Spheriodal multipolar expansions for intermolecular energy in crystal theory .: II. Lattice energy of the orthorhombic structure of actylene crystal

The spheroidal formalism for the interaction energy between two non-overlapping ellipsoidal charge distributions is applied to the determination of the lattice energy of the orthorhombic structure of the acetylene crystal. The molecules are assimilated to quadrupolar prolate ellipsoids and the pair potential is assumed to be a sum of two terms: a Kihara corepotential extended to prolate ellipsoids and the spheroidal quadrupolar interaction. The value so obtained for the lattice energy is ?25.01 kJ mole^? while an evaluation of the corresponding observed value is ?23.81 kJmole^?.     

The heat of dehydration of halophilic bacteria as measured by differential scanning calorimetry (DSC)

The heat of dehydration of two species of halophilic bacteria and of red cell pellets was measured by DSC. The molar heat of dehydration of H. marismortui was found to be 50.4 kJ mole^?1 H₂O, whereas that of H. halobium was 46.2 kJ mole^?1 H₂O, and that of human red blood cell 40.6 kJ mole^?1 H₂O. The molar heat of dehydration of H. marismortui has been shown to be composed of three fractions; the second one has a molar heat of 58 kJ mole^?1 H₂O and the third one 108 kJ mole^?1 H₂O.     

Thermodynamique de composes azotes. VII. Etude thermochimique du pyrazole et de l'imidazole

Enthalpies of sublimation for pyrazole and imidazole have been obtained by calorimetry at 298.15K. The ΔH⁰_sub (298.15 K) values for these two compounds are, respectively, 69.16 ± 0.32 and 74.50 ± 0.40 kJ mole^?1. From literature data obtained by combustion calorimetry for ΔH⁰_f (c, 298.15 K), the enthalpies of formation of these compounds in the gaseous state (pyrazole: 185.1 ± 2.3 kJ mole^?, imidazole: 133.0 ± 1.7 kJ mole^?1) have been derived. Several energy values related to the molecular structure of these two compounds (as resonance energy, enthalpy of isomerization, …) have been determined. The study of pyrazole has enabled us to contribute to the evaluation of some characteristics of the NN bond.     

Evaluation of metal hydride thermograms by a differential-correction technique

A least-squares linear-Taylor differential-correction technique has been used for the rapid evaluation of thermogravimetric curves obtained during the decomposition of magnesium hydride, iron—titanium hydride and lanthanum—nickel hydride. For magnesium hydride and iron—titanium hydride the Avrami—Erofe'ev equation fits the experimental data, thus indicating that nucleation is the rate-determining step under thermogravimetric conditions. For lanthanum—nickel hydride a combination of the Avrami—Erofe'ev equation and the phase boundary movement equation fits the data up to a fractional decomposition of 0.8. For magnesium hydride decomposition the activation energy E and the pre-exponential factor Z are dependent on the hydrogen pressure (E = 101.2 kJ mole^?1 and Z = 8.96 × 10⁷ at 0.30 MPa, while E = 66.3 kJ mole^?1 and Z = 4.77 × 10⁷ at 0.11 MPa). For iron—titanium hydride (E = 28.4 kJ mole^?1) and lanthanum—nickel hydride (E = 13.4 kJ mole^?1) the values are independent of pressure.     

Angular dependence of the vicinal interproton spin–spin coupling in silacyclohexanes. The conformational energy term of the methyl group in 1-methyl-1-silacyclohexane

An approximate Karplus-Conroy relationship between the vicinal coupling constants J(H SiCH ) in a silaethane fragment and the corresponding torsional angles τ in silacyclohexanes is proposed. The relationship ³J(H SiCH ) VS τ is asymmetric. The ¹H NMR parameters and conformational features of cis- and trans-3,5-dimethyl-1-silacyclonexane and 3-silabicyclo[3.2.1]octane are discussed, and the conformational energy term for the methyl group in 1-methyl-1-silacyclohexane is found to be approximately 1.45 kJ mole^?1 in favour of the axial position for the methyl group, in good agreement with previously calculated values.     

Kinetics of the dissociation and cis-trans isomerization of o,o'-azodioxytoluene (dimeric o-nitrosotoluene)

The dimer-monomer reactions were investigated for the system cis and transo,o'-azodioxytoluene-o-nitrosotoluene in acetonitrile solvent. For the reaction cis dimer-monomer the following thermodynamic and activation parameters have been derived: ΔH°=58.5±2.5 kJ mole^?1, ΔS°=206.2±3.8 J mole^?1 K^?1, ΔH^≠=63.6±3.3 kJ mole^?1, ΔS^≠=6.3±0.3 J mole^?1 K^?1. The corresponding values for the reaction trans dimer-monomer are: ΔH°=45.6±2.1 kJ mole^?1, ΔS°=162.7±7.1 J mole^?1 K^?1, ΔH^≠=80.8±2.9 kj mole^?1, ΔS^≠=-13.4±0.8 mole^?1 K^?1. There is no evidence of a direct cis-trans isomerization (i.e. a reaction not proceeding via the monomer). NMR and various perturbation techniques monitoring the visible absorption of the monomer were employed.     

