An Electron Spin Resonance Investigation of the Mechanism of the Intramolecular Cation Migration of Alkali Metal Semiquinone Ion-pairs

1971 ◽  
Vol 49 (14) ◽  
pp. 2412-2417 ◽  
Author(s):  
T. E. Gough ◽  
P. R. Hindle
Keyword(s):  
Exchange Process ◽  
Ion Pairs ◽  
Ion Pair ◽  
Kinetic Characteristics ◽  
Exchange Reactions ◽  
Ionic Interaction ◽  
Free Energy Of Activation ◽  
Enthalpy Of Activation ◽  
Cation Migration ◽  
Spin Resonance

A systematic survey of the kinetic characteristics of the intramolecular cation exchange reactions of semiquinone ion-pairs is described. A linear correlation exists between the free energy of activation for the exchange and the strength of the ionic interaction within the ion pair; however, this correlation does not extend to the enthalpy of activation. The significance of the kinetic parameters is discussed in terms of the role solvation plays in determining the course of the exchange process.

Kinetics and mechanism of substitution reactions of (dimethylsulfoxide)pentaamminecobalt(III) ion in dimethylsulfoxide solvent: complications due to redox and conjugate base processes

1976 ◽  
Vol 54 (23) ◽  
pp. 3685-3692 ◽  
Author(s):  
S. T. Danny Lo ◽  
Evelyn M. Oudeman ◽  
Jean C. Hansen ◽  
Thomas W. Swaddle
Keyword(s):  
Ion Pairs ◽  
Activation Parameters ◽  
Rate Coefficients ◽  
Solvent Exchange ◽  
Exchange Reactions ◽  
Substitution Reactions ◽  
Enthalpy Of Activation ◽  
A Minor ◽  
Conjugate Base ◽  
Anation Rate

Simple anation and solvent exchange reactions of Co(NH3)5DMSO3+ in DMSO are accompanied by reactions in which the conjugate base of this complex undergoes either internal redox to cobalt(II) or relatively rapid substitution. These conjugate base reactions are eliminated by addition of H+, although a minor redox pathway persists within ion pairs of Co(NH3)5DMSO3+ with chloride or bromide. The latter pathway is evidently not mechanistically related to the solvent exchange or anation reactions, which proceed by dissociative interchange (Id) according to the activation parameters (volume of activation = +10 cm3 mol−1 for DMSO exchange; enthalpy of activation = 123, 121, and ∼126 kJ mol−1 for DMSO exchange and bromide and chloride anation respectively). Enthalpies of activation for solvent exchange and for the limiting anation rate are shown to be better criteria of mechanism than the corresponding rate coefficients.

scholarly journals Ion-pair Reactivity in Isotopic Exchange Reactions. III. Ion-pairs of Tetraalkyl Ammonium Halides.

1970 ◽  
Vol 24 ◽  
pp. 2826-2838 ◽  
Author(s):  
Per Beronius ◽  
Ann-Margret Nilsson ◽  
Göran Wikander ◽  
P. Karrer ◽  
Akira Shimizu
Keyword(s):  
Isotopic Exchange ◽  
Ion Pairs ◽  
Ion Pair ◽  
Exchange Reactions ◽  
Ammonium Halides

Electron Spin Resonance of Manganese Nitrate in Diethylacetamide-Water Solution

1981 ◽  
Vol 36 (7) ◽  
pp. 751-758
Author(s):  
V. Kleinmann ◽  
M. Stockhausen
Keyword(s):  
Room Temperature ◽  
Water Solution ◽  
Ion Pairs ◽  
Chemical Species ◽  
Ionic Species ◽  
Esr Spectra ◽  
Ion Pair ◽  
Small Water ◽  
Spin Resonance ◽  
Solvated Ions

Abstract le c tro n S p in R e s o n a n c e o f M a n g a n e se N i t r a t e in D ie th y la c e ta m id e -W a te r S o lu tio n At small water concentrations, ESR spectra at room temperature exhibit distinguishable con­ tributions which are ascribed to the following ionic species: (I) a small fraction of residual manga­ nese ions with mixed amide-water solvation, (II) amide solvated ions (having altered hyperfine splitting and gr-factor due to nitrate in an outer coordination sphere, so that they may be con­ sidered loose ion pairs), (III) tight ion pair species. Presumably, (II) and (III) are not well defined "chemical" species but constituents of fluctuating aggregations.

An electron spin resonance study of the mechanism of intermolecular cation exchange reactions

1970 ◽  
Vol 48 (24) ◽  
pp. 3959-3960 ◽  
Author(s):  
T. E. Gough ◽  
P. R. Hindle
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Ion Pairs ◽  
Electron Spin Resonance Study ◽  
Resonance Spectroscopy ◽  
Exchange Reactions ◽  
Spin Resonance ◽  
Triple Ion Formation ◽  
Triple Ion ◽  
Spin Resonance Study

A survey of the effects, as detected by electron spin resonance spectroscopy, of adding NaX (X− = Ph4B−, ClO4−, I−) to sodium-semiquinone ion pairs is given. When X− = Ph4B− triple ion formation was observed, but when X− = ClO4− or I− intermolecular cation scrambling occurred. It is postulated that such scrambling reactions proceed via the triple ion.

