Molar excess volumes of ternary mixtures of nonelectrolytes

Molar excess volumes V^E_ijk of methylenebromide i + pyridine j + β-picoline (k, cyclohexane (i) + pyridine (j) + β-picoline(K), benzene(i)+toluene(j)+1,2-dichloroethane(k), benzene(i) + 0-xylene(j) + 1,2-dichloroethane(k) and benzene(i) + p-xylene(j) + 1,2-dichloroethane(k) mixtures have been determined dilatometrically at 298.15 K. The data have been examined in terms of Sanchez and Lacombe theory and the graph-theoretical approach, and it is found that they are described well by the latter. Self- and cross-volume interaction coefficients V_jk, V_jjk and V_jkk, etc., have also been evaluated and the values utilised to study molecular interactions between the jth and kth molecular species in the presence of the ith in these i + j + k mixtures.     

Critical properties of the vapor—liquid equilibria of the binary system acetone—n-pentane

Hajjar, R.F., Cherry, R.H. and Kay, W.B., 1986. Critical properties of the vapor—liquid equilibria of the binary system acetone—n-pentane. Fluid Phase Equilibria, 25: 137–146.The P—V—T—x properties for the acetone—n-pentane azeotrope-forming system have been measured by the technique developed by Kay. The experimental uncertainties have been estimated at 0.05 K, 2.4 kPa and 0.06% of the volume. The results for eight different compositions covering the range 180 to 200°C and 2.5 to 4.0 MPa are given. Smoothed critical loci have been plotted. The critical temperatures and pressures were correlated by a quadratic relationship of the form Q_cm = Σ_iΣ_jx_ix_jQ_cij where i, j = 1, 2. The maximum discrepancy in the critical temperature was 0.6 K and in the critical pressure was 0.012 MPa.     

Molecular interactions in binary mixtures of non-electrolytes: Molar excess enthalpies

Molar excess enthalpies, H^E, for pyridine (i) + α-picoline (j), + β-picoline (j), + γ-picoline (j); pyridine (i) + cyclohexane (j); β-picoline (i) + cyclohexane (j); methylenebromide (i) + pyridine (j), + β-picoline (j) mixtures have been measured calorimetrically as a function of temperature and composition. The H^E data at 298.15 and 308.15 K have been analysed in terms of the Sanchez and Lacombe theory and the “graph theoretical approach”. The graph theoretical approach describes the H^E data well for all these mixtures. This approach has been critically examined and it is found to provide an insight into the nature of molecular interactions between the components of these mixtures. NMR studies on methylene bromide (i) + β-picoline (j) andβ-picoline (i) + pyridine (j) further support these conclusions.     

Deformation directions obtained from atom-atom potentials: molecular deformations in crystals

Forces of interatomic interactions F_ij calculated from atom-atom potentials as -dV_ij/dr_ij allow us to interpret angular deformations in the ring of sodium p-nitrobenzoate trihydrate. Calculations were made for distances r_ij between the ith and jth atoms belonging to different species less than the sum of the van der Waals radii of i and j. Calculations are based on very precise X-ray measurement of the cyrstal structure.     

Molar excess enthalpies of ternary mixtures of non-electrolytes

Molar excess enthalpies, H^E_ijk(T₁, x_i, x_j), for methylenebromide (i)+pyridine (j)+β-picoline (k); pyridine (i)+β-picoline (j)+cyclohexane (k); benzene (i)+toluene (j)+1,2-dichloroethane (k); benzene (i)+o-xylene (j)+1,2-dichloroethane (k); and benzene (i)+p-xylene (j)+1,2-dichloroethane (k) mixtures have been measured calorimetrically as a function of temperature and composition. The data have been analysed in terms of the Sanchez and Lacombe theory and using an approach employing the “graph theoretical” concept of connectivity parameters to characterize its pure components. It has been observed that the H^E_ijk (T, x_i, x_j) data calculated from the “graph theoretical” approach using ³ξ values based on δ^v considerations (that take into consideration the valency of individual atoms of the molecular graph constituent components) best reproduces the corresponding experimental H^E_ijk data.     

Azeotropy in Terpolymerization

This work deals with the determination of the various azeotropies in radical terpolymerization: unitary azeotropy (m_i = M_i); binary azeotropy (m_i/m_j. = M_i/M_j), and ternary or true azeotropy (M_j = m_j for j = 1, 2, 3). General analytical solutions are given which are easily handled by a computer. In addition, these calculations show the existence of pseudo-azeotropy where the deviation between polymer and monomer feed compositions is very small, not only at the beginning of the reaction, but also with increasing conversion.     

