Equilibrium anionic polymerization of β-methoxypropionaldehyde

Anionic polymerization of β-methoxypropionaldehyde (MPA) was carried out in tetrahydrofuran (THF) by using benzophenone–monolithium complex as an initiator. An equilibrium between polymerization and depolymerization was observed at a temperature range of ?90 to ?70°C. From the temperature dependence of the equilibrium monomer concentration, thermodynamic parameters for the polymerization of MPA in THF were evaluated as follows: ΔH_ss = ?4.8 ± 0.2 kcal/mole, ΔH_SS = ?22.4 ± 1.3 cal/mole-deg, and (T_c)_ss = ?59°C. The thermodynamic change upon the conversion of liquid monomer to condensed polymer was computed from both the partial mixing energy of MPA with THF and the linear relationship between the equilibrium volume fraction of MPA monomer and that of the resulting polymer: ΔH_1c = ?4.7 ± 0.2 kcal/mole, ΔS_1c = ?19.5 ± 1.3 cal/mole-deg, and (T_c)_1c = ?35°C.     

Equilibrium cyclotrimerization of ether oxygen-substituted aliphatic aldehydes

This article describes the equilibrium cyclotrimerization of β-methoxypropionaldehyde (MPA), 4,7-dioxaoctanal (DOA), and n-octanal (OA) initiated by boron trifluoride etherate in toluene at a temperature range of ?10 to 25°C. The enthalpy and entropy changes corresponding to the conversion of 1 mole of the monomers to 1/3 mole of their cyclic trimers in toluene solution, at the initial monomer concentration of 1 mole/liter, were evaluated as follows: ΔH_ss = ?5.9 ± 0.3 kcal/mole and ΔS_ss = ?19.1 ± 1.3 cal/mole deg for the MPA system; ΔH_ss = ?7.4 ± 0.4 kcal/mole and ΔS_ss = ?24.1 ± 1.7 cal/mole deg for the DOA system; ΔH_ss = ?6.1 ± 0.4 kcal/mole and ΔS_ss = ?21.2 ± 1.5 cal/mole deg for the OA system. The comparison of these values with those in their polymerization indicates that the cyclotrimerization of aldehydes is thermodynamically of greater advantage than their polymerization. The effects of long and polar substituents are discussed from the view-point of the intermolecular interactions by the polar groups in monomers and their cyclic trimers.     

Equilibrium anionic polymerization of 4,7-dioxaoctanal and n-octanal

Equilibrium anionic polymerization of 4,7-dioxaoctanal (DOA) and n-octanal (OA) was carried out in tetrahydrofuran in the temperature range of ?90 to ?68°C, and thermodynamic parameters were evaluated as follows: ΔH_ss = ?4.0 ± 0.1 kcal/mole, ΔS_ss = ?18.4 ± 0.5 cal/mole-deg, and T_c,ss = ?56°C for the DOA system; ΔH_sc = ?3.4 ± 0.1 kcal/mole, ΔS_sc = ?15.7 ± 0.4 cal/mole-deg, and T_c,sc = ?59°C for the OA system. Comparison of these values with those in the cases of β-methoxypropionaldehyde and n-valeraldehyde made it clear that the aliphatic aldehyde having a longer alkyl group polymerizes with smaller changes of enthalpy and entropy and that the polar-substituted aldehydes have higher polymerizability than the corresponding unsubstituted aliphatic aldehydes in the temperature range studied. These effects of substituents are interpreted from the viewpoint of the intermolecular interactions of polar groups in monomers and their polymers.     

Anionic polymerization of p-diisopropenylbenzene in tetrahydrofuran: Reactivity of pendent double bond

Anionic polymerization of p-diisopropenylbenene was found to be an equilibrium polymerization not only with respect to the monomer but also with respect to the pendent double bond. The polymerization was studied from kinetic as well as from the thermodynamic point of view, especially to ascertain the reactivity of the pendent double bond as compared with the double bond of monomeric analog. It was shown that the crosslinking rate constant of the pendent double bond is lower by about three to four orders than the propagation rate constant of the monomeric analog. The rate of cyclization was also very slow. From the equilibrium, the heat and entropy of polymerization of the monomer were determined as ΔH_ss = ?5.8 kcal/mole and ΔS_ss = ?18.0 cal/deg mole, respectively, and those of the pendent double bond as ΔH_ss = ?6.3 kcal/mole and ΔS_ss = ?27.8 cal/deg mole. When compared with the polymerization of α-methylstyrene, the low thermodynamic polymerizability of the pendent double bond is attributed to the low heat of polymerization, which may arise from the large steric hindrance of neighboring groups. The effect is much smaller for the equilibrium than for the rate of polymerization, however.     