Ion pairs and heat capacity of activation for 2,2-disubstituted cyclopropyl bromides

1976 ◽  
Vol 54 (8) ◽  
pp. 1246-1252 ◽  
Author(s):  
Surendra Singh ◽  
Ross Elmore Robertson
Keyword(s):  
Heat Capacity ◽  
Transition State ◽  
Relative Rate ◽  
Ion Pairs ◽  
Water Structure ◽  
Ion Pair ◽  
External Effects ◽  
Enthalpy Of Activation ◽  
Rate Ratios ◽  
Hydrolysis Of

The temperature dependence of the rates of hydrolysis of 2,2-dimethylcyclopropyl bromide, 2,2-cis-vinyl-trans-methylcyclopropyl bromide and 2,2-cis-methyl-trans-vinylcyclopropyl bromide have been determined in water. The temperature coefficient of the enthalpy of activation (ΔCp≠) for these compounds was determined to be −52, −27 and −37 cal deg−1 mol−1 respectively. The relative rate ratios for hydrolysis of the 2,2-methylvinylcyclopropyl bromides with respect to the appropriate 2-vinylcyclopropyl bromide isomer indicate a considerable progress towards allyl cations at the transition state in contrast to the indications of the ΔCp≠ values.The ΔCp≠ term for such reactions in water depends to an important degree on the external effects of charge development on water structure but is insensitive to internal electrostatic effects. In the three examples of ΔCp≠ reported in this study, all tend to show small external effects in spite of evidence which might suggest larger. The differences in ΔCp≠ are attributed to the particular shape and charge distribution of the quasi-ion pair.

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.

scholarly journals Tripodal, Squaramide-Based Ion Pair Receptor for Effective Extraction of Sulfate Salt

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2751
Author(s):  
Damian Jagleniec ◽  
Marcin Wilczek ◽  
Jan Romański
Keyword(s):  
Ion Pairs ◽  
Binding Mode ◽  
Selective Extraction ◽  
Ion Pair ◽  
Hofmeister Series ◽  
Sulfate Salt ◽  
Lower Affinity ◽  
High Affinity ◽  
Binding Domains ◽  
Hydrated Sulfate

Combining three features—the high affinity of squaramides toward anions, cooperation in ion pair binding and preorganization of the binding domains in the tripodal platform—led to the effective receptor 2. The lack of at least one of these key elements in the structures of reference receptors 3 and 4 caused a lower affinity towards ion pairs. Receptor 2 was found to form an intramolecular network in wet chloroform, which changed into inorganic–organic associates after contact with ions and allowed salts to be extracted from an aqueous to an organic phase. The disparity in the binding mode of 2 with sulfates and with other monovalent anions led to the selective extraction of extremely hydrated sulfate anions in the presence of more lipophilic salts, thus overcoming the Hofmeister series.

Catalytic deuterium exchange reactions with organics. XXIV. Electron spin resonance studies of adsorption on platinum oxide

1966 ◽  
Vol 19 (4) ◽  
pp. 529 ◽  
Author(s):  
IT Ernst ◽  
JL Garnett ◽  
WA Sollich-Baumgartner
Keyword(s):  
Transition Metal Oxides ◽  
Hydrogen Exchange ◽  
Platinum Oxide ◽  
Active Species ◽  
Paramagnetic Species ◽  
Charge Transfer Complexes ◽  
Severe Reaction ◽  
Exchange Reactions ◽  
Spin Resonance ◽  
Solid Liquid

The formation of paramagnetic species on catalyst surfaces at room temperature through the interaction of polynuclear aromatics in solid, liquid, or solute form with hydrated platinum oxide (PtO2,2H2O) is reported. The results are attributed to the formation of charge-transfer complexes, where the transferred electrons couple weakly, forming essentially a "diradicaloid" complex with a low-lying, thermally populated, triplet state. The effect of solvent, particle size, oxygen, water of crystallization, and temperature on the generation and stability of these e.s.r. active species has been investigated. The possible importance of these paramagnetic species in catalytic self-activation and hydrogen exchange reactions has been discussed. The following Group VIII transition metal oxides gave no e.s.r. spectra under relatively severe reaction conditions such as 1 hr at 120�: PdO; Ru02,2H20; RuO2; Rh2O3; IrO2,2H2O; ReO2; and NiO.

Kinetics of Ion-Pair Effect of Aquation of Bromopentaammine Cobalt(III) Complex in Different Dicarboxylate Media

2011 ◽  
Vol 324 ◽  
pp. 166-169 ◽  
Author(s):  
Farah Zeitouni ◽  
Gehan El-Subruiti ◽  
Ghassan Younes ◽  
Mohammad Amira
Keyword(s):  
Free Energy ◽  
Solvent Effect ◽  
Compensation Effect ◽  
Ion Pairing ◽  
Reaction Rates ◽  
Ion Pair ◽  
Free Energy Of Activation ◽  
Different Types ◽  
Different Temperatures ◽  
Kinetics Of

The rate of aquation of bromopentaammine cobalt(III) ion in the presence of different types of dicarboxylate solutions containing tert-butanol (40% V/V) have been measured spectrophotometrically at different temperatures (30-600°C) in the light of the effects of ion-pairing on reaction rates and mechanism. The thermodynamic and extrathermodynamic parameters of activation have been calculated and discussed in terms of solvent effect on the ion-pair aquation reaction. The free energy of activation ∆Gip* is more or less linearly varied among the studied dicarboxylate ion-pairing ligands indicating the presence of compensation effect between ∆Hip* and ∆Sip*. Comparing the kip values with respect of different buffers at 40% of ter-butanol is introduced.

Ion pair binding by an l-tyrosine-based polymerizable molecular receptor

2015 ◽  
Vol 39 (8) ◽  
pp. 6216-6222 ◽  
Author(s):  
Szymon Zdanowski ◽  
Jan Romański
Keyword(s):  
Ion Pairs ◽  
Functional Polymers ◽  
Ion Pair

A polymerizable molecular receptor able to bind ion pairs and new functional polymers containing the receptor units were synthesized and characterized.

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