Determination of enthalpies of formation of organic free radicals from bond dissociation energies 1. Hydrocarbon radicals

The enthalpies of formation (ΔH _f ^o) for 24 hydrocarbon radicals (R^?), mainly polycyclic aromatic radicals with the complex structure, were determined from the published data on bond dissociation energies. The ΔH _f ^o values of the corresponding molecules were calculated, in the majority of cases, by the macroincrement method. Calculations by the group contribution method were performed. Some ΔH _f ^o(R^?) values were compared to those calculated by the additive-group method. Calculations were performed, and the conjugation energies of the radicals were discussed. The errors of determination of the ΔH _f ^o(R^?) values found were estimated. Due to this work, the database for ΔH _f ^o values of hydrocarbon radicals was increased more than by 25%.     

The strain-sensing behaviors of carbon black/polypropylene and carbon nanotubes/polypropylene conductive composites prepared by the vacuum-assisted hot compression

The strain-sensing behaviors of carbon black (CB)/polypropylene (PP) and carbon nanotubes (CNTs)/PP conductive composites prepared by the vacuum-assisted hot compression were studied and compared. When ten extension-retraction cycles were applied, it was found for CB/PP, the value of the maximum responsivity (ΔR/R ₀, ΔR—the instantaneous variation of the resistance during the test, R ₀—the original resistance) decreased gradually with increasing the cycle number, but it began to rise from the seventh cycle. The value of the min ΔR/R ₀ increased during the whole test. While for CNTs/PP, both the values of the max and min ΔR/R ₀ decreased rapidly. It is suggested that the different behaviors mainly depend on the distinction in the dimension of the conductive fillers and the preparation technique.     

High-energy collisional activation studied via angle-resolved translational energy spectra of survivor ions

Angle-resolved translational energy spectroscopy has been applied to Cs₄I ₊ ³ ions that survived 8 keV collisions with a range of collision gas targets, including inert gases and deuterium. The experimental data comprise values of the translational energy loss ΔT_R as a function of the (laboratory-frame) scattering angle θ _R for each collision gas under conditions such that single-collision events dominated the scattering. The values of ΔT_R increase with θ _R, in accordance with very general expectations. However for any value of θ _R, the values of ΔT_R for helium and deuterium as targets were almost indistinguishable from one another but were at least five to six times larger than those for neon and all other collision gases. These data have been shown to be consistent with theoretical considerations based upon conservation of energy and linear momentum. Theoretical approaches include the simple “elasticlimit” model, which makes no mechanistic assumptions, and a particular “binary-model” theory, which excludes electronic excitation as a possibility. Both theories are consistent with the experimental data and interpret the surprisingly large values of ΔT_R for low-mass targets in terms of large recoil energies of the target required to ensure conservation of momentum. The most likely alternative candidate as sink for ΔT_R is internal excitation of the target, but this possibility was excluded in the present work by choosing ΔT_R values less than the lowest excitation energies of the inert gas targets. Moreover, such an interpretation cannot explain the similar results obtained using helium and deuterium, which were markedly different from those obtained for all other collision gases.     

Thermal decomposition of zinc and cadmium zirconyl oxalates

The enthalpy of formation at 298.15 K of the polymer Al₁₃O₄(OH)₂₈(H₂O)³⁺₈ and an amorphous aluminium trihydroxide gel was studied using an original differential calorimetric method, already developed for adsorption experiments, and aluminium-27 NMR spectroscopy data. ΔH_f “Al₁₃” (298.15 K) = ? 602 ± 60.2 kJ mole^?1 and ΔH_f Al(OH)₃ (298.15 K) = ? 51 ± 5 kJ mole^?1. Using theoretical values of ΔG_R “Al₁₃” and ΔG_R Al(OH)₃, we calculated ΔG_f “Al₁₃” (298.15 K) = ? 13282 kJ mole^?1; ΔS_f “Al₁₃” (298.15 K) = + 42.2 kJ mole^?1; ΔG_f Al(OH)₃ (298.15 K) = ? 782.5 kJ mole^?1; and ΔS_f Al(OH)₃ (298.15 K) = + 2.4 kJ mole^?1.     

Graphical and visualizing method of identification of selected groups of aliphatic compounds in thin-layer chromatography

A new method of group identification was established for selected aliphatic compounds giving homologous series, based upon constant ΔR_M and directional coefficient “a” values (the “a” values being tangents of the angle between the course of the R_M = f(n_c) function and the “x” axis).The results presented concern identification of higher fatty acids and their ethyl esters, amides of higher fatty acids, higher aliphatic amines, ethylalkyl ketones, and dicarboxylic acids.Simultaneously, another method of identifying groups of aliphatic compounds was established, taking advantage of differentiated visualizing effects.     

