Dimers, Trimers and Tetramers

Attempts to prepare the lower aggregates have led either to higher aggregates or to disproportionated products. Nonetheless, use of the extremely bulky terphenyl ligand Ar = C6H3-2,6-Dipp2 allowed the first dimer of the type Ar SnSnAr to be 

Sekiguchi, S. Nagase, The Chemistry of Organic Silicon Compounds, 

WlBERG, W. Niedermayer, H. Noth, M. Warchold, Z. Anorg. Allg. Chem., 2001, 627, 1717-1722. 

OrganosUicon Chemistry IV From Molecules to Mate- 

Matsumoto, K. Higuchi, Y. Hoshino, H. Koike, Y. Naoi, Y. Nagai, Chem. Commun., 1988, 1083-1084. 

---

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

Components Skydrol 500B tri-n-butyl- Skydrol LD tri-n-butyl- Dimers, trimers and tetramers Mixture of oligomers of linear... 

Cyclotriphosphazine Not reported Dimers, trimers and tetramers of cyclotriphosphazene Table 3-4... 

Wiped-Film Evaporator/02 Reactivation of Catalyst. In this technology [38], spent or-ganophosphine-modified rhodium catalyst is first concentrated in a wiped-film evaporator where most of the organophosphine is removed. The rhodium concentrate is contacted with air to break down phosphido bridges in rhodium clusters. This air treated concentrate may then be used as a catalyst precursor. This procedure is suitable in circumstances where most of the aldehyde dimers, trimers and tetramers are sufficiently volatile to be removed in a wiped-film evaporator. 

Oligomer. A low molecular weight polymer consisting of a few repeating. monomer units. Dimers, trimers, and tetramers are oligomers. 

Alfonso, Gotor, and coworkers have also affected diasteroeselective amplification from racemic libraries and achiral guests [4]. Mixtures of cyclohexyl-1,2-diamine (rac) and 2,6-diformyl-pyridine led to a mixture of homo- and heterochiral dimers, trimers, and tetramers (Fig. 5.4). The addition of Ba(II) slightly amplified the homochiral over the heterochiral dimer (1.6 1). Templafing with Cd(II) instead led to a preponderance of trimers, as evidence by ESI-MS. However, the large number of signals in the H and C NMR spectra indicated a heterochiral trimer. Amplification of the C -symmetric heterochiral trimer (Fig. 5.4) was confirmed by... 

Ekthawatchai S, Kamchonwongpaisan S, Kongsaeree P, Tamchompo B, Thebtaranonth Y, Yuthavong Y. (2001) C-16 artemisinin derivatives and their antimalarial and cytotoxic activities Synthesis of artemisinin monomers, dimers, trimers and tetramers by nucleophilic additions to artemisitene. JMed Chem 44 4688 695. 

Synthesis of dimers, trimers and tetramers of artemisinin (1) have been carried out in an attempt to improve the solubility and bioavailability of artemisinin (1) and consequently its antiproliferative activity. 

In polymerization an olefin can react with another olefin to generate dimers, trimers, and tetramers of the olefin. As a simple example, isobutylene reacts to give a highly branched Cg olefin. 

Monitoring of acetaldehyde-induced polymerization of catechin and epicatechin by HPLC-MS demonstrated the formation of several methylmethine-linked flavanol dimers, trimers, and tetramers. Detection of the intermediate ethanol adducts confirmed the mechanism postulated by Timberlake and Bridle, which involves protonation of acetaldehyde in the acidic medium, followed by nucleophilic attack of the resulting carbocation by the flavan unit. The ethanol adduct then loses a water molecule and gives a new carbocation that undergoes nucleophilic attack by another flavanol molecule. Four dimers (C6-C6, C8-C8, and C6-C8, R and S) were formed from each monomeric flavanol. When both epicatechin and catechin units were present, additional isomers containing both types of units were... 

Starting from 3,6-dimethylthieno[3,2-3]thiophene 71a and 3,6-dimethylselenolo[3,2-/ ]selenophene 71b <1994H(38)143>, their dimers, trimers, and tetramers, in which each thieno[3,2-3]thiophene unit and selenolosele-nophene unit was regularly connected at their a-positions, were satisfactorily synthesized (Scheme 4) <1996X471 >. 

Di-, tri- and tetrasaccharides These carbohydrates are dimers, trimers and tetramers of monosaccharides, and are formed from two, three or four monosaccharide molecules, with the elimination of one, two or three molecules of water. For example, sucrose is a disaccharide composed of two monosaccharides, glucose and fructose. 

Exposure-induced Reaction Products. Gel permeation chromatograms of EP, MRS, and EAP were measured before and after exposure at 20 /uC/cm2. The results are summerized in Figures 8 to 10. In the case of EP resist, shown in Figure 8, peaks 1, 2, and 3 represent epoxy novolac dimer, trimer, and tetramer, respectively. Peak 4 represents the main component of the poly(p-vinyl phenol) resin and peak 5 indicates the presence of exposure-induced high molecular weight components in the resin. 

Studies of the association of ethanol molecules in carbon tetrachloride solution have been made by infrared spectroscopy, permitting the evaluation of the enthalpies of formation of the dimer, trimer, and tetramer.76 The value for the tetramer, 22.56 kcal/mole, corresponds to 5.64 kcal/mole for the energy of the hydrogen bond (no correction for van der Waals attraction is made because the interaction with the solvent counteracts it). This value agrees moderately well with the value obtained above from the enthalpy of sublimation. The values for the dimer and the trimer, 5.09 and 10.18 kcal/mole, presumably correspond to one and two hydrogen bonds, respectively. 

Chloroplasts contain large 120- to 169-kb circular genomes encoding about 100 proteins (Chapter 23). A characteristic feature of most chloroplast DNA is the presence of long inverted repeat sequences (10,058 bp in the liverwort, 25,339 bp in tobacco).463 464 These are separated by 19,813 and 81,095 bp single copy regions in the liverwort and by similar sized regions in tobacco. Plastid DNA exists as a mixture of monomeric molecules with smaller amounts of dimers, trimers, and tetramers.464... 

Mol%. N-Butyl-p-xylene. Sum of dimer, trimer, and tetramer of isobutylene. Octyl-p-xylene. Di-p-xylylmethane. The reaction was performed at 303 K for 30 min. p-Xylene, 0.28 mol isobutylene, 0.37 mmol min catalyst, 0.45 g. 

More recently Okawara, Hotta and Shimura (48) hydrolyzed the more reactive dichlorodiethoxysilane in a benzene-pyridine mixture, isolated the corresponding linear dimer, tetramer, and pentamer, and obtained evidence for the presence of smaller amounts of the cyclic dimer, trimer and tetramer. The partial hydrolysis of tetramethoxy-, tetra-ethoxy-, tetra-n-butoxy- and tetra-iso-pentoxysilane in alcohol-water mixtures was studied by Takatani (83) and the following products isolated ... 

---