Properties of strong hydrogen-bonded systems. II. Ab initioSCF-MO study of the hydrogen bond between nitric acid and ammonia

The hydrogen-bonded complex between nitric acid and ammonia molecules has been studied by the ab initio molecular orbital method using the 4-31G basis set. The calculated interaction energy for the complex (ΔE = ?91.4 kJ mole^?1) indicates that one is dealing with the strongest “nonionic” H-bonded complex considered hitherto by theoretical methods. Other properties of the hydrogen-bonded complex such as geometrical parameters, dipole moment, amount of charge transfer, and stretching force constants of the O? H and (OH)… N bonds are calculated and discussed.     

Lattice energies: calculations from pressure—volume data,and uncertainties in the results

A method of calculating lattice energies is developed, which reproduces directly the observed pressure—volume curve of some simple ionic solids. The results in general are close to the experimental values, and show deviations usually between 5 and 10 kJ mole^?1. The calculated values are not systematically too high or too low. Some estimates are made of the effect of errors in the P–V curve on the calculated lattice energies.     

Kinetics of oxidation of methanol and mono-deutero-methanol by chromium(VI) in perchloric acid medium

Kinetics of the oxidation of methanol and mono-deutero-methanol by Cr(VI) over a wide range of temperature (25–40°) have been studied in perchloric acid medium at constant ionic strength (μ = 1.0 M) adjusted with sodium perchlorate. Each reaction is first order with respect to the substrate and dichromate concentrations but the order with respect to [H⁺] is nearly 3 in each case. Both these reactions take place at almost the same rate under identical experimental conditions. The activation parameters of the reactions are not widely different and the values of ΔH3 and ΔS3 for the oxidation of methanol are 79.5 kJ mole ^-1 and - 38.1 J deg^-1 mole^-1 respectively, whereas the corresponding values for the deuterated compound are 83.8 kJ mole^-1 and -23.9 J deg^-1 mole^-1. The probable mechanism of the reactions is discussed.     

Mass spectrometric evidence for the very high stability f gaseous ThIr and ThPt and method of calculating dissociation energies of diatomic intermetallic compounds with multiple bonds

The dissociation energes, D⁰₀, of the molecules ThIr and ThPt have been measured by high temperature Knudsen cell mass spectrometry as 136.4=10 and 130.7=10 kcal mole^?1 or 570.7±41.8 and 546.6±41.8 kJ mole^?1, respectively.A method is proposed for the calculation of dissociation energies of gaseous intermetallic compounds with multiple bonds.     

An ab initio study of the geometry and energy of six planar conformers of β-hydroxyacrolein

Ab initio calculations with full geometry optimization have been carried out on the planar cCc, cTc, tTc, tCt, tTt, and cCt conformers of β-hydroxyacrolein using the 4-21G basis set, and on the cCc and cCt conformers using the 4-31G basis set. The hydrogen-bonded cCc conformer is the most stable and the cCt conformer the least stable, with the other conformers following the above sequence. β-Hydroxy substitution has scarcely any influence on the geometry of the trans-acrolein structure, whereas the geometry of the cis-acrolein structure shows significant changes which depend on whether the O? H group is cis or trans with respect to the CHO group about the C?C bond. The ΔE_T values for cis → trans isomerization about the C? C bond in cCt and cTc support the hypothesis that these changes in geometry are the result of a destabilizing interaction in cCt and a stabilizing interaction in cTc. The geometry of the hydrogen-bonded structure cCc sets it apart from all the other conformers: it has by far the longest C?C, the longest C?O, the longest O? H, the shortest C? C, and the shortest C? O. Its formation from cCt involves a lengthening of C?C, C?O, and O? H and a shortening of C? C and C? O, indicating a delocalization of charge within the ring. 4-21G calculations have also been made for a distorted cCt structure that has the same bond lengths and angles as the equilibrium cCc structure, and the distortion energy, cCt (equm. geom.) → cCt (distorted geom.), is found to be +13.1 kJ mole^?1. Taking the energy of this distorted cCt structure as the baseline, the hydrogen-bonding energy in cCc is found to be —80.3 kJ mole^?1.     

DSC determination of the fusion and sublimation enthalpy of bis(2,4-pentanedionato)beryllium(II) and tris(2,4-pentanedionato)aluminium(III)

The sublimation enthalpy of bis(2,4-pentanedionato)beryllium(II) and of tris(2,4-pentanedionato)aluminium(III) has been determined by differential scanning calorimetry as 85.3 ± 3.5 kJ mole^?1 and 125.6 ± 3.2 kJ mole^?1, respectively. The corresponding fusion enthalpies are 15.67 ± 0.74 and 28.71 ± 1.34 kJ mole^?1, respectively.     