Distribution of reaction products (theory). XI. H + F2

The availability for the first time of detailed rate constants k(V′, R′, T′) (where V′, R′ and T′ are product vibrational, rotational and translational excitation) for the highly exothermic reaction H + F₂ → HF(V′, R′) + F has prompted the 3D classical-trajectory study reported here. The potential-energy surface is found to be predominantly repulsive ($\text{A}$_⊥ ≈ 42%, R_⊥ ≈ 58%) corresponding to the rather low fractional conversion of reaction energy into vibration ((f′V) = 0.58 from experiment, and 0.56 from theory). In the homologous series of reactions H + X₂ (X  F, Cl, Br, I) the percentage of repulsive energy-release decreases for X  Cl, Br, I, but increases from X  F to Cl. It is shown that this cannot be due to charge in mass-combination, but can plausibly be explained by the anomolously short range of interaction between the separating X atoms in the case X  F. It is predicted that the more-forward scattered HF will be more rotationally excited. The form of the cross section function S_r(T) (where T is reagent translation) is analysed. In accordance with the expectation for a strongly exothermic reaction, it is found that S_r(T) rises more steeply than S_r(V) (where V is reagent vibrational energy). The effect on the product energy distribution conforms qualitatively to the “adiabatic” behaviour noted in previous work: ΔT → ΔT′ + ΔR′; ΔV → ΔV′. The explanation is to be found in reaction through more-compressed or more-extended intermediate configurations than are characteristic of room temperature reaction. We note the existence of an amplification effect: (ΔT′ + ΔR′)/ΔT ≈ 2, and ΔV′/ΔV ≈ 2.     

Untersuchungen an molekülkomplexen von n-σ-TYP MITT. I. über freie enthalpie—kraftkonstantenkorrelationen von molekülkomplexen des jods m

Linear correlations have been found between the ΔG⁰ values of the molecular complexes R₁R₂R₃PO/I₂, R₁R₂SO/I₂ and R₁R₂SeO/I₂ and the PO, SO and SeO valence force constants, respectively. The nature of the correlation is determined by the ZO donor bond and not by the donor atom, where Z is P, S or Se. The change on ΔG⁰ values for an equal change in the ZO valence force constants increases in the order R₁R₂SO/I₂?R₁R₂R₃PO/I₂ < R₁ R₂SeO/I₂. Seleninyl complexes with I₂ are more stable than the analogous thionyl complexes. From ΔG⁰—f_zo correlation deductions can be made about the nature of the ZO donor bond and ΔG⁰ values can be evaluated from vibrational spectra. A linear correlation exists between the ΔG⁰ values of corresponding thionyl and seleninyl complexes which is of the same form as the correlation between the valence force constants of analogous thionyl and seleninyl compounds.     

Effects of stress ratio on fatigue crack growth of thermoset epoxy resin

The influences of stress ratio (R) on fatigue crack growth (FCG) of thermoset epoxy resin with polyamine hardener were investigated. The FCG growth rates (da/dN) have been correlated by the linear-elastic fracture mechanics parameters (ΔK and K_max), and nonlinear-elastic fracture mechanics parameter (ΔJ). The effects of R on FCG were observed when the ΔK and ΔJ were used as fracture mechanics parameters for FCG. However, the K_max successfully characterized FCG under cyclic-dependent condition (FCGs at R = 0.1 and 0.4); but it failed to characterize the FCG under time-dependent condition (FCG at R = 0.7). As a time-dependent fracture mechanics parameter, C* was applied to correlate the time-dependent FCG rate (da/dt). A reasonable agreement was obtained between time-dependent FCG (R = 0.7) and creep crack growth (CCG) results.     

Probability of failure of the watershed algorithm for peak detection in comprehensive two-dimensional chromatography

The watershed algorithm is the most common method used for peak detection and integration in two-dimensional chromatography. However, the retention time variability in the second dimension may render the algorithm to fail. A study calculating the probabilities of failure of the watershed algorithm was performed. The main objective was to calculate the maximum second-dimension retention time variability, Δ²t_R,crit, above which the algorithm fails. Several models to calculate Δ²t_R,crit were developed and evaluated: (a) exact model; (b) simplified model and (c) simple-modified model. Model (c) gave the best performance and allowed to deduce an analytical expression for the probability of failure of the watershed algorithm as a function of experimental Δ²t_R, modulation time and peak width in the first and second dimensions. It could be demonstrated that the probability of failure of the watershed algorithm under normal conditions in GC × GC is around 15–20%. Small changes of Δ²t_R, modulation time and/or peak width in the first and second dimension could induce subtle changes in the probability of failure of the watershed algorithm. Theoretical equations were verified with experimental results from a diesel sample injected in GC × GC and were found to be in good agreement with the experiments.     

