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  • 1995-1999  (3,212)
  • Chemical Engineering  (1,635)
  • Theoretical, Physical and Computational Chemistry  (1,576)
  • Nuclear reactions
  • 101
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 419-425 
    ISSN: 0894-3230
    Keywords: 5-nitro-5′-dimethylamino-2,2′-bisthiophene ; π* probe dye ; cyclic voltammetry ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclic voltamograms of the solvatochromic dye 5-nitro-5′-dimethylamino-2,2′-bisthiophene (1), introduced recently as a sensitive π* probe, were recorded in different solvents. An EPR spectrum of the anionic radical of 1 in DMSO was obtained and compared with other spectra of analogous substituted bisthiophene radicals. It was found that the presence of a donor- acceptor pair of substituents in 1-⋅ reduces significantly the rotational barrier of the radical compared with the unsubstituted bithienyl radical anion 2-⋅. This is the result of an electronic repulsion between the donor ring fragment and the added electron in the coplanar radical, which does not exist in 2-⋅. © 1998 John Wiley & Sons, Ltd.
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  • 102
    ISSN: 0894-3230
    Keywords: calixarene sulphonates ; amino acids ; proteins ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interactions of calixarene sulphonates with the basic amino acids arginine and lysine were studied by 1H NMR spectroscopy. Strong electrostatic binding occurs for calix[4]arene sulphonate with both lysine and arginine at pH 1 and 5. For the higher calixarenes, only weak interactions at the faces of the flattened macrocycles occur. This binding is in contrast to the inhibition of protein-protein interactions by the calixarenes where the calix[6]arene and calix[8]arene sulphonates show much stronger effects. © 1998 John Wiley & Sons, Ltd.
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  • 103
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 715-721 
    ISSN: 0894-3230
    Keywords: unsaturated nitriles ; homolytic reactions ; cyclization ; tert-butylmercury halides ; proton donors ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclizations are observed in the homolytic reactions of t-BuHgI with CH2=CHCH2YCH2CN [Y = CH2, O, CMe2, C(CO2Et)2, NCH2CN] and CH2=CHCH2CH2YCH2CN [Y = CH2, O, C(CO2Et)2] in Me2SO in the presence of hydriodic acid. Only with Y = C(CO2Et)2 does the adduct radical, t-BuCH2ĊHCH2YCH2CN, undergo facile 5-exo cyclization in the absence of a proton donor. The other 5-exo and all 6-exo cyclizations require substrate protonation to yield t-BuCH2ĊH(CH2)nYCH2C≡NH+ (n = 1, 2), which cyclizes readily to the iminium radical cation followed by electron transfer with I- or t-BuHgI2- to form the imine as a precursor to the cyclopentanone or cyclohexanone upon hydrolysis. For CH2=CHCH2C(CO2Et)2CH2CN the formation of the cyclopentanone is dramatically promoted by NH4I in the dark in the absence of any other acid. In this case, where cyclization of the adduct radical occurs readily without substrate activation, protonation of the cyclized iminyl radical allows the electron transfer with I- or t-BuHgI2- to occur with regeneration of t-Buċ. A similar effect is observed with CH2=CHCH2C(CO2Et)2CH2N3 where only a slow reaction is observed upon photolysis with t-BuHgI in the absence of NH4I, although apparently cyclization of t-BuCH2ĊHCH2C(CO2Et)2CH2N3 (with loss of N2) occurs readily. In the presence of NH4I the cyclized aminyl radical can be protonated and the resulting amine radical cation readily reduced by I- or t-BuHgI2- to continue a chain process. With the thioesters CH2=CHCH2YCH2C(O)SPh [Y = O, CH2, CMe2, C(CO2Et)2], significant cyclization upon photolysis with t-BuHgX occurred only for Y = C(CO2Et)2. © 1998 John Wiley & Sons, Ltd.
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  • 104
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 895-902 
    ISSN: 0894-3230
    Keywords: 1-amino-2,4-dinitrobenzenes ; structures ; single-crystal x-ray diffraction ; UV-visible spectrophotometry ; NMR spectroscopy ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal structures of 1-pyrrolidino-2,4-dinitrobenzene (3) and 1-morpholino-2,4-dinitrobenzene (4) were determined by single-crystal x-ray diffraction and the structures in solution were investigated by UV-visible spectrophotometry and 13C and 1H NMR spectrosccopy. Compound 4 crystallizes in the monoclinic space group P21/n with one independent molecule per asymmetric unit and 3 crystallizes in triclinic P-1 with three independent molecules per asymmetric unit. Rotation of the o-nitro group and of the amino group out of the aromatic plane was observed in both the solid state and in solution for both compounds. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 105
    ISSN: 0894-3230
    Keywords: cryptand ; fluorescence titration ; lanthanide coordination ; proton transfer ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Lanthanide [lanthanum(III), 2; europium(III), 3; and gadolinium(III), 4] cryptates of a tris-phenylphenol N8O3 Schiff-base cryptand (H3L) were synthesized by transmetallation with [Na(H3L)]ClO4·3H2O (1) and characterized by spectroscopic and crystal structure analyses. Both 3 and 4 are isomophous and isostructural. The complexes crystallize in the triclinic space group P-1 with cell parameters for 3 of a = 14.9833(2), b = 15.42670(10), c = 16.3770(3) Å, α = 75.3760(10), β = 68.2640(10), γ = 77.0540(10)° and Z = 2 and for 4 of a = 14.9976(3), b = 15.4417(3), c = 16.35350(10) Å, α = 75.4980(10), β = 68.3180(10), γ = 76.8790(10)° and Z = 2. The structures reveal that one lanthanide ion is unsymmetrically encapsulated in the cryptand cavity with a second ligand (solvent DMF). Solution NMR and solid structural studies demonstrated that there are intracavity and intermolecular proton transfer processes during lanthanide complexation towards the cryptand. A fluorimetric titration in acetonitrile for Eu(III) ion to 1 afforded a novel fluorescence intensity (IF)-equivalents of Eu(III) ion (x) plot signaling a quenching (0 〈 x 〈 0.2)-enhancement (0.2 〈 x 〈 1) change with formation of the kinetically stable 1:1 cryptate. An energy-transfer mechanism is discussed. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 106
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 857-870 
    ISSN: 0894-3230
    Keywords: Yukawa-Tsuno equation ; substituent effect ; α-hydroxybenzylic cation ; benzoyl compound ; ab initio calculation ; basicity ; proton affinity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structures of α-hydroxybenzylic cations and their conjugate bases, which cover a wide variation of stability, were optimized by means of ab initio molecular orbital method at the RHF/6-31G* level. Total energies were calculated at the MP2/6-31G*//RHF/6-31G* + ZPE (scaled 0.9) level. Calculated relative proton affinities of the respective neutral molecules (benzoyl compounds; conjugate bases of α-hydroxybenzylic cations) agreed well with the corresponding basicities in the gas phase. The geometries of α-amino-α-hydroxybenzyl and α-hydroxy-α-dimethylaminobenzyl cations were also optimized at the fixed dihedral angles between the cationic 2pπ orbital and the benzene π orbital (φ), and between the cationic 2pπ orbital and lone pair electron orbital of the α-substituent (θ). The changes in Wiberg bond orders and the rotational potentials about φ and θ showed that the degree of resonance interaction between the cationic center and phenyl ring is balanced by the electronic effects of α-substituents in benzylic cations. The obtained theoretical indices of all parent cations such as Mulliken population, Wiberg bond order and bond lengths were correlated linearly with the resonance demand parameter (r value) which were given by the Yukawa-Tsuno substituent effect analysis in the gas phase and in aqueous solution. These relationships are consistent with those for other benzylic cations such as destabilized carbocations and sterically hindered cations studied previously. This confirms that the empirical r value has a definitive physical meaning, i.e. a measure of the resonance interaction between the cationic center and the aryl moiety. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 107
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 1-9 
    ISSN: 0894-3230
    Keywords: benzothiazole-2-thiol ; formation mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation of benzothiazole-2-thiol from aniline, carbon disulphide and sulphur at 230°C was shown to occur by a sequence of three principal steps. Labelling experiments confirmed that both sulphur atoms originate from carbon disulphide. An initial polar reaction to form thiocarbanilide via phenylcarbamic acid and a tetrahedral intermediate is followed by radical cyclization of these to benzothiazole-2-thiol and 2-phenylaminobenzothiazole; the latter is converted into the desired product by a polar displacement of aniline by H2S. Mechanisms for the formation of minor byproducts are also considered. © 1998 John Wiley & Sons, Ltd.
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  • 108
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 223-229 
    ISSN: 0894-3230
    Keywords: Solvolysis ; Grunwald-Winstein-type analysis ; Hammett-type analysis ; YxBnCl scale ; 1-aryl-1-phenylmethyl cations ; Mulliken population analysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants of solvolysis of α-tert-butyl(2-naphthyl)methyl chloride (1), 9-fluorenyl chloride (2) and a series of monosubstituted benzhydryl chlorides (3) in a wide range of solvents were measured. Grunwald-Winstein-type correlation analysis of log k for 2 and 3 against YBnCl, with or without nucleophilicity N, yielded less satisfactory linear correlations than that against log k(1). A new scale of solvent ionizing power, YxBnCl, for the correlation of solvolytic reactivities of benzylic chlorides with extended charge delocalization based on log k(1) was developed. Application to the mechanistic study suggested the solvolysis of 2 and 4-nitrobenzhydryl chloride were non-limiting. Hammett plots against σ+ constants exhibited more negative ρ values in less nucleophilic solvents. In a benzhydryl chloride containing a strong deactivating substituent, such as 4-nitro, the positive charge delocalizes mainly over the unsubstituted ring in the cationic transition state. The uneven charge distribution was also confirmed by Mulliken population analysis at the level of the RHF/6-31G*//RHF/3-21G(*) basis set for cations. Comparison of the results of correlation analysis using the equation log(k/k0) = mY vs the equation log(k/k0) = mY+hI, and using the equation log(k/k0) = mY+lN vs the equation log(k/k0) = mY+lN+hI indicated the use of YBnCl or YxBnCl could give a better understanding of solvolytic mechanisms than the combinatorial use of YCl and I. © 1998 John Wiley & Sons, Ltd.
