Search

A study of the strong N-X⋅⋅⋅- O-N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N-halosaccharins and pyridine N-oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from -47.5 to -120.3 kJ mol-1 ; the strongest N-I⋅⋅⋅- O-N+ XBs approaching those of 3-center-4-electron [N-I-N]+ halogen-bonded systems (ca. 160 kJ mol-1 ). 1 H NMR association constants (KXB ) determined in CDCl3 and [D6 ]acetone vary from 2.0×100 to >108 m-1 and correlate well with the calculated donor×acceptor complexation enthalpies found between -38.4 and -77.5 kJ mol-1 . In X-ray crystal structures, the N-iodosaccharin-PyNO complexes manifest short interaction ratios (RXB ) between 0.65-0.67 for the N-I⋅⋅⋅- O-N+ halogen bond.

The structural and electronic properties of ${\mathrm{KTaO}}_{3}$/${\mathrm{KZnF}}_{3}$ and ${\mathrm{KTaO}}_{3}$/${\mathrm{KNiF}}_{3}$ oxyfluoride superlattices are studied from first-principles density functional theory calculations. We highlight, that beyond a critical layer thickness, these systems exhibit an insulator to metal transition that gives rise to the appearance of two-dimensional electron and hole gas, confined both, due the band alignment, within the oxide layer. The origin of the insulator to metal transition is related to the polar discontinuity at the interfaces. The behavior is discussed in terms of a simple electrostatic model and compared to that of the prototypical ${\mathrm{LaAlO}}_{3}$/${\mathrm{SrTiO}}_{3}$ oxide system. The magnetic properties ${\mathrm{KTaO}}_{3}$/${\mathrm{KNiF}}_{3}$ superlattices are further discussed, revealing a sizable Rashba-type spin splitting at these interfaces, much larger than in similar oxide/oxide systems.

The dynamics of the electrochemical double layer in ionic liquids can be experimentally probed by a number of experimental techniques. Earlier, we reported on the results of an X-ray photoelectron spectroscopic investigation under applied square-wave bias of two distinct frequencies. Our studies had revealed counterintuitive properties involving the physical and temporal progression of the effect of the electrochemical double layer that could not be modeled with conventional equivalent-circuit approaches. Herein, we present a new coarse-grained modeling methodology that accounts for particle diffusion, migration, and ion-association equilibrium. Our model is computationally efficient enough to be used to predict and match the results at extended time scales and distances of the experiment. Modeling efforts predict that a crucial component of the behavior is controlled by the ion-pairing equilibrium, an often overlooked aspect of ionic liquids.

© 2017, Indian Academy of Sciences. The environment of a solute molecule in an ionic liquid is likely to have large fluctuating electrostatic fields, and so the electrostatic properties of such a solute including its charge distribution and its polarizability may make a difference to both its static and dynamic properties. We have developed a new model for the static electrostatic distribution in the CS 2 molecule with 7 charged sites and anisotropic polarizability on the carbon site and isotropic polarizability on the sulfurs. We have investigated static and dynamic properties of the neat liquid and solutions of CS 2 in an ionic liquid, [dmim][NTf 2 ]. [Figure not available: see fulltext.] .

Single-molecule transistor experiments offer the ultimate probe of a molecule’s redox chemistry. With a combined quantum mechanics/molecular mechanics computational method and an electrostatic model of the junction, the Coulomb blockade diamonds can be reconstructed. We present computations on 1,4-diamino-benzene (OPVN) in a molecular transport junction, and focus on the chemical features such as electrostatic stabilization, importance of binding group, and binding distance. Thus the explicit construction of the Coulomb blockade diamonds offers a method for direct comparison between different molecular junctions and thus also with experiments.

A simple electrostatic model explains the enhanced stereoselectivity of N-oxide catalyzed allylations compared to propargylations, which in turn explicates the dearth of stereoselective N-oxide propargylation catalysts. These results suggest that N-oxide catalysts that are effective for both allylations and propargylations can be designed by targeting inherently stereoselective ligand configurations and through the manipulation of distortion effects in the operative transition states.

The temperature dependence of spontaneous polarization and the primary pyroelectric coefficient of stoichiometric lithium niobate crystals are calculated and the specific features of structural ordering of lithium niobate in the ferroelectric phase are analyzed using a modified electrostatic model. The reasons that experimentally observed anomalies of the primary pyroelectric coefficient occur are discussed.

