Association constants and enthalpies of formation of heteroassociates of anions of cresol red and thymol blue

The tendency of anions of sulfophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, cresol red, thymol blue, and non-substituted phenol red. It was spectrophotometrically determined that single (HAn⁻) and doubly charged anions (An²⁻) of sulfophthaleines can form stable heteroassociates of the composition Ct⁺ · HAn⁻ and (Ct⁺)₂ · An²⁻ with cations (Ct⁺) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated semi-empirically and compared with experimentally determined values of the equilibrium association constants.     

A modified MNDO procedure for calculating the heats of formation of organic anions

A modification of the MNDO method is suggested based on the relation ζ_A=ζ_A ⁰(1 + ϰ_AQ_A) for Slater parameters that takes into account the dependence of overlap integrals and the MNDO parameters (expressed via these integrals) on atomic charges Q_A. The core parameters U_μμ include corrections for nonorthogonality of basis functions of atoms in a molecule. For free atoms, the parameters were determined from the condition of reproducible electron affinities. The method is advantageous for calculating the heats of formation of anions, particularly those with the charge concentrated on one atom. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 3–11, January-February, 1994. Translated by O. Kharlamova     

Molecular constants of some hexahalide anions

Modified force fields have been applied to the hexachlorides and hexabromides anions of technetium. Mean amplitudes of vibration are also calculated at 0 K and 298 K. Trends of calculated data are discussed. The observed frequencies are 100% fitted by both the modified force fields used.     

Bond indices and heats of formation of some nitriles

The definition of bond index introduced by Ehrenson, and written in terms of bond order and overlap integrals, has been applied to a series of nitriles. A good correlation between heats of formation and a linear equation in the indices for each bond present is obtained. This was extended to include the results for a set of hydrocarbons.     

Determination of heats of formation of praseodymium antimonides

A systematic investigation of the heats of formation in the Pr-Sb system has been performed using a small-furnace, isoperibolic calorimeter. The compositions and the equilibrium states of the samples have been checked by metallographic and X-ray analyses. The following values have been found for the various compounds (kJ/g atom±2): Pr₂Sb:-99; Pr₅Sb₃:-112; Pr₄Sb₃:-120; PrSb:-126; PrSb₂:-97.The data available (both the results obtained in this work and those already known) are discussed briefly and related to the possible shape of the phase diagram.

---

Zusammenfassung Es wurde eine systematische Untersuchung der Bildungswärmen im Pr/Sb-System unter Verwendung eines Kleinofen-Isoperibolkalorimeters ausgeführt. Die Zusammensetzung und der Gleichgewichtszustand der Proben wurden durch metallographische und röntgenographische Analyse ermittelt. Für die einzelnen Verbindungen wurden folgende Werte (kJ·mol^–1 ±2.0) gefunden: Pr₂Sb:-99; Pr₅Sb₃:-112; Pr₄Sb₃:-120;PrSb:-126; PrSb₂:-97. Die als Ergebnis dieser Arbeit erhaltenen und aus der Literatur bereits bekannte Daten werden kurz diskutiert und mit einem möglichen Phasendiagramm in Verbindung gebracht.

---

-Sb, . . ( (-)^–1 ±2.0): Pr₂Sb-99; Pr₅Sb₃-112; PrSb₃-120; PrSb-126; PrSb₂-97. .

     

Calculation of heats of formation for carbocyclic compounds

A method previously described is applied to the heats of formation of gaseous saturated and unsaturated alicyclic and aromatic hydrocarbons as well as hydrocarbons with several conjugated double bonds. Some energy parameters of carbon in these compounds are evaluated.     