Some considerations on the microwave electrodeless discharge: Plasma diagnostics in argon,helium or nitrogen atmospheres

Plasma diagnostics of several microwave plasmas are determined by making electrical (with double floating probes) and optical measurements in pure Ar, He or N₂ plasmas, and also in Ar plasmas containing various metals, i.e. Cs, Tl or Zn; plasma parameters, such as, electric field (E), electron (j_e) and ion (j_i) current densities, electron density (n_e), electron temperature (T_e) electron conductivity (σ_e), ion density (n_i), electron mean free path (λ_e) electron (μ_e) and ion (μ_i) mobilities and electron [(v_e)_drift] and ion [(v_i)_drift] volocities are either directly measured or calculated. The reversal temperature (T_r) of excited (0.96 eV lower level) thallium atoms is measured, and the steady-state conditions of the plasma are analyzed by the energy balance equation. The experimental measurements indicate that the electric field strength E decreases as the space charge decreases (ionization extent) increases. Although the plasma appears to be under steady-state conditions, it is not under local thermodynamic equilibrium conditions, i.e. T_e >T_r. In addition, the measurements indicate that there is a deficiency of electrons in the plasma (n_e < n_i), probably due to electron affinity processes; and the plasma has a small positive space charge.     

Acid—base equilibria in the mixed solvent 80% dimethyl sulfoxide—20% water : Part I. definition of ph scale and determination of pk values of aliphatic monocarboxylic acids

The acid—base equilibria in the mixed solvent, 80% dimethyl sulfoxide—water, have been investigated by potentiometric measurements with a glass—silver—silver chloride electrode couple. The response of the glass electrode is quick and reproducible over the whole pH scale. The autoprotolysis constant (itK_SH) of the mixed solvent has been determined; the value obtained, pK_SH = 18.40, agrees well with reported data. The pK_a values of the following aliphatic monocarboxylic acids are reported: formic, acetic, propionic, n-butyric, iso-butyric, n-valeric, iso-valeric, capric, pentadecanoic, stearic, monochloroacetic. The mixed solvent offers better titration conditions than water for the determination of these acids.     

Substituent effects in the reaction of phenols with polyacrylonitrile radicals

Substituent effects in the reactivities of phenols towards polyacrylonitrile radicals have been studied in terms of Swain and Luptons' field (F_k) and resonance (R_k) components of the substituent parameters and the unique positional weighting factors (f_j and r_j) proposed by Williams and Norrington, with the aid of the following equation:

$\text{P}{}_{\mathrm{i}}\text{= x}{}_{\mathrm{i}}\text{?}{}_{\mathrm{i}}\text{F}{}_{\mathrm{k}}\text{+ ß}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{K}{}_{\mathrm{i}}\text{+ e}{}_{\mathrm{i}}\text{+}\text{P}\text{i}\text{o}$

P_i′s are the rate parameters, P_i⁰ being that for a standard reference compound. Two types of rate parameters have been employed—one, suggested by Simonyi, Tüdös and Pospisil (β) and another, suggested by us, (K), which is obtained from a plot of [Monomer]/(rate of polymerisation) vs [Phenol]. The correlations have been found to be quite satisfactory with both β and K. An attempt has been made to ascertain the nature of the transition state from the reaction parameters α_i and β_i; a dipolar transition state is suggested. The anomalous kinetic behaviour of hydroxy phenols has been discussed.     

Contacts between segments in the random-flight model of polymer chains

The probabilities of single and double contacts, and correlations among contacts were calculated for the random-flight model of a polymer chain. The problem was studied earlier by various authors using the Gaussian statistics of the random-flight chain, which is applicable only for long chains, and for contacts which are formed by pair of residues (i,j) which are far from each other (i.e. |i−j|≫1). We used the exact (non-Gaussian) solution of the random flight model, so that our results are applicable also for residues which are relatively close to each other. We applied the results to close contacts of the β-sheet type and α-helix type in proteins, and compared the exact solutions of the problem with Gaussian approximations.     

