Synthesis and Rearrangement of Silylated Oxy-Cope Systems

Addition of allyl or vinyl organometallic reagents to chiral a,b\alpha,\beta- or b,g\beta,\gamma -unsaturated acylsilanes afforded stereoselectively 3-silylated 3-hydroxy-1,5-dienes that are stereoselectively converted to d,e\delta,\varepsilon-unsaturated acylsilanes by the thermal oxy-Cope rearrangement. The rearrangement is restricted to compounds possessing an (alkoxy)methyl substituent at the silicon moiety; upon heating, analogous compounds with the t-BuMe₂_2Si group in the 3-position led to decomposition only. The (alkoxy)methyl group at silicon is supposed to act as a weak internal base, which accelerates the rearrangment reaction.     

Stereo-dynamics study of O + HCl → OH + Cl reaction on the <Superscript>3</Superscript>A″, <Superscript>3</Superscript>A′, and <Superscript>1</Superscript>A′ states

Using three accurate potential energy surfaces of the ³A″, ³A′, and ¹A′ states constructed recently, we present a quasi-classical trajectory (QCT) calculation for O + HCl (v = 0, j = 0) → OH + Cl reaction at the collision energies (E _col) of 14.0–20.0 kcal/mol. The three angular distribution functions—P(q_r ) P(\theta_{r} ) , P(j_r ) P(\varphi_{r} ) , and P(q_r ,j_r ) P(\theta_{r} ,\varphi_{r} ) , together with the four commonly used polarization-dependent differential cross-sections, \frac2ps \fracds₀₀ dw_t , \frac2ps \fracds₂₀ dw_t , \frac2ps \fracds_{22 +} dw_t , \textand \frac2ps \fracds_{21 -} dw_t {\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{00} }}{{d\omega_{t} }}},\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{20} }}{{d\omega_{t} }}},\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{22 + } }}{{d\omega_{t} }}},\,{\text{and}}\,{\frac{2\pi }{\sigma }}\,{\frac{{d\sigma_{21 - } }}{{d\omega_{t} }}} are exhibited to get an insight into the alignment and the orientation of the product OH radical. There is a similar behavior of the tendency scattering direction for the two triplet electronic states (³A″ and ³A′)—backward scattering dominates, however, forward scattering prevails for the case of ¹A′ state. Also, obvious differences have been found in the stereo-dynamical information, which reveals the influences of the potential energy surface and the collision energy. The degrees of polarization and the influence of the collision energy on the stereo-dynamics characters of the title reaction are both demonstrated in the order of ³A′ > ³A″ > ¹A′.     

Chiral Acylsilanes in Organic Synthesis. Part 3. Silicon-directed stereoselective preparation and Ireland ester-enolate rearrangement of O-acyl-substituted α-silylated allyl alcohols

Stereocontrolled addition of alk-1-enylmetal reagents to the chiral (alkoxymethyl)-substituted acylsilanes (±)- 6 gave rise to α-silylated allyl alcohols, which were converted to the corresponding acetates or propionates 11–16 (Scheme 2). Deprotonation and silylation with Me₃SiCl afforded – in an Ireland ester-enolate-accelerated Claisen rearrangement – stereoselectively αδ-silylated γδ-unsaturated carboxylic acids 18–24 (Scheme 4). The Me₃Si groups in α-position to the COOH group of these compounds were removed chemoselectively in presence of the chiral silyl group in δ-position by treatment with Bu₄NF · 3 H₂O or Et₃N · 3 HF (→ 27–32 ; Scheme 5). The reaction sequence allows a novel stereocontrolled access to chiral C-frameworks possessing a vinylsilane moiety with its full reaction potential.     

