Host-guest interactions. I. Volumes of the sucrose +β-cyclodextrin+water ternary systems at 25°C

Densities of sucrose+-cyclodextrin+water (SUC+CYC+W) ternary systems were measured at 25°C and mean apparent molar volumes of SUC+CYC (V_,m) in water in each composite mixture have been evaluated. Apparent molar volumes of SUC (V_,suc) have also been computed from the volume data of each ternary composite mixture. Variation of V_,m and V_,suc with respect to the total molality m_t of SUC+CYC and to that of SUC m_suc show the formation of inclusion complexes between SUC and CYC molecules with 12 and 11 stochiometries in composite mixtures of mole ratios 0.588 and 1.12 respectively.     

Rotational dependence of the proton-transfer reaction HBr+ + CO2 → HOCO+ + Br. II. Comparison of HBr+ (2Π(3/2)) and HBr+ (2Π(1/2))

The effects of reactant ion rotational excitation on the exothermic proton-transfer reactions of HBr(+)((2)Π(1/2)) and DBr(+)((2)Π(1/2)), respectively, with CO(2) were studied in a guided ion beam apparatus. Cross sections are presented for collision energies in the center of mass system E(c.m.) in the range of 0.23 to 1.90 eV. The HBr(+)/DBr(+) ions were prepared in a state-selective manner by resonance enhanced multiphoton ionization. The mean rotational energy was varied from 3.4 to 46.8 meV for HBr(+)((2)Π(1/2)) and from 1.8 to 40.9 meV for DBr(+)((2)Π(1/2)). Both reactions studied are inhibited by collision energy, as expected for exothermic reactions. For all collision energies considered, the cross section decreases with increasing rotational energy of the ion, but the degree of the rotational dependence differs depending on the collision energy. For E(c.m.) = 0.31 eV, the cross sections of the deuteron transfer are significantly larger than those of the proton transfer. For higher E(c.m.) they differ very little. The current results for the exothermic proton transfer are systematically compared to previously published data for the endothermic proton transfer starting from HBr(+)((2)Π(3/2)) [L. Paetow et al., J. Chem. Phys. 132, 174305 (2010)]. Additional new data regarding the latter reaction are presented to further confirm the conclusions. The dependences on rotational excitation found cannot be explained by the corresponding change in the total energy of the system. For both the endothermic and the exothermic reaction, the cross section is maximized for the smallest rotational energy, at least well above the threshold.     

Manifestation of macroscopic correlations in elementary reaction kinetics. II. Irreversible reaction A+B→C

The applicability of the Encounter Theory (ET) (the prototype of the Collision Theory) concepts for widely occurring diffusion assisted irreversible bulk reaction A+B→C (for example, radical reaction) in dilute solutions with arbitrary ratio of initial concentrations of reactants has been treated theoretically with modern many-particle method for the derivation of non-Markovian binary kinetic equations. The method shows that, just as in the reaction A+A→C considered earlier, the agreement with the Encounter Theory is observed when the familiar Integral Encounter Theory is used which is just a step in the derivation of kinetic equations in the framework of the method employed. It allows for two-particle correlations only, and fails to consider the correlation of reactant simultaneously with a partner and with a reactant in the bulk. However, the next step leading to the Modified Encounter Theory under reduction of equations to a regular form both extends the time applicability interval of ET homogeneous rate equation (as for reactions proceeding in excess of one of the reactants), and yields the inhomogeneous equation of the Generalized Encounter Theory (GET) that reveals macroscopic correlations induced by the encounters in a reservoir of free walks in full agreement with physical considerations. This means that the encounters of reactants in solution are correlated at rather large time interval of the reaction course. However, unlike the reaction A+A→C of identical reactants, the reaction A+B→C accumulation of the above macroscopic correlations (even with the initial concentrations of reactants being equal) proceeds much slower. Another distinction is that for the reaction A+A→C the long-term behavior of ET and GET kinetics is the same, while in the reaction A+B→C these kinetics behave differently. It is of interest that just taking account of the above macroscopic correlations in the reaction A+B→C (in GET) results in the universal character of the long-term behavior of the kinetics for the case of equal initial concentrations of reactants and that where one of the reactants is in excess. This is more natural from the point of view of the reaction course on the encounters of reactants in solutions.     