Surface treatment of borosilicate glass beakers for prevention of sodium contamination

Pyrex glass beakers are treated with molten Ca(NO₃)₂-KNO₃ (20:80 mol %) mixture at 500°C for 3 h. Treated beakers can be used successfully in wet oxidation of SRM-1571 Orchard Leaves for sodium determination; at least 10 oxidations can be done without sodium contamination. Mass spectrometry is used to investigate the depth profiles of glass components within 60 nm of the glass surfaces and to clarify the mechanism of the sodium contamination.     

Topological and thermodynamic investigations of molecular interactions in binary mixtures: Molar excess volumes and molar excess enthalpies

Molar excess volumes and molar excess enthalpies of butyl acetate (i) with cyclohexane or benzene or toluene or o-, m- or p-xylene (j) binary mixtures have been measured dilatometrically and calorimetrically over the entire composition range at 308.15 K. The observed data have also been analyzed in terms of graph theoretical approach. The analysis of V^E data by graph theoretical approach suggests that butyl acetate in pure state exists as associated entity and (i + j) mixtures are characterized by the presence of (i–j) molecular entity. It has further been observed that V^E and H^E values calculated by this approach agree well with the corresponding experimental values. The presence of molecular entity is further confirmed by IR study of (i + j) mixture.     

Predicting retention data in gas-liquid chromatography by multivariate analysis

Satisfactory reproduction of the retention data matrix in the case of a series of mono-substituted benzenes and a series of aliphatic substances proves the general character of the prediction equation

where x_Qi, φ_j are the retention data x of unknown solute Q_i on phase φ_j; a_Qi, b_Qi, c_Qi and d_Qi are regression coefficients which to some extent account for forces of orientation, charge transfer and association; and x_STi, φ_j are independent variables representing the retention data of the four compounds of the standard set of substances on a given phase φ_j. These four compounds are selected by diverse methods of multivariate analysis. The predicted values show very satisfactory agreement with the observed values.     

An objective computer-oriented method for the calculation of formation constants from the formation function. A weighted least-squares curve fitting

A computer program has been developed that calculates, using the weighted least-squares technique, the overall formation constants, B_i, of mononuclear complexes, the standard deviations of B_i, SDV_i, and an estimate of goodness of fit, Goodness-of-Fit Parameter (GOFP), given a set of average ligand numbers, VN_j, the corresponding free ligand concentrations, VA_j, and an error parameter P. The formation function used is ∑(VN_j – i) · (B_i) · (VA_j)ⁱ = 0 where i ranges from O to n with a maximum of 10 and j ranges from O to l with a maximum of 40. The B_i and (B_i – SDV_i) must be positive and GOFP must be either unity or as close to unity as possible. An option is available that allows the computation of P, if it is not provided, so that GOFP is equal or very close to unity. The method has been applied to the formation of the complexes Cadmium-Imidazole, Cobalt(II)-Bis(2-Quinaldylphenyl Ketone), Copper-Ammonia, Silver-4-Aminobutan-1-ol Nitrate, and Copper(II)-Bis(2-Quinaldylphenyl Ketone). The results are quite satisfactory and reliable as compared with other computational techniques. Input data and results for the five complexes mentioned are shown.     

Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities

Differential scanning calorimetry (DSC) has become a popular tool to investigate thermal transitions in food ingredients such as gelatin. Upon heating commercial gelatin samples beyond glass transition (T _g) and melting (T _m) temperatures, a relatively large endothermic transition (T _i) can be observed. We have observed that both the peak temperature and the enthalpy of the T _i transition are influenced by the integrity of the seal of the DSC pans used for the analysis. This study shows that escape of moisture from the DSC pan appears to be responsible for this effect. The effect of different types of DSC pans, as well as technique of sealing them on the T _i transition were evaluated using DSC, SDT, and TG–MS.     

Exponential gap relation and the rotational inelasticity of H2M systems

Previously published values of state-to-state integral inelastic cross sections for the H₂(J_i)—M (M  H, He, Li, Li⁺, H₂, CO₂) systems are fitted to the exponential gap relation for the rotational inelastic process to obtain the C value that reflects the magnitudes of relative cross sections. While the vibration of the rotor seems to have little influence, the C value is shown to decrease dramatically with increase in initial collision energy T_i, ΔC/ΔT_i being larger at lower T_i for all systems analysed, in accord with the prediction of the surprisal synthesis of Procaccia and Levine. For the only case of H₂(J_i)-Li⁺ for which results are available for several J_i, C decreases with increase in J_i or J_i(J_i + 1)). The C value predicted by Procaccia and Levine for H₂M systems falls within the range of C values calculated for the various collision partners. However, there is a noticeable change in C (albeit within a factor of two) with change in M, indicating that dynamical factors do play an important role in rotational inelastic processes.     