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  • 109
    ISSN: 0894-3230
    Keywords: Solvent-solute interactions ; β-carotene ; electronic absorption spectrum ; solvent effects ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvent effects on the wavenumber of the maximum of the longest wavelength electronic absorption band of all-trans-β-carotene were determined in 34 solvents. Together with results from previous studies, a data set for 51 solvents, mostly non-hydrogen bond donors, was constructed. This information was analyzed in terms of reaction field models and also showed its value for correlation purposes when used either alone or in combination with standard empirical solvent polarity-polarizability scales. © 1998 John Wiley & Sons, Ltd.
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  • 110
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 177-184 
    ISSN: 0894-3230
    Keywords: nitro derivatives of phenols ; pyrolysis initiation reactions ; impact sensitivity ; UHF-SCF-AM1 MO method ; activation energy. ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The UHF-SCF-AM1 MO method was applied to the study of two kinds of pyrolysis reactions of six nitro derivatives of phenols (homolysis reaction by rupture of the C - NO2 bond into radicals and isomerization reaction involving phenolic hydrogen transferring to oxygen on the NO2 group). The molecular geometries of reactants, transition states and products were fully optimized. The potential energy curves and activation energies were first obtained. The results show that this category of compounds is more easily initiated via isomerization reactions than by homolysis reactions. The parallel relationship among the Wiberg bond order of the pyrolysis-initiation H - O bond in the molecule of a reactant, the activation energy of the isomerization reaction breaking the H - O bond and impact sensitivity of the reactant gives ‘the principle of the smallest bond order’ (PSBO) powerful support. The sensitizing effect of a phenol group was elucidated based on calculation results. The different influences of OH and NO2 groups on the heat of formation of a molecule are discussed. © 1998 John Wiley & Sons, Ltd.
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  • 111
    ISSN: 0894-3230
    Keywords: 3-methyl-2, 4-diphenyl-3-azabicyclo[3.3.1]nonan-9α-ol esters ; analgesics ; synthesis ; structure ; conformation ; pharmacological assays ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of esters derived from 3-methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9α-ol (1) was synthesized and studied by 1H and 13C NMR spectroscopy, and the crystal structure of 3-methyl-2,4-diphenyl-9α-(3,5-dimethylbenzoyloxy)-3-azabicyclo[3.3.1]nonane (2) was determined by x-ray diffraction. The compounds studied display in CDCl3 a preferred flattened chair-chair conformation. This bicycle conformation is similar to that found for 2 in the crystal state. Pharmacological assays on mice were performed to evaluate drug-induced behavioral alteration, peripheral or central acute toxicity and analgesic activity. © 1998 John Wiley & Sons, Ltd.
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  • 112
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 101-108 
    ISSN: 0894-3230
    Keywords: encounter complexes ; 1-cyanonaphthalene ; norbornadiene ; stereospecific ; nucleophilic trapping ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photo-induced electron donor-acceptor reactions between 1-cyanonaphthalene (CNN) and norbornadiene (N) generate products of several structure types. Methanol adducts (1-3) formed in polar solvents are rationalized via the radical cation, N+·, and stereospecific (exo-) nucleophilic attack by methanol. In less polar solvents, CNN and N form [2 + 2]-cycloadducts, exclusively on the exo-face of N. In non-polar solvents containing methanol, CNN, N and methanol combine to form 1:1:1 adducts, containing the sensitizer on the endo- and the methoxy groups on the exo-face. The formation of these products is rationalized via the trapping of encounter complexes of different geometries. Any rearrangement of the norbornenyl system can be eliminated, since neither tricyclyl nor 7-methoxynorbornenyl structures are formed. Apparently, the alcohol captures an endo-encounter complex of CNN and N by attack from the exo-face, similar to the attack of methanol on N+·. © 1998 John Wiley & Sons, Ltd.
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  • 113
    ISSN: 0894-3230
    Keywords: aromaticity ; Diels-Alder transition states ; Diels-Alder adducts ; reaction mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semiempirical, ab initio and DFT investigations on the mechanism of the Diels-Alder reactions of a set of masked dienes (ring-fused dienes), viz. o-quinodimethane, anthracene and α-vinylnaphthalene, with ethylene, and reactions of α-vinylnaphthalene with maleic anhydride and p-benzoquinone were performed with a view to understanding the role of masking factors on the activation and reaction energies. The reactions were found to occur in a concerted fashion through synchronous transition states (TSs) in the first two reactions and through asynchronous TS in the other case. Of the compounds studied, o-quinodimethane is the most reactive diene both in a kinetic and a thermodynamic sense. α-Vinylnaphthalene reacts faster with maleic anhydride than p-benzoquinone, as expected, and two possible stereoselective TSs, one endo and the other exo, have been located for the reactions of α-vinylnaphthalene with the above dienophiles. Calculations show that the relative gain or loss of aromatic stabilization of the benzonoid ring in the transition state and in the product seems to play a major role in the kinetic and thermodynamic control of these reactions. © 1998 John Wiley & Sons, Ltd.
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  • 114
    ISSN: 0894-3230
    Keywords: methylbenzoic acids ; infrared spectra ; conformation ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Infrared spectra of all isomers of polymethyl-substituted benzoic acids were recorded in the carbonyl and hydroxyl regions in tetrachloromethane at various concentrations and interpreted in terms of conformation. According to a plot of ν(C=O) of the monomeric form vs Hammett substituent constants σ, these compounds may be classified into two classes. Derivatives with none or only one methyl group in the ortho position are concluded to exist in an equilibrium of two planar conformations, unless the equilibrium is degenerate. Derivatives with two ortho-situated methyl groups are concluded to take up one non-planar conformation. These findings are supported by the shape of the hydroxyl and carbonyl bands, which are unsymmetrical in the former class, although they could not be reliably separated into bands pertinent to the individual conformers. This conclusion is at variance with the common interpretation which has invariably ascribed to these and similar ortho derivatives non-planar conformations with a variable torsional angle. © 1998 John Wiley & Sons, Ltd.
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  • 115
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 15-24 
    ISSN: 0894-3230
    Keywords: electrophilic reactions ; electron transfer reactions ; electron-rich alkenes ; tetracyanoethylene ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Both experimental and theoretical studies confirm that the formation of aryl vinyl ether and aryl vinyl sulfide cation radicals from the corresponding neutral substrates correlates with the Brown σ+ parameters as opposed to Hammett σ values. Peak oxidation potentials for both classes of substrates correlate preferentially with σ+, as do gas-phase ionization energies calculated by both semi-empirical and ab initio methods. In contrast, the protonation energies of the same substrates, which relate to carbocation formation, correlate preferentially with σ values, as do rates of protonation and other electrophilic additions. These observations permit a sharp distinction between electrophilic and electron transfer reactions of these two common classes of electron-rich substrates. Using this criterion, the cycloadditions of tetracyanoethylene to these substrates are found to proceed via an electrophilic mechanism, rather than by a previously proposed electron transfer mechanism. © 1998 John Wiley & Sons, Ltd.
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  • 116
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    Journal of Physical Organic Chemistry 11 (1998), S. 25-30 
    ISSN: 0894-3230
    Keywords: 1,ω-bis(2-bromopyridinium)alkanes ; hydroxide ion ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of OH- ion with 1,ω-bis(2-bromopyridinium)alkanes, where the reaction centers are separated by a varying number of methylene groups, was investigated to model the increased velocity of OH- attack on premicellar aggregated N-alkylpyridinium compounds. 1,ω-Bis(2-bromopyridinium)alkanes (RPBr) [R  =  propane (I), butane (II), pentane (III), hexane (IV) and octane (V)] were synthesized and characterized by standard procedures. The kinetics of I-V with OH- ion fitted two consecutive first-order reactions. The intermediate products, 1-(2-pyridone)-ω-(2-bromopyridinium)alkane, and also the final products 1,ω-bis(2-pyridone)alkanes, were isolated. Deuterium isotope effects, activation parameters and salt effects on the reaction rates suggest that OH- attack is rate limiting and there is a through-space acceleration of the initial attack due to the proximity of the positive charges. These results place an upper limit of 20-fold for the electrostatic acceleration in OH- attack in premicellar aggregates. © 1998 John Wiley & Sons, Ltd.
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  • 117
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    Journal of Physical Organic Chemistry 11 (1998), S. 47-53 
    ISSN: 0894-3230
    Keywords: N,N′-dicyclohexyl-O-(1-methylheptyl)isourea ; OH-acidic compounds ; acetic acid ; kinetics ; mechanisms ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic investigations on the reaction of N,N′-dicyclohexyl-O-(1-methylheptyl)isourea with acetic acid are described. The conversion proceeds partly through the intermediacy of a methylheptylcarbenium ion. However, in dilute solution an SN2 mechanism prevails. The results are discussed in terms of the simultaneous existence of two discrete mechanisms. © 1998 John Wiley & Sons, Ltd.
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  • 118
    ISSN: 0894-3230
    Keywords: calixarenes ; complexes ; conformation ; crystal structure ; 1H NMR ; 13C NMR ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal structure of 25,27-dihydroxy-26,28-bis(diethoxyphosphoryloxy)-tert-butylcalix[4]arene (1) (hexane solvate, 1:1) was determined by x-ray crystallography. The crystal data are P21/n, a  =  12.652(1) Å, b  =  12.564(2) Å, c  =  18.781(4) Å, β  =  105.56(1)°, V  =  2876.0(8) Å3, Z  =  2. In this complex the molecule adopts a 1,2-alternate conformation. Both the calixarene and hexane molecules are centrosymmetric. The phenol units in the asymmetric part of the calix are inclined with respect to the main macrocyclic plane by 115.46(6)° and 128.01(7)° for the phosphorylated and the non-phosphorylated ring, respectively. Self-inclusion of the ethyl chains in the half-cavities is observed. One intramolecular O - H…O and several intermolecular C - H…O hydrogen bonds are present. In the 1H NMR spectrum one average AX spin system for methylene bridge protons can be interpreted as fast (on the NMR time-scale) interconversion of non-phosphorylated phenol fragments. © 1998 John Wiley & Sons, Ltd.
