Formation by intermolecular

Ultrasonic interferometry has been used to study ternary mixtures of dimethylsulphoxide, phenol and o-cresol in carbon tetrachloride. The variation of adiabatic compressibility and intermolecular free length with the concentration suggested the occurrence of complex formation by intermolecular hydrogen bonding, which was confirmed from IR spectra [90]. 

The most important synthetic asset of the xanthate transfer methodology lies in its ability to induce carbon-carbon bond formation by intermolecular addition to unactivated olefins. Again, this is possible because the initial radical has a comparatively long lifetime in the medium. Unhindered, terminal olefins are the best substrates, but other types of olefins (especially strained or lacking allylic hydrogens) may be made to react in some cases. Three examples of additions are collected in Scheme 18. The first involves formation and capture of a trifluoroacetonyl radical, a species hitherto only studied by mass spectrometry but never employed in synthesis [34a]. This reaction represents a convenient route to various, otherwise inaccessible, trifluoromethyl ketones. In the second example a tetrazolylmethyl radical, also a previously unused intermediate, is intercepted by a latent allyl glycine [34b]. The amino acid moiety may be part of the xanthate partner as highlighted by the last example [34c]. 

Active species in the polymerization of cyclic acetals undergo fast isomerization. This results in chain transfer to polymer, that is, formation (by intramolecular reaction) of cyclic structures or formation (by intermolecular reaction) of branched oxonium ions, followed by exchange of the linear fragments of the chain (transacetaiization) (cf. Scheme 18). 

Complexation of this type often result in inter- or intramolecular chelate bridging, as shown in Eqs. (1) and (2), respectively. In complex formation by intermolecular chelate bridging, the resulting macromolecule-metal complex is often insoluble in water and in organic solvents. Furthermore, the coordination structure is unclear. Intramolecular macromolecule—metal complexes, however, are usually soluble either in water or in organic solvents. The macromolecule-metal complexes with uniform structures are formed when a metal ion, such as a cupric and a ferric ion, with a labile ligand... 

It should be noted that fibres with high heat resistance can be also obtained by treating modified fibres of type 6, containing hydroxyimino groups, with Fe3 and Ni2+ salts, which is again explained by the formation of intermolecular chemical bonds. 

These results made it possible to arrive at a sufficiently well-grounded conclusion that the effect of raised heat resistance caused by the formation of intermolecular chemical bonds is not very significant, and that the usually observed considerable increase of heat resistance of PAN fibres as a result of a crosslinkage with bifunctional compounds, is caused not by the formation of intermolecular chemical bonds, as it has usually been thought45, 46, but by cyclization reactions of the nitrile groups with the formation of naphthyridine cycles47. ... 

This mechanism of initiation is confirmed by the fact that, when the PAN-PEO block copolymer is treated with diisocyanate in benzene in the presence of pyridine acting as catalyst, copolymers lose their solubility in DMF as a result of the formation of intermolecular chemical bonds75). 

The formation of ECC is not only an extension of a portion of the macromolecule but also a mutual orientational ordering of these portions belonging to different molecules (intermolecular crystallization), as a result of which the structure of ECC is similar to that of a nematic liquid crystal. After the melt is supercooled below the melting temperature, the processes of mutual orientation related to the displacement of molecules virtually cannot occur because the viscosity of the system drastically increases and the chain mobility decreases. Hence, the state of one-dimensional orientational order should be already attained in the melt. During crystallization this ordering ensures the aggregation of extended portions to crystals of the ECC type fixed by intermolecular interactons on cooling. 

Examples of the intermolecular C-P bond formation by means of radical phosphonation and phosphination have been achieved by reaction of aryl halides with trialkyl phosphites and chlorodiphenylphosphine, respectively, in the presence of (TMSlsSiH under standard radical conditions. The phosphonation reaction (Reaction 71) worked well either under UV irradiation at room temperature or in refluxing toluene. The radical phosphina-tion (Reaction 72) required pyridine in boiling benzene for 20 h. Phosphinated products were handled as phosphine sulfides. Scheme 15 shows the reaction mechanism for the phosphination procedure that involves in situ formation of tetraphenylbiphosphine. This approach has also been extended to the phosphination of alkyl halides and sequential radical cyclization/phosphination reaction. ... 

In order to safely identify k0 with intramolecular carbenic reactions (e.g., k and the formation of alkene 4 in Scheme 1), product analysis should demonstrate that the yield of intramolecular products exceeds 90%, while dimer, azine, and solvent-derived (intermolecular) carbene products should be absent or minimal. If these conditions are not met, mechanistic interpretation is often ambiguous, a result that is well illustrated by the saga of benzylchlorocarbene (see below, Section IV.C). Less desirably, k0 can be corrected for competitive intermolecular carbenic reactions. Bimolecular reactions like dimerization and azine formation can be minimized by working at low carbene precursor concentrations, and careful experimental practice should include quantitative product studies at several precursor concentrations to highlight potential product contamination by intermolecular processes. 

Helical columns of bifunctional ureidotriazines have also been created in water.40 In this solvent the aromatic cores of compound 39 stack and create a hydrophobic environment that favors the formation of intermolecular hydrogen bonds. The chiral side chains can express their chirality within the columnar polymer because of the helicity generated by the backbone. In contrast, for monofunctional 68 water interferes with the hydrogen bonding and 68 does not stack to form a column. As a consequence the chiral side chain does not express its chirality in the aromatic system. For 39, the bifunctional nature allows for a high local concentration of stacking units. A comparison might be made here to the individual DNA bases that also do not dimerize and stack in water, unless they are connected to a polymer backbone. 

X-ray diffraction analysis of P.R.177 disclosed a twisting of the two an-thraquinone units by 75° relative to each other. This allows optimum formation of intermolecular hydrogen bonds [8],... 

Exciplexes are the excited-state complexes that can be formed by partners of different origin [33]. Their formation on intermolecular interaction can provide a fluorescence reporting signal [28, 34]. The advantage of their formation in high-concentration matrices is the large Stokes shift that, as we will see below, can prohibit the homo-FRET. 

Aqueous NaOH (50%, 80 ml) is added to a vigorously stirred solution of the glycoside (5 mmol) and TBA-Br (0.16 g, 0.5 mmol) in CH2Br2 (50 g) at 60-65°C. The reaction is monitored by TLC and, on completion, the organic phase is separated, washed well with H20, dried (MgS04), and evaporated to yield the acetals (replacement of CH2Br2 by CH2Cl2 and reaction temperatures of 25-35°C allows the formation of intermolecular acetals, but not intramolecular acetals). 

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],... 

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