Cyclic trimer

Boronic acids readily dehydrate at moderate temperatures (or over P4O10 at room temperature) to give trimeric cyclic anhydrides known as trialkyl(aryl)boroxines ... 

The NMR spectrum of 44 shows the upheld shift of H(2) and downfield shift of H(8) signals of 9-MeAd moieties, as compared with the parent system. This parameter constitutes a convenient diagnostic tool for monitoring the formation and structural assignment of analogous trimeric cyclic metallacali-xarene systems (92JA10647). 

Thiocarbonyl Compounds Aliphatic thials or thi-ones exist as trimeric, cyclic sulfides. Aralkyl thiones... 

Thiocarbonyl Compounds Aliphatic thials or thiones exist as trimeric, cyclic sulfides. Aralkyl thiones may exist either as monomers or trimers, whereas diaryl thiones, such as thiobenzophenone, exist only as monomers. The C=S group is less polar than the C=0 group and has a considerably weaker bond. In consequence, the band is not intense, and it falls at lower frequencies, where it is much more susceptible to coupling effects. Identification is therefore difficult and uncertain. 

Boroxines have trimeric, cyclic structures with planar rings of alternating boron and oxygen atoms. The alkyl groups are also in the plane of the ring. Boron can also be incorporated into numerous carbon ring systems. 

Ibbitson and Moore (IS) Infrared-dielectric measurements Linear dimers and trimers, cyclic tetramers... 

Under suitable reaction conditions, the dimer that is initially formed can react further to yield trimers of type 8b. It has not yet been possible to isolate these compounds, since they are always converted into the trimeric cyclic quinones 13a. Indeed, 8b is also converted into 13a by phenol oxidation under weakly basic conditions. The stability of conocurvone la is therefore due to the presence of hydroxy groups at position 2 of the monomer, which prevent cyclization. This cyclization via a symmetrical dimer of type 12b explains why none of the known hydro-xylated cyc/o-trimers (e. g. cyc/o-trijuglone 13b) display C3-symmetry with respect to the pen -hydroxy groups. 

Typical target assemblies of synkinesis are noncovalent dimers, charge-transfer complexes, hetero-dimers and -trimers, cyclic or helical oligomers, inherently asymmetrical or helical membranes in the form of vesicles, spheres, tubules, and rods, as well as macroscopic surface monolayers. Pores and domains in vesicle membranes and gaps of molecular size in surface monolayers are other synkinetic targets. They may function as receptors or reactive, enzyme-like surface clefts (Fendler, 1982 Fuhrhop 1982 Israelaehvili, 1992 Fuhrhop and Koning). 

When supramolecular polymers are treated with bulky stopper groups, they may form poly[2]rotaxane daisy chains [45-53]. Harada et al. [31] treated 6-p-aminoCiO-a-CD (40 mM) with 2M excess 2,4,6-trinitrobenzenesulfonic acid sodium salt (TNBS) as bulky stoppers in aqueous solutions. The resulting precipitate was found to be mainly a cyclic trimer by H NMR and TOF mass spectra. After purification of the crude product, the 2D ROESY spectrum of the cyclic trimer shows cross-peaks between phenyl protons close to an amino group and secondary hydroxyl groups (0(2)H). A trinitrophenyl group is found at the secondary hydroxyl group side. A proposed structure of a cyclic trimer (cyclic daisy chain) is shown in Fig. 3.12. Kaneda et al. [38] reported the preparation of cyclic di[2]rota-xane fashion constructed tail-to-tail by azobenzene derivatives of permethylated a-CDs and showed its computer-generated supramolecular structures (Fig. 3.13). Easton et al. [39] also reported the preparation of cyclic di[2]rotaxane constructed by stilbene-appended a-CDs in tail-to-tail fashion (Fig. 3.14). Kaneda et al. [40]... 

Trimeric cyclic condensation products of boronic acids - the boroxines - can be prepared and isolated. Their use instead of free boronic acids may help to overcome... 

The thermal degradation of PET (250-320 C) in an inert atmosphere gives carbon dioxide, acetaldehyde and methane, benzene, acetylene, 2-methyldioxane and water as the basic gaseous products, and these are released in considerable amounts. Terephthalic acid and oligomeric products (dimers, trimers, cyclic, tetra- and pentamers) are found among the poorly volatile products of the thermal degradation of PET [45, 53]. The half-life temperature for PET is 450 °C. 

Acetal homopolymer has a T oi about 175°C (347°F) and specific gravity of 1.41 g/cc acetal copolymer has a T oi about 165°C (329°F) and specific gravity of 1.42 [5]. Acetal polymers are synthesized entirely from formaldehyde directly, as noted earlier, or by copolymerization of the formaldehyde cyclic trimer (cyclic oligomer) trioxane and cyclic ethers. 

The synthesis of the trimeric cyclic saccharide antibiotic anthrobacilin A has been reported. The structure of antibiotic T01718B has been examined by synthesis of the epimers 26. ... 

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