Determination of the Hydrolysis Constants and Solubility Product of Chromium(III) from Reduction of Dichromate Solutions by ICP-OES and UV–Visible Spectroscopy

The determination of equilibrium constants is difficult when several chemical species are simultaneously present in solution. In this investigation, optical emission spectroscopic determinations of chromium(III) concentration in a 10⁻⁴ mol⋅dm⁻³ solution, prepared from K₂Cr₂O₇ reduced in HNO₃ or HCl media, were used to construct the pCr_(aq)–pC _H diagram. This diagram was used to calculate the pC _H borderline of precipitation, to estimate the solubility product (log₁₀K_sp,Cr(OH)3^*)(\log_{10}K_{\mathrm{sp,Cr(OH)}_{3}}^{*}), and the hydrolysis constants (log₁₀b_Cr,H^*,log₁₀b_Cr,2H^*(\log_{10}\beta_{\mathrm{Cr,H}}^{*},\log_{10}\beta_{\mathrm{Cr,2H}}^{*}, and log₁₀b_Cr,3H^*)\log_{10}\beta_{\mathrm{Cr,3H}}^{*}) of Cr(III). The hydrolysis constants were also calculated using the SQUAD and SUPERQUAD software, along with the average ligand number method. UV-Vis absorption data and associated variables were used in SQUAD, SUPERQUAD, and the average ligand calculations. Results are: 9.00±0.04 for the pC _H at the onset of precipitation, 12.40 for log₁₀K_sp,Cr(OH)3^*\log_{10}K_{\mathrm{sp,Cr(OH)}_{3}}^{*}, −3.52±0.02 for log₁₀b_Cr,H^*\log_{10}\beta_{\mathrm{Cr,H}}^{*}, −9.30±0.87 for log₁₀b_Cr,2H^*\log_{10}\beta_{\mathrm{Cr,2H}}^{*} and −17.18±0.16 for log₁₀b_Cr,3H^*\log_{10}\beta_{\mathrm{Cr,3H}}^{*}, respectively. All methods produced essentially the same values for the hydrolysis constants of Cr(III).     

Synthesis of uniform polyurethane particles by step growth polymerization in a dispersed medium

Polyurethane microspheres were prepared by polyaddition of ethylene glycol (EG) and tolylene-2,4-diisocyanate (TDI) at 60 °C in cyclohexane as the organic dispersion medium, in the presence of dibutyl tin dilaurate (DBTDL) as catalyst and poly(styrene)-b-poly(ethylene oxide) block copolymers or P-hydroxypolystyrenes as the steric stabilizers. Different parameters such as the manner of addition of the reactants, the concentration, and length of the stabilizer were varied to tune the polyurethane particle size. When P-OH polystyrenes of low molar mass ([`(M)]_n\bar M_n =2000-3000 g mol^-1) were used as the reactive stabilizers of dispersion, polyurethane particles in a tunable size range of 0.2-5 µm with a narrow size distribution (span = 0.7) could be prepared.     

Thermochemistry of 2-Aminopyridine (C<Subscript>5</Subscript>H<Subscript>6</Subscript>N<Subscript>2</Subscript>)(s)

The molar enthalpies of solution of 2-aminopyridine at various molalities were measured at T=298.15 K in double-distilled water by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the molar enthalpy of solution of the title compound at infinite dilution was calculated to be D_solH_m^￥ = 14.34 kJ·mol^-1\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\infty} = 14.34~\mbox{kJ}\cdot\mbox{mol}^{-1}, and Pitzer’s ion interaction parameters b_MX^(0)L, b_MX^(1)L\beta_{\mathrm{MX}}^{(0)L}, \beta_{\mathrm{MX}}^{(1)L}, and C_MX^fLC_{\mathrm{MX}}^{\phi L} were obtained. Values of the relative apparent molar enthalpies ( ^φ L) and relative partial molar enthalpies of the compound ([`(L)]₂)\bar{L}_{2}) were derived from the experimental enthalpies of solution of the compound. The standard molar enthalpy of formation of the cation C₅H₇N₂ ⁺\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{ +} in aqueous solution was calculated to be D_fH_m^o(C₅H₇N₂⁺,aq)=-(2.096±0.801) kJ·mol^-1\Delta_{\mathrm{f}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{+},\mbox{aq})=-(2.096\pm 0.801)~\mbox{kJ}\cdot\mbox{mol}^{-1}.     

