Diels–Alder reactions of 3,6-disubstituted 1,2,4,5-tetrazines. Synthesis and X-ray crystal structures of diazafluoranthene derivatives

2009 ◽  
Vol 7 (10) ◽  
pp. 2082 ◽  
Author(s):  
Nelli Rahanyan ◽  
Anthony Linden ◽  
Kim K. Baldridge ◽  
Jay S. Siegel
Keyword(s):  
Crystal Structures ◽  
Diels Alder ◽  
X Ray

X-ray Structural Analysis for the Prediction on the Nature of the Retro Diels - Alder Pathway: Concerted or Stepwise. Structural Studies on Nitrosobenzene Cycloadducts

2009 ◽  
Vol 62 (12) ◽  
pp. 1695 ◽  
Author(s):  
Jesse Roth-Barton ◽  
Jonathan M. White
Keyword(s):  
Structural Analysis ◽  
Crystal Structures ◽  
Diels Alder ◽  
Structure Parameters ◽  
Structural Studies ◽  
Structural Effects ◽  
X Ray ◽  
Early Stages ◽  
Clear Differentiation

Crystal structures of nitrosobenzene cycloadducts 5–7 reveal structural effects consistent with the early stages of the retro Diels–Alder fragmentation. There is a clear differentiation between the structure parameters of cycloadduct 5, which reacts by a concerted synchronous pathway and that of cycloadduct 6, which must react by a two-step pathway. Based on these data, cycloadduct 7 is predicted to react by a highly asynchronous or two-step pathway.

Photochemistry of Hemicyclone Diels-Alder Adducts of Substituted Benzoquinones

1986 ◽  
Vol 39 (10) ◽  
pp. 1537 ◽  
Author(s):  
JM Coxon ◽  
MJ Oconnell ◽  
PJ Steel
Keyword(s):  
Crystal Structures ◽  
Diels Alder ◽  
X Ray

The Diels -Alder reactions between hemicyclone and a number of substituted benzoquinones are reported. Photolysis of the products produces pentacyclo [5,4,0,02,6,03,10,05,9] undecane derivatives and/or 2- oxapentacyclo [6,4,0,01,4,03,7,05,9] dodecane derivatives depending on the substituents. X-ray crystal structures of oxetan (8) and cyanohydrin (33) are also reported.

The X-Ray Crystal Structures of a 1,9- and a 7,8-Diels-Alder monoadduct of C70

1995 ◽  
Vol 78 (2) ◽  
pp. 344-354 ◽  
Author(s):  
Paul Seiler ◽  
Andreas Herrmann ◽  
Fran�ois Diederich
Keyword(s):  
Crystal Structures ◽  
Diels Alder ◽  
X Ray

The synthesis and reactivity of α-oxosulfines

1989 ◽  
Vol 67 (3) ◽  
pp. 369-381 ◽  
Author(s):  
Ian W. J. Still ◽  
Donald V. Frazer ◽  
Donna K. T. Hutchinson ◽  
Jeffery F. Sawyer
Keyword(s):  
Crystal Structures ◽  
Reaction Pathway ◽  
Reactive Intermediates ◽  
Crystallographic Analysis ◽  
Diels Alder ◽  
Electrophilic Addition ◽  
X Ray ◽  
Major Reaction ◽  
Sulfenic Acids

Thiochroman-4-one and cyclohexanone have been converted into the corresponding α-oxosulfines and the behaviour of these reactive intermediates with a range of alkenes and alkynes has been examined. In contrast to some earlier work, the major reaction pathway does not involve formation of the initially expected Diels–Alder adducts but instead a series of adducts involving electrophilic addition to the alkene or alkyne, with concomitant deoxygenation and incorporation of chlorine. The structures of these adducts have been determined by the usual spectroscopic means and, in two representative cases, by X-ray crystallographic analysis. The crystal structures, which include unusual features such as relatively short S … O nonbonding contacts, are discussed in detail. Keywords: (α-oxo)sulfines, sulfenic acids, X-ray analysis, electrophilic addition.

Transmission electron microscope studies in special ceramics

1978 ◽  
Vol 36 (1) ◽  
pp. 268-269
Author(s):  
A. Zangvil ◽  
L.J. Gauckler ◽  
G. Schneider ◽  
M. Rühle
Keyword(s):  
Phase Diagrams ◽  
Crystal Structures ◽  
Thin Foil ◽  
Limited Extent ◽  
Complex Materials ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Lattice Resolution

The use of high temperature special ceramics which are usually complex materials based on oxides, nitrides, carbides and borides of silicon and aluminum, is critically dependent on their thermomechanical and other physical properties. The investigations of the phase diagrams, crystal structures and microstructural features are essential for better understanding of the macro-properties. Phase diagrams and crystal structures have been studied mainly by X-ray diffraction (XRD). Transmission electron microscopy (TEM) has contributed to this field to a very limited extent; it has been used more extensively in the study of microstructure, phase transformations and lattice defects. Often only TEM can give solutions to numerous problems in the above fields, since the various phases exist in extremely fine grains and subgrain structures; single crystals of appreciable size are often not available. Examples with some of our experimental results from two multicomponent systems are presented here. The standard ion thinning technique was used for the preparation of thin foil samples, which were then investigated with JEOL 200A and Siemens ELMISKOP 102 (for the lattice resolution work) electron microscopes.

Crystal Structures of Fragments D and Double-D from Fibrinogen and Fibrin

1999 ◽  
Vol 82 (08) ◽  
pp. 271-276 ◽  
Author(s):  
Glen Spraggon ◽  
Stephen Everse ◽  
Russell Doolittle
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Crystal Structures ◽  
Structure And Function ◽  
X Ray ◽  
Long Period ◽  
And Function

IntroductionAfter a long period of anticipation,1 the last two years have witnessed the first high-resolution x-ray structures of fragments from fibrinogen and fibrin.2-7 The results confirmed many aspects of fibrinogen structure and function that had previously been inferred from electron microscopy and biochemistry and revealed some unexpected features. Several matters have remained stubbornly unsettled, however, and much more work remains to be done. Here, we review several of the most significant findings that have accompanied the new x-ray structures and discuss some of the problems of the fibrinogen-fibrin conversion that remain unresolved. * Abbreviations: GPR—Gly-Pro-Arg-derivatives; GPRPam—Gly-Pro-Arg-Pro-amide; GHRPam—Gly-His-Arg-Pro-amide

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