Molecular structure and conformational composition of 1-Chlorobutane, 1-Bromobutane,and 1-Iodobutane as determined by gas-phase electron diffraction and ab initio calculations

Gas-phase electron diffraction (ED), together with ab initio molecular orbital calculations, have been used to determine the structure and conformational composition of 1-chlorobutane, 1-bromobutane, and 1-iodobutane. These molecules may in principle exist as mixtures of five different conformers, but only three or four of these were observed in gas phase at temperatures of the ED experiments, 18C, 18C, and 23C, respectively. The observed conformational compositions (1-chlorobutane, 1-bromobutane, and 1-iodobutane) were AA (13 ± 12%, 21 ± 14%, 19 ± 17%), GA (60±13%, 33±32%, 17±31%), AG (12±16%, 8±12%, <1%), and GG (12 ±16%, 38± 34%, 64±31%). A and G denotesanti andgauche positions for the X-C₁-C₂-C₃ (X=Cl, Br, I), and the C₁-C₂-C₃-C₄ torsion angles. The results for the most important distances (r _g) and angles () from the combined ED/ab initio study for the GA conformer of 1-chlorobutane, with estimated 2 uncertainties, arer(C₁-C₂)=1.519(3)å,r (C₂-C₃)=1.530(3) å,r (C₃-C₄)=1.543(3) å,r (C₁-Cl)=1.800(4) å, <C₁C₂C₃=114.3(6), <C₂C₃C₄=112.0(6), <CCCl=112.3(5). The results for the GA conformer of 1-bromobutane arer (C₁-C₂)=1.513(4) å,r (C₂-C₃)=1.526(4) å,r (C₃-C₄)=1.540(4) å,r(C₁-Br)=1.959(8) å, <C₁C₂C₃=115.3(11), <C₂C₃C₄=112.8(11),<CCBr=112.1(14). The results for 1-chlorobutane and 1-bromobutane are compared with those from earlier electron diffraction investigations. The results for the GA conformer of 1-iodobutane arer (C₁-C₂)=1.506(5) å,r (C₂-C₃)=1.518(5) å,r (C₃-C₄)=1.535(5) å,r (C₁-I)=2.133(11) å, <C₁C₂C₃=116.8(15), <C₂C₃C₄=115.3(15), <CCI=110.2(14). Differences in length between the different C-H bonds in each molecule, between the different C-C bonds, between the different CCH angles, and between the different CCC angles were kept constant at the values obtained from the ab initio calculations.     

Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G^*(6D) basis set. Least-squares refinement of a model withC _s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, =119.0±0.2 (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1, 120.7±0.1, and 119.0±0.3, respectively. Important bond distances are r _g(C-C)=1.398±0.003 å andr _g(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is ¦¦=44±4. The equilibrium dihedral angle is calculated to be 41.8 at the HF level and 43.6 at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(C_ortho-C_meta) -r(C_ipso-C_ortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.     

Eigenvalues of large even annulenes in terms ofK 3,S 4 andS 5

Squares of the adjacency matrices of bipartite cycles (C_v) can be block-factored into matrices which correspond to vertex-weighted complete graphs forv = 6, vertex-weighted strongly regular graphs forv = 8 and 10, and vertex-weighted metrically regular graphs forv > 10. Using this fact and some properties of strongly and metrically regular graphs, it is shown that eigenvalues of large bipartite C _v graphs (i.e. large even annulenes) can be expressed by the general formula ± (2 ± (2 ± (... ± (2 +r _p)) ...), wherev = 2 ⁿ ×p,n is the number of surd () signs required andp = 3, 4 and 5. Here,r ₃,r ₄, andr ₅, are the eigenvalues of the complete graphK ₃ and the strongly regular graphsS ₄ andS ₅ respectively. The procedure does not require construction of characteristic polynomials for the determination of eigenvalues, and brings out a common topological origin for the two-fold degeneracies observed in the eigenvalue spectra of all even cycles and many odd cycles.     