Equilibrium anionic polymerization of the isopropenyl monomers containing aromatic heterocycles

The anionic polymerization of three monomers, 2-isopropenyl-4,5-dimethyloxazole(I), 2-isopropenylthiazole(II), and 2-isopropenylpyridine(III), was studied in THF. These monomers produced red-colored living polymers on addition of sodium naphthalene or living α-methylstyrene tetramer as an initiator. It was observed that a considerable amount of monomer remained in the respective living polymer–monomer system, indicating that an equilibrium between the polymer and the monomer existed as in the case of α-methylstyrene. At lower temperatures, the conversion of the monomer to the polymer increased. The equilibrium monomer concentrations [M_e] were determined at different temperatures, and the heats (ΔH) and the entropies (ΔS°) of polymerization were obtained by plotting In(1/[M_e]) against 1/T as ΔH = ?9.4, ?6.8, and ?6.2 kcal/mole, ΔS°S = ?22.9, ?16.5, and ?16.6, eu for I, II, and III, respectively.     

Solution-Structure and Aggregation Behavior of Two Dilithiostyrene Derivatives

The solution structure and the aggregation behavior of (E)-2-lithio-1-(2-lithiophenyl)-1-phenylpent-1-ene ( 1 ) and (Z)-2-lithio-1-(2-lithiophenyl)ethene ( 2 ) were investigated by one- and two-dimensional ¹H-, ¹³C-, and ⁶Li-NMR spectroscopy. In Et₂O, both systems form dimers which show homonuclear scalar ⁶Li,⁶Li spin-spin coupling. In the case of 2 , extensive ⁶Li,¹H coupling is observed. In tetrahdrofuran and in the presence of 2 mol of N,N,N′,N′-tetramethylethylylenediamine (tmeda), the dimeric structure of 1 coexists with a monomer. The activation parameters for intra-aggregate exchange in the dimers of 1 and 2 ( 1 (Et₂O): ΔH≠ = 62.6 ± 13.9 kJ/mol, ΔS≠ = 5.8 ± 14.0 J/mol K, ΔG≠(263) = 61.1 kJ/mol; 2 (dimethoxyethane): ΔH≠ = 36.9 ± 6.5 kJ/mol, ΔS≠ = ?61 ± 25 J/mol K, ΔG≠(263) = 54.0 kJ/mol) and the thermodynamic parameters for the dimer-monomer equilibrium for 1 (ΔH°; = 26.7 ± 5.5 kJ/mol, ΔS° = 63 ± 27 J/mol K), where the monomer is favored at low temperature, were determined by dynamic NMR studies.     

Reaction of tetramethyl-1,2-dioxetane with triphenylphosphine: Activation parameters for the formation of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane

The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d₆ produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS^≠ = ?28 eu; k_30° = 1.8 m^?1sec^?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS^≠ = ?24 eu, k_30° = 1.3 M^?1sec^?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS^≠ = ?29 eu, k_30° = 4.9 M^?1 sec^?1.     

Kinetics and thermodynamics of anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane

Kinetic activation parameters and thermodynamic functions describing the reversible anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane (1,3-propylene methyl phosphate) were determined. Enthalpy and entropy of the anionic propagation ? depropagation equilibrium were found to be close to those found previously by the present authors for the cationic polymerization, while the activation parameters of propagation and depropagation differ substantially for both processes and reflect the differences in the involved mechanisms. Thus, data for anionic polymerization (and cationic polymerization in parentheses) are: ΔH_1s° = ?0.7 kcal/mole (?1.1); ΔS_1s° = ?2.8 cal/mole-deg (?5.4); ΔH_p^? = 26.7 kcal/mole, and ΔS_p^? = ?6.1 cal/mole-deg. The polymers obtained have low degrees of polymerization (DP _n ≤ 10) because of the extensive chain transfer, leaving cyclic end groups in macromolecules. The presence, structure and concentration of the end groups have been determined by ¹H-, ³¹P-, and ¹³C-NMR spectra.     

