Intermolecular processes

Li has reported that cationic gold(III) complexes also catalyze the intermolecular hydroamination of terminal alkynes with aniline derivatives [17]. For example, reaction of a neat 1 1.5 mixture of phenylacetylene and aniline catalyzed by AUCI3 at room temperature followed by reduction with sodium borohydride led to isolation 

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Ring closures considered under this heading are essentially intramolecular cyclodehydrations (or their equivalent) and bear many resemblances to the intermolecular processes discussed in Section 4.03.3. They are more suited to the synthesis of ring-fused systems because of the ease of access to the requisite precursors. 

In another fluxional process involving ruthenium instead of rhodium, it has been shown that the rate-controlling step is the complex dissociation and that the ligand exchanges between the two annular nitrogen atoms by an intermolecular process. 

The above value for R = H corresponds to an intermolecular process, either assisted by the solvent (in solution) or by other NH-pyrazole molecules (in solution and in the solid state) while metal migrations are probably intramolecular (the bigger the metal, the easier) and those of COR correspond (for R = NHR ) to a dissociation-recombination mechanism. Minkin [quoted in 96MI(15)339] suggests that a tautomeric process should... 

The N-azo compound 5 thus obtained can isomerize by an intermolecular process to give the C-azo derivative " ... 

The intermolecular process is employed almost exclusively for the preparation of 1H-azepines and in most cases involves addition of a singlet nitrene133 to the arene to give, initially, an unstable 7-azabicyclo[4.1.0]hepta-2,4-diene (benzaziridine) intermediate, e. g. 1, which undergoes an electrocyclic ring opening to the l//-azepine, e. g. 2. 

Non-heteroatom-stabilised Fischer carbene complexes also react with alkenes to give mixtures of olefin metathesis products and cyclopropane derivatives which are frequently the minor reaction products [19]. Furthermore, non-heteroatom-stabilised vinylcarbene complexes, generated in situ by reaction of an alkoxy- or aminocarbene complex with an alkyne, are able to react with different types of alkenes in an intramolecular or intermolecular process to produce bicyclic compounds containing a cyclopropane ring [20]. 

The two main reasons for studying the reversible reaction (3) were (a) to complete the picture of the Koch reaction in terms of quantitative information and (b) to set up a scale of reactivity towards a neutral nucleophile for carbonium ions of different structure. The first item is important from a practical point of view because there are reactions competing with the carbonylation step (3), which can be divided into intramolecular and intermolecular processes. Rearrangement of the intermediate alkylcarbonium ion, e.g. 

When HCl salts of arylalkylamines are heated at 200-300°C, migration occurs. This is called the Hofmann-Martius reaction. It is an intermolecular reaction, since crossing is found. For example, methylanilinium bromide gave not only the normal products o- and p-toluidine but also aniline and di- and trimethylanilines." As would be expected for an intermolecular process, there is isomerization when R is primary. 

Imino esters with any or all of the three groups being alkyl also rearrange, but they require catalysis by H2SO4 or a trace of methyl iodide or methyl sulfate. The mechanism is different, involving an intermolecular process.This is also true for derivatives for formamide (Ar = H). 

As shown in the preceding examples, although intramolecular Pd-catalyzed poly-cyclization is a well-established procedure, some few examples exist of polycycliza-tions where the first step is an intermolecular process. In this respect, the Pd°-cata-lyzed domino reaction of allenes in the presences of iodobenzene reported by Tanaka and coworkers [40] is an intriguing transformation. As an example the Pd-catalyzed reaction of 6/1-60 in the presence of iodobenzene led to 6/1-61 in 49% yield, allowing the formation of three rings in one sequence (Scheme 6/1.14). 

Fluorescence and Main Intermolecular Processes Affecting Fluorescence Properties 190... 

Fig. 1 Jablonski diagram of energy level for describing processes absorption, fluorescence and phosphorescence in complex molecules where kf and /c arc the radiative and nonradiative rates of fluorescence, respectively, kj and kTnr are the radiative and nonradiative rates of phosphorescence, respectively, k-lsc is the interconversion rate, and kmt is the rate of intermolecular processes Av denotes the Stokes shift of fluorescence...

