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Preparation, structure and stereodynamics of phosphorus-bridged calixarenes (1994)

Aleksiuk, Oleg ; Grynszpan, Flavio ; Biali, Silvio E.

Springer

Journal of inclusion phenomena and macrocyclic chemistry 19 (1994), S. 237-256

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ISSN: 1573-1111

Keywords: Calixarenes ; preparation ; conformation ; dynamics

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract The pyrolysis of several dialkylphosphate ester derivatives of calix[4]arenes yielded the same phosphorus bridged compound7. Under the pyrolytic conditions the phosphate groups may be cleaved or intermolecularly transferred. X-ray crystallography of the bridged calixarenes7 and8 shows that they exist in a chiral ‘flattened cone’ (fc) conformation. The bridged calixarenes undergo in solution a dynamic process with a barrier of about 10.1 kcal mol−1 for7 and8 and 13.1 kcal mol−1 for10, respectively. The dynamic processes result in enantiomerization of the systems. Pyrolysis of partially phosphorylated calix[6]arenes resulted in the formation of two products (11 and12), each consisting of two subunits of three proximal rings bridged by a phosphate group. The rotational barriers for11 and12 are 14.4 and 8.8 kcal mol−1, indicating that the bridged calix[6]arene system12 is appreciably more flexible than11.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00708985

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Crystal and molecular structures of dimesitylketene and bis(3,5-dibromo-2,4,6-trimethylphenyl)ketene. Intrinsic torsional angles and buttressing effects in 1,1-dimesitylvinyl propellers (1989)

Biali, Silvio E. ; Gozin, Michael ; Rappoport, Zvi

Chichester : Wiley-Blackwell

Journal of Physical Organic Chemistry 2 (1989), S. 271-280

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ISSN: 0894-3230

Keywords: Organic Chemistry ; Physical Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The crystal and molecular structures of dimesitylketene (1) and bis(3,5-dibromo-2,4,6-trimethylphenyl)ketene (2), the first free ketenes to be studied by X-ray diffraction, have been determined. The molecules of 1 and 2 have crystallographic C1 and C2 symmetry, respectively, and exist in a propeller conformation. Molecular mechanics calculations of 1 and 2 using a modification of Allinger's new allene parameters reproduce satisfactorily the structural parameters of the ketenes. The torsional angles of the aryl rings in 1 and 2 are similar (ca. 50°) and are regarded as ‘intrinsic’ values for a 1,1-dimesitylvinyl propeller. From the similarity in aryl torsional angles in 1 and 2 it is concluded that the buttressing effects in 2 (if any) are not markedly manifested in the structural parameters of 2.

Additional Material: 2 Ill.