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  • 119
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    Journal of Physical Organic Chemistry 11 (1998), S. 31-35 
    ISSN: 0894-3230
    Keywords: allyl alcohol ; oxidation ; alkaline periodate ; palladium(II) catalyst ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The oxidation of allyl alcohol by alkaline species of periodate, H2IO63-, was found to be catalysed by micro amounts of Pd(II) in 0.2 mol dm-3 alkali solution. The active species of the catalyst was found to be PdCl+. A mechanism involving the interaction of the catalyst and substrate in prior equilibria leading to the formation of a π-complex is proposed and the rate is derived. © 1998 John Wiley & Sons, Ltd.
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  • 120
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    Journal of Physical Organic Chemistry 11 (1998), S. 10-14 
    ISSN: 0894-3230
    Keywords: equilibrium acidities ; homolytic bond dissociation enthalpies ; benzaldoximes ; phenyl methyl ketoximes ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The equilibrium acidities in DMSO of nine p- and m-substituted benzaldoximes and eight p-substituted phenyl methyl ketoximes were measured. Estimates of the homolytic bond dissociation energies (BDEs) of the acidic O - H bonds in these compounds were made by combination of their pKHA values with the oxidation potentials of their conjugate bases, Eox(A-), using the equation BDE  =  1.37pKHA + 23.06Eox(A-) + 73.3 kcal (1 kcal  =  4.184 KJ). Plots of Eox(A-) vs pKHA for p-substituted benzaldoximes and p-substituted phenyl methyl ketoximes were linear with slopes near unity. Consequently, as required by the above equation, the BDEs estimated for the O - H bonds in these oximes were constant, being 88.3 ± 0.3 and 89.2 ± 0.4 kcal, respectively. © 1998 John Wiley & Sons, Ltd.
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  • 121
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 297-301 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Baker-Strehlow methodology was developed to provide an objective approach to prediction of blast pressures from vapor cloud explosions. The complete methodology was first published in 1994 [1]. Since then, it has evolved through ongoing research and use in VCE hazard analyses, facility siting studies and accident investigations. This article gives a brief overview of a paper on recent developments in the Baker-Strehlow methodology presented at the 31st Loss Prevention Symposium in Houston on March 9-13, 1997. Because the entire paper is too lengthy to be presented here, the following discussions may be lacking in some details. A copy of the complete paper can be obtained from the American Institute of Chemical Engineers (AIChE).Since the Baker-Strehlow method was first published, it has been used extensively in VCE hazard assessments in refineries and chemical plants. As expected, many practical lessons have been learned during the course of the hazard assessments, and the Baker-Strehlow method has evolved as a result. The changes have been evolutionary, not revolutionary. In keeping with the goals of the original study in which the methodology was developed, all changes have been incorporated with the intent of achieving an objective methodology to provide consistent prediction of VCE blast effects.The revisions to the Baker-Strehlow method resulting from experience gained during plant walk-downs and hazard assessments include: Systematic identification of “potential explosion sites” or “PESs,”Selection of the level of confinement for mixed zones of 2D and 3D confinement,Deciding on flame expansion when confinement is elevated above the vapor cloud,Selecting the reactivity for a fuel that is a mixture of fuels with differing reactivities,Predicting blast loads when there are multiple PES's within a vapor cloud considering different ignition source locations.
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    Process Safety Progress 17 (1998), S. 20-22 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most audits try to look at a representative selection of the plant procedures and equipment. An alternative is a survey, a look in depth at selected procedures (such as those for testing alarms and trips, issuing permits-to-work, controlling modifications, taking samples or testing relief devices) or selected equipment (such as level glasses or equipment for handling LPG). If the procedure or equipment is well-chosen, surveys may make a bigger contribution to safety, per person-hour, than a conventional audit.
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    Process Safety Progress 17 (1998), S. 86-97 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Regulatory issues related to material safety have made the accurate measurement and/or prediction of flash points essential. The flash point is one of the major physical properties used to determine the fire and explosion hazards of a liquid. Flash points are used by virtually all governmental entities worldwide to define “flammable” and “combustible” materials for shipping and safety regulations.A model is described here for the calculation of closed cup flash points for multicomponent, single liquid phase, mixtures. The model is based upon rigorous vapor/liquid equilibrium calculations supplemented with information about the lower flammable limits (LFL's) and heats of combustion (ΔHc's) for the mixture's constituent components. The closed cup flash points predicted with this model are typically within ± 5°C of the experimentally reported values. Such a model is useful as a means of verifying experimental data and as a tool for screening product formulations prior to experimental flash point determination. The model should considerably enhance the safety evaluation portion of the product development cycle, thus leading to shortened product time-to-market cycles. While flash points calculated with this model are in excellent agreement with experiment, experimental determination is still encouraged for critìcal safety applications.
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  • 124
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    Process Safety Progress 17 (1998), S. 134-137 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: National Advisory Committee's Acute Exposure Guideline Levels (AEGLs) for ammonia are critically evaluated. The technical bases for concern about AEGL-2 and AEGL-3 values derived by the committee are summarized recommendations made.
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  • 125
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    Process Safety Progress 17 (1998), S. 127-133 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An explosion and flash fire in a fixed bed reactor occurred at a municipal wastewater treatment plant (WWTP). Two employees were injured in the accident. The accident occurred in an ozone treatment building where ozone was used to treat odors from the offgas of the sludge concentration units. Excess ozone manually was routed to the fixed bed reactor (ozone destruct unit) where the ozone is catalytically transformed into oxygen before being discharged to the atmosphere.An investigation of the accident was conducted to determine the root cause of the explosion and flash fire and identify corrective actions which the WWTP management could undertake to prevent a recurrence. This investigation included site inspections, interview with the injured employees, sampling and analysis of various materials, an explosion dynamics analysis, and a root cause analysis.It was concluded that cooling oil from one of the ozone generation units entered the main ozone gas line due to a crack in one of the reactor's dielectric tubes. The cooling oil was vented into the ozone destruct unit when an employee opened a ball valve on the main ozone gas line. The cooling oil, essentially a saturated hydrocarbon mixture, reacted exothermically when it contacted the manganese dioxide catalyst. The exothermic reaction resulted in an explosion which propelled the access panel outwards and dispersed the catalyst pellets. A flash fire followed the explosion. The flash fire burned two employees and caused thermal damage to a nearby control panel.Although this accident was the first of its kind at this facility, this was not the first time that the ozone generator had experienced a failure of a dielectric tube. Thus, there was a significant probability that a dielectric tube failure could leak cooling oil into the main ozone gas line. This failure event could, in turn, result in another explosion and flash fire. The WWTP staff neither designed nor fabricated the ozone generator-destructor system. Therefore, it did not seem appropriate for the WWTP staff to modify the ozone system. Instead, it was recommended that the ozone destruct unit be taken out of service. The WWTP management acted on this recommendation.
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  • 126
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    Process Safety Progress 17 (1998), S. 171-175 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An explosion occurred in a petroleum product storage tank at a refinery. The liquid petroleum product was a heavy oil used as an asphalt extender. There were no injuries, but the cleanup was costly. The storage tank was one of several which received the product stream from a dehydration unit. The accident occurred shortly after the refinery was brought back on-line following a shutdown for schduled maintenance.This was the first incident of this kind to occur at this facility. Analysis of the process data and eyewitness observations indicated that the dehydration tower, which was supposed to be maintained at a minimum of 100°C during the shutdown, was allowed to drift below 100°C for an unknown period of time. This deviation enabled liquid water to enter the storage tank. Three operational factors contributed to the accident. Corrective actions were recommended to prevent a recurrence of a similar incident.
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  • 127
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    Process Safety Progress 17 (1998), S. 184-189 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dust explosions have been with us for a long time. The first record of a dust explosion occurred in Turin, Italy, on December 14, 1785 [1]. The detailed record of this event is left to us by Count Morozzo. The event took place in Mr. Giacomelli's bakery. We know from his account that the weather was unseasonably dry, that a boy who worked in the bakery was using a shovel to stir and transfer the flour to a chute from a store room to the bakery and he had a lighted lamp to work by. The rest, as the saying goes, is history. No one was killed, and the building was saved by the sagacious fact of having plenty of windows. Since that first record, of course, there have been many explosions with much loss of life and significant economic consequences.
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  • 128
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    Process Safety Progress 17 (1998), S. 190-195 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The RSST DIERS vent sizing methodology is revised to provide realistic design equations for reactive systems consistent with available large-scale experience. Using easy to obtain RSST data such as rate of temperature rise and rate of pressure rise excellent agreement is illustrated for hybrid, vapor and gassy reactive systems.
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    Process Safety Progress 17 (1998), S. 196-199 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: From the 1960s onwards, the chemical and oil industries developed and used a number of new safety techniques which, in time, became second nature to those who applied them. They included the use of QRA for deciding priorities, Hazop and audits for identifying problems, inherently safer design for avoiding hazards, and more thorough investigation of incidents for identifying underlying causes. However, it has not yet become second nature to remember the accidents of the past and the actions needed to prevent them happening again.I joined industry in 1944 and moved to production in 1952. Then, and for at least 15 years afterwards, safety was a non-technical subject that could be left to arts graduates and elderly foremen. There was concern that people should not be hurt - great attention was paid to the lost-time accident rate - but there was no realization, that it was a subject worthy of systematic study by experienced technologists.This view changed at the end of the 1960s. A new generation of plants had been built, operating at higher temperatures and pressures and containing larger inventories of hazardous chemicals; the result was a series of fires and explosions and a worsening fatal accident rate. Figure 1 shows the situation in ICI, at the time the UK, s largest chemical company. Other companies experienced a similar state of affairs.As a result in 1968, I was appointed one of the company's first technical safety advisers, an unusual appointment at the time for someone with my experience, and if the reason for my appointment had not been so obvious I would have wondered what I had done wrong. I and my colleagues tried to apply the same sort of systematic thinking to safety that we applied in our other professional work. We developed some new concepts and techniques and adopted others. A common feature of our ides, realized only in restrospect, was that they consisted of more than mere problem-solving techniques. Once people had got used to these new concepts and used them a few times, they began to look at a whole range of problems in a different way.