Activity Coefficients of HCl + GdCl3 + H2O System from 5 to 55°C. Application of Pitzer Formalism

The emf of the cell

Intramolecular [2 + 2] photocycloaddition. 2. Mechanism of intramolecular photocyclization of α,ω-bis(p-vinylphenyl)alkanes

From the photophysical measurements of the title reaction, the formation of cyclophanes is concluded to be facilitated by high microscopic concentration of styrene moieties and depressed by strain loaded at the transition state.     

Structural and spectral consequences of ion pairing II. a theoretical study of CIO−3Li+ and ClO−3Na+

The structure of ClO⁻₃M⁺ ion pairs (M = Li, Na) has been examined with the aid of ab initio molecular orbital calculations. The calculations support recent experimental findings that ClO⁻₃ M ion paris have C_3v rather than C_s configurations. Results from these studies also show that the metal cation prefers to coordinate at the base of the chlorate anion pyramidal structure along the C₃ axis. Calculated vibrational frequencies, intensities, isotopic frequency shifts, and isotopic substituted frequency and intensity patterns render support to this conclusion. New vibrational assignments of observed and some unassignable bands from previous matrix-isolation and molten gas phase spectroscopic studies of ClO⁻₃M⁺ ion pairs are provided.     

Synthesis and Properties of Azoles and Their Derivatives. 52. Periselectivity of [2+3] Cycloaddition of Nitrones to trans-β-Cyanonitroethylene in the Light of FMO Theory

[2+3] Cycloaddition reaction of nitrones with trans--cyanonitroethylene may theoretically lead to regioisomeric nitroisoxazolidines and isomeric oxadiazoles. However, 4- and 5-nitroisoxazolidines were really obtained as only reaction products. Periselectivity of this reaction is rationalized in terms of the FMO theory.     

Photoelectron spectroscopic study of the E⊗e Jahn-Teller effect in the presence of a tunable spin-orbit interaction. I. Photoionization dynamics of methyl iodide and rotational fine structure of CH3I+ and CD3I+

The high-resolution single-photon pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the X?(+) (2)E(3/2)←X?(1)A(1) transition of CH(3)I and CD(3)I have been recorded. The spectral resolution of better than 0.15 cm(-1) enabled the observation of the rotational structure. CH(3)I(+) and CD(3)I(+) are subject to a weak E?e Jahn-Teller effect and strong spin-orbit coupling. The treatment of the rovibronic structure of the photoelectron spectra in the corresponding spin double group, C(3v)(2)(M), including the effects of the spin-orbit interaction and the vibrational angular momentum, allowed the reproduction of the experimentally observed transitions with spectroscopic accuracy. The relevant spin-orbit and linear Jahn-Teller coupling parameters of the X?(+) ground state were derived from the analysis of the spectra of the two isotopomers, and improved values were obtained for the adiabatic ionization energies [E(I)(CH(3)I)/hc=76931.35(20) cm(-1) and E(I)(CD(3)I)/hc=76957.40(20) cm(-1)] and the rotational constants of the cations. Rovibronic photoionization selection rules were derived for transitions connecting neutral states following Hund's-case-(b)-type angular momentum coupling and ionic states following Hund's-case-(a)-type coupling. The selection rules, expressed in terms of the angular momentum projection quantum number P, account for all observed transitions and provide an explanation for the nonobservation of several rotational sub-bands in the mass-analyzed threshold-ionization spectra of CH(3)I and CD(3)I reported recently by Lee et al. [J. Chem. Phys. 128, 044310 (2008)].     

A review of: “Nineteenth Century Attitudes: Men of Science (Chemists and Chemistry Series,Vol. 13)”. Sydney Ross. Kluwer Academic Publishers; Dordrecht, 1991. pp. xi+235. $69.00.

