Redshifts and blueshifts of OH vibrations

Ab initio calculations of potential energy, dipole moment, equilibrium OH distance, force constants, and anharmonic frequencies, and correlations between these quantities, are presented for a water molecule and an OH^? ion in a uniform electric field of varying field strength. It is explained why a bound H₂O molecule in nature always experiences a frequency downshift with respect to the free molecule, and a bound OH^? ion either a downshift or an upshift. The frequency-field variation is well accounted for by the expression Δν_OH ∝ ?E_∥·(dμ/dr_OH + 1/2 · ?μ/?r_OH). A frequency maximum occurs at the field strength where ?μ/?r_OH ～ 0. Two cases can be discerned: (1) the frequency maximum falls at a positive field strength when dμ/dr_OH is negative (this is the situation for OH^?), and (2) the maximum frequency falls at a negative field when dμ/dr_OH is positive (this occurs for water). In general, for an OH bond in a bonding situation where the intermolecular interactions are dominated by electrostatic forces, the nonlinearity of the frequency shift with respect to an applied field is governed by how close to the frequency maximum one is, i.e., by both dμ/dr_OH and ?μ/?r_OH. Correlation curves between the external linear force constant, k^ext, and r_OH,e are closely linear over the whole field range studied here, whereas the frequency vs. r_OH,e and force constants vs. r_OH,e correlation curves form two approximately linear, parallel branches, corresponding to “before” and “after” the maximum in the frequency vs. field curves. Each branch of the v vs. r_OH,e curves has a slope of ～ ?16,000 cm^?1/Å. © 1993 John Wiley & Sons, Inc.     

Rapid Ring‐Opening Polymerization of D,L‐Lactide by Microwaves

Summary: Poly(D ,L ‐lactide) with a molar mass of 10⁵ g · mol⁻¹ and a yield over 90% was produced in 10 min by the ring‐opening polymerization of D ,L ‐lactide under microwave irradiation with forward power of 255 W. A degradation of the poly(D ,L ‐lactide) was also induced by microwaves with a power level over 340 W. The molar mass of poly(D ,L ‐lactide) was dependent upon the competition between the polymerization of D ,L ‐lactide and the degradation of the resulting polymer.

Profiles of molar mass versus microwave irradiation time (1.8 g DLLA, 0.1% Sn(Oct)₂).     

Synthesis of Amphiphilic Supramolecular Miktoarm Star Copolymers by Molecular Recognition

Synthesis of novel amphiphilic supramolecular miktoarm star copolymers has been achieved through complementary molecular recognition and interactions between carboxy groups and amino groups. Polystyrenes carrying two and one carboxy groups at the middle of the polymer chain are used as precursors to react with poly(ethylene oxide) (PEO) end‐capped with a primary amine functionality (–NH₂) or a quaternary ammonium hydroxide functionality (–N⁺(CH₂CH₃)₃OH⁻). The result suggests that the basicity of the amine plays a key role in the molecular recognition procedure. The efficiency of ionic bond formation can be enhanced from 40% up to 97% by using PEO‐N⁺(CH₂CH₃)₃OH⁻ instead of PEO‐NH₂. The obtained supramolecular polymers can be dissociated in dilute acid solution at room temperature.

     

Redshifts and blueshifts of OH vibrations

Ab initio calculations of potential energy, dipole moment, equilibrium OH distance, force constants, and anharmonic frequencies, and correlation between these quantities, are presented for a water molecule and an OH^? ion in a uniform electric field of varying field strength. It is explained why a bound H₂O molecule in nature always experiences a frequency downshift with respect to the free molecule, and a bound OH^?1 ion, either a downshift or an upshift. The frequency-field variation is well accounted for by the expression Δν_OH α ?E‖ · (d μ/dr_OH + 1/2 · ?μ/?r_OH). A frequency maximum occurs at the field strength where ?μ‖^tot/?r_OH ～ 0. Two cases can be discerned: (1) the frequency maximum falls at a positive field strength when dμ/dr_OH is positive (this is the situation for OH^?), and (2) the maximum frequency falls at a negative field when dμ/dr_OH is negative (this occurs for water). In general, for an OH bond in a bonding situation where the intermolecular interactions are dominated by electrostatic forces, the nonlinearity of the frequency shift with respect to an applied field is governed by how close to the frequency maximum one is, i.e., by both dμ/dr_OH and ?μ/?r_OH. Correlation curves between the external linear force constant, k^ext, and r_OH,e are closely linear over the whole field range studied here, whereas the frequency vs. r_OH,e and force constants vs. r_OH,e correlation curves form two approximately linear, parallel branches, corresponding to “before” and “after” the maximum in the frequency vs. field curves. Each branch of the ν vs. r_OH,e curves has a slope of ～ ? 16,000 cm^?1/Å. © 1993 John Wiley & Sons, Inc.     