Equilibrium anionic polymerization of n-valeraldehyde

This paper describes an anionic polymerization of n-valeraldehyde (VA) in tetrahydrofuran (THF) initiated by benzophenone-monolithium complex in a high vacuum system. In spite of the deposition of the resulting polymer an equilibrium state between the monomer and the polymer was observed at a temperature range of ?90 to ?68°C. From the linear relationship between the equilibrium monomer concentration and the polymerization temperature, values of ?5.3 ± 0.3 kcal/mole and ?25.7 ± 1.4 cal/mole-deg, respectively, were evaluated for the enthalpy change and the entropy change in the present system. The effect of polar substituents on the polymerizability of aldehydes is discussed from the comparison of these values with those in the case of β-methoxypropionaldehyde.     

Dynamic proton magnetic resonance studies on complex spin systems. Non-mutual three-spin exchange in N-(trideuteriomethyl)-2-cyanoaziridine

At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH⁰ = ?475±20 cal mol^?1 (?1.987 ± 0.084 kJ mol^?1) and ΔS⁰ = 0.43±0.08 cal mol^?1 K^?1 (1.80±0.33 J mol^?1 K^?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔH_tc^≠ = 17.52±0.18 kcal mol^?1 (73.30±0.75 kJ mol^?1), ΔS_tc^≠ = ?2.08±0.50 cal mol^?1 K^?1 (?8.70±2.09 J mol^?1 K^?1) and ΔG_tc^≠ (300 K) = 18.14±0.03 kcal mol^?1 (75.90±0.13 kJ mol^?1) for the trans → cis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.     

A study of helix formation in polydimethysiloxane by Raman scattering

Depolarization ratios ρ of the Raman bands due to CH₃ stretching at 2907 cm^?1 and the Si? O skeletal mode at 491 cm^?1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to ?45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.     

Complexation of neptunium(V) by salicylate,phthalate and citrate ligands in a pH 7.5 phosphate buffered system

Conditional stability constants, enthalpies and entropies of complexation at pH 7.5 and ionic strength 0.1 have been determined for neptunium(V) complexes of phosphate, salicylate, phthalate and citrate. Phosphate forms a complex with log β = 2.36 ± 0.42 at 25°C, ΔH°_c = ? 69.9 kJ/mole and ΔS°_c = ? 188 J/mole-K. At pH 7.5 salicylate does not form a complex with neptunium(V) due to the low charge density of the NpO₂⁺ ion and incomplete ionization of the salicylate ion. Phthalate forms a complex with log β = 3.43 ± 0.33 at 25°C, ΔH°_c = 33.5 kJ/mole and ΔS°_c = 182 J/mole-K. Citrate forms a complex with log β = 4.84 ± 0.72 at 25°C, ΔH°_c = 14.0 kJ/mole and ΔS°_c = 140 J/mole-K. In all cases, only 1:1 complexes were identified.     

Die NO-katalysierte Isomerisierung von 3-Methylen-1,5,5-trimethyl-cyclohexen zu 1,3,5,5-Tetramethyl-1,3-cyclohexadien in der Gas-Phase. Thermodynamische Daten aus Gleichgewichtsmessungen

