Seawater—A test of multicomponent electrolyte solution theories. II. Enthalpy of mixing and dilution of the major sea salts

In a continuing effort to predict the physicochemical properties of seawater from the properties of single aqueous electrolyte solutions, the pairwise heats of mixing at constant molal ionic strength,I=1.0 ional, have been determined for the six possible pairs of salts from the set (NaCl, Na₂SO₄, MgCl₂, MgSO₄) at 30°C. In addition, heats of dilution for two aqueous solutions formed from these salts and havingI=1.0 ional have been determined at 30°C. In order to present the most thermodynamically consistent results, it was found necessary to apply a correction term to the relative apparent equivalent enthalpies given in the literature at 30°C. These correction terms derived from a consideration of published results on heats of dilution at very low concentrations. Further, in order to make predictions for seawater at 25°C, it was deemed desirable to refit existing heat-capacity data. The heats relative apparent equivalent enthalpies for the two mixtures mentioned as well as for seawater. The estimates are based on the theoretical equation of Reilly and Wood for charge-asymmetric mixtures which derives from the work of Friedman. In the most applicable cases, the estimates agree with experimental relative apparent equivalent enthalpies to within 5%. In general, the results substantiate the theoretical equation.Taken in part from the Ph.D. dissertation of W. H. Leung, University of Miami, Miami, Florida 33149.     

A flow microcalorimeter for measuring the heats of mixing of binary liquids by A continuous process

In order to measure heats of mixing or heats of dilution for many solutions by a continuous process accurately, a twin conduction type flow microcalorimeter has been constructed, improving the design of the same type of calorimeter reported previously. The thermal stability of the heat sink was enhanced by enlarged contact area of the main heat sink block with a thermostated water bath. Mixing efficiency of the mixing cell and the stability of the base line were improved by the use of a new mixing cell having a long mixing zone and symmetrically arranged sample and reference cells. Waiting time for establishment of thermal steady state was also reduced by sandwiching each of the cell by a pair of wide thermopiles plates and a pair of sub-blocks. Heats of dilution of aqueous urea solutions were measured by a continuous process, and results obtained well agreed with accepted values by Guckeret al. The accuracy and thermal resolution in this calorimeter were estimated to be less than 0.05% and 3 J·s^–1.The authors are grateful to Professor S. Murakami of Osaka City University for helpful discussion.     

Thermodynamic study of binary mixtures of isomeric butylamines with methanol enthalpy of hydrogen bonded complex

Heats of mixing of the binary mixtures ofn-, sec-, iso- andt-butylamines with methanol were determined in the entire concentration range. All the four systems showed a strong exothermic behaviour. The exothermic heats of mixing vary in the ordert-BuNH₂ >n-BuNH₂ > sec-BuNH₂ > iso-BuNH₂. The enthalpy of hydrogen bond in the methanol-butylamine complexes was calculated by means of a thermochemical cycle and found to vary in the ordert-BuNH₂ >n-BuNH₂ > iso-BuNH₂ > sec-BuNH₂. This order is different than that found for the hydrogen bond due to self-association. The difference has been explained in the light of steric and electromeric effects arising out of the substitution of the methyl groups in the alkyl chain of the butylamine. NCL Communication No. 2356 (Part of the Ph.D. Thesis submitted to the Bombay University by the first author).     

Enthalpy of hydrogen bonded alcohol-butyl amine complexes by a simpler calorimetric method

The heats of mixing ofn-butyl amine with methanol andn-propanol have been determined at 30° C and the enthalpies of alcohol-amine complex formation have been calculated by thermochemical cycle. The enthalpies of complex formation of butyl amine with methanol andn-propanol were found to be-44.3 kJ/mole and-39.4 kj/mole respectively. The heats of mixing of synthetically prepared 1:1 molar mixtures of n-butyl amine with methanol, ethanol andn-propanol withn-hexane have also been determined at 30° C. The enthalpy of amine-alcohol complexes was obtained from the partial molar heats of dissociation of the complexes inn-hexane. The values agree with those obtained by the thermochemical cycle method. NCL Communication No. 2561.     

The relation of solvent heats of mixing to the enthalpies of proton transfer of some amines in methanol-water mixtures

Enthalpies of reaction for proton transfer in methanol-water mixtures are related to the enthalpies of mixing of methanol and water. The data are direct calorimetric measurements of the standard enthalpies of proton transfer in methanol-water mixtures of varying composition using the bases quinuclidine triethylamine, and tris(hydroxymethyl)aminomethane. Other possible applications of the principle are mentioned.decreased     

A new calorimeter for simultaneous measurement of isotherms and heats of adsorption

A new calorimeter designed for simultaneous measurements of heats and isotherms of gas adsorption and desorption systems is presented. It consists of a volumetric/manometric gas adsorption instrument, the adsorption vessel of which is placed within a second vessel filled with inert gas. This gas acts as a sensor, as not only its temperature but also its pressure is increased if heat is released from the adsorption vessel via the sensor gas to its thermostated surroundings. Indeed, the time integral of the sensor gas pressure signal turned out to be strongly related to the total heat released from the adsorption vessel.A basic theoretical equation of the measurement procedure is given. Results of numerous calibration measurements are presented. The question of what type and amount of sensor gas should be used to achieve high sensitivity of the instrument is discussed.Two examples of measurements of heats of adsorption and adsorption isotherms are given, namely adsorption of N₂ on alumina oxide (CRM-BAM-PM-104) at 77 K and CO₂ on zeolite Na13X and wessalite DAY both at 298 K.     