Structure and charge distribution of some alkynoyl cations

We have performedab initio calculations to determine the structure and charge distribution of some alkynoyl cations and their parent alkynoyl fluorides. We have used Mulliken population analysis and a new technique developed by Yáñez, Stewart and Pople. Our results indicate that the mesomeric form O⁺C–CC–R is one of the most important contributors to the structure of these cations, in agreement with experimental conclusions. We have also found that the participation of mesomeric form O=C=C=C⁺ -R is not negligible and increases with -substitution. In the 3-phenylpropynoyl cation substantial delocalization of charge into the phenyl group occurs. Calculations from YSP population analysis are in good agreement with experimental evidence.     

Determination of hexavalent chromium by using speciated isotope-dilution mass spectrometry after microwave speciated extraction of environmental and other solid materials

Precise and accurate determination of hexavalent chromium in different types of solid environmental sample is regarded as a technical challenge with significant potential error if historically accepted methods are used. Microwave-assisted alkaline extraction (0.5 mol L^–1 NaOH+0.28 mol L^–1 Na₂CO₃) followed by anion-exchange chromatographic separation and inductively coupled plasma mass spectrophotometric detection has been shown to provide accurate and precise results. To obtain a better understanding of potential species conversion during and/or after extraction steps, speciated isotope-dilution mass spectrometry (SIDMS) (EPA Method 6800) metrology has been successfully applied as a diagnostic tool with the modified accompanying extraction version of EPA Method 3060A. In our study, aggregate materials distributed over a large area of a major western US state were found to contain a high concentration of total chromium (195±13 to 709±19 g g^–1) and significant amounts of Cr⁶⁺ (141±6 to 341±29 g g^–1) which are at least three orders of magnitude higher than the US EPA threshold limit (0.5 g g^–1). Sediment samples from a major western US state, studied independently, were found to contain less (1.77±0.34 g g^–1) or no Cr⁶⁺ in the presence of significant total chromium.     

Molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide from gas-phase electron diffraction

The molecular structure of 1,1-dimethylsilacyclopentene-3,4-oxide has been determined by electron diffraction in the gas phase. The experimental data are consistent withC _s molecular symmetry and boat conformation with a flattened end at the silicon atom. The flap angles characterizing the orientation of C-Si-C and C-O-C planes with respect to the four coplanar carbon atoms of the ring are 16.6 ± 0.6 and 73.3 ± 0.6, respectively. Bond lengths (r_g) are Si-C₆, 1.866 ±0.008; Si-C₂, 1.899 ± 0.008; C₂-C₃, 1.513 ± 0.005; C₃-C₄ (bridge), 1.477 ± 0.013; C-O, 1.443 ± 0.007; (C-H)_mean 1.116 ± 0.003 å. Bond angles are <C₅-Si-C₂, 96.2 ± 0.4; <Si-C₂-C₃, 103.9 ± 0.3; <C₂-C₃-C₄, 116.5 ± 0.3; <C₃-C₄-O, 59.2 ± 0.5; zC₄-C₃-H₉, 109.0 ± 3.5; <C₂-C₃-H₉, 132.9 ± 3.1; <C₆-Si-C₁₂, 114.6 ± 0.8; <Si-C₆-H₁₅, 109.7 ± 0.9.     

Characterization of a total diet reference material (ARC/CL HDP) for contents of essential and toxic elements

Summary A total diet reference material (RM) was prepared by employing material leftover from a nationwide Finnish hospital diet study. The material was carefully homogenized using Ti-blades, freeze-dried, rehomogenized with Ti-blades, passed through a 2 mm nylon sieve and carefully mixed in large glass cylinders. Homogeneity of the material divided into 20 g samples in polyethylene bottles was tested by taking ten 0.5 g samples from the beginning and end of the bottling line and analyzing them for Zn and Mg. The homogeneity was within 1.0% for both Zn and Mg. An interlaboratory comparison study involving reliable reference laboratories that employed a total of seven methods based on independent analytical principles was conducted on the contents of 14 mineral elements. After the exclusion of outliers the recommended concentrations (on a dry weight basis) expressed as the medians±95% confidence limits were established as follows: Ca=2.86±0.124 mg/g, Mg=785±25 g/g, K=9.42±0.30 mg/g, Na=7.87±0.57 mg/g, Fe=30.4±0.9 g/g, Mn=12.9±0.58 g/g, Zn=28.9±1.3 g/g, Cu=3.18±0.19 g/g, Mo=262±35 ng/g, Ni=271±38 ng/g, Se=181±17 ng/g, Pb=43±8 ng/g, Cd=21±3 ng/g and Hg=6.6±3.6 ng/g. All of the above recommended concentration ranges, except that for Ni, fell into category A, i.e. values recommended with a high degree of confidence according to the certification criteria established by Pszonicki.     

