Trimolecular

Trimolecular reactions have also been discussed for molecular reactions postulating concerted reactions via cyclic intennediate complexes, for example... 

However, the postulated trimolecular mechanism is highly questionable. The third-order rate law would also be consistent with mechanisms arising from consecutive bimolecular elementary reactions, such as... 

When the perturbation is small, the reaction system is always close to equilibrium. Therefore, the relaxation follows generalized first-order kinetics, even if bi- or trimolecular steps are involved (see chapter A3.41. Take, for example, the reversible bimolecular step... 

Uiiimolecular and trimolecular or hrst and drhd-order reactions are also known, but these are less frequent in occunence than bimolecular reactions. Examples of each of the drree orders of gaseous reaction are ... 

During activation of the coagulation cascade, coagulation factors form multimolecular (often trimolecular)... 

FKI. X. Trimolecular. linear, foiir-cemcrecl transition state proposed for methane tictivation by rhodium porphyrins." ... 

Rh(TMP)- under these conditions, and in fact the selective activation of methane in benzene solution is a distinctive and unusual feature of this system, given that aryl C—H activation ought to be thermodynamically favored over alkyl C—H activation. The proposed linear transition state proposed in Fig. 8 is the key to this different reactivity. The corresponding trimolecular transition state for an arene would be expected to be bent, and this would be precluded by the bulky TMP... 

Bimolecular and Trimolecular Reactions of Dioxygen with the Double Bond of Olefin... 

Later, both reactions were proved experimentally by Cooper and Melville in 1951 [58] and Miller and Mayo in 1956 [54]. In addition, the trimolecular reaction 2 RH + 02 was predicted in 1960 and experimentally proved in 1961 [59,60]. 

In addition to the bimolecular reactions of organic compounds with dioxygen, free radicals are generated in an oxidized substrate in the liquid phase by the trimolecular reaction [3,8,9]... 

The trimolecular reaction of two dioxygen molecules with two C—H bonds of one hydrocarbon was observed in ethylbenzene oxidation [43]. 

Rate Constants and Activation Energies of the Trimolecular Reaction 2RH + 02 —> Free Radicals (Experimental Data)... 

Unsaturated compounds react with dioxygen by trimolecular reaction also [48]. It is very probable that this reaction proceeds via preliminary formation of a CTC. The formed complex reacts with another olefin molecule. 

TABLE 4.5 Rate Constants of the Trimolecular Reaction RCH=CH2 RCHCH2OOCH2CHR + o2 + ch2=chr ... 

The values of the rate constants of the trimolecular reactions 2RCH=CH2 + 02 are collected in Table 4.5. 

In alcohol undergoing oxidation in the absence of initiators, free radicals are formed by bimolecular and trimolecular reactions of alcohol with dioxygen [8,9] ... 

This shows that the free radical generation proceeds via the trimolecular reaction (see Chapter 2). 

The preference of the trimolecular reaction over bimolecular RH + 02 is the result of weak C—H bond in diacetals and a polar media (see Chapter 4). The last factor is important for the energy of formation of very polar TS of the trimolecular reaction. The rate constants of trimolecular reactions are presented in Table 7.14. 

Rate Constants of Radical Generation by Trimolecular Reaction of Dioxygen with Ethers [68]... 

In thermal oxidation, chain initiation takes place by the reaction of the aldehyde with dioxygen. Two reactions of chain generation in autoxidized aldehydes, namely, bimolecular and trimolecular, were proved [25]. 

The trimolecular reaction of dioxygen with the weakest C—H bonds of two nonsaturated esters. 

The trimolecular reaction of dioxygen with double bonds of two molecules of non-saturated esters. As in the case of a similar bimolecular reaction, this reaction seems to be preceded by CTC formation. 

Free radical formation in oxidized organic compounds occurs through a few reactions of oxygen bimolecular and trimolecular reactions with the weakest C—H bond and double bond (see Chapter 4). The study of free radical generation in polymers (PE, PP) proved that free radicals are produced by the reaction with dioxigen. The rate of initiation was found to be proportional to the partial pressure of oxygen [6,97]. This rate in a polymer solution is proportional to the product [PH] x [02]. The values of the apparent rate constants (/ti0) of free radical formation by the reaction of dioxygen (v 0 = k 0[PH][O2]) are collected in Table 13.8. 

The overwhelming majority of reactions are bimolecular. Some reactions are unimolecular and a mere handful of processes proceed as a trimolecular reactions. No quadrimolecular (or higher order) reactions are known. 

A concerted mechanism has also been discussed [29,30], involving either a 2+2+1 or 3+2 mechanism. To avoid trimolecular reactions this requires an interaction between Rh(I) and silanes prior to the reaction with a ketone. Interaction of silanes not leading to oxidative addition usually requires high-valent metals as we have seen in Chapter 2. The model is shown in Figure 18.16 it proved useful for the explanation of the enantiomers formed in different instances. The formation of a rhodium-carbon bond is included and thus formation of silyl enol ethers remains a viable side-path. 

Ab initio calculations and density functional theory studies of the gas-phase addition of HF to CH2=CH2 have revealed the possibility of forming trimolecular (two HF and one ethylene) and dimolecular (one FIF and one ethylene) complexes and transition-state structures and of the catalytic effect of the second molecule of the reagent. An energetically favourable pathway was selected on the basis of the computed potential-energy surface for these two reactions. ... 

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