Raman and Infrared Spectroscopic Investigation of Speciation in BeSO<Subscript>4</Subscript>(aq)

Measurements have been made of the Raman spectra of aqueous solutions of Be(ClO₄)₂, BeCl₂, (NH₄)₂SO₄ and BeSO₄ to 50 cm⁻¹. In some cases low concentrations (0.000770 mol⋅kg⁻¹) have been used and two temperatures (23 and 40 °C) were studied. In BeSO₄(aq), the ν ₁-SO₄^2-\mathrm{SO}_{4}^{2-} mode at 980 cm⁻¹ broadens with increasing concentration and shifts to higher wavenumbers. At the same time, a band at 1014 cm⁻¹ is detectable with this mode being assigned to [BeOSO₃], an inner-sphere complex (ISC). Confirmation of this assignment is provided by the simultaneous appearance of stretching bands for the Be²⁺-OSO₃^2-\mathrm{Be}^{2+}\mbox{-}\mathrm{OSO}_{3}^{2-} bond of the complex at 240 cm⁻¹ and for the BeO₄ skeleton mode of the [(H₂O)₃BeOSO₃] unit at 498 cm⁻¹. The ISC concentration increases with higher temperatures. The similarity of the n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} Raman bands for BeSO₄ in H₂O and D₂O is further strong evidence for formation of an ISC. After subtraction of the ISC component at 1014 cm⁻¹, the n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} band in BeSO₄(aq) showed systematic differences from that in (NH₄)₂SO₄(aq). This is consistent with a n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} mode at 982.7 cm⁻¹ that can be assigned to the occurrence of an outer-sphere complex ion (OSCs). These observations are shown to be in agreement with results derived from previous relaxation measurements. Infrared spectroscopic data show features that are also consistent with a beryllium sulfato complex such as the appearance of a broad and weak n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} mode at ∼1014 cm⁻¹, normally infrared forbidden, and a broad and asymmetric n₃-SO₄^2-\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-} band contour which could be fitted with four band components (including n₃-SO₄^2-(aq)\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-}(\mathrm{aq})). The formation of ISCs in BeSO₄(aq) is much more pronounced than in the similar MgSO₄(aq) system studied recently.     

New Insights into Buffer-Ionic Salt Interactions: Solubilities,Transfer Gibbs Energies,and Transfer Molar Volumes of TAPS and TAPSO from Water to Aqueous Electrolyte Solutions

The solubilities of N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) or N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) in water and in aqueous solutions of CH₃COOK (KAc), KBr, KCl, or NaCl were determined from density measurements at 298.15 K. The solubilities of TAPS in aqueous solution decrease with increasing concentration of the salts (salting-out effect), whereas those of TAPSO increase with increasing concentration of the salts (salting-in effect). The solubility and density data were further used to calculate the apparent transfer Gibbs energies, Δ_tr G, and transfer molar volumes, D_trV_f^o\Delta_{\mathrm{tr}}V_{\phi}^{\mathrm{o}}, of these buffers from water to aqueous electrolyte solutions at 298.15 K. The contributions of various functional groups of TAPS, TAPSO, and the related buffers (tris(hydroxymethyl)aminomethane, TRIS, and N-tris[hydroxymethyl]-4-amino-butanesulfonic acid, TABS) to the transfer properties were systematically estimated from the calculated Δ_tr G and D_trV_f^o\Delta_{\mathrm{tr}}V_{\phi}^{\mathrm{o}}.     

