The free-radical reaction of tri-n-butyltin hydride with peroxides

Rate constants for the tri-n-butyltin radical ( Sn · ) induced decomposition of a number of peroxides have been measured in benzene at 10°C. The values range from ～100 M^?1 sec^?1 for di-t-butyl peroxide to 2.6 × 10⁷ M^?1 sec^?1 for di-t-butyl diperoxyisophthalate. The majority of the peroxides, including diethyl peroxide, diacetyl peroxide, and t-butyl peracetate, have rate constants of ～10⁵ M^?1 sec^?1. It is shown that di-n-alkyl disulfides are ten times as reactive toward Sn · as di-n-alkyl peroxides, although the exothermicities of these reactions are ～15 and ～39 kcal/mole, respectively. The enhanced reactivity of the disulfides is attributed to the easier formation of an intermediate or transition state with 9 electrons around sulfur, compared with an analogous species with 9 electrons around oxygen. The following bond strengths (kcal/mole) have been estimated: D[ Sn ? OR] = 77; D[ Sn ? H] = 82; D[ Sn ? SR] = 83; and D[ Sn ? OC(O)R] = 86, where R = alkyl. Rate constants for reaction of Sn · with some benzyl esters have also been measured. It has been found that t-butoxy radicals can add to benzene and abstract hydrogen from benzene at ambient temperatures.     

Reactivity ratios of styrene and methyl methacrylate at 90°C

From the conversion–composition data of Gruber and Elias, the reactivity ratios of styrene (M₁) and methyl methacrylate (M₂) were calculated to be r₁ = 0.55 ± 0.02 and r₂ = 0.58 ± 0.06 at 90°C. The least-squares method was then used on these and literature values at other temperatures to obtain the Arrhenius expressions: In r₁ = 0.04736 – (235.45/T), and ln r₂ = 0.1183 – (285.36/T). Using literature values for the homopolymerization steps, A₁₁ = 2.2 × 10⁷l./mole-sec., E₁₁ = 7.8 kcal./mole, and A₂₂ = 0.51 × 10⁷ l./mole-sec.^?1, E₂₂ = 6.3 kcal./mole, activation energies and frequency factors were then calculated for the cross-polymerization steps: A₁₂ = 2.1 × 10⁷ l./mole-sec., E₁₂ = 7.3 kcal./mole, and A₂₁ = 0.45 × 10⁷ l./mole-sec., E₂₁ = 5.7 kcal./mole.     

Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems

The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S^- and M represent the initiator and D₄, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k₁ = 2.3 × 10^?4 l./mole-sec., k₂ < 2.3 × 10^?5 sec.^?1, k₃ = 2.75 × 10^?2l./mole-sec. k₄ ≈ 1.17 × 10^?2 sec.^?1, K₁ > 10 l./mole and K₂ ≈ 2.35 l./mole. The rate constants k₁ and k₃ were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K₂, indicating zero ΔH and positive ΔS in the propagation reaction.     

Photolysis of poly(tert-butyl acrylate) in the region of the glass transition temperature

The thin film (1 × 10^?5 cm.) photolysis (2537 A.) of poly(tert-butyl acrylate) under 1 atm. helium pressure has been investigated in detail. Isobutene was the only significant volatile product in the temperature range 20–110°C. The reaction was demonstrated to be initially a first-order decomposition with an energy of activation of 3.3 kcal./mole in the glassy state. Above the glass transition temperature a value of 1.8 kcal./mole was found. The rate of isobutene formation is autoaccelerated when a minimum of one acrylic acid unit is generated per chain. The initial quantum yield for the formation of isobutene varies from 0.083 to 0.17 over the temperature range studied. There was no dependence of quantum yield on the exciting wavelength using sources of 1849, 2537, and 3660 A. The intensity exponent was found to be unity, consistent with first-order decomposition kinetics.     