Crystal and molecular structure of 5-trifluorothymine, a metabolite from human urine: Role of fluorine in stacking and hydrogen bonded interactions

The crystal structure of the metabolite from urine, 5-trifluorothymine [5F₃T] has been determined by single crystal X-ray diffractometric methods. Crystals of 5F₃T are monoclinic, space group P2₁/c with cell dimensions a = 6.7468(2), b = 15.0740(6), c = 13.4405(6), β = 90.412(2), V = 1366.88(8), Z = 8 (two molecules per asymmetric unit). Crystal structure of 5F₃T was determined with 3039 independent data and refined by full-matrix least squares methods to a final reliability factor of 0.047. Molecules of 5F₃T are connected by dimeric type of NH?O hydrogen bonding linking molecules related by a center of inversion into an extensive layer of dimeric molecules. These layers are stacked on top of each other at a stacking distance of 3.280 Å with a head-to-head stacking of the fluorine atoms on top of each other with no hydrogen bonding involving the fluorine atoms.     

1,2,3-三氮杂苯-水簇复合物氢键结构与性质的理论研究

在B3LYP/6-31 G**水平上对1,2,3-三氮杂苯和水形成1∶1,1∶2和1∶3复合物的基态氢键结构进行几何优化和性质计算,结果表明复合物之间存在较强的氢键作用。氢键的形成使水分子中H-O键振动频率减小(红移)。NBO分析表明,最稳定的1∶1,1∶2和1∶3复合物发生分子间电荷转移总量分别为0.0222e,0.0261e和0.0273e。     

The conformation of the hydrogen bonded complex cyclohexene oxide⋯HCl: A rotational study

Cyclohexene oxide and its hydrogen bonded complex cyclohexene oxide⋯HCl have been investigated using a molecular beam Fourier Transform microwave spectrometer. The spectra of the parent species of cyclohexene oxide and its ¹³C and ¹⁸O isotopomers have been measured in their natural abundances. This has allowed obtaining the substitution and effective structures of the monomer heavy atom skeleton. A fast mixing nozzle has been designed to generate the complex preventing the reaction between the components. Only the equatorial conformer of the complex has been detected and its ³⁵Cl and ³⁷Cl isotopic species have been measured in their natural abundances. From the spectroscopic data the hydrogen bond structural parameters were obtained assuming that the structures of the monomers do not change upon complexation. HCl lies in the COC bisecting plane forming a non-linear hydrogen bond to the equatorial non-bonding electron pair at oxygen. The geometries of the axial and equatorial conformers have been optimized at MP2/6-311++G(d,p) level of theory predicting the equatorial conformer as the most stable one. The non-observation of the axial form is discussed.     

Methyl hydrogen peroxide dimer: A structural study

Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol⁻¹.     

Effect of hydrogen bonding of solvent on the thermodynamic stability of cadmium ethylenediamine complexes

Changes in the stability of the cadmium(ii) ethylenediamine complexes in mixed water—DMSO solvents were studied by pH-metry and calorimetry. Complex cations [Cd(en)]²⁺, [Cd(en)₂]²⁺, and [Cd(en)₃]²⁺ are formed in aqueous solutions, and the [Cd(en)₄]²⁺ complex with a partially dentate ligand is stable in DMSO. An increase in the DMSO content in a solvent increases the stability of the complexes. The maximum increase in logK is observed for coordinatively saturated compounds. The thermodynamics of complexation is discussed from the viewpoint of solvation approach. Principal differences in the influence of aqueous-alcohol and aqueous-aprotic solvents on the stability of the metal amino complexes were revealed. Protolytic solvents exert a destabilizing effect on the multiligand complexes, because the coordination sphere is involved in H bonding.     

Intermolecular hydrogen bonds: Comparison of associates in crystals and liquids

The density and sound velocity were measured within wide ranges of temperature for a number of liquids (water, formamide, diols, aliphatic alcohols, cellosolves, ketones), in which various types of H-associate can exist. The temperature dependences of the adiabatic and molar adiabatic compressibility, density, and molar volume are analyzed. The values of the molar adiabatic compressibility permit one to evaluate the dimensionality of H-associates existing in liquids; the values of adiabatic compressibility do not offer this possibility. The terms responsible for the similarity and difference between H-associates in crystals and liquids are discussed.     