Rate parameters for transfer reactions of some polymer radicals: in terms of Swain and Lupton's f and r and the unique positional weighting factors of Williams and Norrington

Rate parameters of the reaction of phenols, deuterated phenols and nitrobenzenes with polyvinylacetate radicals and of aromatic thiols with polymethylmethacrylate radicals have been correlated with Swain and Lupton's substituent constants (F_k and R_k) and Williams and Norrington's unique positional weighting factors (f_j and r_j) by the following equation: $\text{P}{}_{\mathrm{i}}\text{= α}{}_{\mathrm{i}}\text{?}{}_{\mathrm{j}}\text{F}{}_{\mathrm{k}}\text{+ β}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{R}{}_{\mathrm{k}}\text{+ e}{}_{\mathrm{i}}\text{+ P}{}^0{}_{\mathrm{i}}$where P_i's are the rate parameters, P⁰_i being that for a standard reference state. The correlations were found to be quite satisfactory. The sign and magnitude, and the ratio of the reaction dependent parameters α_i and β_i throw light on the nature of the transition state and the relative contributions of the mesomeric and inductive effects. The present studies also show that the mesomeric effect of meta-substituents is significantly greater than reported by earlier workers.     

Enantioselective synthesis of (S)- and (R)-6-hydroxy-8-nonene-carboxylates by asymmetric catalysis: a formal synthesis of (R)-α-lipoic acid and its (S)-antipode

A short and efficient enantioselective synthesis of (S)- and (R)-configured 6-hydroxy-8-nonene-carboxylates — precursors to (R)-α-lipoic acid and its (S)-enantiomer — by allylation of alkoxycarbonyl substituted aldehydes with allyltrimethylstannane and BINOL/Ti(OiPr)₄ catalyst is described. The best results in terms of enantiomeric purity and yield are obtained employing 10 mol% of the titanium-species without molecular sieves.     

Measurement of state-to-state rotational transfer rates in collision of I2*(B 0u+, υ = 15, j) with 3He, 4He,Ne, Ar,H2, D2 and I2

The selective laser excitation and induced fluorescence observation technique has been used to study rotationally inelastic collisions of I₂^*(B 0_u⁺, υ = 15,j) with I₂, ³He, ⁴He, Ne, Ar, H₂ and D₂. For each collision partner, several initial rotational levels ranging from j_i = 12 up to j_i = 146 have been excited. For purely rotational transfer within the υ = 15 level, our data are perfectly consistent with energy sudden (eventually corrected) scaling laws. Thus, any thermally averaged rate constant, k(j_i → j_f), can be expressed as a function of the basis rate constants k(l → 0). Furthermore, these k(l → 0) are found to follow simple empirical fitting laws. Consequently any k(j_i → j_f) can be predicted given a set of two or three fitting parameters. Collisions with relatively heavy particles (I₂, Ar and Ne) are well described by using the inverse power fitting law k(l → 0) = b[l(l+1)]^?γ, where b = 1.7, 1.2 and 1.2×10^?10 cm³ s^?1 and γ = 1.08, 1.02 and 1.17 for I₂^*-Ne, I₂^*-Ar and I₂^*-I₂ collisions respectively. For collisions with light particles (³He, ⁴He, H₂ and D₂), k(l → 0) shows a sharp decrease with l which can be accounted for by a hybrid power-exponential fitting law k(l → 0) = b[l(l+1)]^?γ exp[-l(l+1)/l^* (l^*+1)], where b = 0.84, 0.71, 2.77 and 2.78×10^?10 cm³ s^?1l⁺ = 20.6, 23.1, 18.8 and 31.4, and γ = 0.66, 0.66, 0.78 and 0.91 for I₂^*-³He, I₂^*-He, I₂^*-H₂ and I₂^*-D₂ collisions, respectively. We confirm that the rotational transfer dynamics in heavy molecules is mainly governed by angular momentum exchange.     

Construction of orthogonal subspaces

An orthogonalization procedure is presented that allows construction of at least (n?m) vectors orthogonal to {X_j}, j equals; 1, m, by linear combinations solely among {η_i}, i equals; 1, n, n>m, and 〈X_j/η_i〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).