CH⋅⋅⋅N Hydrogen‐Bonding Interaction in 7‐Azaindole:CHX3 (X=F,Cl) Complexes

The C?H???Y (Y=hydrogen‐bond acceptor) interactions are somewhat unconventional in the context of hydrogen‐bonding interactions. Typical C?H stretching frequency shifts in the hydrogen‐bond donor C?H group are not only small, that is, of the order of a few tens of cm^?1, but also bidirectional, that is, they can be red or blue shifted depending on the hydrogen‐bond acceptor. In this work we examine the C?H???N interaction in complexes of 7‐azaindole with CHCl₃ and CHF₃ that are prepared in the gas phase through supersonic jet expansion using the fluorescence depletion by infra‐red (FDIR) method. Although the hydrogen‐bond acceptor, 7‐azaindole, has multiple sites of interaction, it is found that the C?H???N hydrogen‐bonding interaction prevails over the others. The electronic excitation spectra suggest that both complexes are more stabilized in the S₁ state than in the S₀ state. The C?H stretching frequency is found to be red shifted by 82 cm^?1 in the CHCl₃ complex, which is the largest redshift reported so far in gas‐phase investigations of 1:1 haloform complexes with various substrates. In the CHF₃ complex the observed C?H frequency is blue shifted by 4 cm^?1. This is at variance with the frequency shifts that are predicted using several computational methods; these predict at best a redshift of 8.5 cm^?1. This discrepancy is analogous to that reported for the pyridine‐CHF₃ complex [W. A. Herrebout, S. M. Melikova, S. N. Delanoye, K. S. Rutkowski, D. N. Shchepkin, B. J. van der Veken, J. Phys. Chem. A­ 2005 , 109, 3038], in which the blueshift is termed a pseudo blueshift and is shown to be due to the shifting of levels caused by Fermi resonance between the overtones of the C?H bending and stretching modes. The dissociation energies, (D₀), of the CHCl₃ and CHF₃ complexes are computed (MP2/aug‐cc‐pVDZ level) as 6.46 and 5.06 kcal mol^?1, respectively.     

Alternating copolymerization of the styrene–methyl methacrylate system complexed with diethylaluminum chloride

The rate and molecular weight profiles were obtained for the spontaneous alternating copolymerizations conducted with diethylaluminum chloride. The rate formally fitted an expression, R = k_p[MMA][Sty], and the rate constant was established by two distinct methods: (1) from the yield versus time data and (2) from initial rate over a range of initial concentrations; it was determined as 5.4 × 10^?6 l./mole-sec with E_a = 4.2 kcal/mole. Molecular weights were determined by gel-permeation chromatography. No increase in molecular weight was observed with increased reaction time. Thus living centers or diradicals are not involved in the process. The M?_n shows a steady decrease with increase in monomer-diethylaluminum chloride concentration but the rate is maximum at equimolar monomer concentrations. The data are interpreted on a chain-transfer mechanism and show close agreement to a model in which the excess complexed acceptor monomer is the transfer agent. The chain-transfer constant of 7.1 × 10^?4 l./mole-sec is several orders of magnitude greater than for uncomplexed systems.     

Molecular interpretation of miscibility in polyamide-6 blends with alkali ionomers of sulfonated polystyrene

Blends of polyamide-6 with lithium ionomers of 9.8 and 5.4 mole percent sulfonated polystyrene, formed by combining solutions of these polymers, are miscible over a wide compositional range, but those with the equivalent sodium ionomers are not. The molecular origin of this difference is addressed by studying the far infared and infrared spectra of the blends and pure materials to follow changes in the interactions between the cations and their surroundings, and changes in the interactions between functional groups. Based on analysis of these spectra, a molecular level interpretation of the blending is proposed. The initial step involves both the interaction of one amide carbonyl with an Li⁺ ion and simultaneous hydrogen bonding between an amide N? H and a sulfonate group. This eventually leads to formation of an Li(>CO)⁺_n(n ～ 4) entity while the sulfonates are converted to the acid form through hydrogen bonding to the amide N? H groups. The Na⁺ ion does not interact strongly enough with the amide groups to leave its sulfonate environment to a significant extent. © 1995 John Wiley & Sons, Inc.     

