Partitioning of pi-electrons in rings of polycyclic benzenoid hydrocarbons. 2.1. Catacondensed coronoids

Various types of coronoids are examined for finding the partitioning of pi-electrons in individual benzenoid rings of polycyclic aromatic hydrocarbons. A class of catacondensed coronoids, namely fibonacenes, has four pi-electrons in every ring. Most other catacondensed coronoids have more than one type of benzenoid ring, each type with a different partition, but the average per ring is always four pi-electrons. For the class of catacondensed coronoids that have an acenic hole, simple quadratic equations in terms of their number R of rings exist for the partitions of pi-electrons in the three possible ring types.     

The splitting of d-orbitals in less symmetrical molecules containing a cyclopentadienyl ligand

The splitting of d orbitals in an electrostatic field due to a cyclopentadienyl ring and four ligands arranged at the corners of a square is investigated. It is shown that, although the symmetry of the molecule is C _s, the effective symmetry for the d ¹ and d ² systems is G _4v. The linear combinations for the d ² system in C _1v symmetry are given and the matrix elements for the secular determinant are listed. The results may be applied to a discussion of the bonding in tricarbonyl--cyclopentadienylethyl-molybdenum, whose structure is related to the idealized model considered.

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Zusammenfassung Bei der Aufspaltung der d-ZustÄnde in einem elektrostatischen Feld, welches erstens von einem Cyclopentadienyl-Ring und zweitens von vier an den Ecken eines Quadrates angeordneten Liganden hervorgerufen wird, ist die effektive Symmetrie D _4v — trotz der C _s-Symmetrie des Moleküls. Für das d ²-System werden die Linearkombinationen der Slaterdeterminanten und die Elemente der Störmatrix angegeben. Das Ganze lÄ\t sich z. B. auf die Diskussion von Tricarbonyl--cyclopentadienylÄthylmolybdÄn anwenden, dessen Struktur der des behandelten Modells sehr Ähnlich ist.

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Résumé La décomposition des orbitales d dans le champ d'un groupe cyclopentadiényl et de quatre ligandes arrangés en carré est étudiée. Pour les systèmes d ¹ et d ², la symétrie effective est C _4v , celle de la molécule n'étant que C _s. Pour d ², on donne les combinaisons linéaires adapté à la symétrie C _4v , et la matrice des énergie perturbatrices. Les résultats s'appliquent à la discussion du cyclopentadiényl-éthyl-molybdène tricarbonyle dont la structure ressemble le modèle étudié.

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On leave from: Institut Rudjer Bokovi, Zagreb, Yugoslavia     

Maximum overlap hybridization in cyclopropane and some related molecules

The hybridization in cyclopropane, spiropentane, nortricyclene and 1,1 -dimethyl cyclopropane is calculated applying the criterion of maximum overlap. The s-p content in the general hybrids is found to be sensitive to changes in the interorbital angle _ij. The results give information about the strain associated with bent bonds and its delocalization. The application also allows calculations of skeletal angles, such as C₁ C₂ C₃ in nortricyclene, which determine the geometry of the molecule.

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Zusammenfassung Die Hybridisierung in Cyclopropan, Spiropentan, Nortricyclen und 1,1-Dimethylcyclopropan wird mittels des Kriteriums der maximalen Überlappung berechnet. Dabei findet man eine starke Abhängigkeit des s- (p-) Anteils von dem von den Orbitalen gebildeten Winkel _ij. Daraus lassen sich Aussagen über die Spannung in Systemen mit anomalen Bindungswinkeln gewinnen. Der C₁ C₂ C₃-Winkel in Nortricyclen wird bestimmt.

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Résumé Nous calculons l'hybridation dans cyclopropane, spiropentane, nortricycléne et 1,1-diméthyl-cyclopropane à l'aide du critère de recouvrement maximal. Le rapport s/p dans les hybrides est sensible aux angles _ij entre les orbitales. Les résultats donnent des informations sur la tension dans les liaisons courbées. On peut aussi calculer des angles de squelette, comme C₁ C₂ C₃ dans le nortricyclène.

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Academic year 1964/65 at: Department of Chemistry, University of Ottawa, Ottawa, Ont., Canada.     

