Normalkoordinatenanalyse von Alkenen; Propen

Handschuh, Petra; Nagel, B.; Fruwert, J.

doi:10.1002/zfch.19810210515

Cited by 4 publications

(1 citation statement)

References 2 publications

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“…3090 and 2990 cm –1 , respectively, while the methine C–H stretching frequency is intermediate at ca. 3020 cm –1 . − The positions shift to lower frequencies for σ-vinyl groups associated with heavier atoms such as Si and Ge, whose spectra have been analyzed in detail. − For the specific example of HCl 2 Si-CHCH 2 , the methylene ν as and ν s modes are observed at 3071 and 2936 cm –1 , respectively, while the C–H stretch associated with the carbon bonded to silicon, Si-CH=, occurs at 2992 cm –1 (Table ). , Intense bands at 1595 and 1267 cm –1 are the CC stretch and the in-plane bending mode of the CH 2 group, respectively.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site

et al. 2017

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The structure and mechanism of the formation of sites which initiate ethylene polymerization in the atomically dispersed Phillips catalyst (Cr/ SiO 2 ) are two of the great unsolved mysteries of heterogeneous catalysis. After CO or C 2 H 4 reduction of silica-supported Cr VI ions to Cr II ions in the precatalyst, exposure to ethylene results in the formation of organoCr III sites that are capable of initiating polymerization without recourse to an external alkylating cocatalyst. In this work, a Phillips catalyst prepared, via sol−gel chemistry, as a mesoporous, optically transparent monolith was reduced with CO to the spectroscopically determined Cr II end point. Ethylene causes rapid reoxidation of these Cr II sites to Cr III , even at low temperatures. Solid-state 13 C CP-MAS NMR, IR, and Raman spectroscopies reveal that the resulting sites contain a vinyl ligand, described as (≡SiO) 2 Cr III −CHCH 2 although likely with a higher coordination number, which are capable of initiating polymerization. The formation of these vinyl sites is an incommensurate redox reaction involving one-electron oxidation of Cr II via ethylene disproportionation. The accompanying formation of organic radical intermediates and their characteristic reaction products suggest that the key step is homolysis of a Cr−ethyl bond. Plausible pathways for the initiation mechanism are suggested.

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Section: Resultsmentioning

confidence: 99%

Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site

et al. 2017

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Normalkoordinatenanalyse von Alkenen; Entwicklung eines gemeinsamen Kraftfeldes für Propen, Isobuten, trans‐But‐2‐en und cis‐But‐2‐en)

Handschuh¹,

Nage²,

Fruwert

1983

Zeitschrift fuer Chemie

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How Predictable Are IR Transition Moment Directions? Vibrational Transitions in Propene and Deuterated Propenes

et al. 1996

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Transition moment directions of mid-infrared transitions in four isotopomers of propene, CH2CHCH3, CH2CDCH3, CD2CHCD3, and CD2CDCD3, have been determined from linear dichroism spectra recorded in stretched polyethylene as solvent. The results were compared with expectations based on bond directions and with results of ab initio calculations at levels of approximations ranging up to CCSD/6-311G**. The former procedure is found to be unreliable, even for high frequency vibrations. With rare exceptions, the highest levels of ab initio theory agree with the experimental directions to within about ±20°, and for intense transitions, to within the experimental uncertainty of about ±(5−10)°.

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Normalkoordinatenanalyse von Alkenen; Propen

Cited by 4 publications

References 2 publications

Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site

Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site

Normalkoordinatenanalyse von Alkenen; Entwicklung eines gemeinsamen Kraftfeldes für Propen, Isobuten, trans‐But‐2‐en und cis‐But‐2‐en)

How Predictable Are IR Transition Moment Directions? Vibrational Transitions in Propene and Deuterated Propenes

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