Kinetics and rate constants for the reaction of tri-n-butylgermanium hydride with methyl iodide and carbon tetrachloride. The combination of methyl and trichloromethyl radicals in solution.

The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH₃? and CCl₃? radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ～1–3 × 10⁹ M^?1 sec^?1. Rate constants for hydrogen atom abstraction by CH₃? and CCl₃? radicals are both ～1?2 × 10⁵ M^?1 sec^?1. Tri-n-butyltin hydride is about 10–20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride. The strength of the germanium–hydrogen bond, D(n-Bu₃Ge–H) is estimated to be approximately 84 kcal/mole.     

GIAO,DFT, AIM and NBO analysis of the N?H···O intramolecular hydrogen‐bond influence on the 1J(N,H) coupling constant in push–pull diaminoenones

In the series of diaminoenones, large high‐frequency shifts of the ¹H NMR of the N? H group in the cis‐position relative to the carbonyl group suggests strong N? H···O intramolecular hydrogen bonding comprising a six‐membered chelate ring. The N? H···O hydrogen bond causes an increase of the ¹J(N,H) coupling constant by 2–4 Hz and high‐frequency shift of the ¹⁵N signal by 9–10 ppm despite of the lengthening of the relevant N? H bond. These experimental trends are substantiated by gauge‐independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3‐bis(isopropylamino)‐1‐(aryl)prop‐2‐en‐1‐one (12) for conformations with the Z‐ and E‐orientations of the carbonyl group relative to the N? H group. The effects of the N? H···O hydrogen‐bond on the NMR parameters are analyzed with the atoms‐in‐molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N? H···O hydrogen bond as compared with that of 1,1‐di(pyrrol‐2‐yl)‐2‐formylethene (13) where N? H···O hydrogen bridge establishes a seven‐membered chelate ring, and the corresponding ¹J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) →σ*_{N? H} hyperconjugative interaction is weakened on going from the six‐membered chelate ring to the seven‐membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N? H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the ¹J(N,H) value as a consequence of the N? H···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies in fluorinated 1,3-diketones and related compounds Part XII. Synthesis and spectroscopic studies of some new polyfluorinated 1,3-diketones,and their copper 1,3-diketonates

New polyfluorinated 1,3-diketones have been prepared from polyfluorinated acetophenones and appropriate esters in the presence of sodamide. The corresponding copper 1,3-diketonates have been obtained by treating a methanolic solution of polyfluorinated 1,3-diketone with methanolic solution of copper acetate. The polyfluorinated 1,3-diketones have been characterized by elemental as well as by spectral studies, viz: I.R., ¹H N.M.R. and ¹⁹F N.M.R. In I.R., characteristic absorptions observed are: CF stretching bands (1300 ? 1000) cm^?1, CF deformation modes (900 ? 700 cm^?1) and intramolecular hydrogen bonding (3000 ? 2500 cm^?1). In ¹H N.M.R. methine ( = C$\text{H}$) signal is observed at δ 6.2 ? 6.8 ppm and enolic proton resonance signal at δ 13 ? 15 ppm indicating the presence of strong hydrogen bonding in such polyfluorinated 1,3-diketones.     

Protonated Bis(quinuclidine) Included in a Novel “Bichannel” (Urea)–Chloride Host: a Very Large Urea Channel

The synthesis, crystal structure and properties of a novel ternary inclusion compound formed by protonated bis(quinuclidine) inserted in a urea–chloride anionic host, urea⁵[quinuclidine²H]⁺Cl^- (1), are reported. In the host structure each urea molecule interacts with adjacent urea molecules via N-H ?O hydrogen bonds forming a channel arrangement. Each hexagonal channel is linked through halide ions by N-H ?Cl hydrogen bonds forming a bichannel-like structure. The channel width of the host (14.32?Å) is one of the largest known for a urea host derivative. The compound may be described as a commensurate species, c ^g/c ^h=0.98. Conductivity determined for 1 at room temperature is 4.00?×?10^-6 (Ω?cm)^-1, and it increases with temperature to 3.33?×?10^-4 (Ω?cm)^-1 at 77°C. Aspects of the thermal stability of the product are discussed.     