Apparent Molar Volumes and Heat Capacities of Aqueous Trifluoromethanesulfonic Acid and Its Sodium Salt from 283 to 328 K

Apparent molar heat capacities C_\textp,fC_{{\text{p}},\phi } and volumes V_fV_\phi of aqueous trifluoromethanesulfonic (triflic) acid, HCF₃SO₃ (aq.) were determined with a Picker flow microcalorimeter and vibrating-tube densimeter at temperatures from 283 to 328 K and molalities from 0.05 to 9.5 mol-kg^-1. Values of V_fV_\phi and C_\textp,fC_{{\text{p}},\phi } display a maximum near 0.8 mol-kg^-1. V_fV_\phi also displays a shallow minimum at ~5 mol-kg^-1, while C_\textp,fC_{{\text{p}},\phi } continues to decrease smoothly up to the limit of our measurements at 9.5 mol-kg^-1. We attribute this behavior to ion–ion interaction between triflate and the hydrated proton to form the aqueous complex H_2n+1O_n⁺ CF₃SO₃^- (aq.), n = 5. Standard partial molar properties C_p^o and V^o are consistent with results obtained from NaCF₃SO₃ (aq.) and yield values for the triflate anion CF₃SO₃^- (aq.), over this range.     

Natural bond orbital population analysis of para-substituted O-nitrosyl carboxylate compounds

Theoretical study of several para-substituted O-nitrosyl carboxylate compounds has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to $ n_{{{\text{O}}_{1} }} \to \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} Theoretical study of several para-substituted O-nitrosyl carboxylate compounds has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to n_\textO1 ? s_{\textO3 - \textN2} ^* n_{{{\text{O}}_{1} }} \to \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} delocalization and is responsible for the longer O₃–N₂ bond lengths in para-substituted O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized s_{\textO3 -\textN2} \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} orbital in the idealized Lewis structure, or increased occupancy of s_{\textO3 - \textN2} ^* \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital of s_{\textO3 -\textN2} \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of substituent groups and the partial charges distribution on the skeletal atoms may approve anticipating that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra- and intermolecular interaction.     

Reduction of 3‐Aminoquinoline‐2,4(1H,3H)‐diones and Deamination of the Reaction Products

3‐Aminoquinoline‐2,4‐diones were stereoselectively reduced with NaBH₄ to give cis‐3‐amino‐3,4‐dihydro‐4‐hydroxyquinolin‐2(1H)‐ones. Using triphosgene (=bis(trichloromethyl) carbonate), these compounds were converted to 3,3a‐dihydrooxazolo[4,5‐c]quinoline‐2,4(5H,9bH)‐diones. The deamination of the reduction products using HNO₂ afforded mixtures of several compounds, from which 3‐alkyl/aryl‐2,3‐dihydro‐1H‐indol‐2‐ones and their 3‐hydroxy and 3‐nitro derivatives were isolated as the products of the molecular rearrangement.     

Calculating the standard values of the heat capacity of alkaline metal ions and iodide ions in a mixed N-methylpyrrolidone-water solvent at 298.15 K

A system of ionic components of [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 is proposed for the standard partial molar heat capacities [`(C)]_p2⁰\bar C_{p2}^0 of electrolytes in a mixed N-methylpyrrolidone (MP)-water solvent. The [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 values are calculated for Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Rb<sup>+</sup>, Cs<sup>+</sup>, and I<sup>−</sup> ions in a mixed MP-water solvent at 298.15 K. The individual components of [`(C)]_p,i⁰\bar C_{p,i}^0 values and their dependence on the solvent composition and ion size are considered.     