Ab-initioMRD–CI calculations on a C?NO2 decomposition pathway of nitrobenzene

To study molecular decomposition pathways it is necessary to use ab initio multireference determinant–configuration interaction or MCSCF (multiconfiguration SCF ) calculations. The MRD –CI (multireference double excitation–configuration interaction technique of Buenker and Peyerimhoff) calculations on the decomposition pathway of nitrobenzene were carried out using all of the occupied molecular orbitals in the region of the bond being dissociated, plus all of the virtual orbitals. An effective CI Hamiltonian was used into which were folded the effects of all of the occupied molecular orbitals from which excitations were not allowed. So far we have investigated the lowest ¹A₁, ³A₁, ¹A₂, ³A₂, ¹B₁, ³B₁, ¹B₂, ³B₂ states and are investigating the higher states. Our results show a wealth of structure in the potential energy surfaces for the various electronic states of nitrobenzene as a function of distance. A number of the states are predissociative and change dominant configuration one or more times along these potential energy surfaces.     

Über Oberflächenverbindungen von Übergangsmetallen. VIII. Die Komplexbildung von koordinativ ungesättigtem Oberflächen-Chrom (II) mit Oxiden des Stickstoffs

On Surface Compounds of Transition Metals. VIII. Complex Formation of a Coordinatively Unsaturated Cr^II Surface Compound with Nitrogen Oxides N₂O forms with surface-Cr(II) a relatively unstable light blue compound of the stoichiometry 1:1, while addition of NO results in formation of a very stable dark brown, diamagnetic surface complex . By reaction with O₂ this complex undergoes — depending on reaction temperature — either replacement of NO unter reoxidation of the metal (→Cr(VI)) or/and reaction of the ligand (→NO₂). Direct reaction of NO₂ with results in the same products as stepwise addition of NO and 1/2 O₂. reacts with HCl/ROH under formation of the soluble, paramagnetic kation [Cr(NO)(ROH)_n]²⁺, which is formulated as [Cr(II)(NO)]²⁺ ? [Cr(I)(NO⁺)]²⁺ accordingly to the e.s.r. spectra.     

Green Polymer Chemistry: II. Enzymatic Synthesis of Methacrylate‐Terminated Polyisobutylenes

Methacrylate‐terminated polyisobutylenes (PIB‐MAs) were synthesized by transesterification of vinyl methacrylate by hydroxyl‐terminated polyisobutylenes (PIB‐OH) using Candida antarctica lipase B (Novozyme 435) catalyst in hexane at 50 °C. PIB CH₂ CH₂ CH₂ OH and Glissopal OH, synthesized by anti‐Markovnikov hydrobromination of allyl‐terminated PIB and Glissopal®2300 followed by hydrolysis, were quantitatively converted into the corresponding PIB‐MAs. ¹H and ¹³C NMR spectroscopy verified the formation of the expected structures. This “green” chemistry is a very promising methodology for polymer functionalization in general, and biomaterial synthesis in particular.

     

The potential energy surface for the [C2H2O]+˙ system: The ketene radical cation [CH2CO]+˙ and its isomers

Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C₂H₂O]^+˙ potential energy surface. Four [C₂H₂O]^+˙ isomers have been identified as potentially stable, observable ions. These are the experimentally well-known ketene radical cation, [CH₂?C?O]^+˙ (a), and the presently unknown ethynol radical cation, [CH₂?C? OH]^+˙ (b), the oxirene radical cation (c) and an ion resembling a complex of CO with [CH₂]^+˙, (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol^?1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.     

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

The solubility of precipitated Cd(OH)₂ was determined at 25°C in 1 M NaClO₄, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH⁺, Cd(OH)₂, Cd(OH), CdNH, Cd(NH₃), Cd(NH₃), Cd(NH₃) and Cd(OH)₂NH₃. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.     