Kinetics of the molybdate catalyzed oxidation of iodide by hydrogen peroxide

The kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped-flow method. The results are interpreted in terms of the mechanism and the implied rate law where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k₄ = (3.3 ± 1) × 10² 1./mole · s, K₁ = (1.2 ± 0.6) × 10⁴ 1./mole, K₂ = (1.3 ± 0.7) × 10³ 1./mole, and K₃ = (4 ± 3) × 10² 1./mole at 298°K.     

Studies on anionic polymerization of lactams. Part II. Effect of cocatalysts on the polymerization of pyrrolidone

The rates of addition of pyrrolidonate magnesium bromide (PyMgBr) to N-benzoyl-, N-acetyl-, and N-methylpyrrolidone were measured in solution in tetrahydrofuran (THF). The values found for the rate constants at 25°C. were 9.5 × 10^?2, 2.8 × 10^?2, and 5 × 10^?4 l./mole-sec., respectively. The rate constant for addition of PyMgBr to pyrrolidone was also measured and found to be 3 × 10^?9l./mole-sec. Possible causes for the large difference between the values of these constants are discussed.     

Hydrogen bonding and crystallization in biodegradable multiblock poly(ester urethane) copolymer

The hydrogen bonding and crystallization of a biodegradable poly(ester urethane) copolymer based on poly(L ‐lactide) (PLLA) as the soft segment were investigated by FTIR. On slow cooling from melt, the onset and the progress of the crystallization of the urethane hard segments were correlated to the position, width, and relative intensity of the hydrogen‐bonded N? H stretching band. The interconversion between the “free” and hydrogen‐bonded N? H and C?O groups in the urethane units in the process was also revealed by 2D correlation analysis of the FTIR data. The crystallization of the PLLA soft segments was monitored by the ester C?O stretching and the skeletal vibrations. It was revealed that the PLLA crystallization was restricted by the phase separation and the urethane crystallization, and at cooling rates of 10 °C/min or higher, the crystallization of the PLLA soft segments was prohibited. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 685–695, 2009     

FTIR analysis of hydrogen bonding in amorphous linear aromatic polyurethanes. I. Influence of temperature

Fourier-transform infrared spectral studies of an amorphous linear aromatic polyurethane at various temperatures were performed. Hydrogen bonding was studied in the N? H stretching (3347 cm^?1) and the bending (1535 cm^?1) regions, using the band decomposition technique. The variations with temperature are used to calculate the ratio of the absorptivity coefficients for the H-bonded to the “free” N? H vibrations. This ratio is found to be independent of temperature. The enthalpy and the entropy of hydrogen bond dissociation are also obtained as 9.6 kJ mol^?1 and 44.8 J mol^?1 K^?1, respectively. Two C?C in-plane vibrational bands of the aromatic rings at 1614 and 1598 cm^?1 were studied at different temperatures. The integrated absorbance for both bands decreases clearly and regularly with increasing temperature, and both bands shift to lower wavenumbers. This strongly suggests a specific interaction for the aromatic rings, probably N? H … π hydrogen bonds, which will be discussed in detail in the second part of this series. © 1994 John Wiley & Sons, Inc.     

Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N‐Oxide Complexes

A study of the strong N?X???^?O?N⁺ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X???O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X???O XBs. The XB interaction energies vary from ?47.5 to ?120.3 kJ mol^?1; the strongest N?I???^?O?N⁺ XBs approaching those of 3‐center‐4‐electron [N?I?N]⁺ halogen‐bonded systems (ca. 160 kJ mol^?1). ¹H NMR association constants (K_XB) determined in CDCl₃ and [D₆]acetone vary from 2.0×10⁰ to >10⁸ m ^?1 and correlate well with the calculated donor×acceptor complexation enthalpies found between ?38.4 and ?77.5 kJ mol^?1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (R_XB) between 0.65–0.67 for the N?I???^?O?N⁺ halogen bond.     