Various methods to parameterize an exciton model of amide I vibrations are suggested and analyzed. In the spirit of a systematic fragmentation scheme, small model peptides are employed as building-blocks to construct the vibrations of a polypeptide. As an example, extensive density functional theory (DFT) calculations at the B3LYP/6-31+G(d) theoretical level of glycine tripeptide are presented, which serve as reference data for testing various approximate schemes. The combination of a DFT description of next-neighbor interactions via dipeptide building blocks combined with an electrostatic model to account for the long-range interactions appears as a promising approach to achieve spectroscopic accuracy at low computational cost.

Pi-facial diastereoselectivity on a carbonyl group in carbonyl ene reaction has been determined using DFT calculation. The effect produced by the electropositive and electronegative group or atom present at the adjacent center reveals that, the face selectivity on the carbonyl group is guided by Cieplak or electrostatic model. The general acyclic model evolved from this observation can be used for determining the preferred orientation of the substituent on the transition structure of type-II ene cyclization.

A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] (2), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] (1). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian. FCT. Grant Number: UID/Multi/04349/2013 FCT (Portugal). Grant Numbers: SFRH/BD/84628/2012, SFRH/BPD/74194/2010 FCT (Portugal). Grant Number: PTDC/QEQ‐SUP/1413/2012 FCT (Portugal). Grant Number: RECI/QEQ‐QIN/0189/2012 SPINMOL FP7-ERC-247384 ERC-2014-CoG-647301 DECRESIM MAT2011‐22785 A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] (2), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] (1). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian.

A consistent set of atomic electronegativities of main block and d-block transition elements has been obtained from the position and value of the molecular electrostatic potential bond critical point of the C-E bond of a methyl-element-hydride system, H(3)C-EH(n) (E is an element and n = 0, 1, 2, 3, 4, and 5 depending on the position of E in the periodic table). The new scale shows very good agreement with the popular electronegativity scales such as Pauling, Allen, Allred-Rochow, Mulliken, and Sanderson scales of electronegativity, especially for the main block elements. The present scale of electronegativity for transition elements is expected to be more accurate than the previously derived values because of a more consistent approach. Further, the same approach has led to the evaluation of group electronegativities when the hydrogens of E are replaced by other substituent groups. These group electronegativity values are found to correlate well with Inamoto and Mullay scales.

A series of nonempirical intermolecular potentials has been developed for the cyanuric chloride dimer, using the overlap model to determine the anisotropy of the repulsive wall around each atom. Calibration against intermolecular perturbation theory calculations enables the penetration and charge-transfer energy to be explicitly included with the exchange-repulsion to give a simple repulsion model in an anisotropic atom−atom form. These model repulsion potentials are used in conjunction with an atomic multipole electrostatic model and an atom−atom dispersion model to give nonempirical potential models, which are tested for their ability to reproduce the crystal structure of cyanuric chloride. The best nonempirical potential is successfully used to construct a simpler transferable model for closely related azaaromatic chlorides. The nonempirical potential reproduces the experimental space group of cyanuric chloride, unlike some empirically fitted repulsion−dispersion potentials. This first nonempirical rep...

Electrostatic potential in the vicinity of the surface of a cation-exchange resin has been evaluated by modeling chromatographic retention. Binary mixtures of K + and its crown ether complex in methanol are used as mobile phases, and two types of solutes, that is, cationic and crown ether probes, have been examined. The cationic probes show the sigmoidal retention changes with increasing concentration of a crown ether incorporated into the mobile phase, whereas crown ether probes give retention maximums. The model derived from the Poisson-Boltzmann theory well explains these specific changes in probe retention and gives the electrostatic potential at the closest approach of each probe molecule. The closest approaches for probe molecules correlate well with their molecular sizes. In addition, changes in retention of cationic probes also correlate well with the electrostatic potential changes at the closest approaches of probe molecules, indicating that simple sensing of the electrostatic potential is feasible using probe retention. The reduction of crown ether complexation occurs in the vicinity of the cation-exchange resin surface and causes the specific retention behaviors of crown ether probes in the mobile-phase systems composed of K + and its complex with a modifier crown ether.

