The electronic structure and optical activity of conjugated dienes: 1,3-Butadiene and α- and β-phellandrene

The optical activity of conjugated dienes is investigated by means of ab initio SCF–CI calculations. The computed electronic spectrum of trans-1,3-butadiene is shown to be in good agreement with the results of more rigorous calculations of the valence transitions and in satisfactory agreement with experiment. The optical rotatory strengths of the lower electronic transitions of twisted 1,3-butadiene as a function of dihedral angle are presented and simulated CD spectra are produced. The N → V₁ (π₂ → π₃*) transition is predicted to have a positive rotational strength for all dihedral angles that correspond to a right-handed twist of the chromophore, in accord with the empirically deduced “diene rule” although for a twist angle of 60°, the rotatory strength is calculated to be almost zero. The role of the orientation of allylic bonds is investigated in the model system 1-butene in which the rotational strength of the π → π* transition as a function of rotation about the 2,3 bond is determined. The effect of allylic bond disposition in dienes on the optical activity of the long-wavelength π₂ → π₃* transition is simulated by use of the exciton coupling model of Harada and Nakanishi in which two 1-butene molecules with suitable geometries are coupled via interactions of the electric dipole transition moments of their π → π* transitions. The model systems 1,3-butadiene and 1-butene are used to rationalize the apparently anomalous optical activity of (?)-α-phellandrene and (?)-β-phellandrene, both of which should have a diene chromophore with a right-handed twist in their most stable conformers and so should be dextrorotatory. The experimental CD spectrum of α-phellandrene is determined at several temperatures down to ?180°C. The observed variation of the apparent rotational strength of the N → V₁ transition is in good agreement with that predicted by use of the exciton coupling model.     

Complexes of the ethylpyridines with the halides of cobalt(II), nickel(II) and copper(II)

A series of complexes has been prepared with the halides of cobalt(II), nickel(II), copper(II) and 2-,3-,4-ethylpyridine. The compounds were essentially all octahedral with the exception of those formed between 2-ethylpyridine and the cobalt(II) halides. The stereochemical configurations were deduced using spectral and magnetic properties. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis.

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Zusammenfassung Eine Reihe von Komplexen wurde aus den Halogeniden von Cobalt(II), Nickel(II), Kupfer(II) und 2-, 3-, 4-äthylpyridin hergestellt. Die Verbindungen waren im Wesentlichen alle oktaedrisch, mit Ausnahme jener, die aus 2-äthylpyridin und den Cobalt(II) halogeniden gebildet wurden. Die stereochemischen Konfigurationen wurden aus den spektralen und magnetischen Eigenschaften abgeleitet. Der Zerfall der Komplexe wurde durch Thermogravimetrie und Differentialthermoanalyse untersucht.

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Résumé Une série de complexes a été préparée avec les halogénures de cobalt(II), nickel(II), cuivre(II) et éthyl-2-, 3-, 4- pyridine. La plupart des composés sont octaédriques, à l'exception de ceux formés à partir de l'éthyl-2 pyridine et les halogénures de cobalt(II). Les configurations stéréochimiques ont été déduites des propriétés spectrales et magnétiques. La dé composition des complexes a été suivie par thermogravimétrie et analyse thermique différentielle.

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2-, 3-, 4- (II), (II) (II). , , , (II) 2-. , . .

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The authors wish to thank Beckman Instruments Ltd for the use of the Far IR spectrophotometer, IR 720 M.     

1H and 199Hg NMR spectra of methylmercury(II) complexes. Effects of basicity and ortho substitution in pyridines(L) in complexes [MeHgL]NO3

Linear complexes [MeHgL]NO₃ (L = substituted pyridine) have been prepared and their ¹H and ¹⁹⁹Hg NMR spectra measured and compared with other complexes of this series reported previously. The coupling constant J(¹H?¹⁹⁹Hg) correlates directly with pKa and with the gas phase enthalpy of ionization [ΔG_i(g)] of LH⁺; with J(¹H?¹⁹⁹Hg) decreasing with increasing pKa or ΔG_i(g). The chemical shift, δ, for ¹⁹⁹Hg does not correlate with either pKa or ΔG_i(g). Complexes without substituents in the 2 position of pyridine have δ¹⁹⁹Hg ca. 80–100 ppm downfield from MeHgNO₃, those with one methyl group in the 2 position ca. 125–150 ppm, and those with methyl groups in the 2 and 6 position (or benzyl or 3′-methylpyridyl groups in the 2 position) ca. 160–200 ppm downfield from MeHgNO₃. The coupling constant J(¹H?¹⁹⁹Hg) is found to be more useful than δ¹⁹⁹Hg in determination of solution structures of MeHg(II) complexes of this type of ligand.     

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXVI Structural Studies in the Copper(I) Halide : Norbornadiene System

The structural characterizations of some copper(I) halide (CuX) adducts with norbornadiene (nbd) are recorded. CuCl : nbd (1:1)₄ (a redetermination), (2:1)_2(|), are systems both based around Cu₄Cl₄ cubane-type cluster arrays. CuBr : nbd (7:3)_(|)( 0.5 MeOH), a complex polymer with 3-symmetry, is believed to be the complex previously described as an adduct of 2:1 stoichiometry. Attempts to obtain an iodide counterpart have resulted in the definition of an ephemeral adduct CuI : MeCN (3:2)_(|). 0.5 C₇H₈ in which, remarkably, the nbd is uncoordinated; the complex is a polymer, related to the [AgX(quinoline)]_(|) (X = Cl, Br) saddle polymer.     

Backward error analysis for totally positive linear systems

Summary Gauss elimination applied to ann×n matrixA in floating point arithmetic produces (if successful) a factorization which differs fromA by no more than , for some of ordern times the unit roundoff. IfA is totally positive, then both computed factors and are nonnegative for sufficiently small unit roundoff and one obtains pleasantly small bounds for the perturbation inA which would account for the rounding errors committed in solvingAx=b forx by Gauss eliminationwithout pivoting. It follows that the banded linear system for the B-spline coefficients of an interpolating spline function can be solved safely by Gauss elimination without pivoting.Sponsored by the United States Army under Contract No. DAAG29-75-C-0024 and the National Science Foundation under Grant No. MPS72-00381 A01.     

Cavity Ring Down Laser Absorption Spectroscopy of NiI

用激光蒸发/反应、超声射流和光腔衰荡吸收光谱方法研究NiI在445～510 nm的吸收光谱. 发现两个新的跃迁体系[21.3]²?_5/2～X²?_5/2和[21.9]²Π_3/2～X²?_5/2,并且观察到了同位素分子⁵⁸NiI和⁶⁰NiI光谱. 同时计算得到了电子态[21.3]^{2相似文献}   

Reconstruction of Random Colourings

Reconstruction problems have been studied in a number of contexts including biology, information theory and statistical physics. We consider the reconstruction problem for random k-colourings on the Δ-ary tree for large k. Bhatnagar et al. [2] showed non-reconstruction when . We tighten this result and show non-reconstruction when , which is very close to the best known bound establishing reconstruction which is . Supported by NSF grants DMS-0528488 and DMS-0548249.     

Cyclopolymerization. XIII. Cyclopolymerization of Diallylaminomethylphenols

New highly substituted benzyl diallylamino monomers were prepared from substituted phenols by use of the Mannich reaction. Their ability to cyclopolymerize as the free phenols and the structures and properties of the pomers formed were investigated.