Criss-cross structure

Because the criss-cross cycloaddition reaction is a sequence of two [3+2] cycloaddition steps, the reaction with a,co-diolefins offers a new entry into macro-molecular chemistry New types of polymers with interesting structures and prop erties can be synthesized [213, 214, 215] (equation 48)... 

Some examples of the lateral cyclization of suitable O-allyl and O-propargyl derivatives were discussed in CHEC-11(1996) <1996CHEC-II(8)747>. Thermal reaction of silyl diazoacetate 303 in xylene provides unspecific decomposition and a minor amount (about 2%) of a colorless solid can be precipitated with ether. The X-ray diffraction analysis identified the structure 305, which is a product of the lateral criss-cross cycloaddition of primarily formed azine 304 (Scheme 43) <2000T4139>. 

Figs. 1 and 2 depict the crystal structures of SQA [4-7]. The structure consists of parallel sheets of C4 squares, the sheets facing such that the directions of the 0-H...0 bonds criss-cross in each sheet, so as to minimize the repulsive effects and avoid steric interactions. The structure is thus essentially two-dimensional, with the C4 planes held together by weak van der Waals forces. 

However, the structures of the isolated products formed upon elimination of one molecule of HNCY are not the expected azomethine imines 7 (X = S) and 14 (X = S), respectively instead, the corresponding tautomers, enehydrazines 15 (X = S) and 16 (X = O) resulting from a 1,4-H shift are formed (Scheme 3) (93TH, OITH). At higher temperature, the criss-cross reaction is completely reversed to give the parent azoalkene 5. 

In the crossed linker model the odd and even nucleosomes form a double helical structure with the linker DNA criss-crossing the condensed fibre transversely. The double helical pitch is about 26 nm and the fibre diameter would depend on the length of the linker. A model in which a repeating unit of a trinucleosome forms a... 

Red phosphorus is made by heating the white form at 400° for several hours. As many as six modifications may exist, none of which is structurally characterized, with one possible exception, Red, crystalline, so-called Hittorf s phosphorus has been structurally characterized,4 but there is no evidence that this occurs in ordinary red phosphorus, though it may. It is made by a complex process involving slow heating in molten lead, followed by slow cooling. The structure is extremely complex, involving a criss-cross packing of infinite tubular chains of P atoms. 

CF3)2C(0-S02F)N]2 (5— 25%) (yields were variable and non-reproducible), Previous work on the formation of criss-cross cycloadducts (l,3- 2,4-addition) from hexafluoroacstone azine and electron-rich olefins has been extended. For example, the reaction of the azine with isobutene at ca. 70 "C (12—24 h) was shown to give initially a 1 1 adduct (91 %), which combined slowly (14 days) with isobutene at 20 "C to give the criss-cross adduct (75) quantitatively. The initial product was formulated as the Diels-Alder adduct (76), but others have shown unequivocally by JIT-ray structure analysis of crystalline material obtained in hi yield (85 %) (CFj)8 (CF3)s... 

Figure 3.45 Molecular structure of [Cu3iSei5(SeSiMe3)(PtBu2Me)i2] (20) (without PtBu2Me groups). Cu shaded spheres, Se black spheres P white spheres Si criss-cross pattern C small black spheres.

Black CuO is made by heating the elements (equation 22.99) or by thermal decomposition of solid Cu(N03)2 or CUCO3 (equation 22.104). Its structure consists of square planar CUO4 units linked by bridging O atoms into chains these lie in a criss-cross arrangement so that each O atom is in a distorted tetrahedral site. Figure 22.29b shows a... 

Three parapoxviruses of domestic animals occasionally cause infections in humans orf virus, normally causing a disease of sheep, pseudocowpox (synonyms milker s nodule, paravaccinia) and bovine pustular stomatitis viruses, normally causing diseases of cattle. Parapoxviruses (DNA viruses) are ovoid particles that vary from about 260 nm long by 160 nm wide for orf virus to 300 nm by 190 nm for pseudocowpox virus. A tubular, thread like structure 10-20 nm wide and perhaps 1000 nm long forms a criss-cross pattern on the surface of negatively stained parapoxvirus virions. 

Van Alphen claimed higher yields for this product (yield not reported). The structure and hence the criss-cross addition of the 1,3-dipolar type was confirmed. 

Above we saw a criss-cross addition of benzalazine with MA involving two 1,3-dipoles. A number of other reagents which fall in the class of 1,3-dipoles, e.g., diazoalkanes, nitrile oxides, and azides, also react with MA to yield intermediates with unique structural features. Many of these products are formed in good yields, thus increasing their importance as intermediates for the synthesis of other compounds, such as pharmaceuticals and monomers. 

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