Synthesis and physicochemical properties of new N-pyridyl derivatives of 3-phenyl and 3,3-diphenylsuccinimides (1-12) have been described. The obtained compounds were evaluated in respect of their anticonvulsant activity. The N-pyridyl derivatives of 3-phenylsuccinimides (7-12) abolished the protection against MES- and scMET-induced seizures, whereas N-pyridyl derivatives of 3,3-diphenylsuccinimides (1-6) were inactive. After molecular modelling and quantum-chemistry calculations the theoretical activity test was applied (W. Kwiatkowski, J. Karolak-Wojciechowska, SAR and QSAR Envir. Res. 1 (1993) 233; Chem. Abstr. 120, 153001 (1994). J. Karolak-Wojciechowska, M. Blaszczyk, W. Kwiatkowski, J. Obniska, A. Zejc, J. Chem. Cryst. 27 (1997) 297; Chem. Abstr. 127, 277834k (1997)). The molecular electrostatic potential (MEP) of the active compounds differed significantly from that of the inactive ones.

Intermolecular interaction models which include electrostatic, dispersion and repulsion terms were used to predict the structure of a number of sulfur dioxide dimers. The models combine a distributed multipole analysis (to represent the electrostatic contribution) with atom-atom potential terms (to represent the dispersion and repulsion terms). It is concluded that the simple Buckingham-Fowler electrostatic model performs as well as, or better than, the models investigated in this study in many cases.

The Buckingham-Fowler electrostatic model has been applied to a number of known weakly bound complexes of SO2 with the objective of predicting the geometries of these complexes. In most of the cases investigated, this relatively simple model has reproduced many features of the angular geometries of the complexes remarkably well, even in cases where the experimental structures were found to be very asymmetric in nature. However, for the butadiene and furan complexes with SO2, the predicted geometries did not resemble the experimental determinations, despite numerous attempts to produce these structures.

On the bases of experimental results from gas phase and electrostatic theory a modified thermodynamic model for substituent and solvent effects on organic acids has been derived. It is found that the present model is quantitatively and simultaneously consistent with the experimental results obtained from gas phase, aqueous solution and mixed solvents such as ethanol–H2O.

The reaction of N-acyl-o-aminophenol with 1-naphthoyl chloride in the presence of triethylamine gave N- (1-naphthoyl) -O-acyl derivative, while the same product was obtained from the reaction between N- (1-naphthoyl) -o-aminophenol and acyl chloride (RCOCl: R=CH2OEt, CH2OPh, or OCH2Ph). The hydrazinolysis of the product revealed that the equilibrium between acyl-exchanged iso mers lies almost completely in favor of N-(1-naphthoyl)-O-acyl-o-aminophenol. This interesting result was explained on the basis of the strong electron-donating ability of an oxygen atom incorporated into the substituent Ras well as of the electrostatic model of exchanged isomer pair.

The structures and electrochemical behavior of a series of symmetric dinuclear complexes in which two iron centers are bridged by three bis[4-(4'-methyl-2,2'-bipyridinyl)]alkane ligands are presented. Square wave voltammetry was used to characterize the extent of interaction between the metal-centered halves. Because the saturated linkages preclude significant electron delocalization, the observed interaction is concluded to be almost purely Coulombic in nature. Furthermore, molecular modeling and X-ray crystallographic data confirm that the iron-iron separation in the complex containing three methylenes in the linkages is nearly identical to the ironiron separation in the complex containing two methylenes in the linkages. Using a simple electrostatic model and employing structural parameters obtained from X-ray data and molecular modeling, the electrochemical trends within the series are interpreted.

Copper fining trials with ale and lager worts under conditions whereby the pH of wort was artificially manipulated prior to fining, demonstrated that the optimal copper fining rate decreased with increasing values of wort pH. Clarification of acidified worts (pH

We have studied a model of the order-disorder phase transitions in CsLiSO4 and CsLiCrO4. In this model a BX4 tetrahedron has four equilibrium orientations in a disordered hexagonal phase. The constants of the interaction between ordered BX4 groups are calculated in the framework of the electrostatic model. It is shown that these constants have a competitive nature. The Monte Carlo method is applied to study the phase diagrams and thermodynamic properties of the phase transitions. The results obtained are in good agreement with experimental data.