Determination of Mg,Al, P,Cu and Mn in biological fluids by neutron activation analysis

Thermal and epithermal neutron activation analysis has been applied to determine the concentrations of magnesium, aluminium, phosphorus, copper and manganese in two biological fluids: blood serum and market milk. Both epithermal neutron irradiation and radiochemical separation (a chromatographic column of HAP) were used to get rid of the interferences from 24-Na. Strongly acidic solutions of the irradiated samples were passed through the columns of HAP, where sodium was completely adsorbed while, Al, Cu, Mg and Mn were eluted with an efficiency of 99±1%. Since both Al and P were determined through the formation of²⁸Al (2.24 min) thermal and epithermal neutron activation have been applied in order to determine the contribution of each radionuclide to²⁸Al activity. The determination of Mg, Al and P in milk samples was done instrumentally, whereas in the case of blood serum with higher concentration of Na, a radiochemical separation is essential in both cases. The concentrations of Al, Cu, Mg, Mn and P in blood serum and market milk were found to be 0.24±0.02 and 1.85±0.09 g Al/ml, 1.35±0.04 and 0.068±0.005 g Cu/ml, 22.9±1 and 98.9±8.6 g Mg/ml, 22±3 and 16±2 ng Mn/ml and 167±13 and 865±32 g P/ml, respectively.     

Simple and Rapid Method for Determination of Selenium in Breast Milk by HG-AFS

A digestion procedure using H₂SO₄/HNO₃/H₂O₂ was found to be effective for destruction of human milk samples. In conjunction with a sensitive hydride generation atomic fluorescence spectrometry detection system, it is suitable for determination of selenium in those samples where the available mass of breast milk and the low selenium concentration are limiting factors. Only 1g of milk sample is needed. The procedure is simple, rapid and of low contamination potential since it is performed in the same Teflon tube from weighing to measurement. The digestion of 20 samples is completed in three hours. The detection limit is 0.25±0.04ngg^–1 of a measured solution of sample or 2.5ngg^–1 of milk. The relative uncertainty is 10% (coverage factor of 2.3, 95% probability). Because of these advantages the method is particularly suitable for epidemiological studies. The mean concentration of selenium in 62 samples of human milk from lactating women residing in the North East of Italy was 12±3ngg^–1, which is in the range of reference data.     

Thermodynamic properties of alkali halides. II. Enthalpies of dilution and heat capacities in water at 25°C

The enthalpies of dilution and volumetric specific heats of most alkali halides were measured in water at 25°C with flow microcalorimeters in the concentration range 0.01 to 1m. Apparent molal relative enthalpies _L, derived from the enthalpies of dilution, can be represented by a parametric equation in molality. Combining _L with osmotic data, excess entropies can be calculated. Excess free energies, enthalpies, and entropies are compared at 0.5m, and the observed trends are consistent with a model of structural interactions in aqueous alkali halide solutions. The apparent molal heat capacities _C were fitted with the equation _C= _C ^° +A_C(d₀m)^1/2+B _C m. The _C ^° are, in general, additive to better than 1 J-K^–1-mole^–1 and reflect mostly the structural part of ion-solvent interactions. Taking _C ^° (H⁺)=0, conventional ionic _C ^° are obtained. The parameterB _C for different pairs of ions follows approximately the same trends as the corresponding parameterB _V for apparent molal volumes and seems to reflect structural interactions between the ions.     