As seen from (1) and (2), intermolecular processes may reduce essentially the lifetime and the fluorescence quantum yield. Hence, controlling the changes of these characteristics, we can monitor their occurrence and determine some characteristics of intermolecular reactions. Such processes can involve other particles, when they interact directly with the fluorophore (bimolecular reactions) or participate (as energy acceptors) in deactivation of S) state, owing to nonradiative or radiative energy transfer. Table 1 gives the main known intermolecular reactions and interactions, which can be divided into four groups ... 

Table 1 Classification of the main intermolecular processes in solutions of organic molecules...

The findings contrasted with common conceptions that intramolecular reactions require dilution to restrict competing intermolecular processes. Indeed, under the optimal conditions, the temperature (385 °C) was nearly 150 °C higher than that normally employed and the reaction time was less than 1 min instead of many minutes. The yield was 86% and the process was performed continuously under the newly established conditions (Scheme 2.9) [45]. 

A slight increase in the turbidity upon heating of aqueous solutions of the s-fractions of the NVCl/NVIAz-copolymers obtained from the feeds with initial comonomer molar ratios of 75 25 (Tcp 65 °C) and 80 20 (Tcp 66 °C) could be due to the micellization phenomena, although the absence of DSC peaks over the same temperature range testified to the non-cooperative character of the process. This could indicate that the chains of these s-type copolymers had, nevertheless, a certain amount of oligoNVCl blocks non-buried by the hydrophilic microenvironment sufficiently well and thus capable of participating in the hydrophobically-induced associative intermolecular processes at elevated temperatures. At the same time, the sequence of monomer units in the s-copolymers obtained from the feeds with the initial comonomer ratios of 85 15 and 90 10 (mole/mole) corresponded to the block-copolymers of another type. The basis for such a conclusion is the lack of macroscopic heat-induced phase separation at elevated temperatures (Fig. 3 a and b) and, simultaneously, the transi-... 

No evidence has yet been obtained in support of such a mechanism in the present context, and it is unlikely that it has general applicability. NMR measurements for example provide no support for a conformational change of PCu(I) on association with Cr(III) complexes (13). Moreover it has in one case been demonstrated that ket in (4) is not dependent on ionic strength, consistant with an intramolecular as opposed to intermolecular process (11). Although caution is required, particularly as isolated examples of (7) - (8) may exist, the invoking of such a mechanism seems to be a case of looking for greater complexity than may actually exist. A reasonable stance, and one which we have adopted, is that discussion should proceed in terms of (5) -(6) until evidence in support of (7) - (8) is obtained. 

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. 

Thus, within the approximations on which scheme (1) is based, the yield Y/( 1 + Y) of ring product is solely determined by the value of the initial monomer concentration relative to the kintra/kdim ratio, which Stoll et al. termed the cyclisation constant C. C has units of mol 1 1 and represents the monomer concentration at which intra- and intermolecular processes occur at the same rate. That Stoll et al. disregarded the fact that two monomer units are used up in the intermolecular condensation, as well as that the monomer disappears by reaction with functional groups at the ends of polymer chains was pointed out by Morawetz and Goodman (1970), who proposed an alternative approximate solution to the problem, as based on... 

It is remarkable that in the same year, 1934, two independent approaches, those of Stoll et al. and of Kuhn, led to the definition of two quantities which are conceptually quite similar and can be practically identical in many actual cases. In either case the intramolecular reaction is compared to a corresponding intermolecular process. This is the dimerisation reaction of the bifunctional reactant in the definition of the cyclisation constant C in the case of the effective concentration Crff Winter must be determined with the aid of an inter-molecular model reaction, the choice of which is not always obvious and can possibly lead to conceptual as well as experimental difficulties. It is also worth noting that although these early workers established a firm basis for interpretation of physical as well as of preparative aspects of intramolecular reactions, no extensive use of quantities C and Qff appears to have been made in the chemical literature over more than three decades after their definition. This is in spite of the enormous development of studies in the field of... 

Functionalization of Activated Alkyl Groups 10.03.2.2.1 Intermolecular processes... 

However, the decarbonylation reaction can be suppressed by the use of specially tailored chelating groups. Intermolecular processes involving dienes and salicylaldehydes are now known, and are thought to proceed via a double chelation mechanism, akin to the Jun-type system. Rhodium-catalyzed reactions lead to hydroacylated products, under relatively mild conditions (Equation (134)).117... 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

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