Excess hyperpolarizabilities: the irreducible tensor approach

The irreducible spherical and Cartesian tensors built of the products of two interaction tensors: the second order tensor resulting from the product of two second order tensors \sf T_a l \sf T_l b{{\sf T}_{\alpha\,\lambda}\,{\sf T}_{\lambda\,\beta}} contracted once with the index λ, third order tensor \sf T_a b l \sf T_l g{{\sf T}_{\alpha\,\beta\,\lambda} {\sf T}_{\lambda\,\gamma}} appearing as a product of the third order interaction tensor \sf T_a b l{{\sf T}_{\alpha\,\beta\,\lambda}} and the second order one \sf T_l g{{\sf T}_{\lambda\,\gamma}} contracted once with the index λ and the fourth order product of two second order tensors \sf T_a b \sf T_gd{{\sf T}_{\alpha\,\beta}\,{\sf T}_{\gamma\delta}}, have been considered. This type of products is encountered, e.g., within the London’s dispersive energy formula, inside the second-order virial coefficients of many physical parameters such as the dielectric constant, the Kerr constant, the induced polarizability and hyperpolarizability of a pair of molecules and in other induced quantities. Our results are applied explicitly to the excess induced first and second pair hyperpolarizability.     

Evidence of Different Stoichiometries for the Limiting Carbonate Complexes across the Lanthanide(III) Series

The stoichiometries of limiting carbonate complexes of lanthanide(III) ions were investigated by solubility measurements of hydrated NaLn(CO3)2 solid compounds (Ln = La, Nd, Eu and Dy) at room temperature in aqueous solutions of high ionic strength (3.5 mol⋅kg−1 NaClO4) and high CO32-\mathrm{CO_{3}^{2-}} concentrations (0.1 to 1.5 mol⋅kg−1). The results were interpreted by considering the stability of carbonate complexes, with limiting species found to be La(CO3)45-\mathrm{La(CO_{3})_{4}^{5-}}, Nd(CO3)45-\mathrm{Nd(CO_{3})_{4}^{5-}}, Eu(CO3)33-\mathrm{Eu(CO_{3})_{3}^{3-}} and Dy(CO3)33-\mathrm{Dy(CO_{3})_{3}^{3-}}. TRLFS measurements on the Eu and Dy solutions confirmed the predominance of a single aqueous complex in all the samples. Equilibrium constants were determined for the reaction Ln(CO3)33-+CO32-\mathrm{Ln(CO_{3})_{3}^{3-}}+\mathrm{CO_{3}^{2-}} ⇌ Ln(CO3)45-\mathrm{Ln(CO_{3})_{4}^{5-}}: log10K3.5m NaClO44,La=0.7±0.3\log_{10}K\mathrm{^{3.5m\:NaClO_{4}}_{4,La}=0.7\pm0.3}, log10K3.5m NaClO44,Nd=1.3±0.3\log_{10}K\mathrm{^{3.5m\:NaClO_{4}}_{4,Nd}=1.3\pm0.3}, and for Ln = Eu and Dy, log10K3.5m NaClO44,Ln ￡ -0.4\log_{10}K\mathrm{^{3.5m\:NaClO_{4}}_{4,Ln}\leq-0.4}. These results suggest that tetracarbonato complexes are stable only for the light lanthanide ions in up to 1.5 molal CO32-\mathrm{CO_{3}^{2-}} aqueous solutions, in agreement with our recent capillary electrophoresis study. Comparison with literature results indicates that analogies between actinide(III) and lanthanide(III) ions of similar ionic radii do not hold in concentrated carbonate solutions. Am(CO3)33-\mathrm{Am(CO_{3})_{3}^{3-}} was previously evidenced by solubility measurements, whereas we have observed that Nd(CO3)45-\mathrm{Nd(CO_{3})_{4}^{5-}} predominates in similar conditions. We may speculate that small chemical differences between Ln(III) and An(III) could result in macroscopic differences when their coordination sphere is complete.     