Abstract

The potential of polytetrafluoroethylene (PTFE) membranes as water‐in‐oil (W/O) emulsification devices was investigated to obtain uniformly sized droplets and to convert them into microcapsules and polymer particles via subsequent treatments. Uniform W/O emulsion droplets have not been achieved using glass membranes unless the membrane was rendered hydrophobic by treatment with silanes. If a PTFE membrane is capable of providing uniform droplets for a W/O emulsion, a coordinated membrane emulsification system can be established since glass membranes have been so successful for O/W (oil‐in‐water) emulsification. In order to examine the feasibility of PTFE membrane emulsification, O/W and W/O emulsion characteristics prepared using PTFE membranes were compared with those prepared by the conventional SPG (Shirasu porous glass) membrane emulsification method. A 3 wt.% sodium chloride solution was dispersed in kerosene using a low HLB surfactant. Effects of the membrane pore size, permeation pressure, and the type of emulsifiers and concentration on the droplet size and on the size distribution (CV, coefficient of variation) were investigated. The CV of the droplets was fairly low, and the average droplet size was correlated with the critical permeation pressure of the dispersed phase, revealing that the PTFE membrane could be used as a one‐pass membrane emulsification device. Low CV values were maintained with a Span 85 (HLB = 1.8) concentration, 0.2–5.0 wt.% and a range of HLB from 1.8–5.0. For a brief demonstration of practical applications, nylon‐6,10 microcapsules prepared by interfacial polycondensation and poly(acrylamide) hydrogels from inverse suspension polymerization are illustrated.     

Synthesis and properties of azoles and their derivatives. 45. Regio-and stereoselectivity of the [2+3]-cycloaddition ofE-β-nitrostyrene toZ-C-phenyl-N-arylnitrones

It is shown using spectroscopic methods that the [2+3]-cycloaddition of Z-C-phenyl-N-arylnitrones to E--nitrostyrene is regiospecific and leads to a mixture of the corresponding (3SR,4SR,5SR)- and (3SR,4SR,5SR)-2-aryl-4-nitro-3,5-diphenylisoxazolidines. The regioselectivity of the reaction is explained in terms of hard and soft acid and base theory.For communication 44, see [1]Institute of Organic Chemistry and Technology, T. Kosciuszko Krakow Polytechnic, 31–155 Krakow. Poland: e-mail: pebarans(ausk.pk.edu.pl. Translated from Khimiya Geterotsiklicheskikh Soedinenii No. 6. pp. 840–846, June, 2000.     

The effect of styrene α-substituents on the regiochemistry of [2+2] cycloadditions with difluoroallene.

Consistent with our hypothesis for a mechanism involving two kinetically-distinct diradical intermediates, the observed effects of styrene α-substituents can be explained as deriving either from steric effects or radical stabilizing effects.     

A review of: “Principles of Colloid and Surface Chemistry”. Paul C. Hiemanz. Marcel Dekker,Inc., New York and Basel, 1977. xi+516 pp.m $22.50

A general reaction model for styrene hydrogenation in the CTAB/l-hexanol(l-pentanol or l-butanol)/water reversed micellar solutions was proposed to interpret the catalytic behavior of monodisperse nickel boride particles prepared in situ. Based on this model, the effect of reversed micellar components on hydrogenation activity of the catalyst has been discussed in detail. It is worth noticing that, in the three reversed micellar systems, adding ethanol into the reversed micellar solutions will result in the change of catalyst's activity in the different ways, i.e. decrease for the reversed micellar solution with the low CTAB concentration (6 wt%) and increase for those with the high CTAB content (23 wt % or 38 wt%). The result is attributed to the combined     

Complexation thermodynamics of imine-type bis(benzocrown ether)s. Part I. Sandwich complexation of K+, Rb+, Cs+ and Tl+ with polymethylene andm-Phenylene bridged carbonylhydrazones of 4′-formylbenzo-15-crown-5

The complexation thermodynamics of polymethylene andm-phenylene bridged carbonylhydrazones of 4-formylbenzo-15-crown-5 with K⁺, Rb⁺, Cs⁺ and Tl⁺ was investigated by spectrophotometric titrations in methanol at 283–313 K. The carbonylhydrazone sequences in the bridge of the bis(benzocrown ether)s are optical sensors for the sandwich complexation of metal ions. Within the homologous series of polymethylene bridged carbonylhydrazones a stability peak was found for the sandwich complexes of the propylene bridged compound with K⁺, Rb⁺ and Tl⁺. The potassium complex of this ligand shows the highest stability constant compared to all other known bis(benzo-15-crown-5) complexes with K⁺ in methanol.In terms of thermodynamics the formation of intramolecular sandwich complexes is driven by a gain of enthalpy. The unusual high gains of enthalpy and losses of entropy on formation of the most stable sandwich complexes allow us to propose an additional stabilization of the sandwich arrangement by intramolecular hydrogen bridge bonds. The H ^o-TS ^o diagram gave an excellent straight line allowing discussion of the enthalpy-entropy compensation effect at these complexation reactions.     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.