Zur Darstellung von Cyclophosphaten,Cyclophosphatophosphonaten, Diphosphonaten und Diphosphiten in Harnstoffschmelzen

Preparation of Cyclophosphates, Cyclophosphatophosphonates, Diphosphonates, and Di-phosphites in Urea Melts Ammonium cyclotriphosphate (NH₄)P₃O₉, ammonium cyclotetraphosphate [P^IV? P^IV ? O? ]₂, ammonium cyclotriphosphatophosphonates Ammonium organyldiphosphonates And ammonium diphosphites are prepared in high yields on heating acidic phosphates, phosphonates, and phosphites in urea or urea/ammonium nitrate melts. The mechanism of the dehydration of phosphorus compounds containing POH groups in molten urea is discussed.     

Unimolecular Gas-Phase Oxidation of Terminal Hydroxy Groups in [FeO(CH2)nOH]+ Complexes (n = 2–8). A Case for O?H Bond Activation by Late Transition-Metal Ions. Preliminary Communication

In contrast to Fe⁺/diol complexes, gas-phase dehydrogenation of the corresponding Fe^II alkoxides, [FeO(CH₂)_nCH₂OH]⁺, is a highly specific process in the course of which oxidation of the terminal OH group takes place. Based on labeling studies, this is the exclusive mechanism for n = 2 and 3 (Scheme: path ); for higher homologues, as for example [FeOf(CH₂)₇CH₂OH]⁺, the labeling data demonstrate that an additional mechanism is operative, involving the dehydrogenation of internal positions of the alkyl chain (path ). The Fe⁺-mediated oxidation –CH₂OH → –CHO +H₂: constitutes one of the rare examples of O-H bond activation by late cationic transition-metal ions.     

Reactions of isopropylperoxy radicals with NO and NO2

The rate constants for the reactions have been measured directly by flash photolysis and kinetic spectroscopy. At room temperature, k₃ = (3.4 ± 0.1) × 10⁹ L/mol·s, independent of pressure in the range of 55–400 torr, and k₆ = (2.1 ± 0.2) × 10⁹ L/mol·s.     

Organische Phosphorverbindungen XXIX. Eine neue Methode zur Darstellung von dialkylaminomethylsubstituierten Phosphonig- und Phosphinsäuren der allgemeinen Formel R2NCH2PH(O)OH und (R2NCH2)2P(O)OH [1]

A new method for the preparation of dialkylaminomethyl-phosphonous and-phosphinic acids, R₂NCH₂P(O)H(OH) and (R₂NCH₂)₂P(O)OH, is described. This involves reaction of hypophosphorous acid with hydroxymethyl-dialkyl-amines or a mixture of formaldehyde and a secondary amine. and The crystalline acids form monohydrates which are stable up to the melting points of the acids. The IR. and ³¹P-NMR. spectra are reported.     

Mössbauer Spectroscopic Studies of the Hydroxofluorostannate(IV) Complexes

Mössbauer isomer shifts of ¹¹⁹Sn in a series of complexes K₂Sn(OH)_6-mF_m observed at 78 K were ?0.05, ?0.05, ?0.24, ?0.27 and ?0.40 mm s^?1, respectively, for m=0, 2, 4, 5 and 6. These IS values were linearly related to both m and (the average Pauling electronegativity of the ligands): . The IS straight line was compatible within experimental error with the one reported by Parish and Row-botham for the hexahalogenostannate complexes SnX₄Y₂², namely, The revised IS straight line including both series of complexes could be expressed by the equation Quadrupole splittings observed in the complexes of m = 2,4 and 5 were 1.16, 0.80 and 0.73 mm s^?1 respectively. They were linearly related to both m and .     