The composition of equilibrated gaseous mixtures of 3-methylene-1,5,5-trimethylcyclohexene (MTC) and 1,3,5,5-tetramethyl-1,3-cyclohexadiene (TECD) have been measured for temperatures ranging between 302 and 410°C. Nitrogen oxide was used as catalyst. Equilibrium was approached from either side. The least squares regression analysis of the observed temperature dependence of the equilibrium constants K_1.2 = k₁/k₂ = (TECD)_eq./(MTC)_eq. yields (with standard errors) This results in ΔH_1.2(300°K) = 0.4 ± 0.3 kcal/mole and ΔS_1.2(300°K) = 1.4 ± 0.8 cal/°-mole. The fact that the reaction is practically thermoneutral implies that the secondary, «biallylic» C? H bond in MTC is equally strong as the primary «biallylic» C? H bond of the 1-methyl group in TECD. The observed enthalpy and entropy differences between the two isomers are in agreement with prediction based on the concept of additivity of thermodynamic increment properties (ref. [5]). The results of this work also yield a value of 23.7 cal/°-mole for the entropy contribution characteristic of the 1,3-cyclohexadiene ring structure. When combined with the ARRHENIUS parameters, reported earlier [1] for k₁, the results of this work yield for the back reaction log k₂ (1/mole-s) = 8.25–30.2/4.58 × 10^?3 T(°K).     

Anionic polymerization of norbornene trisulfide (exo-3,4,5-trithia-tricyclo[5.2.1.02.6]decane)

The anionic polymerization of norbornene trisulfide initiated with sodium thiophenoxide (sodium cation solvated with dibenzo-18-crown-6 ether) was studied. Polymers with high molecular weights were obtained (M _n up to 10⁵, osmometrically). Molecular weights calculated for living polymerization conditions (i.e., one molecule of initiator yields one macromolecule) agree well with M _n measured by osmometry. ¹H-NMR, ¹³C-{¹H}-NMR, and Raman spectra of the polymer are given. Thermodynamics of polymerization in toluene solvent is described. Enthalpy ΔH_ss = ?(1.39 ± 0.17) kcal mol^?1 and entropy ΔS_ss = ?(7.52 ± 0.55) cal mol^?1 deg^?1 coefficients of polymerization were evaluated from the temperature dependence of the equilibrium monomer concentration determined dilatometrically.     

Applications of carbon-13 resonance spectroscopy—XV : The degenerate cope-rearrangement of bullvalene

The temperature dependence of the ¹³C-NMR spectrum of bullvalene has been studied from ?67 to +128°C using fourier transform spectroscopy and ¹H broadband decoupling. Lineshape analysis based on the Anderson-Kubo-Sack theory yielded E_a=13·9±0·1 kcal/mole, log A= 14·0±0·1, ΔH3 = 13·3±0·1 kcal/mole, and ΔS3 = 3·4±0·4 e.u. The pertinent features of dynamic ¹³C-NMR spectroscopy are discussed.     

Dynamic changes in composition of extracts of natural products as monitored by in situ NMR

The direct in situ NMR observation and quantification, based on the aldehyde –CH chemical shift region, of the inter‐conversion of secoiridoid derivatives due to temperature and solvent effects is demonstrated in complex extracts of natural products without prior isolation of the individual components. The equilibrium between the aldehyde hydrate form and the dialdehyde form of the oleuropein aglycon of an olive leaf aqueous extract in D₂O was shown to be temperature dependent. The resulting thermodynamic values of the Van't Hoff plot with ΔH^o = ?26.34 ± 1.00 kJ mol^?1 and TΔS° (298 K) = ?24.70 ± 1.00 kJ mol^?1 demonstrate a significant entropy term which nearly compensates the effect of enthalpy at room temperature. The equilibrium between the two diastereomeric hemiacetal forms and the dialdehyde form of the oleuropein 6‐O‐β‐d ‐glucopyranoside aglycon of an olive leaf aqueous extract in CD₃OD was also shown to be strongly temperature dependent again because of the significant entropy term (TΔS° (298 K) = ?26.50 ± 1.39 kJ mol^?1) compared with that of the enthalpy term (ΔH^o = ?36.64 ± 1.46 kJ mol^?1). This is the first demonstration of the significant role of the entropy parameter in determining the equilibrium of chemical transformations in complex mixtures of natural products due to solvent and temperature effects. Copyright © 2014 John Wiley & Sons, Ltd.     