Polarographisches Verhalten der C2-Halogenkohlenwasserstoffe

Summary Investigations on the polarographic and voltammetric behaviour of organic halogen compounds were carried out in order to obtain information on the redox properties and how to develop determination and detection methods. In this second report the dp-polarographic behaviour of the halogen substituted C₂-compounds has been studied in different supporting electrolytes and in various solvents. The electrode processes are discussed and the possibilities for the polarographic determination of the C₂-halogen hydrocarbons. The detection limit is 0.25 g · ml^–1 and the linear current-concentration relationship is observed up to 25 g · ml^–1. A simple and rapid method is proposed for the dp-polarographic determination of 1,2-dibromoethane in gasoline; the relative standard deviation for 20 g · ml^–1 is ±1.8%.     

Komplexe des zweiwertigen Kobalts mit p-Methylbenzamidoxim

Zusammenfassung Die Komplexbildung des Kobalts mit p-Methylbenzamidoxim (pMBz) in alkal. Lösung wurde spektrophotometrisch untersucht. Die Ligandenzahl und die Bildungskonstanten wurden nach logarithmischen Methoden bestimmt. Bei niedrigeren Konzentrationen des pMBz entsteht ein Komplex 11 (bei höheren 12). Die Bildungskonstanten bei 25°C und =0,02 sind ₁=(2,95±±0,06)·10⁵ und =21,±0,3.

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Co(II) complexes of p-Methylbenzamideoxime

The complex formation of cobalt with p-methyl benzamidoxime in alkaline solution was investigated spectrophotometrically, and the ligand number and the formation constants were determined by logarithmic methods. At low pMBz concentrations a 11 complex is formed and at higher ones a 12 complex. The formation constants are ₁=(2,95±0,06)·10⁵ and ₂=21,8±0,3 at 25°C and =0,02.

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Mit 6 Abbildungen     

Photometric Determination of Zirconium with Semimethylthymol Blue

The complexation of zirconium(IV) with Semimethylthymol Blue (H₄L) was studied by spectrophotometry. The formation of the (ZrOH)₂(H₂L)²⁺ ₂ complex with log = 20.68 ± 0.12 and ₅₆₅ = (7.26 ± 0.02) × 10⁴ was revealed by the isomolar series and molar ratio methods. A simple, reliable, and sensitive method was developed for the photometric determination of zirconium. The calibration plot is linear in the concentration range of 10^–6–10^–5 M zirconium. In a sample of frit 24–70 containing 5.7% ZrO₂, 5.44 ± 0.15% ZrO₂ was found.     

A new spectrophotometric method for the determination of dimethyl formamide

Summary The spectrophotometric determination of dimethyl formamide comprises hydrolysation to dimethyl amine and reaction with carbon disulphide to dithiocarbamate, which gives a yellow complex (_max=430 nm) with copper(II). Standard deviation was ±0.0086 g/ml. There are no interferences from various copollutants.     

Crystalline Inclusion Compounds Derived from 1,1'-Bis(ethenyl-2-pyridyl)ferrocene and (±)-1,1'-Bi-2-naphthol in Different Solvents

Crystallization of organometallic dipyridine(1,1'-bis(ethenyl-2-pyridyl)-ferrocene) (1) with(±)-1,1'-bi-2-naphthol (2) from EtOH,i-PrOH, (±)-2-BuOH, and MeOH forms crystallineinclusion compounds of stoichiometries1 2 C₂H₅OH (3, 1 2 C₃H₇OH (4),1 2 C₄H₉OH (5),and 1 2 CH₃OHH₂O(6), respectively. Thecrystalline species 3, 4, and 5 areisostructural with the three molecular componentsinterlinked by hydrogen bonds to form a columnarstructure. In 6, the four molecular componentsare interlinked by hydrogen bonds to form atwo-dimensional framework structure.     

The viscoelasticity of spinnable solutions of alkyltrimethylammonium salicylates

The viscoelasticity has been measured for aqueous solutions of tetradecyl-and hexadecyltrimethylammonium salicylates (C₁₄TASal, C₁₆TASal). The aqueous solutions of C₁₄TASal without salt displayed the gel-like behavior at 10.0×10^–2 g cm^–3, but those more dilute than 3.2×10^–2 g cm^–3 presented the viscoelasticity similar to that of a Maxwell liquid. The Maxwell-like behavior was converted to the polymer-like one on the addition of (0.1–0.2) M NaBr or (0.02–0.2) M NaSal. The gel-like viscoelasticity can be connected with the spinnability of cohesive fracture failure, and the Maxwell-like and polymer-like viscoelasticities are concerned with the spinnability of ductile failure. The gel-like and Maxwell-like viscoelasticities originate in the pseudo-network formed by the pseudo-linkages between rodlike micelles, while the polymer-like viscoelasticity is caused by the entanglement of long rodlike micelles in semidilute and concentrated solutions. The aqueous solutions of C₁₆TASal behaved very similar to those of C₁₄TASal.     