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    Process Safety Progress 17 (1998), S. W3 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 131
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    Process Safety Progress 17 (1998), S. 259-262 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Case histories of 65 incidents in runaway reactions and emergency relief in Taiwan were analyzed and classified into several categories according to their causes, materials involved, equipment types, reaction types, and ignition sources. The cases in reactors and storage tanks were examined in more detail owing to the higher probability or larger potential hazard in these two types of equipments. The most common consequence of the incidents are explosions, fires, and atmospheric release of toxic chemicals. The most severe case was a thermal explosion from an organic peroxide storage area which caused the death of 33 persons. Popping and direct releasing of process chemicals to the atmosphere from relieving devices cause the greatest environmental concerns to the community close to the plants. Runaway reactions in batch type reactors occur frequently due to various operational mistakes. Heat of reaction is the most frequent ignition source of runaway reactions and emergency relief.
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  • 132
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    Process Safety Progress 17 (1998), S. S3 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    Process Safety Progress 17 (1998), S. 61-67 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Risk assessments have been performed to determine the risk associated with the transportation of hazardous wastes through a city. In the course of these assessments, a number of modeling issues arose relating to transportation accident rates, the characterization of incidents, the effect of thermal radiation, the impact of exposure to toxic chemicals, and the threshold for acceptable risk. This paper discusses these issues.
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    Process Safety Progress 17 (1998), S. S3 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 135
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    Process Safety Progress 17 (1998), S. 98-103 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents the design of ribbon wound pressure vessels useful for Ammonia, Urea and Methanol plants. The design is to create a thin shell of 1/5 the total wall thickness required, weld it to the end pieces, and wind 4 to 8 mm thick ribbons of 80 mm width at an angle of 15 to 30 degrees on the inner shell, using a prestress. The ribbons are welded at the ends and an even number of layers are wound cross-helically on to the shell. With more than 7000 vessels over the pressure range of 50 to 350 atmospheres in use in the various chemical industries in China over the past 30 years, their safety record has been excellent. Of particular interest has been the application of this technology in the Ammonia and Urea plants, where the design allows fabrication of these vessels at substantial reduction in cost, and early delivery, when compared to the mono wall technology.
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  • 136
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    Process Safety Progress 17 (1998), S. 124-126 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple analytical method is presented for estimating the hybrid minimum ignition energy (HMIE) of dust-gas mixtures, based on the assumed generality of Bartknecht's well-known test data for mixtures of propane with a series of dusts in air. Since the HMIE equation requires input data which might be unavailable, the use of conservative default methods is discussed.
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  • 137
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    Process Safety Progress 17 (1998), S. 138-148 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A large and potentially hazardous decrease in aldehyde autoignition temperature (AIT) occurs with increased pressure. The AIT-pressure curve determined in a 5 L stainless steel sphere was similar for propionaldehyde and butyraldehyde in air, falling from about 185°C at atmospheric pressure to 90°C at 140 psia. Reduction of oxygen concentration had little effect on propionaldehyde AIT. At 100°C and 140 psia, autoignitions accompanied by at least a doubling of pressure were observed above 4% oxygen. In the presence of a few grams of free liquid, propionaldehyde vapor ignited in air at initial conditions significantly below the AIT. The mechanism appears to involve rapid Fe-catalyzed exothermic liquid-phase oxidation leading to autoignition of the adjacent heated gas layer. An acetaldehyde vapor-air mixture in the presence of free liquid and rust exploded at room temperature when air pressure was increased to 95 psia; this result is discussed with reference to a cylinder overpressurization that occurred while making up an ostensibly sub-LFL calibration mixture with compressed air. Propionaldehyde's limiting oxygen concentration (LOC) was investigated in the near-autoignition region using the same 5L apparatus; the findings are discussed with reference to an overpressurization incident in an air-liquid partial oxidation reactor. The general results are used to illustrate the application of LOC in partial oxidation processes subject to autoignition and to discuss elements of the current ASTM draft test method for LOC, which does not address test difficulties associated with condensable and/or reactive gas systems.
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    Process Safety Progress 17 (1998), S. F3 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 139
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    Process Safety Progress 17 (1998), S. 157-170 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Risk analysis in chemical process industries is an elaborate exercise involving several steps from preliminary hazard identification to development of credible accident scenarios, to preparation of strategies for prevention or control of damage.All this requires substantial inputs of time and money. In order to get an approximate yet workable assessment of risk at much lesser costs, indices have been developed which link typical findings of elaborate risk analysis to scales of risk. The scales, in turn, provide workable measures of hazards/risks/safety.In the past, indices have been reported for swift risk assessment - the noteworthy among them include Dow fire and explosion index, Mond fire, explosion and toxicity index, IFAL index, and mortality index. A few rapid ranking techniques have also been proposed.This paper presents a new system of methodologies for Hazard Identification and Ranking (HIRA). The system consists of two indices: one for fire and explosion hazards and another for the hazard due to likely release of toxic chemical. The magnitudes of these indices indicate the severity of the likely accident; in terms of the size of the impacted area.HIRA has been applied to a typical chemical process industry - a sulfolane plant - and its performance has been compared with that of the Dow's and the Mond's indices. The study reveals that HIRA is more sensitive and accurate than the other indices.
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    Process Safety Progress 17 (1998), S. 288-296 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An ammonia storage tank was built at the BASF Antwerp site in 1969 on land reclaimed from the sea. After several years of operation uneven foundation settlement, of up 2, occurred. In order to assure stability of this area for the next operation period (at least 10 years) measures were taken to ensure continued safe operation. One key measure was strain gauge monitoring at the location of maximum stress.
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    Process Safety Progress 17 (1998), S. 39-42 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Under OSHA 1910.119, all Process Safety Management (PSM) facilities are required to keep their pressure relief system design information current. This article demonstrates why a pressure relief system design verification effort must be based on an equipment list, rather than a relief device list, in order to ensure that every piece of equipment is adequately protected. The formerly common practice of simply checking the design bases of all existing relief devices is deficient is deficient since this technique does not systematically ensure that every piece of equipment is protected.The “Berwanger Method” is a step by step process for designing or analyzing a pressure relief system to meet OSHA 1910.119 Process Safety Information (PSI) and Process Hazard Analysis (PHA) mandates. The method uses a relational database which tracks the relationships between protected equipment, potential overpressure scenarios, and protective devices.The challenge facing an operating company does not end once the design basis has been “verified” - the design basis information must also be maintained and be readily accessible to avoid costly reinvention of the wheel down the road. The “Berwanger Method” also addresses these maintenance issues.
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    Process Safety Progress 17 (1998), S. 49-60 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper reports on a comprehensive literature search and small scale experimental work on the reaction characteristics of phosphorous trichloride and water. More than 30 tests were conducted, including both closed and open test cells. The water to phosphorus trichloride molar ratio was varied from 1 to 25. When in contact, water and phosphorus trichloride will form two liquid layers with a reaction starting at the interface. The impact of variables on reaction rates including the interface surface area, layer depth, and stirring were investigated experimentally. A reaction rate model that fits all the measured data is presented. Case studies illustrating the use of this data for emergency relief systems and vent containment design are presented in reference. [1].
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    Process Safety Progress 17 (1998), S. 68-73 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two major accidents in the 80's: the summit Tunnel Fire, England and Piper Alpha disaster, an offshore platform in the North Sea; and very recently, possible explosion of the Boeing, TWA flight 800 at New York, makes it imperative that further research into the mechonisms of the ignition of flammable vapor/air mixture in contact with hot surfaces needs to be done. There have been a number of studies of ignition by hot surfaces, but in all these studies the ignition sources were wire, sphere or strip, i.e., most of them were flat surfaces. But to the authors' knowledge, other variables which affect the ignition mechanism such as irregular geometrical shapes have not been studied. The purpose of this paper is to examine how the degree of confinement (or, configuration), size and orientation, of the heated surface affects the ignition temperature of the flammable vapors. The results were obtained by experimentnal and by computational fluid dynamics.
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    Process Safety Progress 17 (1998), S. 272-277 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: EPA's Risk Management Program regulation, promulgated in June 1996 as 40 CFR Part 68 requires subject industries to submit Risk Management Plans by June 1999. This plan requires hazard assessment of the operations of a facility using worst case scenarios and alternative releases. EPA has provided an Off-site Consequence Analysis (OCA) guidance to help facilities in their hazard assessment.OxyChem will be significantly impacted by the RMP rule. This paper outlines OxyChem's general experience and its strategy in planning to comply with this rule. OxyChem's approach in the development of the scenarios required by the rule is described in this paper. Limitations involved in the use of EPA's look-up tables or a single modeling solution for conducting all of the OCA are discussed. A three tiered OCA approach is presented as a possible alternative.
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  • 145
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    Journal of Physical Organic Chemistry 11 (1998), S. 201-208 
    ISSN: 0894-3230
    Keywords: indolizines ; cycloaddition ; reaction mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The peculiarities of [8+2] cycloaddition reactions of indolizines with dienophiles are reviewed. Quantum chemical SINDO1, AM1 and ab initio calculations of transition states were performed for [8+2] cycloaddition reactions of indolizine and 6-nitroindolizine with a series of alkenes with donor and acceptor groups. The calculations predict a dipolar cycloaddition mechanism (electrophilic addition and ring closure) for reactions of indolizine and 6-nitroindolizine with nitroethylene. For the reaction of 6-nitroindolizine with N,N-dimethylaminoethylene, the predicted mechanism corresponds to a previously unknown ‘inverse’ dipolar cycloaddition (nucleophilic addition and ring closure). © 1998 John Wiley & Sons, Ltd.