Excess Molar Volumes, Excess Viscosities and Ultrasonic Speeds of Sound of Binary Mixtures of 1,2-Dimethoxyethane with Some Aromatic Liquids at 298.15 K

Densities, viscosities and ultrasonic speeds of sound for binary mixtures of 1,2-dimethoxyethane (DME) with benzene, toluene, chlorobenzene, benzyl chloride, benzaldehyde, nitrobenzene, and aniline are reported over the entire composition range at ambient pressure and temperature (i.e., T=298.15 K and p=1.01×10⁵ Pa). These experimental data were utilized to derive the excess molar volumes (V_m^EV_{\mathrm{m}}^{\mathrm{E}}), excess viscosities (η ^E), and various acoustic parameters including the deviation in isentropic compressibility (Δκ _S ), internal pressure (π _I), and excess enthalpy (H ^E). From the excess molar volumes (V_m^EV_{\mathrm{m}}^{\mathrm{E}}), the excess partial molar volumes ([`(V)]<sub>m,1</sub><sup>E</sup>\overline{V}_{\mathrm{m},1}^{\mathrm{E}} and [`(V)]_m,2^E\overline{V}_{\mathrm{m},2}^{\mathrm{E}}) and excess partial molar volumes at infinite dilution ([`(V)]<sub>m,1</sub><sup>0,E</sup>\overline{V}_{\mathrm{m},1}^{0,\mathrm{E}} and [`(V)]_m,2^0,E\overline{V}_{\mathrm{m},2}^{0,\mathrm{E}}) were derived and discussed for each liquid component in the mixtures. The excess/deviation properties were found to be either negative or positive, depending on the molecular interactions and the nature of the liquid mixtures.     

Thermochemical study on ternary complex of dysprosium <Emphasis Type="Italic">m</Emphasis>-nitrobenzoic acid with <Emphasis Type="Italic">o</Emphasis>-phenanthroline

A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)₃phen]₂·4H₂O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H₂O(s)], [6m-HNBA(s)], [2DyCl₃·6H₂O(s)], and [Dy(m-NBA)₃phen]₂·4H₂O(s) in the calorimetric solvent (V_DMSO:V_MeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H₂O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl₃·6H₂O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol⁻¹, and \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol⁻¹, respectively. The enthalpy change of the reaction was determined to be \Updelta_\textr H_\textm^q = 3 6 9. 4 9 ±0. 5 6   \textkJ·\textmol ^{- 1} . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of formation of [Dy(m-NBA)₃phen]₂·4H₂O(s) was estimated to be \Updelta_\textf H_\textm^q \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = −5525 ± 6 kJ·mol⁻¹.     

Stereoselective formation of phenylthio groups substituted 1-metalla-3-titanacyclobutanes

Desulfurizative titanation of group 14 metal compounds bearing two or four bis(phenylthio)methyl groups with the low-valent titanium reagent Cp₂Ti[P(OEt)₃]₂ produced phenylthio groups substituted 1-metalla-3-titanacyclobutanes stereoselectively. The molecular structures of the titanacycles were unambiguously confirmed by X-ray diffraction analysis.     

Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

The measurement uncertainty of ratios which share uncertainty components in numerator and denominator

When calculations are made of ratios of values of the same kind of quantity, correlations often arise from the use of the same instrument to make the measurement. The combined uncertainty in this case is usually much smaller than that from a treatment in which the numerator and denominator are assumed to be independent. For a simple ratio % MathType!MTEF!2!1!+- % feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOuamaala % aabaGaamyyaaqaaiaadkgaaaaaaa!389F! R^a/_b R{a \over b} , with a and b having the identical uncertainty u, the relative uncertainty in R is given by % MathType!MTEF!2!1!+- % feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaada % WcaaqaaiaadwhaaeaacaWGHbaaamaabmaabaGaaGymaiabgkHiTiaa % dkfaaiaawIcacaGLPaaaaiaawEa7caGLiWoaaaa!3F05! | ^u/_a( 1 - R ) | \left| {{u \over a}\left( {1 - R} \right)} \right| . This type of positive correlation usually reduces uncertainty and may cancel when the ratio is unity. An example from the EURACHEM guide, Quantification of Uncertainty in Analytical Measurement, overestimates the combined uncertainty of a titration by assuming complete independence of terms in a ratio.