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A kinetic and product investigation of stilbene bromination over a very wide reactivity range indicates that bromine bridging is not the only stereochemistry-determining factor. The stereochemical outcome of bromination is controlled by its association with its nucleophilic partners and its lifetime, as well as by the bridged or unbridged structure of the cationic intermediate. Lifetimes of the ionic intermediates of nucleophilic substitutions influence the pathway followed under specific reaction conditions.

The bromination of cis- and trans-4,4'-dimethoxystibenes with Br2 and tetrabutylammonium tribromide (TBAT) led to the formation of bromocarbenium bromide. Analysis of the activation parameters of 1,2-dichloromethane and chloroform during the formation of bromocarbenium bromide indicated the nucleophilic role of the Br- ion in the TBAT-mediated bromination process. Furthermore, the ionization of the pi-complex to a bromocarbenium-bromide ion pair competed with the formation of a bromocarbenium tribromide ion pair.

The apparent activation energy of the bromination of (E)-2,2,3,4,5,5- hexamethylhex-3-ene (HMH, 2) in 1,2-dichloroethane (DCE) is negative and that of tetraisobutylethylene (TIBE) in acetic acid is slightly positive, and it incorporates the formation of a 2-Br2 charge transfer complex in the first step. In DCE, a second complex containing two Br2 molecules is formed by exothermic affiliation and ionizes to a bromonium ion paired to a tribromide anion stabilized by charge delocalization.

1,2-dichloroethane was analyzed at 5, 25 and 50 degrees Celsius to determine the bromination of 5H-dibenz(b,f)azepine-5-carbonyl chloride. Variation in rate law from overall third order to overall fourth order accompany enhancement in Br2 concentrations and reduction in temperature. The breakdown of the ionic intermediate to 2 is the rate determining process.

The effect of bromide-tribromide-pentabromide equilibrium on stilbene bromination was investigated through the computation of electronic spectra and formation constant of the product from the spectrophotometric data. Results show that the formation of the ionic intermediate can be reversible inspite of the presence of bromide counteranions at low concentrations. It was likewise demonstrated that the predominant products of the reaction was affected by bromine equilibrium.

Excess entropy scaling relationships for diffusivity of ions in room-temperature ionic liquids are tested using molecular dynamics simulations for a model ionic liquid, dimethyl imidazolium chloride. The thermodynamic excess entropy of the single ions (estimated from the ion-ion pair correlation functions) is shown to be very strongly correlated with the diffusivity. An essential feature of these systems, the fact that the heavier and larger cation has a greater diffusivity with respect to the anion, is correctly captured by the excess entropy calculations, which estimates the diffusivity ratio between the two ions with noticeable precision. [ABSTRACT FROM AUTHOR]

In this work, we study the solvation thermodynamics and other solvation properties of small ions in two room-temperature ionic liquids, dimethyl imidazolium hexafluorophosphate [mmim] [pf6] and dimethyl imidazolium chloride [mmim][cl] with the reference interaction site model (RISM). The nature of the charge affects several aspects of solvation, from electrostriction to the mutual disposition of cations around the solute; nevertheless, the long-range screening behavior of the liquid appears to be insensitive to both charge and dimensions of the solute. The ion solvation is energy driven, as expected for the nature of the solvent, and displays a marked asymmetry between cation and anion solvation chemical potential. Such asymmetry is dependent, even qualitatively, on the ionic liquid chosen as solvent. Partial molar volumes of ions in solution are found to follow the nature of ion-solvent interaction. [ABSTRACT FROM AUTHOR]

The equilibrium constants for ion pair formation of pyridines are analyzed by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water, whereas pyridine basicity is less sensitive to the substituent effect in ionic liquids than in water.

Hammett correlations were used to examine the reaction mechanism and the effect of ionic liquids (ILs) on the Menschukin reaction between N-methylimidazole and benzyl halides. The hypothesis based on the influence of dynamic heterogeneity in ionic media on the time scale of the lifetime of a transition state suggested that inside the IL the Menschutkin reaction of benzyl chloride with N-methylimidazole could follow different reaction pathways.

The solvent effect on the rate of tautomerization of 2-nitrocyclohexanone in several organic solvents has depended on the permittivity of the solvent, but a different behavior is seen on some ionic liquids (ILs). The kinetic results are discussed in terms of the Bronsted equation, which have shown that on passing from molecular solvents to ILs the transition state structure of the enolization reaction has become markedly enolate-like.

A tetra-azido calix[4]arene derivative has reacted with ethynyl tetra-O-benzyl-C-galactoside in the presence of CuI and i-[Pr.sub.2]EtN in three different ionic liquids. The reactions are performed by thermal and microwave dielectric heating and the click CuAAC in ionic liquids is a complementary green method to that using water as a solvent.

The thermodynamic study of the copper(I)-catalyzed azide-alkyne click reaction in ionic liquids (ILs) is reported. The reaction involves cycloaddtion of a sugar azide with sugar acetylene in presence of 10 ILs as well as in standard molecular solvents (toluene and DMF) to yield 1,4-disubstituted triazole-linked C-disaccharide.