Die Deprotonierung von Metall-Aquoionen I.: Be · aq2+ Solvatations-Isomerie

The reaction of Be · aq²⁺ with OH^? leeds not only to loss of protons by the metalaquo ion but also to structural changes in the solvation sphere. These can be studied by following the pH variations during the first decisecond after mixing the solutions of metal salt and alkali hydroxide. The equilibrium Be²⁺ ? BeOH⁺ is reached within 5 milliseconds if acid free Beryllium solutions are used. If the metal solution is strongly acidic, however, the establishment of the equilibrium needs more time because of the slowness of the process H⁺ + BeOH⁺ → Be²⁺ (k ～ 10⁵ M^?1, s^?1). The extraction of two protons produces in the first instance an unstable Be(OH) species which transforms into the stable isomer Be(OH)₂ (solvatation isomerism) in a first-order reaction of half-life of 7 ms. This isomerisation causes almost complete disappearance of BeOH⁺ from the equilibrium Be²⁺ ? BeOH⁺ ? Be(OH)₂. (KAKIHANA & SILLEN state that the relaxed solutions contain only Be²⁺, Be(OH)₂, Be₃(OH) and some Be₂OH³⁺.) The formation of the polynuclear species Be₃(OH) needs about 30 seconds to go to completion.     

Structures and relative energies of gas phase [C3H7O]+ ions

Ab initio molecular orbital calculations have been carried out for 17 possible isomeric [C₃H₇O]⁺ structures. Optimized geometries have been obtained with a split-valence basis set and improved relative energies determined with polarization basis sets and with incorporation of electron correlation. The results agree well with available experimental data. In particular, (CH₃)₂COH⁺, CH₃CH₂CHOH⁺, CH₃CHOCH₃⁺, CH₃CH₂OCH₂⁺, and have been confirmed as low-energy isomers. Six additional structures appear to be energetically accessible and to offer a reasonable prospect for experimental observation. These are CH₂CHCH₂OH₂⁺, CH₂C(CH₃)OH₂⁺, CH₃CHCHOH₂⁺, CH₂CHOHCH₃⁺, and .     

Fabrication of Highly Photoluminescent TiO2/PPV Hybrid Nanoparticle‐Polymer Fibers by Electrospinning

In this study, we have synthesized highly photoluminescent TiO₂/poly (phenylene vinylene) (PPV) hybrid nanoparticle‐polymer fibers by electrospinning a PPV precursor added to a TiO₂ sol‐gel solution. The diameters of the hybrid fibers ranged from 100–300 nm and the average size of TiO₂ nanoparticles within the fibers was 10–60 nm. FT‐IR analysis indicated that a new band around 1 632 cm⁻¹ assigned to the Ti O C vibration appeared, which resulted in the stronger luminance of the fluorescence of the TiO₂/PPV hybrid fibers compared to free standing PPV nanofibers.

     

Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions

A ternary blend of the bisiminopyridine chromium (III) (Cr‐ 1 ) with the bisiminopyridine iron (II) (Fe‐ 2 ) post‐metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr‐ 3 ) was supported on mesoporous silica to produce novel multiple single‐site catalysts and polyethylene reactor blends with tailor‐made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO‐treated silica was Fe‐ 2 followed by Cr‐ 1 and Cr‐ 3 . Cosupporting does not impair the single‐site nature of the blend components producing polyethylene fractions with = 10⁴ g · mol⁻¹ on Cr‐ 1 , = 3 × 10⁵ g · mol⁻¹ on Fe‐ 2 , and = 3 × 10⁶ g · mol⁻¹ on Cr‐ 3 . As a function of the Fe‐ 2 /Cr‐ 1 /Cr‐ 2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor‐made polyethylene reactor blends with ultra‐broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe‐ 2 /Cr‐ 1 was constant, the ultra‐high molecular polyethylene (UHMWPE, > 10⁶ g · mol⁻¹) content was varied between 8 and 16 wt.‐% as a function of the Cr‐ 3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe‐ 2 /Cr‐ 3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr‐ 1 . Due to the intimate mixing of low and ultra‐high molecular weight polyethylenes (UHMPEs) produced on cosupported single‐site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

     

The photochemistry of hexafluoroacetylacetone in the vapour phase. Occurrence of a novel HF elimination reaction

Photolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2-difluoro-2,3-dihydro-5-trifluoromethylfuran-3-one: The HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF₂ radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, (9) The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both ?₁ and ?₅ depend on pressure and the ratio ?₁/?₅ increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio ?₁/?₅ increases as the vibrational energy of electronically excited HFAA increases.     

A shock tube study of reactions of atomic oxygen with isocyanic acid

Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N₂O/Ar mixtures. Quantitative time-histories of the NH(X³Σ^?) and OH(X²Π_i) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: and were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: and cm³ mol^?1 s^?1. The minimum and maximum rate constant factors (?,F) define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be: .