Trimerization intermolecular

At low temperature there are two resolved peaks for the methyl substituents, but the observed splitting is reduced on increasing temperature. X-ray diffraction results show that the unit cell consists of a cyclic trimeric arrangement to 3,5-di-methylpyrazole molecules. Within this trimer, the 3,5-dimethylpyrazole molecules have C2v symmetry, the cyclic trimer has threefold symmetry, and the hydrogen involved in the tautomeric process is refined with half occupancy. These results indicate that, at room temperature, a trimer-trimer intermolecular tau-tomerism takes place in 3,5-dimethylpyrazole. In contrast, for pyrazole, the N-H... 

Single-Stack Acceptor. Simple charge-transfer salts formed from the planar acceptor TCNQ have a stacked arrangement with the TCNQ units facing each other (intermolecular distances of ca 0.3 nm (- 3). Complex salts of TCNQ such as TEA(TCNQ)2 consist of stacks of parallel TCNQ molecules, with cation sites between the stacks (17). The interatomic distance between TCNQ units is not always uniform in these salts, and formation of TCNQ dimers (as in TEA(TCNQ)2) and trimers (as in Cs2(TCNQ)Q can lead to complex crystal stmctures for the chainlike salts. 

Lipase-catalyzed intermolecular condensation of diacids with diols results in a mixture of macrocycUc lactones and liuear oligomers. Interestingly, the reaction temperature has a strong effect on the product distribution. The condensation of a,(D-diacids with a,(D-dialcohols catalyzed by Candida glindracea or Pseudomonas sp. Upases leads to macrocycUc lactones at temperatures between 55 and 75°C (91), but at lower temperatures (<45°C) the formation of oligomeric esters predorninates. Optically active trimers and pentamers can be produced at room temperature by PPL or Chromobacterium viscosum Upase-catalyzed condensation of bis (2,2,2-trichloroethyl) (+)-3-meth5ladipate and 1,6-hexanediol (92). 

Malacria and coworkers [274] used an intermolecular trimerization of alkynes to gain efficient access to the skeleton of the phyllocladane family. Thus, the Co-cata-lyzed reaction of the polyunsaturated precursor 6/4-4 gave 6/4-5 in 42% yield. Here, six new carbon-carbon bonds and four stereogenic centers are formed. The first step is formation of the cyclopentane derivative 6/4-6 by a Co-catalyzed Conia-ene-type reaction [275] which, on addition o f his( Iri me ill y I si ly 1) e thy ne (btmse), led to the benzocyclobutenes 6/4-7 (Scheme 6/4.2). The reaction is terminated by the addition of dppe and heating to reflux in decane to give the desired products 6/4-5 by an electrocyclic ring opening, followed by [4+2] cycloaddition. 

Chiral methylzinc aminoalkoxides 146a-c were obtained from the reaction of ZnMe2 with aminoalcohols, having chiral centers in their carbon backbones (Scheme 92).211 The methylzinc aminoalkoxides crystallize dimeric and trimeric with the formation of intermolecular zinc-oxygen bonds and creation of additional chiral centers. 

The preparation of single isomers for methanol dimer, trimer, and presumably tetramer [16] in a supersonic jet expansion contrasts the structural diversity that can be prepared and manipulated in cryogenic matrices [34]. It underscores the ability of supersonic jet expansions to funnel all intermolecular isomers down to the global minimum, if there are no major barriers to overcome on the way. 

Interestingly, the formation of dimers and trimers by intermolecular aminolysis has also been observed in concentrated solution (>1%) of the mono-bactam aztreonam (5.8) [124],... 

Transition metal-catalyzed intermolecular [2 + 2 + 2] cyclotrimerization of alkynes to benzene derivatives has been extensively studied. In this section, the focus is on the cyclo-trimerizations of the substrates bearing three independent unsaturated bond components. The key issue with this type of process usually involves the challenge of controlling regioselectivity [1—1]. However, 1,3,5-trisubstituted benzene 44 can be obtained as the sole product in good yield when 3-butyn-2-one 43 is used as the substrate for the cyclotrimerization catalyzed by Rh2(pfb)4 (pfb=perfluorobutyrate) in the presence of EtsSiH under a CO atmosphere (Eq. 11) [30]. 

Steps creating more than two new connections are to be avoided since the probability of dimer, trimer. .. polymer formation increases rapidly with the number of connections to be made, especially if these connections are all intermolecular. The first step of path b in Figure 3 requires four connections, three of which are intermolecular. Paths c and A (Figure 3) are somewhat preferable since three connections are made in one step, one of which is intermolecular. All other steps in Figures 3 and 4 create only two new connections, only one of which is intermolecular in case of ring formation. 

The SCF-MI BSSE free method does not take into account dispersion forces, connected to electronic intermolecular correlation effects. By using the SCF-MI wave function as a starting point, however, a non orthogonal BSSE free Cl procedure can be developed. This approach was applied to compute intermolecular interactions in water dimer and trimer the resulting ab initio values were used to generate a new NCC-like potential (Niesar et al, 1990). Molecular dynamics simulation of liquid water were performed and satisfactory results obtained (Raimondi et al, 1997). 

Intermolecular cyclocondensation of anthranilic acid by heating with polyphosphoric acid gave a mixture of products from which the trimer (702) having the title structure was isolated (84MI6). 

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