We performed neutron spectroscopy and neutron-diffraction experiments on both natural and laboratory-made methane hydrates. The experiments focussed on the rotational dynamics and the orientational scattering density of the encaged methane molecules. The measurements are accompanied by calculations of the rotational potentials on the basis of a simple electrostatic model of the orientational interactions.

Effect of the carbon content on the stationary surface (Ns) on retention values in reversed-phase liquid chromatography (RPLC) and ion-pair liquid chromatography (RP-IPC) has been investigated. The k'RP and k'ip values are linearly related with Ns in RPLC and RP-IPC. The linear relationship almost passes through the origin in the former case, but does not pass through origin in the latter case. There is a stronger effect of carbon content on the retention in RP-IPC than that in RPLC. It can be concluded that the retention mechanism of RP-IPC is different from that of RPLC. Effect of the carbon content on the stationary surface on retention in RP-IPC can be explained by the electrostatic model, which also confirms the validity of the electrostatioc model for RP-IPC.

The formation of polaron and/or bipolaron species upon chemical doping and photo- or electro-chemical generation is a scientific and technological problem which is still object of discussion. Here we use a simple electrostatic model to study the role of the interchain interaction in stabilizing or destabilizing the bipolaronic structure, which is usually neglected in theoretical studies. The results show that, as a consequence of the interchain interactions in the bulk system, a bipolaron generated on a single oligomer chain more than 12 units long will soon split into two polarons on adjacent chains, this process being maximized for specific interchain distances.

We present a strategy for comparing the global properties of competing potential models. By systematically sampling the potential energy surface of crystalline tetracene, we assess how the number, energy and structure of its minima are modified by switching on (or off) the Coulombic interactions. The increased complexity of the Coulombic potential leads to a more "rugged" potential energy surface with a larger number of minima, but the effect is not large. In fact, we find a subset of minima stable only in presence of the Coulombic interactions, a smaller subset stable only in their absence, and a large majority stable in both cases. Among these, there is a very good, but not perfect, correlation between the energies and the structures computed with and without the electrostatic interactions. Although electrostatic interactions play a role even in a rigid nonpolar molecule such as tetracene, they are not as crucial as often believed, because altering the electrostatic model (or switching it off completely) leads, in most cases, to equivalent results.

Empirical potentials are proposed to simulate benzene and an excess electron in liquid benzene. The benzene-benzene potential is closely modelled on another that has previously been well tested in the condensed phase. We have improved the electrostatic model of benzene, and to be consistent we have used the same representation for both potentials. The electron-benzene potential is derived in part using ideas from density functional theory, and the principles could equally well be applied to other electron-molecule systems. The electron is found to be repelled from the benzene, except in a few regions of space, mainly close to the molecular plane.

We are testing the idea that placement of fixed charges near one face of the DNA double helix can induce DNA bending by a purely electrostatic mechanism. If stretching forces between DNA phosphates are significant, fixed charges should induce DNA bending by asymmetrically modulating these forces. We have previously tested this hypothesis by adding charged residues to small bZIP DNA binding peptides and monitoring DNA bending using electrophoretic phasing assays. Our results were consistent with an electrostatic model of DNA bending in predicted directions. We now confirm these observations with fluorescence resonance energy transfer (FRET). Using a "U"-shaped DNA probe, we report that DNA bending by charged bZIP peptides is readily detected by FRET. We further show that charged bZIP peptides cause DNA bending rather than DNA twisting.

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.

The densities of commercial Nafion 117 and cast Nafion 1100 films were determined by the hydrostatic weighing method for films fully exchanged with hexaammineruthenium(III), tris(2,2' bipyridyl)ruthenium(II), tetramethylammonium, ferrous, and hydrogen ions. Films were pretreated in either water or concentrated nitric acid prior to cation exchange. All densities ranged between 1.65 and 2.19 g/cm3. Excluding the proton-exchanged films, the average density is 1.90 +/- 0.14 g/cm3, well in excess of the 1.58 g/cm3 commonly employed for Nafion. The density of acid-pretreated Nafion 1100 was constant at 1.95 +/- 0.03 g/cm3 for all cations except the proton. A simple, empirical model based on the Coulombic interaction between the intercalated cation and the sulfonate sites of the Nafion characterizes density for the commercial Nafion 117 films. A modified version of the model is appropriate for water-treated Nafion 1100. Water content of the films and implications for characterizing modified electrodes are discussed.