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  • 146
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    Journal of Physical Organic Chemistry 11 (1998), S. 115-124 
    ISSN: 0894-3230
    Keywords: cross-interaction constants ; gas-phase nucleophilic substitution reactions ; PM3 MO ; benzyl chlorides ; phenoxides ; thiophenoxides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nucleophilic substitution reactions of Y-benzyl chlorides with X-phenoxide and X-thiophenoxide nucleophiles were investigated theoretically using the PM3 semi-empirical MO method. The Leffler-Grunwald rate-equilibrium and Brønsted correlations predict that the degree of bond formation in the transition state (TS) is approximately 45 and 40% on the reaction coordinate for the phenoxides and thiophenoxides, respectively. For a weaker nucleophile, a later TS is obtained with an increased bond making and breaking. The variation of the TS structure with substituents in the nucleophile is thermodynamically controlled and is well correlated by rate-equilibrium relationships. In contrast, the TS variation (a tighter TS) with substituent (for a stronger acceptor Y) in the substrate is dependent only on variations of the intrinsic barrier and so cannot be correlated by such thermodynamically based rate-equilibrium relationships. The gas phase ρX and ρY values are much greater in magnitude than those in solution. A similar gas-phase theoretical cross-interaction constant, ρXY (ca -0.60), is obtained for both phenoxides and thiophenoxides, which is in good agreement with the experimental value (-0.62) for the thiophenoxide reactions in MeOH at 20.0 °C. The oxy and sulfur anion bases lead to a similar TS structure, but a lower reactivity for the former is due to a greater endothermicity of the reaction. A relatively wide range variation of the reaction energies, ΔG°, can be ascribed to the loss of resonance stabilization of anion nucleophiles upon product formation. © 1998 John Wiley & Sons, Ltd.
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  • 147
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    Journal of Physical Organic Chemistry 11 (1998), S. 171-176 
    ISSN: 0894-3230
    Keywords: acetaldehyde ; oxidation ; periodate ; osmium (VIII) catalysis ; ruthenium (III) catalysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Os(VIII) and Ru(III) catalysis of the periodate oxidation of acetaldehyde in aqueous alkaline medium was investigated. The catalytic efficiency is Ru(III)〈Os(VIII). The product of oxidation in both cases is acetate and IO3-. The stoichiometry is the same in both catalyzed reactions, i.e. [IO4-]:[CH3CHO] = 1:1. Probable mechanisms are proposed and discussed. The reaction constants involved in the mechanisms are derived. © 1998 John Wiley & Sons, Ltd.
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  • 148
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    Journal of Physical Organic Chemistry 11 (1998), S. 149-154 
    ISSN: 0894-3230
    Keywords: P - C bond cleavage ; phosphoranyl radicals ; organophosphonate biodegradation ; ab initio calculations ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Barrier heights for P - C bond homolysis in P-hydroxy-P-methyl-P,P-dioxophosphoranyl and P,P,P-trihydroxy-P-methylphosphoranyl were calculated using well correlated levels of electronic structure theory. The best estimate for the difference in barriers between the two indicates that homolysis is more facile for P,P,P-trihydroxy-P-methylphosphoranyl by roughly 9 kcal mol-1. This result suggests that bacterial pathways leading to P - C bond cleavage in organophosphonate derivatives will preferentially proceed via initial one-electron reduction of substrates rather than oxidation. © 1998 John Wiley & Sons, Ltd.
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  • 149
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    Process Safety Progress 17 (1998) 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 150
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    Process Safety Progress 17 (1998), S. 1-8 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recent guidelines released by the U.S. EPA define a worst-case scenario as a release under stable atmospheric conditions defined as Pasquil-Gifford stability class F. Unfortunately, very few tests at F stability have been available heretofore to provide a basis for models. Recent test data with propane releases by the German research organization TUV provide a set of 60 experiments conducted specifically to define the effects of atmospheric stability class on dispersion. Of these, 25 tests were at F stability. A comparable number were at each other stability class A through E. In addition 23 tests were at wind speeds under 1.5 m/s in stable atmospheres. This paper reports on adjustments made to our models based on these new data by reducing the originally-postulated sensitivity to stability class. In spite of considerable scatter in the TUV data, particularly between two different types of propane analyzers, the model allows us to extract information by averaging over the tests.
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  • 151
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    Process Safety Progress 17 (1998), S. 16-19 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A multi-disciplinary team developed a guideline for determining access restriction zones around vented solids handling equipment. The guideline provides a method for ensuring the discharge from a vented explosion will not cause injury to personnel. The steps in this method include: calculating the extent of external hazards from vented explosions; identifying potential areas where personnel could be exposed to a hazard; identifying ways to eliminate or reduce the hazard area; and establishing and documenting any access restrictions needed. Hazard zone calculations use the latest knowledge from research into fireball size, flame length and external pressure equations in VDI 3673. The guideline provides guidance for using this information. Options for mitigating or reducing external hazards from vented explosions are also described. As part of the project, the team audited several solids handling systems to look for potential oversights in existing restricted access areas. Some of the team's learnings from these audits are reviewed.
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  • 152
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    Process Safety Progress 17 (1998), S. 43-48 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper defines situation awareness (SA) and discusses its importance to operator-machine system safety and functioning in the context of process control activities. Specifically, identified are relationships of human detection of critical process cues converying the status of automated control systems and operator interpretation of the meaning and relevance of such information to the potential for negative incidents in chemical processing. Beyond individual operator SA in interacting with control systems, intra- and inter- work team SA are discussed for supporting individual attainment of process control responsibilities. Factors critical to team SA are discussed. “Road blocks” to team SA are also analytically examined. Lastly, methods for assessing individual and team SA are reviewed and vehicles for relating outcomes of these methods to changes in process control operator and team behavior to improve human-machine system safety and performance are relayed.
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  • 153
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    Process Safety Progress 17 (1998) 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 154
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    Process Safety Progress 17 (1998), S. 74-81 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The knowledge of the ingition behavior of dust-air mixtures due to electrical sparks (MIE, Minimum Ignition Energy) and hot surfaces (MIT, Minimum Ignition Temperature) is important for risk assessments in chemical production plants. The ignition behavior determines the extent and hence the cost of preventive protection measures.This paper describes the use of the minimum ignition energy and minimum ignition temperature as very important safety indexes in practice.Based on the latest results from large scale experiments on pneumatic filling of silos with polymeric materials and new results of full scale filling tests using Flexible Intermediate Bulk Containers (FIBC) manufactured from a variety of materials, guidance can be given to ensure safe operation in different situations such as filling, emptying operations, type of powder handled.The aim of this paper is to assist people dealing with product. It reflects the present state of the art and current knowledge of the assessment and measures associated with powder handling.
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  • 155
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    Process Safety Progress 17 (1998), S. 104-106 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In mid-1997, an Advanced Process Control (APC) scheme was implemented at a resins manufacturing complex with the goal of minimizing flare fuel gas usage while maintaining sufficient energy (BTU/SCF flare gas) to be in environmental regulatory compliance. Prior to APC implementation, the flare system was manually controlled by plant operators with minor attention paid to the minimization of fuel gas usage. Since implementation, APC has saved the plant thousands of dollars in fuel gas costs and reduced unnecessary combusted fuel gas emissions.Hazard analysis techniques were used in the development of the control scheme. An overview of the APC used, the economic evaluation, and the hazard analysis techniques used in the project are presented here.
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  • 156
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    Process Safety Progress 17 (1998), S. 107-123 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the risk assessment parlance, especially with reference to chemical process industries, the term “domino effect” is used to denote “chain of accidents,” or situations when a fire/explosion/missile/toxic load generated by an accident in one unit in an industry causes secondary and higher order accidents in other units. The multi-accident catastrophe which occurred in a refinery at Vishakhapatnam, India, on September 14, 1997, claiming 60 lives and causing damages to property worth over Rs 600 million, is the most recent example of the damage potential of domino effect.But, even as the domino effect has been documented since 1947, very little attention has been paid towards modeling this phenomena. In this paper we have provided a conceptual framework based on sets of appropriate models to forecast domino effects, and assess their likely magnitudes and adverse impacts, while conducting risk assessment in a chemical process industry. The utilizability of the framework has been illustrated with a case study.
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  • 157
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    Process Safety Progress 17 (1998) 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 158
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    Process Safety Progress 17 (1998), S. 149-154 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article deals with fire protection for water miscible flammable liquids stored in plastic containers packaged in boxes located on pallets. A series of fire tests was conducted with palletized rack storage arrangements using in-rack sprinkler protection at various levels. The intent of the paper is to present data from this test series for these types of commodities. The paper will identify various existing water miscible flammable liquid products stored in this fashion and provide background information for protecting this type of storage as it relates to NFPA 30 Flammable and Combustible Liquids Code. The test data indicates that further research work is needed in the area of plastic containers for use with the storage of combustible and flammable liquids. Included in the paper are discussions concerning possible protection strategies and suggestions for future research which would benefit those involved in risk management of this type of commodity.
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  • 159
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    Process Safety Progress 17 (1998), S. 176-183 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The safest method to prevent fires and explosions of flammable mixtures in the first place. This method requires detailed knowledge of the flammability region as a function of the fuel, oxygen, and nitrogen concentrations. A triangular flammability diagram is the most useful tool to display the flammability region, and to determine if a flammable mixture is present during plant operations.This paper describes how to draw and use a flammability diagram. A procedure to estimate the flammability region using the available and sometimes limited data is discussed. The paper also shows how to use the flammability diagram with plant operations involving inerting and purging, and from bringing vessels into and out of service. A compilation of flammability diagrams for 30 materials, based on previously published data is provided.An automated apparatus for acquiring data for a flammability diagram is described. The apparatus consists of a 20-L sphere with an automated gas mixing system, a fuse-wire ignition system, and a high speed pressure measurement and data acquisition system. Data derived from the apparatus includes flammability limits, maximum pressure during combustion, and the maximum pressure rate. The effect of fuse-wire ignitor dynamics on the results is studied. A flammability diagram for methane drawn from data obtained from the apparatus, is presented.