FICA,a new chiral derivatizing agent for determining the absolute configuration of secondary alcohols by 19F and 1H NMR spectroscopies

Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both ¹H and ¹⁹F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the ¹H NMR spectra, the signs of Δδ_H (δ_R ? δ_S) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of Δδ_F (δ_R ? δ_S) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on ¹⁹F NMR spectroscopy.     

Chemistry and thermodynamics of the twin charge-ordering transitions in RBaFe2O5+w series

Thermal and volume parameters of the twin charge-ordering Verwey transitions in RBaFe₂O_5+w (R=a rare-earth element) are summarized as a function of R and w. Their determination is exemplified for case R = Dy, for which also synthesis conditions, phase relations, and refined crystal-structure data for the valence-mixed (Fe^2.5+) and charge-ordered (Fe²⁺ and Fe³⁺) phases are reported. Data for the R=Nd, Sm, Eu and Gd variants with wide ranges of oxygen non-stoichiometry suggest that increasing w decreases ΔS and the temperature of the transition in a manner that is similar to a behavior under increasing concentration of an ideal solution of RBaFe₂O₆ in RBaFe₂O₅. Thermal parameters of the transition for the ideal mixed-valence composition RBaFe₂O_5.000 are estimated from such compositional dependences, varying reasonably smoothly as a function of R (radius, electronegativity, polarizability). Parameter ΔV is the only one that follows the structural discontinuity between the charge-ordered R = Nd and variants with smaller trivalent R ions. The ordering of the d_xz orbitals of the Fe²⁺ ions is thus being achieved at a cost of lowering the symmetry when the R size becomes unfavorably large. A definition of the Verwey transition as a first-order orbital ordering of a valence-mixed phase is suggested.     

A method for the calculation of heats of solution (ΔH s ) for organic compounds from the number of constituent carbon atoms and the functional groups

The heat of solution (ΔH _s ) of several homologous series of linear and monofunctional organic compounds (n-alkanes,n-alcohols,n-aldehyds and esters) in polar stationary phase (Carbowax 1540) can be expressed by ΔH _s =a+b·n _R +c·C _G , wherea is a constant,n _R is the number of carbon atoms not belonging to the functional group in the molecule andC _G represents the contribution of each functional group to the ΔH _s value. The accuracy of the ΔH _s values calculated by this equation is sufficient for all the compounds tested (average relative error=1.92%).C _G can be calculated from the plots ΔH _s versusn _R .     

Preparation and temperature-dependent enantioselectivities of homochiral phenolic crown ethers having aryl chiral barriers: thermodynamic parameters for enantioselective complexation with chiral amines

Homochiral crown ether (S,S)-1 containing 1-naphthyl groups as chiral barriers together with the phenol moiety was prepared by using (S)-3 as a chiral subunit which was resolved in enantiomerically pure form by lipase-catalyzed enantioselective acylation of (±)-3. Homochiral phenolic crown ether (S,S)-2, containing phenyl groups as chiral barriers, was also prepared from (S)-5 which was derived from (S)-mandelic acid. The association constants for their complexes with chiral amines in CHCl₃ were determined at various temperatures by the UV–visible spectroscopic method demonstrating that the crown ethers (S,S)-1 and (S,S)-2 displayed the large Δ_R−SΔG values of 6.2 and 6.4 kJ mol⁻¹, respectively, towards the amine 21 at 15°C. Thermodynamic parameters for complex formation were also determined and a linear correlation between TΔ_R−SΔS and Δ_R−SΔH values was observed.     

Dielectric study of dipolar association in dilute solutions of nitrobenzene in benzene

The correlation factors R_p and R_s are determined for the dielectric polarization and the non-linear dielectric effect in dilute solutions of nitrobenzene in benzene. Assuming dipole association of the nitrobenzene molecules to be restricted to dimerization, we determined the concentration x₂ of dimers, their dipole moment μ_dim, and the equilibrium constant K_x and Gibbs energy ΔG of the dimerization process.     

Thermal [1,5] sigmatropic rearrangements in (σ-7-cycloheptatrienyl)triphenyltin and (σ-5-cyclohepta-1,3-dienyl)triphenyltin: A 1H and 13C NMR reinvestigation

It has been confirmed by ¹H and ¹³C NMR spectroscopies that Sn(σ-C₇H₇)Ph₃ undergoes either 1,4- or 1,5-shifts of the SnPh₃ moiety around the cycloheptatrienyl ring with ΔH³ = 13.8 ± 0.4 kcal mol^?1, ΔS3 = ?5.6 ± 1.2 cal mol^?1 deg^?1, and ΔG³₃₀₀ = 15.44 ± 0.14 kcal mol^?1. Similarly, (σ-5-cyclohepta-1,3-dienyl)triphenyltin undergoes 1,5-shifts with ΔH³ = 12.4 ± 0.6 kcal mol^?1, ΔS³ = ?11.2 ± 1.8 cal mol^?1 deg^?1, and ΔG³₃₀₀ = 15.76 ± 0.13 kcal mol^?1. It is therefore probable that Sn(σ-5-C₅H₅)R₃ and Sn(σ-3-indenyl)R₃ do not undergo 1,2-shifts as previously suggested but really undergo 1,5-shifts.     