Theoretical prediction on heats of formation for polyisocyanocubanes

The heats of formation (HOF) for all the 21 polyisocyanocubanes are calculated systematically with density functional theory (DFT) B3LYP and semiempirical MO(MINDO/3, MNDO, AM1 and PM3) methods. First, the accurate HOFs for the 8 title compounds are obtained by means of designed isodesmic reactions at DFT-B3LYP/6-31G* level, and the cubane cage skeleton has not been broken (i.e. choosing cubane as a reference compound) to produce more accurate and reliable results. It is found that there are good linear relationships between the HOFs calculated using the B3LYP/6-31G* and four semiempirical MO methods, respectively, and all of the linear correlation coefficients are more than 0.9971. The HOFs obtained from PM3 calculation are the best among the four semiempirical MO methods. Then, the accurate HOFs at B3LYP/6-31G* level of other 13 polyisocyanocubanes are obtained by systematically correcting their PM3-calculated HOFs. Polyisocyanocubanes have very high HOFs, and the HOFs increase linearly with the increasing of the number of isocyano groups in a molecule. The results show that polyisocyanocubanes are the new generation explosives with highly potential and exploitable value.     

INDO-MO calculations of hyperfine splitting constants for pyridine anions

INDO-MO Calculations have been carried out on the anions of a variety of pyridine derivatives for which e.s.r. data have recently become available. The method gives reasonable results for proton hyperfine splitting constants but calculated nitrogen splitting constants are considerably larger than the experimental values. Some -only calculations are included for the pyridine anion. All methods overestimate the spin density at the nitrogen atom. The orbital populations and excess charges for the pyridine molecule are not in agreement with those of an ab initio calculation.     

Electrolytic formation and destruction of living anions

Electrolysis of solutions of α-methylstyrene in THF resulted in the formation of the characteristic spectra of the living anions in the cathode compartment. The increase in absorbance of the solution was strictly proportional to the charge transferred at the electrode, and was independent of the electrolyte for NaAl(C₂H₅)₄, NaB(C₆H₅)₄, and KB(C₆H₅)₄. For solutions of LiB(C₆H₅)₄ the color decreased spontaneously on standing, and a linear relationship between absorbance and charge transferred was not obtained. Mixing of the anode and cathode solutions resulted in a destruction of the living ends and a disappearance of the color, which could be regenerated by further electrolysis. Reversal of the polarity of the electrodes produced a stoichiometric destruction of the living ends and a decrease in absorbance directly dependent on the charge transferred. The exact stoichiometric dependence furnished means of estimating impurity levels, living anion concentrations, and optical extinction coefficients based on the number of faradays passed through the solution. The control of molecular weight distribution and rate of reaction by these methods is indicated.     

MINDO/3 Calculation of carbocation heats of formation

Heats of formation calculated by MINDO /3 are reported for 42 carbocations for which experimental heats of formation have been published. Errors associated with these calculations can be large, with an overall range of ±13 kcal/mol. Correction of systematic errors in the MINDO /3 calculations by means of hydrocarbon models and isodesmic relationships results in a reduction in the range of errors to ±8 kcal/mol. Comparison with experimental heats of reaction of hydride transfer equilibria minimizes experimental errors and gives an average absolute error of 2 kcal/mol with a range of ±3 kcal/mol.     

Coupling constants in cis-phosphine platinum complexes containing chalcogen-nitride anions

The ³¹P NMR spectra of complexes of the type Pt(SeSN₂)(PR₃)₂ and Pt(Se₂N₂(PR₃)₂) display trans ²J{⁷⁷Se ³¹P} couplings of ca. 30–80 Hz, with no corresponding cis coupling; in contrast Pt(TeSN₂)(PMe₂Ph₂ has both trans and cis ^J{¹²⁵Te ³¹} coupling of 146 Hz and 103 Hz respectively. The ³¹ spectra of the complexes Pt(S₂¹⁵N₂)(PMe₂)P₂ nd [Pt(S₂¹⁵N₂)Cl(PMe₂)Ph)]⁻ show both ²J- and ⁴J{15N ³¹P} couplings, which alter substantially upon protonation of the S₂N₂²⁻ ligand. The ¹⁵N NMR spectra of Pt(S₂¹⁵N₂H)Cl(PMe₂Ph) and Pt(S₃¹⁵N)Cl(PMe₂Ph) show the presence of both ³¹P ¹⁵N and ¹⁹⁵Pt ¹⁵N couplings but no significant ¹⁵N ¹⁵N interactions.     

Dissociation constants of some o,o'-substituted azo dyes

The dissociation constants, pK(a) (H(2)L(-)) and pK(a)(HL(2-)), were determined spectrophotometrically in aqueous media at ionic strength 0.2 for six o,o'-substituted azo dyes, namely C.I. 13900, C.I. 15685, C.I. 18744, C.I. 18760, C.I. 18821 and Calmagite.     