Inductive effect for the phase stability in hydrogen bonded liquid crystals,x-(p/m)BA:9OBAs

A new series of hydrogen bonded liquid crystal (HBLC) complexes, made up with substituted benzoic acids (BAs) and nonyloxy benzoic acid, viz., x-(p/m)BA:9OBAs are reported for x = F, Cl, Br and –CH₃ substituted at para (p) or meta (m) positions of BA moiety. Proton nuclear magnetic resonance (¹H-NMR) spectrum confirms the HBLC complex. Infra red (IR) spectrum confirms linear, double and complementary type of hydrogen bonding (HB) between x-(p/m)BAs and 9OBA. The liquid crystal (LC) phases are characterised by polarisation optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. x-(p/m)BA:9OBA exhibit N, C and G LC phase variance. HB induces tilted phases and enhances LC phase stability. The influence of configuration, size, electronegativity, electron directing capacity and inductive nature of substituent (x) is investigated for the stability of LC phases. An overview of the LC phase data indicates predominant ‘negative inductive effect’ in HBLCs with electron withdrawing substituents. Inductive effect operates effectively for para substitutions. Results are discussed in the wake of reports in other HBLCs.     

Statistical theory for hydrogen bonding fluid system of A_aD_d type(II):Properties of hydrogen bonding networks

Making use of the invariant property of the equilibrium size distribution of the hydrogen bonding clus- ters formed in hydrogen bonding system of AaDd type,the analytical expressions of the free energy in pregel and postgel regimes are obtained.Then the gel free energy and the scaling behavior of the number of hydrogen bonds in gel phase near the critical point are investigated to give the corre- sponding scaling exponents and scaling law.Meanwhile,some properties of intermolecular and in- tramolecular hydrogen bonds in the system,sol and gel phases are discussed.As a result,the explicit relationship between the number of intramolecular hydrogen bonds and hydrogen bonding degree is obtained.     

Statistical theory for hydrogen bonding fluid system of AaDd type (Ⅱ): Properties of hydrogen bonding networks

Making use of the invariant property of the equilibrium size distribution of the hydrogen bonding clusters formed in hydrogen bonding system of AaDd type, the analytical expressions of the free energy in pregel and postgel regimes are obtained. Then the gel free energy and the scaling behavior of the number of hydrogen bonds in gel phase near the critical point are investigated to give the corresponding scaling exponents and scaling law. Meanwhile, some properties of intermolecular and intramolecular hydrogen bonds in the system, sol and gel phases are discussed. As a result, the explicit relationship between the number of intramolecular hydrogen bonds and hydrogen bonding degree is obtained.     

A theoretical investigation of electronic reorganizations accompanying core and valence ionization in simple hydrogen bonded systems

Non-empirical LCAO MO SCF calculations have been carried out on the ground state and core ionized states of some hydrogen bonded dimers, and in the particular case of H₂O the trimer has also been investigated. Comparison of absolute and relative binding energies and relaxation energies with respect to the corresponding monomers reveals that substantial changes occur in going to the associated species. The relaxation energies for a given core hole are shown to increase on going from monomer to dimer indicating that intermolecular contributions to relaxation energies are of the same sign irrespective of the sign for the shift in core binding energy. Creation of a core hole in the dimer species is shown to give rise to substantial changes in hydrogen bond energies compared with the neutral species. In the particular case of valence holes dominantly of 2s and 2p character it is shown that trends in shifts and relaxation energies parallel those for the core hole states.     

A study of association by hydrogen bonding in the system phenol-CCl4 by the nuclear magnetic relaxation method

The system phenol-CCl₄ was studied by measuring proton and deuteron magnetic relaxation rates and self-diffusion coefficients at 25°C. From these data intermolecular relaxation rates have been calculated. By means of an association parameter A, association of phenol molecules with respect to various parts of the molecule has been established. Closest distances of approach between protons and configurations of maximum occurrence probabilities are reported.     

A study of the hydrogen bond by means of comparative calculations

The nature of the hydrogen bond is investigated by means of a comparative analysis of some hydrogen bonded and hydrogen-like bonded systems. It is concluded that the hydrogen bond is determined by electrostatic interaction between the proton and the region of high electron density in the neighbour molecule.     

Statistical theory for hydrogen bonding fluid system of AaDd type (Ⅲ): Equation of state and fluctuations

The equation of the state of the hydrogen bonding fluid system of AaDd type is studied by the principle of statistical mechanics. The influences of hydrogen bonds on the equation of state of the system are obtained based on the change in volume due to hydrogen bonds. Moreover, the number density fluctuations of both molecules and hydrogen bonds as well as their spatial correlation property are investigated. Furthermore, an equation describing relation between the number density correlation function of "molecules-hydrogen bonds" and that of molecules and hydrogen bonds is derived. As application,taking the van der Waals hydrogen bonding fluid as an example, we considered the effect of hydrogen bonds on its relevant statistical properties.