Permanent moment contributions to chiral discrimination

The discrimination energy, giving the difference in the interaction of two leavo molecules and one laevo with one dextro, is calculated where the coupling involves permanent electric and magnetic moments. Fixed electric dipoles arranged helically on a lattice (simulating the electric effects of a helical polymer for example) give chiral fields producing large (≈kT) discriminations. For the pairwise interaction of fixed molecules realistic electric dipole and electric quadrupole moments can lead to discriminations of about 100 cal mole^?1 at 0.5 nm separation. In the hypothetical case of molecules possessing permanent electric and magnetic moments it is four or more orders of magnitude less. In a freely rotating molecule pair the sequence is reversed and electric and magnetic dipoles give much the bigger averaged discrimination energy.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

The heat of dehydration of concentrated sodium chloride and potassium chloride solutions

The molar heats of dehydration, ΔH¯_dehyd., of concentrated sodium chloride and potassium chloride solutions were measured with a differential scanning calorimeter in the scanning and isothermal modes. The overall ΔH¯_dehyd. was found to be 44.5 and 44.3 kJ mole^?1 H₂O for NaCl and KCl solutions respectively. There is an astonishing difference between concentrated NaCl and KCl solutions in the way water is lost. The number of fractions of heat dehydration were 2 for NaCl and 3 for KCl. The excess ΔH¯_dehyd. was about 10 kJ mole^?1 H₂O for fraction II of NaCl, and 17 and 55 kJ mole^?1 H₂O for fractions II and III, respectively, of KCl.     

Thermal decomposition of formates. Part VIII. Thermal dehydration of Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III) formate dihydrates

The thermal dehydration of some rare earth metal formate dihydrates were studied by means of thermogravimetry, differential thermal analysis and differential scanning calorimetry.The dehydration took place successively as a one step reaction for all of the formate dihydrates examined. The reaction order of dehydration was found to be $\text{2}\text{3}$ for all of the salts examined, which indicated that the rate of dehydration was controlled by a chemical process at a phase boundary.The values of the activation energy, frequency factor and the enthalpy change of dehydration for all of the dihydrates were 108–142 kJ mole^?1, 10¹⁶–10¹⁷ min^?1 and 109–147 kJ mole^?1, respectively.Both the temperature at which the dehydration occurred and the enthalpy change increased as the reciprocal of the radius of the metallic ion increased.     

Thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate. Part 3. Isothermal kinetics

The kinetics of the thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate in air were established from isothermal experiments. By heating the solution, first most of the water evaporates to a composition of equimolar amounts of water and manganese nitrate; this concentrated solution then decomposes to γ-Mn(NO₂, NO₂ and water, usually in two steps. The first step can be described best by the model [?ln(1 ? α)]^{$\text{1}\text{2}$} = 8.9 × 10¹¹ exp(?121000/RT)t, whereas the second step is described equally well by several models. The kinetic parameters of these models are quite similar, the average activation energy being 141 kJ mole^?1.The decomposition of anhydrous Mn(NO₃)₂, which proceeds in a single step, can also be described with several similar models. In this case the average activation energy is about 92 kJ mole^?1.     

First principles computation of lattice energies of organic solids: the benzene crystal

We provide a first-principles methodology to obtain converged results for the lattice energy of crystals of small, neutral organic molecules. In particular, we determine the lattice energy of crystalline benzene using an additive system based on the individual interaction energies of benzene dimers. Enthalpy corrections are estimated so that the lattice energy can be directly compared to the experimentally determined sublimation energy. Our best estimate of the sublimation energy is 49.4 kJ mol(-1), just over the typical experimentally reported values of 43-47 kJ mol(-1). Our results underscore the necessity of using highly correlated electronic structure methods to determine thermodynamic properties within chemical accuracy. The first coordination sphere contributes about 90 % of the total lattice energy, and the second coordination sphere contributes the remaining 10 %. Three-body interactions are determined to be negligible.     

Pyrolysis of 1,7-octadiene

Pyrolysis of 1,7-octadiene identified as an intermediate during the thermal degradation of cis-decalin, has been studied between 843 and 953 K. The 1,7-octadiene radical first produced, leads to the formation of α,α-olefinic fragments and to 1-ethyl-1,4-cyclohexadiene. by an internal cyclization. These are the precursors of the aromatic hydrocarbons resulting from the high-temperature pyrolysis of cis-decalin. The activation energy of the cracking of 1,7-octadiene has been calculated to be 180 kJ mole^?1 (43 kcal mole^?1)     

Localized electrons in 1,8-octanediol crystals studied by ESR spectroscopy and pulse radiolysis

Localized electrons in 1,8-octanediol crystals have been studied by pulse radiolysis and ESR spectroscopy. The maximum of the optical absorption is at 625 nm. The decay is first order with an activation energy of 16.3 kJ mole^?1. The assignment of the optical spectrum has been made by ESR at 67 K. When the electron decays the -CH₂CHCH₂- radical grows in.