The pK 1 and pK 2 values of malic, malonic, maleic, succinic, tartaric, and phthalic acids have been determined in ethane-1,2-diol-water media of varying solvent compositions (0-50 wt % ethane-1,2-diol) within the temperature range (25-65°C). An extrathermodynamic analysis of the obtained results have been examined, in the light of ΔH°-ΔS° relationship. The pK values have been correlated with the relative permittivity of the medium according to Born's electrostatic model.

A series of milrinone analogues, namely 6-substituted 3-acetyl-5-acylpyridin-2(1 H )-ones 4a–c , e , f and 7-substituted or unsubstituted 3-acetyl-7,8-dihydro-2,5(1 H ,6 H )-quinolinediones 4g–j , in which the cyano group was replaced by the acetyl function, was prepared. In a preliminary pharmacological investigation on spontaneously beating atria from reserpine-treated guinea-pigs, all new compounds did not induce any inotropic effect equivalent or higher than that of the milrinone chosen as the reference compound. In order to rationalise how the structure modifications influence the activity and the selectivity of the title compounds, a computational study has been performed. The important role of the substituents in positions-3 and -6 on the pyridone nucleus has been highlighted.

An analysis of the stability of a duplex containing G x A mispairs or G x A/A x G tandem during the DNA melting has shown that the duplex stability depends on both DNA sequences and the conformations of the G x A mispairs. The thermodynamics of single pair opening for the G(anti) x A(syn) and G(anti) x A(anti) conformations adopted by a G x A mispair is found to strongly correlate with that of the canonical base pairs, while for the sheared conformation a significant difference is observed.

Summary The perturbation of the high frequency (h.f.), hydroxyl stretching infra red band of a HY zeolite is investigated after adsorption of benzene, toluene, o-xylene, p-xylene, m-xylene and cumene. A shift of the band to a lower frequency accompanied by an increase in intensity is noted. The frequency shift varies in the order, o-xylene > m-xylene ⋍ toluene ⋍ cumene > benzene ⋍ p-xylene. Utilising a theoretical model for the interaction which takes account of only the dielectric properties of the hydroxyl group environment it is demonstrated that the vibrational properties predicted by such a model i.e. frequency shift and intensity change are in close agreement with experimentally determined quantities.

Ab initio studies of acetylene tetramer, (C2H2)4, show that the lowest-energy conformation is a cyclic structure, of C4h symmetry. The potential-energy surface is very flat in the direction of out-of-plane displacements, indicating that it would undergo large-amplitude flexes to the experimentally observed S4 symmetry ring-puckered structure. Interconversion tunnelling between permutationally distinct configurations is shown to be of no significance in the full description of this cluster. The electrostatic model predicts two structures as possible equilibrium conformations of acetylene pentamer. Ab initio studies also show that out-of-plane ring-puckerings are important in both of these. With no further computation, likely favourable structures of higher-order planar acetylenic clusters are predicted. We assert that single-ring cyclic structures become progressively less favourable for clusters larger than acetylene tetramer.

The experimental models of the transfer proton process of ortho -benzoic acid derivatives in DMSO-water solutions were used to check an electrostatic and a thermodynamic model. As in the case of the meta and para derivatives, the electrostatic model was found to be consistent with experimental results.

Absolute hydration enthalpy (H) for cations relates well to lgKΣ, the sum of the logarithms of the individual step chelation constants for metal-dibenzoylmethane complexes. The products d 2 H and d 2 lgKΣ, where d is the bond length, are essentially constant for a given cation valence (v) and increases as v2. These relations fit a simple electrostatic model wherein the polarization of coordinating chelate or hydrate oxygen atoms is proportional to cation charge.

Calcul des parametres d'intensite de transitions 4f-4f d'especes a coordination comme en solutions aqueuses basiques, a rapport Ln 3+ : coordinat=1:3 les coordinats organiques tridentes etant l'oxydiacetate, le dipicolinate, l'iminodiacetate ou le methylimino-diacetate, en considerant les couplages statique (champ cristallin de charges ponctuelles) et dynamique (polarisation du coordinat)

The proton-transfer reaction between title compounds was kinetically studied in toluene and dichloromethane at 25°C up to 1000bar by the use of a high-pressure stopped-flow method. The volumes of activation were explainable on the basis of Kirkwood′s electrostatic model.