Interaction of organic dyes and proteins-determination of the binding constants spectrophotometrically

Summary The spectral change of a small molecule (S) induced by addition of a large molecule (P) was examined theoretically and experimentally, assuming that the interaction betweenS andP follows theLangmuir adsorption isotherm. It was found that intermolecular binding constants could be determined accurately and conveniently by extrapolation to zero of two simple graphic relations, namely, the observed molar extinction coefficient ofS in the presence ofP versus the ratio of (the concentration ofS/the concentration ofP), and of the former versus the reciprocal value of the latter. This spectrophotometric method was applied to the binding of bovine serum albumin and Ponceau3 R and of bovine serum albumin and HABA at p_H 7.0. The results obtained by this method were comparable with those obtained by equilibrium dialysis or by conventional spectrophotometric method.

---

Zusammenfassung Unter der Annahme, daß dieLangmuirsche Absorptionsisotherme auch bei der Assoziation hoch-(HMV) und niedermolekularer Verbindungen (NMV) gilt, wurden die Bindungskonstanten bestimmt. Es wurden die spektralen Änderungen in der UV-Absorption der NMV bei Zusatz verschiedener HMV-Mengen gemessen. Die Bindungskonstanten lassen sich durch Kombination zweier graphischer Darstellungen exakt und einfach bestimmen: erstens aus der Beziehung zwischen dem molaren Extinktionskoeffizienten der NMV in Anwesenheit verschiedener HMV-Konzentrationen und dem Konzentrationsverhältnis von NMV zu HMV und zweitens aus dem Zusammenhang der molaren Extinktionskoeffizienten mit den reziproken Werten des oben genannten Konzentrationsverhältnisses. Mit dieser neuen Methode wurden die Bindungskonstanten bei p_h 7.0 von Rinderserumalbumin und Ponceau 3 R bzw. HABA berechnet und mit den durch andere Methoden bestimmten Konstanten verglichen. Die Werte stimmen mit denen aus der Dialysemethode und aus der üblichen spektralphotometrischen Methode überein.

     

Interaction of sulfophthaleine anions with cationic dyes in aqueous solution

An interaction between the singly and doubly charged anions (HAn⁻ and An²⁻) of sulfophthaleines (phenol red and its derivatives: bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue), and singly charged cations (Ct⁺) of a polymethine (pinacyanol, quinaldine red), results in formation in an aqueous solution of heteroassociate with stoichiometric composition (Ct⁺)·HAn⁻ and (Ct⁺)₂·An²⁻. On the basis of spectrophotometric data the association constants were estimated. By quantum-chemical methods AM1 and PM3 the values of formation and reaction enthalpies of the species formed were calculated and the most probable structure of the heteroassociates was determined.     

Systematic errors in DFT calculations of haloalkane heats of formation

The B3LYP and B3PW91 density functionals were employed with a large [BS1 = 6-311+G(3df,2p)] and small [BS2 = 6-311G(d,p)] basis set to compute enthalpies of formation (at optimized MP2/6-31G(d) geometries and with scaled HF/6-31G(d) frequencies) in the following series of haloalkanes: (1) the 15 fluoro-, chloro-, and chlorofluoromethanes, (2) the 18 fluorinated and chlorinated ethanes. Similar to earlier higher level calculations on haloalkanes, the computed enthalpies exhibited very large, systematic deviations from experiment. It was found that these errors could be largely eliminated using a very simple Bond Additivity Correction (BAC) formula, Delta(f)H degrees (BAC) = Delta(f)H degrees (calc) - n(CX). Delta(CX) [X = F, Cl], in which the BAC parameters, Delta(CF) and Delta(CCl) were determined by fitting the equation to experimental data on the four fluoroethanes and chloroethanes, respectively. The resultant BAC corrected enthalpies of formation are in excellent agreement with experiment, with RMS deviations in the same range as quoted RMS errors in measured enthalpies. Therefore, this simple BAC procedure may be utilized to provide reliable semiquantitative estimates of enthalpies of formation in larger haloalkanes, for which higher level ab initio calculations are not feasible.