The rate of the gas phase iodination of cyclobutane. The heat of formation of the cyclobutyl radical

The gas phase iodination of cyclobutane was studied spectrophotometrically in a static system over the temperature range 589° to 662°K. The early stage of the reaction was found to correspond to the general mechanism where the Arrenius parameters describing k₁ are given by log k₁/M^?1 sec^?1 = 11.66 ± 0.11 – 26.83 ± .31/θ, θ = 2.303RT in kcal/mole. The measured value of E₁, together with the fact that E_?1 = 1 ± 1 kcal/mole, provides ΔH(c-C₄H_7.) = 51.14 ± 1.0 kcal/mole, and the corresponding bond dissociation energy, D(c-C₄H₇? H) = 96.8 ± 1.0 kcal/mole. A bond dissociation energy of 1.8 kcal/mole higher than that for a normal secondary C? H bond corresponds to one half of the extra strain energy in cyclobutene compared to cyclobutane and is in excellent agreement with the recent value of Whittle, determined in a completely different system. Estimates of ΔH and entropy of cyclobutyl iodide are in very good agreement with the equilibrium constant K₁₂ deduced from the kinetic data. Also in good agreement with estimates of Arrhenius parameters is the rate of HI elimination from cyclobutyl iodide.     

Thermal dissociation of SmMnO3

The phase equilibria for the reduction of SmMnO₃ with hydrogen were studied by the static method using a circulation vacuum setup in conjunction with XRD analysis of quenched solid phases. It was established that, over a temperature range of 973–1123 K and a pressure range of 10^?10–10^?16 Pa, SmMnO₃ dissociates by the reaction (1/2)Sm₂O₃ + MnO + (1/4)O₂; in this case, the temperature dependence of the equilibrium oxygen pressure and the Gibbs energy change can be described by the equations log $p_{O_2 } $ [Pa] = 25.35 ? 39150/T ± 0.1, ΔG°_T, kJ/mol = 187.62 ? 0.09T ± 1.62, respectively. Based on the experimental data, the standard thermodynamic functions of formation of SmMnO₃ from elements were calculated: ΔH°_T = ?1485.706 kJ/mol and ΔS°_T = 244.39 J/(mol K).     

Knudsen measurements of the sublimation and the heat of formation of GeSe2 [1]

Knudsen effusion studies of the sublimation of polycrystalline GeSe₂ have been performed employing mass spectrometry in a temperature range of about 610–750 K and vacuum microbalance techniques in the temperature range 614–801 K and at pressures ranging from about 10^?7 ? 10^?4 atm. The results demonstrate that GeSe₂ vaporizes congruently under present experimental conditions according to the predominant reaction (1) GeSe₂(s) = GeSe(g) + 1/2 Se₂(g) and a minor reaction (2) GeSe₂(s) = GeSe₂(g). The mean values for the third law heat and second law entropy of reaction (1) based on direct mass-loss data are ΔH°₂₉₈ = 70.4 ± 2 kcal/mole and ΔS°₂₉₈ = 64.7 ± 2 eu. From these the standard heat of formation and absolute entropy of GeSe₂(s) were calculated to be ?21.7 ± 2 kcal/mole and 24.6 ± 2 eu, respectively.     

Calorimetric Measurements of the Complexation of Cyclosporin A,Ascomycin, Fujimycin,and Rapamycin with Lithium Chloride and with an Immunophilin

Solutions (2 ml) of small linear and cyclic peptides ( 4–11 ), of a peptolide containing nine amino acids and a lactate moiety ( 12 ), of the cyclic undecapeptide cyclosporin A (CS, 1 ), and of the macrolides ascomycin, fujimycin, and rapamycin ( 13–15 ) in THF were added to excess LiCl, LiBr, or LiClO₄ (up to 3000 equiv. in 40 ml THF) in a calorimeter (calorimetric titration). The enthalpies of interaction measured are in the range of ΔH = ?8 to ?37 kcal/mol. A similar experiment was carried out with one of the binding proteins of cyclosporin, the human cyclophilin A, to give the thermodynamic parameters for the complexation ΔH = ?16, ΔG° = ?10 kcal/mol, and ΔS° = ?20 cal/mol·deg. at 25° which corresponds to an equilibrium constant K = 2·10⁷ l/mol, in good agreement with the result of independent measurements using different methods. NMR Measurements of the macrolides in (D₈)THF containing LiCl show strong down-field shifts of signals of the H-atoms next to C?O and C–OH groups in these molecules.