Ein isoperiboles lösungskalorimeter zur messung von lösungsenthalpien der doppelchloride des magnesiums

For measuring solution enthalpies of the strong hygroscopic double chlorides, an isoperibol solution calorimeter was built. Samples of 2–5 g could be solved to a molar dilution 1 : 3000. The temperature difference between reaction vessel and thermostat was measured by a thermopile; the temperature of the thermostat was constant to 2 · 10^?4°C. From the molar enthalpies of solution (ΔH^L), enthalpies for the reactions nACl + MCl₂ = A_sMCl(_{s + 2}) were calculated: ΔHP^R = ? ΔH^L (double chloride) + ΔH^L(n Cl) + ΔH^L(MCL₂) These values are relatively small: about ? 50 kJ for the Cs-compounds, nearly zero for the K- and Na-compounds.     

Impacts of medium,substituents, and specific interactions with water on hydration of carbonyl compounds

Theoretical study on hydration of carbonyl compounds has been done at B3LYP/6-31++G** and MP2/6-31++G** levels. The variations in ΔG _hyd and hydration constants are explored in terms of medium effect, substituent effect, and hydrogen bonding abilities of carbonyl compounds and their hydrated products. The dielectric of medium decreases the ΔG _hyd values thereby favoring the process. The presence of electron-releasing substituents at the carbonyl carbon disfavors the hydration process, while that of electron-withdrawing substituents favor the process. Hydrogen bonding interactions stabilize the product to a larger extent than the carbonyl molecules, thereby favoring the hydration process. Linear correlation between the calculated log K _hyd values and the experimental values is seen in case of specific interactions with water (R = 0.976) than in the case without those interactions (R = 0.955).     

Interaction between chiral ions: synthesis and characterization of tartratovanadates(V) with tris(2,2′-bipyridine) complexes of iron(II) and nickel(II) as cations

Four new compounds composed of chiral complex cations and anions: Δ-[Fe(bpy)₃] Λ-[Fe(bpy)₃][V₄O₈((2R,3R)-tart)₂]·12H₂O (1), Δ-[Fe(bpy)₃]₂Λ-[Fe(bpy)₃]₂[V₄O₈((2R,3R)-tart)₂][V₄O₈((2S,3S)-tart)₂]·24H₂O (2), Δ-[Ni(bpy)₃]Λ-[Ni(bpy)₃][V₄O₈((2R,3R)-tart)₂]·12H₂O (3) and Δ-[Ni(bpy)₃]₂Λ-[Ni(bpy)₃]₂[V₄O₈((2R,3R)-tart)₂][V₄O₈((2S,3S)-tart)₂]·24H₂O (4) have been prepared. The compounds have been characterized by spectral methods, and their thermal decomposition was studied by simultaneous DTA, TG measurements. The final products after dynamic decomposition and additional heating were Fe₂V₄O₁₃ for 1 and 2 and Ni(VO₃)₂ for 3 and 4. The crystal structures determined for 1, 2 and 4 have evidenced that 1 is “hemiracemic” and 2 and 4 are “fully racemic” compounds.     

Trimer–dimer equilibrium studies of alkylaluminum alkoxides

The aluminum alkoxides [MeClAlOEt]₃ (1), [Et₂AlOMe]₃ (2), [Me₂AlOEt]₃ (3), and [EtClAlOEt]₃ (4) were investigated by ¹H NMR spectroscopy to study the o-dichlorobenzene solution equilibrium: 2 [R₂AlOR′]₃⇌3 [R₂AlOR′]₂. The complexes are shown to exist primarily as trimers at room temperature, but increasing concentrations of the dimeric form are observed at higher temperatures. Equilibrium constants, ΔH, and ΔS were determined for the trimer–dimer equilibrium. Values of ΔH for the conversion of 2 moles of trimer are 63(4), 78(1), 85.0(8), and 99(6) kJ for 1, 2, 3, and 4, respectively. The corresponding values of ΔS are 142(7), 184(3), 218(2), and 265(17) J/K, respectively. Thermodynamic parameters are compared with those reported for [Me₂AlOPrⁿ]₃ and [Me₂AlOPh]₃. The characterization of [EtClAlOMe]₃ is also reported.