation of o- and p-aminoacetophenone from the photolysis of acetanilide at 254 nm was determined. There is an increase in the ratio of o/p products when cyclodextrins are added and the total quantum yield is about the same as in water in the presence of γ-CD, higher with β-CD, and lower with α-CD. The association constants between acetanilide and CD were determined and the values are 22.7 M−1 and 30.7 M−1 for α- and β-CD respectively. The quantum yields for the formation of o- and p-aminoacetophenone were measured. The rearrangement occurs in water and in the included acetanilide. The quantum yields for the formation of o-aminoacetophenone and p-aminoacetophenone from the included substrate could be calculated for α- and β-cyclodextrin. Comparing these values with those obtained in water, it is concluded that there is some steric inhibition for rearrangement at the para position when α-cyclodextrin is the host, whereas with β-cyclodextrin the less polar microsolvent effect is responsible for the increase in the total quantum yield relative to water.

Stereospecific 1,3-H Transfer of Indenols Proceeds via Persistent Ion-Pairs Anchored By NH···Pi Interactions

2018 ◽  
Author(s):  
David Ascough ◽  
Fernanda Duarte ◽  
Robert Paton
Keyword(s):  
Computational Analysis ◽  
Ion Pairs ◽  
Ion Pair ◽  
Hydrogen Atom Transfer ◽  
Polar Solvents ◽  
Chirality Transfer ◽  
Activation Barriers ◽  
Sense And Avoid ◽  
Phase Dynamics ◽  
Pi Interactions

The base-catalyzed rearrangement of arylindenols is a rare example of a suprafacial [1,3]-hydrogen atom transfer. The mechanism has been proposed to proceed via sequential [1,5]-sigmatropic shifts, which occur in a selective sense and avoid an achiral intermediate. A computational analysis using quantum chemistry casts serious doubt on these suggestions: these pathways have enormous activation barriers and in constrast to what is observed experimentally, they overwhelmingly favor a racemic product. Instead we propose that a suprafacial [1,3]-prototopic shift occurs in a two-step deprotonation/reprotonation sequence. This mechanism is favored by 15 kcal mol<sup>-1</sup> over that previously proposed. Most importantly, this is also consistent with stereospecificity since reprotonation occurs rapidly on the same p-face. We have used explicitly-solvated molecular dynamics studies to study the persistence and condensed-phase dynamics of the intermediate ion-pair formed in this reaction. Chirality transfer is the result of a particularly resilient contact ion-pair, held together by electrostatic attraction and a critical NH···p interaction which ensures that this species has an appreciable lifetime even in polar solvents such as DMSO and MeOH.

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