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  • 160
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    Process Safety Progress 17 (1998), S. 209-212 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: HFC-227ea (CF3CHFCF3;1, 1, 1, 2, 3, 3, 3-heptafluoropropane) is an effective replacement for Halon 1301 in fire suppression systems, providing rapid extinguishment of flames through a combination of physical and chemical mechanisms. The vast majority of applications for HFC-227ea involve the protection of Class A hazards, which are characterized by low fuel loadings and low energy output, with fire sizes often in the range of 5-10 kW. Mid- and large-scale testing has demonstrated that HFC-227ea, at its minimum design concentration of 7.0% v/v, is effective at extinguishing fires typical of those expected to occur in electronic data processing (EDP) facilities, telecommunication facilities and anechoic chambers. The levels of HF produced following extinguishment of typical Class a fires with HFC-227ea were well below the estimated mammalian LC50 and the human Dangerous Toxic Load (DTL), and do not appear to present a threat to electronic equipment.
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  • 161
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    Process Safety Progress 17 (1998), S. 219-224 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sandia National Laboratories (Sandia) has refined a process for developing inherently safer system designs based on methods used by Sandia to design detonation safety into nuclear weapons. The process was created when Sandia realized that standard engineering practices did not provide the level of safety assurance necessary for nuclear weapon operations, with their potential for catastrophic accidents. A systematic approach, which relies on mutually supportive design principles integrated through fundamental physical principles, was developed to ensure a predictably safe system response under a variety of operational and accident-based stesses. Robust, safe system designs result from this thematic approach to safety, minimizing the number of safety critical features. This safety assurance process has two profound benefits: the process avoids the need to understand or limit the ultimate intensity of off-normal environments and it avoids the requirement to analyze and test a large array of accident environment scenarios (e.g., directional threats, sequencing of environments, time races, etc) to demonstrate conformance to all safety requirements.
    Additional Material: 3 Ill.
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  • 162
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    Process Safety Progress 17 (1998) 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 163
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    Process Safety Progress 17 (1998), S. 233-237 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new method is described to enhance the management of process safety risks such that the number and type of safety systems protecting against any hazard are consistently predicated upon risk. Further, that such an assignment of safety systems can be made consistent throughout an organization. This consistency is gained through standardization of qualitative risk ranking and by setting company guidelines.
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  • 164
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    Process Safety Progress 17 (1998), S. 243-258 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Research was carried out to develop improved protection guidelines for silane handling systems through enhanced understanding of the behavior of releases of this pyrophoric gas. The approach involved addressing three aspects of the problem: the prompt ignition behavior of silane; the reactivity characteristics of quiescent silane/air mixtures; and the rates of reaction of silane leaked into enclosures with and without explosion venting, in the presence of ventilation air flow. A first conclusion, reached from tests in a ventilated cabinet, was that, contrary to prevailing belief, the ventilation flow has no measurable effect on the prompt ignition of the release. From experiments in a 5.1-liter (311-in.3) sphere it was found that silane/air mixtures of concentrations between 1.4 and 4.1% (by volume) are explosive but stable. In this case, piloted ignition tests yielded laminar burning velocities up to 5 m/s (1000 ft/min). Mixtures between 4.5 and 38% (the maximum reached in the tests) were found to be metastable, and would undergo spontaneous ignition after a delay ranging from 15 to 120 seconds, with the shorter values corresponding to higher silane concentrations. Experiments were also performed in a 0.645-m3 (22.8-ft3) vessel both with and without explosion venting, to measure the rates of energy release associated with impulsively-started silane leaks from 1/8 and 1/4-in. (3.2 and 6.4-mm) lines. A method for the prediction of the venting requirements of partial-volume deflagrations (PVD) was evolved into a tool to quantify the pressure rise from ignition of silane leaks in enclosures. These results represent a significant step toward updating existing design recommendations which prescribe ventilation requirements that are based on outdated and, in some instances, misinterpreted data.
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  • 165
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    Process Safety Progress 17 (1998), S. 278-287 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Gas explosion simulators are often used as tools in process plant design. This article presents some properties of gas explosions found using the EXSIM simulation software on three offshore modules with a total of nearly 10,000 simulations. The selected results are chosen for their supposed applicability to structural design in the process industries.Generalized data are presented for the effect of gas cloud size, explosion impulse vs. explosion pressure, pressure and impulse vs. duration, the probability of a “short” explosion, loading rate, pressure-time “shape” function, and the effect of introducing louvers.
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  • 166
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    Process Safety Progress 17 (1998), S. 9-15 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The design and deflagration pressure relief vents is based on correlations developed for various types of combustible materials and for enclosures of different strengths. The primary guideline for deflagration vent design in the US is NFPA 68 Guide for Venting of Deflagrations [5]. That document gives guidance for the design of vents for enclosures containing flammable gases, specifically hydrogen, coke oven gas, propane, and methane. Application of the guide to other gases is achieved using the KG value. Values of KG are published for a relatively small number of gases, as seen in Table D-1 of NFPA 68. This work present KG data on several additional gases obtained in a laboratory scale test vessel along with analysis of the results with respect to published values of fundamental burning velocity.
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  • 167
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    Process Safety Progress 17 (1998), S. 23-31 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In May 1996, the Flammable and Combustible Liquids Code Committee of the National Fire Protection Association (NFPA) proposed for adoption by the Association a new edition of NFPA 30, Flammable and Combustible Liquids Code. This new edition was the culmination of two and one-half years' work by the Committee and included one of the most significant changes to that document in some twenty years: the incorporation of mandatory fire protection criteria for warehouses and other inside areas that store flammable and combustible liquids in containers and portable tanks.
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  • 168
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    Process Safety Progress 17 (1998), S. 32-38 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes the development of a risk ranked Inspection Recommendation procedure that is used by one of Exxon's chemical plants to prioritize repairs that have been identified during equipment inspection.As part of the Company's Safety Management Practices initiative in the late 1980's a procedure was put into place to ensure that an Inspector's repair recommendations were properly addressed by the organization. The initial procedures were successful at “systematizing” the documentation and stewardship-to-completion of the Inspector's recommendation, however, there were complications with the original process: (1)The Inspector made a simple High, Medium or Low assessment of the priority/criticality of the recommendation. Frequently, this resulted in disagreements with Operations about the true priority of the recommendation.(2)If there was agreement on the priority of the recommendation, there was still disagreement on the relative rank within the priority-which high priority was the highest priority?(3)With limited funds to spend on repairs, it was (and is) important to make sure that the money was being spent on the highest risk items that had the greatest risk reduction/cost benefit ratio.To address these concerns, the procedure was modified to incorporate a risk assessment of the recommendation by both the Inspector and Operations. In the new procedure, the Inspector describes the deficiency that he/she finds and assesses the probability of failure within a certain time-frame. Operations must assess the consequences, from an environmental, safety and economics standpoint, were the failure to occur. These assessments are combined in the typical risk equation (risk = probability × consequences) to arrive at a severity index which serves to rank the recommendation relative to the other recommendations. Because Operations participates in the assessment there is very little disagreement about the priority of the recommendation. The severity index puts the recommendations in order so it is quite clear which are the highest priority recommendations. This process has helped to focus the entire organization on those deficiencies that represent the greatest risk with the result that less time and money is spent correcting items that have a low risk/cost benefit ratio, allowing these savings to be used to reduce the higher risks in the plant.
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  • 169
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    Process Safety Progress 17 (1998), S. 200-208 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 14 Ill.
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    Process Safety Progress 17 (1998), S. 213-218 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: On October 31, 1987 a crane lifting a heat exchanger convection section failed and severed a 4″ loading line and a 2″ pressure relief line to an HF alkylation reactor settler drum at a petroleum refinery in Texas City, Texas. Vapors were emitted under pressure for about two hours and the vessel was plugged and drained aproximately 44 hours later. A plume from this accidental release passed through residential areas, damaging some vegetation (brown lawns), and spawning a class action law suit. An extensive analysis was conducted to determine the total inventory loss and to model the blowdown process and the concentrations of HF in the plume. Since the discharge rate was decreasing with time, a peak concentration of HF in the emitted vapors occurred just before the water spray mitigation system became fully operative. Consequently, the mitigation efforts were more effective late in the response when concentrations were already low. The predicted plume concentrations are consistent with observed vegetation damage effects, with concentrations below Emergency Response Planning Guideline Level 3 past 3/4 mile from the source. These results support a policy of sheltering in place during such an event.
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  • 171
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A fifty-five gallon steel drum of a liquid organic peroxide pressurized and ruptured in the mix room of a manufacturing plant. The head of the drum blew off and the ejected material ignited. The resulting fire was extinguished by the building sprinkler system and operating personnel. Although there were no injuries, the fire caused significant damage in the mix room. The investigation of this incident, its likely cause, and the corrective actions will be discussed.
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  • 172
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    Process Safety Progress 17 (1998), S. 238-242 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Brazoria County Petrochemical Council, 13 companies that are working together to enhance relations between industry and the community, united in a joint effort at complying with the EPA's Risk Management Program. One of the significant issues the group had to address was the need to develop meaningful hazard assessment for presentation to the public. The EPA's “Table Look-Up Approach” found in the Offsite Consequence Analysis Guidance document is certainly a good tool; however, the built-in conservatism results in over-estimates of potential hazard areas. Much more meaningful results are shown to be obtained using one of the hazard release models.The value of using a credible scenario with realistic meteorological data is demonstrated through the consistently smaller areas predicted by the PHAST Model for planning purposes. Realistic scenarios/failure modes and realistic model parameters are important so that the risk to the public is not overstated. Proprietary models such as PHAST are invaluable in providing more meaningful consequences for planning purposes.
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  • 173
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    Process Safety Progress 17 (1998), S. 263-271 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Some of the hazards encountered by process plant operators involve the operation of in-line valves to control, start, and to stop flow. Torque required to operate valves may vary according to valve wheel size, in-line pressure, and valve flange position (open/closed). This study determined how valve wheel size, in-line pressure and valve position (open/closed) affect torque required to actuate a valve. Data were gathered with each combination of size, pressure and position for 336 valves in an operating petrochemical process facility. The results indicate that the main effects of valve wheel size, the in-line pressure, and open/closed valve position significantly affect operational torque requirements. In addition, the interaction between position and pressure was significant for operational torque. The implication of these results is that operators are exposed to operational torque requirements that exceed maximum acceptable capabilities that have been determined in previous studies.
