Rotational isomerism in open-chain polychlorinated hydrocarbons: Problems in predicting conformations from carbon-chlorine stretching frequencies

Normal coordinate analysis calculations have been made to determine the carbon-chlorine stretching (v(C-Cl)) frequencies of model rotational isomers of 1,2-dichloroethane, 1,2-dichloropropane, 1,3-dichloropropane, 1,5-dichloropentane and 1,2,3-trichloropropane. The calculations were based on prior calculations on models of a number of primary and secondary monochlorohydrocarbons. The models were derived from the real isomers by ignoring the hydrogen atoms and considering only the heavy atom skeletal structure. The possible effect on v(C-Cl) frequencies of coupling between C-C1 stretching and adjacent CH₂ rocking modes in some isomers was taken into account where necessary. The results, and in some cases the frequency of the highest ∠CCC deformation mode, are used to establish the conformations of rotational isomers present in these molecules in the vapour, liquid and crystalline states. Conclusions are drawn concerning the applicability of known v(C-Cl) frequency structure correlations for monochlorohydrocarbons to polysubstituted chlorohydrocarbons. v(C-Cl) frequency correlations and assignments have also been made for several chloropropanes containing one CCl₃ group.     

Synthesis,Spectrothermal Behaviour and Molecular Structure of Aquaorotatotriethanolaminenickel(II) Monohydrate

The aquaorotatotriethanolaminenickel(II) monohydrate, [Ni(HOr)(H₂O)(tea)]·H₂O ( 1 ), was synthesized and characterized by means of elementel analysis, IR and UV‐Vis, spectroscopy, magnetic susceptibility, thermal analysis and X‐ray diffraction techniques. The nickel ion in [Ni(C₅H₂N₂O₄)(H₂O)(N(C₂H₄OH)₃)] is chelated to the deprotonated N3 pyrimidine atom and to the carboxylate oxygen atom of the bidentate orotate dianion, and to the one nitrogen and two oxygen atoms of the tridentate triethanolamine molecule and its octahedral geometry is completed by an aqua ligand. It crystallizes in the monoclinic system, space group P2₁/c with lattice parameters a = 7.1528(5) Å, b = 19.4903(14) Å, c = 11.8085(8) Å, β = 106.237(5)°, V = 1580.55(19) ų, Z = 4. An extensive three dimensional network of O_w‐H…O, N‐H…O and O‐H…O hydrogen bonds, π‐π and π‐ring interactions are responsible for crystal stabilization. The decomposition reaction take places in the temperature range 20‐1000 °C in the static air atmosphere. Thermal decomposition of 1 proceeds in three stages.     

The Adsorption Kinetics of Cethyltrimethylammonium Bromide (CTAB) onto Powdered Active Carbon

This study investigates the adsorption kinetics of CTAB (cethyltrimethylammonium bromide), a cationic surfactant, onto PAC from aqueous solution with respect to the initial CTAB concentration at 20C. The pseudo-first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, k_i, of intraparticle diffusion, the rate parameter, k₂, of the pseudo-second-order and k₁, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-second-order adsorption mechanism is predominant and the overall rate of the CTAB adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms.     

Determination of Abacavir, Lamivudine and Zidovudine in Pharmaceutical Tablets, Human Serum and in Drug Dissolution Studies by HPLC

A simple, accurate, precise and fully automated method for the simultaneous determination of abacavir, lamivudine and zidovudine in pharmaceutical tablets, human serum samples and drug dissolution studies has been developed. Separation was performed on a 5 μm Zorbax^® C₁₈ column (150 × 4.6 mm ID) with methanol:water:phosphate buffer at pH 5.65 (80:10:10; v/v/v) isocratic elution in less than 7 min with a flow rate of 0.6 mL min^?1.Good sensitivity for all analytes was observed with UV detection at 275 nm. The method allowed quantitation over the 500–3,000 ng mL^?1 range for abacavir and 500–5,000 ng mL^?1 range for lamivudine and zidovudine. The method has been applied, without any interference from excipients or endogenous substances, for the simultaneous determination of these three compounds in tablets. Human serum and drug dissolution studies.     