Determination of boron, carbon, nitrogen and oxygen in nickel by charged particle activation analysis

Summary The determination of boron, carbon, nitrogen and oxygen in nickel by charged particle activation using the reactions ¹⁰B(d, n)¹¹C, ¹²C(d, n)¹³N, ¹⁴N(p, )¹¹C and ¹⁶O(³He, p)¹⁸F is studied. The interference of ¹¹B(p, n)¹¹C with the ¹⁴N(p, )¹¹C reaction is taken into account. ¹¹C, ¹³N and ¹⁸F are separated by oxygen combustion followed by trapping of ¹¹CO₂ in NaOH and by steam distillation of ¹³NH₃ and of H₂Si¹⁸F₆, respectively. The results obtained were 0.129±0.035 g g^–1 for boron, 86.4±8.3 g g^–1 for carbon, 1.077±0.037 g g^–1 for nitrogen and 8.91±1.00 g g^–1 for oxygen. The results for nitrogen and oxygen agreed satisfactorily with those of other analytical methods.Grateful acknowledgement is made to Prof. J. Hoste for his interest shown in this work, to J. Pauwels (B.C.M.N., Geel) for providing the samples, to B. F. Schmitt (Bundesanstalt für Materialprüfung, Berlin) for helpful information concerning the radiochemical separation of ¹¹C and to the NFWO and the IIKW for financial support.     

Determination of Iron(III), Cobalt(II) and Chromium(III) in Various Water Samples by Flame Atomic Absorption Spectrometry After Preconcentration by Means of Saccharomyces Carlsbergensis Immobilized on Amberlite XAD-4

A method for the determination of Fe(III), Co(II) and Cr(III) by flame atomic absorption spectrophotometry (FAAS) after preconcentrating on a column containing S. carlsbergensis immobilized on Amberlite XAD-4 has been developed. The optimum values of pH, amount of adsorbent, elution solution and flow rate of the sample solution were determined for the quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum conditions, recoveries of Fe(III), Co(II) and Cr(III) by S. carlsbergensis immobilized on Amberlite XAD-4 were 99±2, 100±2 and 98±2% at 95% confidence level, respectively. The limit of detections for Fe(III), Co(II) and Cr(III) were 2.8, 3.9 and 7.4ngmL^–1, respectively. The proposed method was applied to the determination of the analytes in various water samples. The validity of the method was checked with spiked water samples. Fe(III), Co(II) and Cr(III) was determined with a relative error of less than 5%.     

The Influence of β- and γ-Cyclodextrin Cavity Size on the Association Constant with Decanoate and Octanoate Anions

This work evaluates the influence of the - and -cyclodextrin (CD) cavity size on the association constant (K_CDA) with decanoate (C₁₀) and octanoate (C₈) anions. The spectral displacement technique with phenolphthalein was used to obtain the 1:1 association constant (K_CDA) in NaHCO₃/NaOH buffer pH 10.5 at 25 °C. The K_CDA value obtained were 2.6 (±0.2) × 10³, 2.5 (±0.5) × 10², for beta;CD–C₁₀ and CD–C₁₀ inclusion complexes, and 5.1 (±0.2) × 10² and 4.7 (±0.2) × 10¹ for CD–C₈ and CD–C₈ inclusion complexes, respectively. The K_CDA values of either acid with CD is approximately 10 times higher than for the same acid with CD, where as for the same cyclodextrin, the K_CDA value is 5 times higher for the C₁₀ association than for the C₈. The data demonstrate that the cyclodextrin cavity size exerts a greater influence on the association constant than the chain length of the acid for these compounds. ¹H NMR studies show that fatty acid protonation has a distinct effect on the chemical shift of CD protons.