Hydrogen bonded networks based on Ni(II)-tetraazamacrocycle (tet-b) complexes: synthesis,isolation and structural characterization of α -[Ni(tet-b)(Cl)](ClO4) and α -[Ni(tet-b)(en)](ClO4)2

Five- and six-coordinate, α-[Ni(tet-b)(Cl)](ClO₄) (1) and α-[Ni(tet-b)(en)](ClO₄)₂ (2) (tet-b?= C-racemic-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) complexes have been synthesized and isolated from the reactions of α-[Ni(tet-b)](ClO₄)₂, which has trans-V (1R,4R,8R,11R,7S,14S or 1S,4S,8S,11S,7R,14R) conformation, with t-Bu₄NCl and ethylenediamine (en), respectively. The complexes have been characterized by X-ray crystallography. The crystal structure of 1 shows a distorted trigonal bipyramidal (TBP) coordination geometry composed of four nitrogen atoms from tet-b and a chloro group with an N₄Cl chromophore about the nickel(II) ion. The complex cations of 1 are assembled by the perchlorate ions via N–H?···?O hydrogen bonding to form 1-D zigzag chains along the [001] direction. The chains are linked through intermolecular hydrogen bonding where the coordinated chloro group of the complex cation forms two-center double hydrogen bonds with the adjacent N–H groups of the macrocyclic ligand along the [100] direction, resulting in a two-dimensional α-network. The crystal structure of 2 shows a distorted octahedral coordination environment consisting of four nitrogen atoms from tet-b and two from en with an N₆ chromophore about nickel(II) ion. The crystal packing analysis shows that the complex cations, α-[Ni(tet-b)(en)]²⁺ are interconnected by perchlorate ions through conventional two-center (N)H?···?O, and bifurcated (N)H?···?O?···?H(N) hydrogen bonding.     

Sorption of organic vapors into drawn and undrawn polyethylene

Drawing of linear polyethylene at 60°C. to an extension ratio of ten drastically reduces the sorption and diffusion of n-pentane, benzene, methylene chloride, and tetrachloroethylene. Methylene chloride was chosen for more detailed study. The sorption is of the normal Fickean type. It is also fully reversible in the temperature range between 25 and 45°C. if the sorbed amount is kept to below 0.5%. At higher concentrations the sample relaxes so that sorption irreversibly increases. The reversible sorption per gram of amorphous component is about 1/6 of that in undrawn polyethylene. The diffusion constant has a larger temperature and concentration dependence than in the undrawn material. At zero concentration the activation energy for diffusion is 34.4 kcal./mole and the diffusion constant at 25°C. is 8 × 10^?11 cm.²/sec. as compared with 14.4 kcal./mole and 1.5 × 10^?8 cm.²/sec. in undrawn PE. Cold drawing reduces the sorption sites without changing their energy content, but drastically cuts down diffusion and increases the activation energy. A smaller part of the increase of the latter is a consequence of the lower enthalpy of the amorphous material and a larger part is probably due to the increased distance between sorption sites.     

Exchange reactions of urethanes with proton-donating compounds: Kinetics of the reactions of phenyl-<Emphasis Type="Italic">N</Emphasis>-phenylurethane with butyl alcohols

The exchange reactions of phenyl-N-phenylurethane with aliphatic alcohols, namely, n-butyl, sec-butyl, and tert-butyl alcohols, in ortho-dichlorobenzene and in the media of the corresponding alcohols were studied. In the absence of a catalyst and proton-donating compounds, the monomolecular cleavage of phenyl-N-phenylurethane to isocyanate and alcohol proceeds at a noticeable rate starting only at 250°C. Between 40 and 80°C, the exchange reactions take place via direct exchange between urethane and the photon-donating compound and are second-order up to high conversions (until the almost complete disappearance of the initial urethane). Activation energies and apparent rate constants have been determined for the exchange reactions of phenyl-N-phenylurethane with butyl alcohols. The rates of the exchange reactions in the alcohol medium are compared with those in ortho-dichlorobenzene.