Calculations are made of the distance dependence of the σ and π diatomic overlap integrals for various metal dx and fx fluoro and chloro systems, whence are derived the derivative quantities, ∂ρπ/∂R and ∂ρπ/∂R, which represent the variation with distance, R, of the Angular Overlap parameters, ρσ and ρπ. For all systems the results indicate that the alternative evaluation of the derivative terms via an electrostatic model yields only modest agreement for the σ quantities and substantially underestimates the π terms. For fx species the predicted R dependence of the ρσ parameters is compared with the limited available experimental data.

Lithium thiocyanate is dimerized in ethers (Et 2 O, Bu 2 O, dimethoxy and diethoxymethane). The dimer is centrosymmetric. An important decrease in the force constant F CN and an increase in F CS are observed with respect to SCN − LiNCS. Hence, the only possible structure involves two lithium bridges between the two nitrogen atoms. A simple electrostatic model well accounts for the mechanical coupling between the two SCN groups through the lithium bridges.

Benson's electrostatic model for calculating enthalpies of formation has been applied to the methylsilanes and some disilanes, conforming recent conclusions from electron-impact measurements that these silanes essentially follow bond additivity rules, with very small interaction corrections. These findings are shown to be consistent with recently measured bond dissociation energies.

The enthalpy of formation of EuF 2+ in solution has been redetermined by titration calorimetry. Experiments at a constant ionic strength of μ = 1.0 M (NaClO 4 ), but at a variety of fluoride titrant concentrations, gave ΔH 101 =(9.61 ± 0.03) kJ/mol at 25 °C. This value is considerably lower than that previously reported in the literature. The corresponding entropy, however, is now consistent with an electrostatic model which has bcen shown to describe the behavior of a wide variety of metal-fluoride complexes.

Partition constants have been determined for a series of trialkylammonium chlorides, bromides, iodides and perchlorates between water and nitrobenzene. Extraction of these salts into nitrobenzene increases in the order Cl - - - 4 - . The extraction constant for salts with the same anion increases with increasing chain length of the ammonium ion from tripropyl to trihexyl. An electrostatic model of the Borncharging type was not sufficient to predict transfer equilibrium constants of the dissociated ions.

We have used an electrostatic model as basis for derived equations to represent the effects of substituents and solvents on the thermodynamics of proton transfer reactions. Equations derived in this manner are related to those based on earlier 'internal-environmental' models and are also discussed in relation to recent gas phase acidity work.

This paper deals with measurements of the heat of the helix-coil transition by microcalorimetry for kappa carrageenans; data are given in the absence of gel in various solvents (H 2 O, Me 2 SO, and formamide) with two counterions (K + , Rb + ). In water, the influence of gel formation on Δ H is pointed out and the influence of the time of ageing is demonstrated. The Δ H values measured in the absence of gel are interpreted in terms of the electrostatic model proposed by Manning; the agreement is quite good if a double helix is formed in water, but a monochain, ordered conformation is suggested for solutions in Me 2 SO and formamide.

Ca-exchanged X dehydrated under vacuum at 500° C and measured at room temperature has 13 Ca in S(I), 5 in S(I′) and 25 in S(II). This distribution and the interatomic distances agree with energy minimization for a simple electrostatic model of the Pauling type, when account is taken of some residual oxygen species in the sodalite cage.

The frequencies and intensities of the fundamental and some overtones of v (CH) of n-propyl acetylene have been measured in a number of different solvents. Mechanical anharmonicity terms have been calculated and a quantitative prediction of the intensity values has been attempted by using a simple electrostatic model which quantitatively represents the frequency changes.

Free energy and enthalpy of single ion solvation in water and propylene carbonate, using electrostatic model

Both the N—N stretching vibration and its combination with the Fermi doublet {ν 1 , 2 ν 2 } of carbon dioxide are infrared active for a nitrogen crystal containing traces of carbon dioxide. The intensities of these normally forbidden bands can be accounted for semiquantitatively by a simple electrostatic model.

A collection of 4 positive and 4 negative point charges arranged as two interpenetrating tetrahedra subject only to Coulombic forces has a minimum electrostatic energy at a ratio of the two tetrahedra sides of 0.783, a value consistent with the observed LiLi to CC distance ratio of 0.73 in the structure of methyllithium tetramer.