Spectroscopic and Electrochemical Studies of Transition Metal Complexes with N,N′-Bis(2-aminothiophenol)-1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane and Structure Effects on Extractability of Ligand towards some Divalent Cations

Summary. La(III), Cu(II), Ni(II), and Zn(II) metal complexes with a novel quadridentate Schiff base derived from 1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane and 2-aminothiophenol were synthesized and characterized by microanalytical data, elemental analysis, magnetic measurements, ¹H NMR, ¹³C NMR, UV-Vis, IR, mass spectra, cyclic voltammetric and conductance measurements. The extractability of divalent cations was evaluated as a function of relationship between distribution ratio of the metal and pH or ligand concentration. The highest extraction percentage of Cu²⁺ and Ni²⁺ showed pH 7.0 and 6.4. It was concluded that the ligand can effectively be used in solvent extraction of copper(II) and nickel(II) from the aqueous phase to the organic phase.     

Structure of 2-{2-[3-methyl-3-(2,4,6-trimethylphenyl) cyclobutyl]-2-oxoethyl}isoindole-1,3-dione

2-{2-[3-Methyl-3-(2,4,6-trimethylphenyl)cyclobutyl]-2-oxoethyl}isoindole-1,3-dione (C₂₄ H₂₅NO₃) was synthesized, and its crystal structure was determined by X-ray crystallographic techniques. The compound crystallizes in the triclinic space group P-1, with unit cell parameters: a = 14.109(9) Å, b = 14.130(8) Å, c = 12.152(6) Å, = 105.62(5)°, = 113.75(4)°, = 98.78(5)°, V = 2039.8(19) ų, D _c= 1.223 g/cm³, and Z = 4. The crystal structure has two crystallographically independent molecules, I and II. These molecules are held together by weak intermolecular C—H···O interactions, forming a continuous chain. The dihedral angles between the N-substituted phthalimide moiety and cyclobutane ring in molecules I and II are 60.37(14) and 68.18(18)°, respectively.     

Microwave‐Assisted Synthesis of Novel 2,4‐Dihydro‐5‐[4‐(trifluoromethyl)phenyl]‐3H‐1,2,4‐triazol‐3‐ones and Potentiometric Determination of Their pKa in Nonaqueous Solvents

The novel 4‐amino‐ or 4‐aryl‐substituted 2,4‐dihydro‐5‐[(4‐trifluoromethyl)phenyl]‐3H‐1,2,4‐triazol‐3‐ones 3a – 3g were synthesized by reaction of N‐(ethoxycarbonyl)‐4‐(trifluoromethyl)benzenehydrazonic acid ethyl ester ( 2 ) and primary amines or hydrazine by microwave irradiation. Compounds 3a – 3g were potentiometrically titrated with tetrabutylammonium hydroxide (Bu₄NOH) in four nonaqueous solvents, i.e., ⁱPrOH, ^tBuOH, MeCN, and N,N‐dimethylformamide (DMF). Also half‐neutralization potential values and the corresponding pK_a values were determined in all cases.     

On the solutions of the linear integral equations of Volterra type

Some boundaries about the solution of the linear Volterra integral equations of the form f(t)=1?K*f were obtained as |f(t)|?1, |f(t)|?2 and |f(t)|?4 in (J. Math. Anal. Appl. 1978; 64 :381–397; Int. J. Math. Math. Sci. 1982; 5 (1):123–131). The boundary of the solution function of an equation in this type was found as |f(t)|?2ⁿ in (Integr. Equ. Oper. Theory 2002; 43 :466–479), where t∈[0, ∞) and n is a natural number such that n?2. In (Math. Comp. 2006; 75 :1175–1199), it is shown that the boundary of the solution function of an equation in the same form can also be derived as that of (Integr. Equ. Oper. Theory 2002; 43 :466–479) under different conditions than those of (Integr. Equ. Oper. Theory 2002; 43 :466–479). In the present paper, the sufficient conditions for the boundedness of functions f, f′, f′′, …, f⁽ⁿ⁺³⁾, (n∈?) defined on the infinite interval [0, ∞) are given by our method, where f is the solution of the equation f(t)=1?K*f. Copyright © 2007 John Wiley & Sons, Ltd.     

Component testing of repairable systems in multistage missions

We consider the component testing problem of a device that is designed to perform a mission consisting of a sequence of stages. Once a stage is over, the device is overhauled to replace all failed components before the next stage starts to improve mission reliability. The components fail exponentially where the failure rate depends on the stage of the mission. The reliability structure of the device involves a series connection of redundant subsystems. The optimal component testing problem is formulated as a semi-infinite linear programme. We present an algorithmic procedure to compute optimal test times based on the column generation technique, and illustrate it with numerical results.