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    Process Safety Progress 17 (1998), S. 83-85 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Safety, health and loss prevention are major areas of interst for the American Institute of Chemical Engineers (AIChE). There has been an evolution of these concerns over the years in the Institute just as it has in industry. This article chronicles this evolution.
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  • 175
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    International Journal of Quantum Chemistry 66 (1998), S. 25-30 
    ISSN: 0020-7608
    Keywords: Hylleraas-CI ; P states of 4He ; variance minimization ; upper and lower bounds ; perturbation theory ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extensive Hylleraas-CI calculations for the lowest Po states of 4He were performed. The dependence of the variational energy values Eκ on the mass parameter κ given by κ=mHe2+/me- is discussed. Furthermore, lower bounds to Eκ were calculated using variance minimization.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 25-30, 1998
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  • 176
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    International Journal of Quantum Chemistry 66 (1998), S. 69-89 
    ISSN: 0020-7608
    Keywords: ab initio ; Hartree-Fock ; crystal orbital ; charge-transfer complexes ; CRYSTAL 92 Routine Package ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio Hartree-Fock crystal-orbital calculations of dimorph tetramethyltetraselenafulvalene-tetracyanoquinodimethane (TMTSF-TCNQ) and dibenzotetrathiafulvalene-tetracyanoquinodimethane (DBTTF-TCNQ), both as red and black crystals, were carried out. The crystal structures of the red and black TMTSF-TCNQ are essentially different from each other, whereas the red and black DBTTF-TCNQ are qualitatively very similar (although not completely isomorphous). The results of the present calculations definitely show that even subtle differences in the crystal structures are crucial for the electronic properties of the systems under study.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 69-89, 1998
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  • 177
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    International Journal of Quantum Chemistry 66 (1998), S. 241-247 
    ISSN: 0020-7608
    Keywords: Hylleraas-CI ; Be atom ; explicitly correlated wave function ; ground-state energy ; double-linked basis set ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hylleraas-configuration interaction (CI) calculations have been carried out with double-linked basis sets for the Be atom. Our best upper bound for the 1S ground state is E0 = -14.6673547Eh. Furthermore, upper bounds for the two lowest excited 1S states have been calculated.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 241-247, 1998
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  • 178
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    International Journal of Quantum Chemistry 66 (1998), S. 249-253 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Discrete models obtained from computer simulation are in increase use to study solvent effects. The approach consists of generating supermolecular structures for quantum mechanical calculations. The properties of the solute are calculated as an ensemble average over configurations generated by the simulation. An analysis of the efficiency of the simulation shows that the number of configurations necessary for the ensemble average can be reduced drastically. As an application to solvatochromism, the calculated spectral shift of the 1B2u(π - π*) transition of benzene in water is shown to be the same whether it is calculated with many but correlated configurations or with just a few uncorrelated configurations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 249-253, 1998
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  • 179
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    International Journal of Quantum Chemistry 66 (1998), S. 273-279 
    ISSN: 0020-7608
    Keywords: Molecular integral ; recurrence formula ; Gaussian-type function ; Laguerre-Sonine polynomial ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recurrence formulas for overlap, nuclear attraction, and electron-repulsion integrals over Laguerre Gaussian-type functions are presented. They have been derived using compact recurrence relations for homogeneous solid spherical harmonic operators but are rather lengthy as compared to those over Cartesian Gaussian-type functions.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 273-279, 1998
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  • 180
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    International Journal of Quantum Chemistry 66 (1998), S. 189-202 
    ISSN: 0020-7608
    Keywords: diacetylene ; dimer ; C8H4 ; ab initio ; DFT ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometry optimizations were performed for singlet, triplet, and quintet states on the planar structures (in C2h and C2v symmetries) of the diacetylene dimer, using restricted open-shell Hartree-Fock (ROHF), unrestricted Hartree-Fock (UHF), and unrestricted hybrid density functional theory (UB3LYP) methods, with 6-31G(d) and 6-311G(d, p) basis sets. The 1Ag state of the planar van der Waals dimer is lower in energy than are any covalently bonded dimers. At our best B3LYP/6-311G(d, p) level, the most stable covalently bonded diacetylene dimer is the 3Bu state in C2h symmetry, 11 kcal mol-1 above the van der Waals dimer, followed by the 3B2 state in C2v symmetry with 13 kcal mol-1 above the van der Waals dimer. Both structures were confirmed to be local minima. The two diacetylene monomers of these structures are bridged through a single bond and they exhibit a small bend at the neighboring carbons to the bridge, trans to the hydrogens. The 1Bu and 5Ag states in C2h and the 1B2 and 5A1 states in C2v are between 39 and 43 kcal mol-1 above the van der Waals dimer.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 189-202, 1998
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  • 181
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    International Journal of Quantum Chemistry 66 (1998), S. 345-363 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This is the second in a series of articles whose ultimate goal is the evaluation of the matrix elements (MEs) of the U(2n) generators in a multishell spin-orbit basis. This extends the existing unitary group approach to spin-dependent configuration interaction (CI) and many-body perturbation theory calculations on molecules to systems where there is a natural partitioning of the electronic orbital space. As a necessary preliminary to obtaining the U(2n) generator MEs in a multishell spin-orbit basis, we must obtain a complete set of adjoint coupling coefficients for the two-shell composite Gelfand-Paldus basis. The zero-shift coefficients were obtained in the first article of the series. In this article, we evaluate the nonzero shift adjoint coupling coefficients for the two-shell composite Gelfand-Paldus basis. We then demonstrate that the one-shell versions of these coefficients may be obtained by taking the Gelfand-Tsetlin limit of the two-shell formulas. These coefficients, together with the zero-shift types, then enable us to write down formulas for the U(2n) generator matrix elements in a two-shell spin-orbit basis. Ultimately, the results of the series may be used to determine the many-electron density matrices for a partitioned system.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 345-363, 1998
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  • 182
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    International Journal of Quantum Chemistry 66 (1998), S. 255-260 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A physical model of an oxidation-reduction reaction for immobilized enzyme is considered. The influence of the electric-field intensity of a biological membrane on the enzyme reaction rate is analyzed. It is shown that the low-frequency dipole-active vibration of the oppostite charge groups of the substrate and enzyme relative to each other leads to multiquantum excitation of the system over the conformational degree of freedom. This excitation provides an abrupt increasing of the tunnel decay rate of the substrate-enzyme complex on a free product and a free enzyme. This way of the reaction is more probable in comparison with the usual overbarrier process. Some consequences for the immobilized cytochrome P-450 are discussed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 255-260, 1998
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  • 183
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    International Journal of Quantum Chemistry 66 (1998), S. 285-286 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron affinities (EA) of B, Al, and Ga are determined accurately at the CCSD(T), QCISD(T), and B3LYP levels of theory. The failure of the QCISD(T) and B3LYP methods reported by Jursic is attributed to his treating the wrong state of the ion.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 285-286, 1998
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  • 184
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    International Journal of Quantum Chemistry 66 (1998), S. 301-307 
    ISSN: 0020-7608
    Keywords: LaC3n+ ; structure ; vibrational frequency ; density functional theory ; Gaussian 92/DFT ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: LaC3n+ (n=0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional method. The basis set is Dunning/Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C2v symmetry, the other two are linear chains with C∞v symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC3+, doublet and quartet for LaC3 and LaC32+, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C2v symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 301-307, 1998
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  • 185
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    International Journal of Quantum Chemistry 66 (1998), S. 435-456 
    ISSN: 0020-7608
    Keywords: semiconductor-insulator interface ; shallow donor ; extended electronic states ; scattering ; photoionization cross section ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Scattering of a conduction electron by a charged shallow donor located near a semiconductor-insulator interface in the semiconductor or by a charged center embedded in the insulator is considered within the model of a hydrogenlike atom in a semi-infinite space. The interface influence is allowed for by spatial confinement of the electron envelope wave function. The impurity electrostatic image at the interface is taken into account. The problem is separable in prolate spheroidal coordinates and thus is solvable exactly. A rapidly convergent expansion is proposed for the angular eigenfunctions. The radial eigenfunctions are calculated directly by numerical integration of the radial boundary value problem. Expansions of the scattering wave function and the scattering amplitude in terms of the eigenfunctions of the problem are obtained. Using the extended and localized state wave functions, the photoionization cross section of a shallow donor near a semiconductor-insulator interface is calculated. It is presented as a superposition of the oscillator strengths of transitions to the partial extended eigenstates that constitute the scattering wave function. Near the interface, the cross section is enhanced significantly and redistributed over the direction of photoionized electron escape. The photoionization threshold follows the localized state energy varying with the donor-interface distance.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 435-456, 1998
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  • 186
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    Keywords: linear operator ; *-algebra ; general topology ; asymptotic analysis ; chemical network systems ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Part IV of this series consists of two complementary subparts devoted to attain the following two goals: (i) By shifting from the previous setting of the Banach algebra B(B)=B(B, B) to a broader setting of the space B(X, B) of all bounded linear operators from a normed space X to a Banach space B, we extend our previous theoretical framework to incorporate part of the theory of additive correlation involving the Asymptotic Linearity Theorems, which have been developed for a study of correlation between structure and properties in molecules having many identical moieties, especially in macromolecules having repeating units. (ii) By reverting our focus to the special algebra B(H) with H being a Hilbert space, we develop a theorem which is useful for a structural analysis of spectral symmetry of linear operators representing physico-chemical network systems.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 57-69, 1998
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  • 187
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    International Journal of Quantum Chemistry 67 (1998), S. 41-55 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CNM (characterization of normal modes) method for extracting chemical information out of vibrational spectra is tested for vibrational spectra of molecules with relatively strong or relatively weak coupling between internal vibrational modes. Symmetry, parameter set stability, and frequency uncertainty tests are applied to check whether internal vibrational modes, internal mode frequencies, and amplitudes Anμ comply with symmetry, are independent of the set of internal parameters ζn used to describe molecular geometry or fulfill a Lorentzian correlation between amplitudes Anμ and frequency differences Δωnμ=ωn-ωμ. In all cases considered, amplitudes Anμ based on adiabatic internal modes and mass or force constant matrices as metric O are superior to any other definition of amplitude. They represent the basic elements of the new CNM method that leads to chemically reasonable results and presents a new way of extracting chemical information out of vibrational spectra. A number of deficiencies of the potential energy distribution (PED) analysis is discussed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 41-55, 1998