Alkylaluminum activator effects on polyethylene branching using a N,N′‐nickel precatalyst appended with bulky 4,4′‐dimethoxybenzhydryl groups

Ten unsymmetrical N,N'‐bis (imino) acenaphthene‐nickel (II) halide complexes, [1‐[2,6‐{(4‐MeOC₆H₄)₂CH}₂–4‐MeC₆H₂N]‐2‐(ArN)C₂C₁₀H₆]NiX₂, each appended with one N‐2,6‐bis(4,4'‐dimethoxybenzhydryl)‐4‐methylphenyl group, have been synthesized and characterized. The molecular structures of Ni1 , Ni3 , Ni5 and Ni6 highlight the variation in steric protection afforded by the inequivalent N‐aryl groups; a distorted tetrahedral geometry is conferred about each nickel center. On activation with diethylaluminum chloride (Et₂AlCl) or methylaluminoxane (MAO), all complexes showed high activity at 30°C for the polymerization of ethylene with the least bulky bromide precatalysts ( Ni1 and Ni4 ), generally the most productive, forming polyethylenes with narrow dispersities [M_w/M_n: < 3.4 (Et₂AlCl), < 4.1 (MAO)] and various levels of branching. Significantly, this level of branching can be influenced by the type of co‐catalyst employed, with Et₂AlCl having a predilection towards polymers displaying significantly higher branching contents than with MAO [T_m: 33.0–82.5°C (Et₂AlCl) vs. 117.9–119.4°C (MAO)]. On the other hand, the molecular weights of the materials obtained with each co‐catalyst were high and, in some cases, entering the ultra‐high molecular weight range [M_w range: 6.8–12.2 × 10⁵ g mol^?1 (Et₂AlCl), 7.2–10.9 × 10⁵ g mol^?1 (MAO)]. Furthermore, good tensile strength (ε_b up to 553.5%) and elastic recovery (up to 84%) have been displayed by selected more branched polymers highlighting their elastomeric properties.     

Exceptionally high molecular weight linear polyethylene by using N,N,N′‐Co catalysts appended with a N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group

The bis(arylimino)pyridines, 2‐[CMeN{2,6‐{(4‐FC₆H₄)₂CH}₂–4‐NO₂}]‐6‐(CMeNAr)C₅H₃N (Ar = 2,6‐Me₂C₆H₃ L1 , 2,6‐Et₂C₆H₃ L2 , 2,6‐i‐Pr₂C₆H₃ L3 , 2,4,6‐Me₃C₆H₂ L4 , 2,6‐Et₂–4‐MeC₆H₂ L5 ), each containing one N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group, have been synthesized by two successive condensation reactions from 2,6‐diacetylpyridine. Their subsequent treatment with anhydrous cobalt (II) chloride gave the corresponding N,N,N′‐CoCl₂ chelates, Co1 – Co5 , in excellent yield. All five complexes have been characterized by ¹H/¹⁹F NMR and IR spectroscopy as well as by elemental analysis. In addition, the molecular structures of Co1 and Co3 have been determined and help to emphasize the differences in steric properties imposed by the inequivalent N‐aryl groups; distorted square pyramidal geometries are adopted by each complex. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), precatalyts Co1 – Co5 collectively exhibited very high activities for ethylene polymerization with 2,6‐dimethyl‐substituted Co1 the most active (up to 1.1 × 10⁷ g (PE) mol^?1 (Co) h^?1); the MAO systems were generally more productive. Linear polyethylenes of exceptionally high molecular weight (M_w up to 1.3 × 10⁶ g mol^?1) were obtained in all cases with the range in dispersities exhibited using MAO as co‐catalyst noticeably narrower than with MMAO [M_w/M_n: 3.55–4.77 ( Co1 – Co5 /MAO) vs. 2.85–12.85 ( Co1 – Co5 /MMAO)]. Significantly, the molecular weights of the polymers generated using this class of cobalt catalyst are higher than any literature values reported to date using related N,N,N‐bis (arylimino)pyridine‐cobalt catalysts.     

Causal loop diagrams as a de-escalation technique

Escalation of commitment, the tendency of decision makers to keep on investing in losing courses of action, has been shown to be a costly decision bias that affects many areas of decision making. Even though escalation is a widely studied phenomenon, there has been comparatively little research on how to avoid this bias. The present study focuses on de-escalation of commitment and proposes that causal loop diagrams (CLDs) can help to decrease escalating commitment to a failing course of action. By means of an experiment, this study shows that using a CLD decreases escalation tendencies.