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  • 188
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    International Journal of Quantum Chemistry 67 (1998), S. 85-100 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The separation of radial electronic and nuclear motions is discussed with special reference to high Rydberg states of molecules. An inverse separation is obtained when the rapid nuclear motion instantaneously adjusts itself to the position of the Rydberg electron. The electron moves in the potential averaged over the position of the nuclei (and their valence electrons). This inverse separation is useful when ωn3 〉 1, where ω is the spacing of nuclear energy states (in au) and n is the principal quantum number of the Rydberg electron whose orbital period increases as n3. The inverse Born-Oppenheimer separation can break down owing to the finite kinetic energy of the Rydberg electron. Like the Born-Oppenheimer separation, its inverse can also be formulated in an adiabatic or a diabatic basis. The diabatic inverse Born-Oppenheimer is practical both for interpretation of zero electron kinetic energy (ZEKE) spectra and for computations. Explicit results are given for a model system of an electron orbiting a vibrating dipole, identifying the relevant coupling constants. The discussion emphasizes the radial motion and the limits discussed here are not quite equivalent to the four (or, actually, five) Hund's coupling cases relevant to angular momentum coupling schemes.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 85-100, 1998
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  • 189
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    International Journal of Quantum Chemistry 66 (1998), S. 109-109 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 190
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    International Journal of Quantum Chemistry 66 (1998), S. 113-117 
    ISSN: 0020-7608
    Keywords: infrared spectra ; Raman spectra ; icosahedral fullerenes ; icosahedral group ; group character ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the bases of the topological structures of the three big classes of icosahedral fullerenes: (1) Cn(Ih, n=60h2; h=1, 2,…), (2) Cn(Ih, n=20h2; h=1, 2,…), and (3) Cn(I, n=20(h2+hk+k2), h〉k; h, k=1, 2,…), we derived formulas for the decomposition of their nuclear motions into irreducible representations. Hence, we obtained the infrared and Raman active modes for all of the icosahedral (Ih and I) fullerenes theoretically.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 113-117, 1998
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  • 191
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    International Journal of Quantum Chemistry 66 (1998), S. 123-130 
    ISSN: 0020-7608
    Keywords: Model of atoms trapped inside solids ; electronic structure ; helium atom ; pressure ; quadrupole moment ; polarizability of trapped atoms ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ground-state energy of the helium atom inside boxes with paraboloidal walls, with the nucleus at the common focus, is calculated variationally. The variational functions are products of geometry-adapted hydrogenic functions, and the interelectronic Coulomb repulsion is represented through its harmonic expansion in parabolic coordinates. The energy, pressure, quadrupole moment, and polarizability of the atom are determined as functions of the positions of the walls for symmetrical boxes.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 123-130, 1998
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  • 192
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    International Journal of Quantum Chemistry 66 (1998), S. 177-187 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a mechanostatistical study of the so-called Fröhlich effect, namely nonthermal amplification of polar vibrations leading to complex behavior in biosystems, like biopolymers and large aggregates of macromolecules. Fröhlich condensation is considered to be of relevance for a certain class of biological processes, in particular in connection with the problem of long-range propagation of signals at physiological temperature. Resorting to a thermomechanical theory appropriate to deal with irreversible processes in systems far from equilibrium, earlier results are extended. We perform an analysis of the case when production of a double excitation of polar vibrations, generated by the action of an external pumping source of metabolic energy, is possible. It is shown that, when this is the case, the process involves a positive feedback mechanism that greatly facilitates and enhances the phenomenon of Fröhlich's condensation, and consequently the possible accompanying biological processes. The results are discussed and eventual connection with experimental observations pointed out.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 177-187, 1998
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  • 193
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    International Journal of Quantum Chemistry 66 (1998), S. 203-217 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometrical parameters, vibrational frequencies, relative stabilities, and dissociation energies of the three stable Cl2O2 isomers and the OClO and ClOO radicals were investigated by density functional theory (DFT). The present analysis shows that DFT using hybrid functionals is capable of describing these systems to at least the same degree of accuracy as ab initio methods. The average absolute bond-length deviation of ClClO2, ClOOCl, and ClO2 from experimental results is 0.024/0.027 Å, with a maximum deviation for the dichlorine peroxide O(SINGLE BOND)O bond equal to 0.072/0.063 Å, for the B3PW91 and B3LYP functionals, respectively. The average absolute bond-angle deviation for the hybrid functionals is 0.8°. Harmonic vibrational frequencies calculated with DFT give for all Cl(SINGLE BOND)O compounds good agreement with experiments. The dissociation energies of ClOOCl, OClO, and ClOO were found to be in good agreement with experiments, the average error being less than 1.2 kcal/mol. The two isomers chloryl chloride (ClClO2) and dichlorine peroxide (ClOOCl) were found to be approximately 9 kcal/mol more stable than the chlorine chlorite (ClOClO) isomer. The ClOO isomer is predicted to be 3.0 kcal/mol more stable than OClO, in accordance with the experimental value of 4 kcal/mol.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 203-217, 1998
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  • 194
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    International Journal of Quantum Chemistry 68 (1998), S. 233-252 
    ISSN: 0020-7608
    Keywords: water trimer ; torsional eigenvalues ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eigenvalues corresponding to the three torsional degrees of freedom were calculated for the water trimer and its deuterated isotopomer in four sets of calculations involving different potential energy surfaces. The four potential surfaces were developed in this work by reparametrization of the CKL function against four sets of ab initio energies calculated with and without counterpoise correction. Transition frequencies corresponding to the low-frequency torsional motions of the trimer were calculated and then compared with those found from experiment to assess the accuracy of each potential energy surface. Although reparametrization of the CKL function to a set of counterpoise-corrected energies yielded transition energies that are in qualitative agreement with those from experiment, reparametrization to another set of counterpoise-corrected energies resulted in highly inaccurate values of the transition energy. As a consequence, our results demonstrate that caution must be exercised in the implementation of the counterpoise method as it does not always lead to more accurate ab initio calculations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 233-252, 1998
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  • 195
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    International Journal of Quantum Chemistry 68 (1998), S. 75-75 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 196
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    International Journal of Quantum Chemistry 68 (1998), S. 79-90 
    ISSN: 0020-7608
    Keywords: ladder operators ; superoperators ; Van Vleck-Primas perturbation method ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present work is a version of Van Vleck-Primas perturbation method in terms of generalized ladder operators. Using the superoperator approach, a fully general, self-consistent and a totally free scheme from representation is developed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 79-90, 1998
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  • 197
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    International Journal of Quantum Chemistry 68 (1998), S. 285-291 
    ISSN: 0020-7608
    Keywords: tight-binding ; band spectrum ; orbital nonorthogonality ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A one-dimensional one-band model is presented which enables a tight-binding calculation to be performed with full rigor. All the multicenter integrals involved in the calculation of the Hamiltonian matrix elements can be analytically computed in terms of a single parameter: the ratio between the lattice spacing and the extension of the “atomic” wave function. Moreover, the exact expression for the spectrum shows how the usual approximations of limiting the range of interactions and neglecting the nonorthogonality of the basis set degrade the results of the calculations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 285-291, 1998
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  • 198
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    International Journal of Quantum Chemistry 68 (1998), S. 273-284 
    ISSN: 0020-7608
    Keywords: C40 cluster molecule ; C40H4 cluster molecule ; C40X4 cluster molecule ; PM3 semiempirical molecular orbital method ; structures of geometrical optimization ; ionization potential ; energy gap ; heat of formation ; atomization energy ; vibration frequency ; 1,3,5,7-tetrahaloadamantane molecules ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Herein we demonstrate that the C40 cluster molecule is easily formed to Td symmetry structure and its ground state is 5A2 open shell with four unpaired electrons. These four unpaired electrons are located at the tip points of the Td symmetry structure. This work also indicates that these four unpaired electrons can easily react with a single valence atom, such as hydrogen or halogen atoms, to form a stable carbon hydrogen cluster molecule, C40H4, and carbon halogen cluster molecules, C40X4 (X=F, Cl, Br, I), respectively. The PM3 semiempirical molecular orbital method from Gaussian 94W computer program package was applied very well to these cluster molecules. According to the results in this study, the structures of geometrical optimization, ionization potential, energy gap, heat of formation, atomization energy, vibration frequency, and the remaining data of C40H4 and C40X4 cluster molecules. The above-calculated data prove that these unknown cluster molecules are stable and have a stable capacity similar to 1,3,5,7-tetrahaloadamantane molecules. They can be possibly synthesized experimentally in the near future.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 273-284, 1998
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  • 199
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    International Journal of Quantum Chemistry 68 (1998), S. 211-217 
    ISSN: 0020-7608
    Keywords: dihedral fullerenes ; infrared and Raman spectra ; NMR spectra ; irreducible representations ; representative patch ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the help of the topological structures of the dihedral (Dp, Dph, Dpd; p=5, 6) fullerenes, we have derived the formulas for the decomposition of their nuclear motions into irreducible representations. So their infrared and Raman active modes have been obtained. Furthermore, by use of the concept of the representative patch we have also derived their nuclear magnetic resonance spectra.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 211-217, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 200
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 68 (1998), S. 351-355 
    ISSN: 0020-7608
    Keywords: hydrogen bonding ; DNA ; base analogs ; stacking interaction ; reaction field ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a recent experimental study, it was reported that replacement of thymine in the adenine-thymine base pair of DNA by its molecular analogs which cannot form proper hydrogen bonds with adenine (A) does not cause disruption of DNA structure and synthesis. AM1 and ab initio molecular orbital calculations and electric field mapping were carried out in order to examine the possibility of pairing of A with each one of two analogs of thymine in the gas phase. Self-consistent reaction field calculations were also carried out on the individual molecules and their pairs using the polarized continuum model in order to examine their stability in aqueous media. Our results are broadly in agreement with the conclusions drawn in the above-mentioned experimental work.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 351-355, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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