Ionization potentials reactions, methyl

IV-methyl pyrolidinone is used in most cases. Figure 5.31 summarizes the main reaction which can take place during the process and the corresponding rate constant. The formation of diamide has also been evidenced.140 The reactivity is governed by the electron affinity of the anhydride and the ionization potential or basicity of the diamine (see Section 5.2.2.1). When a diacid with a low electron affinity reacts with a weak nucleophilic diamine, a low-molecular-weight is obtained, because the reverse reaction is not negligible compared with the forward reaction. 

The low solubility of fullerene (Ceo) in common organic solvents such as THE, MeCN and DCM interferes with its functionalization, which is a key step for its synthetic applications. Solid state photochemistry is a powerful strategy for overcoming this difficulty. Thus a 1 1 mixture of Cgo and 9-methylanthra-cene (Equation 4.10, R = Me) exposed to a high-pressure mercury lamp gives the adduct 72 (R = Me) with 68% conversion [51]. No 9-methylanthracene dimers were detected. Anthracene does not react with Ceo under these conditions this has been correlated to its ionization potential which is lower than that of the 9-methyl derivative. This suggests that the Diels-Alder reaction proceeds via photo-induced electron transfer from 9-methylanthracene to the triplet excited state of Ceo-... 

Nucleophilic Trapping of Radical Cations. To investigate some of the properties of Mh radical cations these intermediates have been generated in two one-electron oxidant systems. The first contains iodine as oxidant and pyridine as nucleophile and solvent (8-10), while the second contains Mn(0Ac) in acetic acid (10,11). Studies with a number of PAH indicate that the formation of pyridinium-PAH or acetoxy-PAH by one-electron oxidation with Mn(0Ac)3 or iodine, respectively, is related to the ionization potential (IP) of the PAH. For PAH with relatively high IP, such as phenanthrene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene, no reaction occurs with these two oxidant systems. Another important factor influencing the specific reactivity of PAH radical cations with nucleophiles is localization of the positive charge at one or a few carbon atoms in the radical cation. 

The rate of the reaction of methyl radicals with 03 has been studied from 243 to 384 K by monitoring the decay of methyl in the presence of excess 03 [99], With the temperature dependence of the rate constant it was estimated that less than 1% of the methyl radicals in the stratosphere react with ozone. The reactions of a series of alkyl radicals (CH3, C2HS, n-C3H7, i -C3H7, and t-C4H9) with ozone were investigated at 298 K [100]. The rate coefficients were found to correlate with the difference between the ionization potential of each radical, and the electron affinity of 03. 

The alpha effect in the SN2 reactions of methyl substrates with three different nucleophiles was shown to correlate with Koopman s theorem ionization potentials for the leaving group.128 This was taken as evidence that (1) the size of the alpha effect in Sn2 reactions depends on the ability of the nucleophile and the leaving group to donate an electron to the methyl group and (2) these transition states have some SET character. The results support the Hoz model129 for the alpha effect. 

Much larger effects of this type are observed in cycloadditions of enol ethers to tetrazines (Fig. 26), a reaction shown by Sauer and co-workers to be an example of a Diels-Alder reaction with inverse electron demand 75. The rates of 3,6-di-(2 -pyridyl)-s-tetrazine to various enol ethers and styrenes are summarized in Fig. 27. These were obtained by measuring the disappearance of the 540 nm band in the absorption spectra of the tetrazine76. These results are of particular interest, since there is little or no correspondence between the electron-donor ability of the enol ether, as measured by the ir ionization potentials (Table 5), and the rate of reaction of the enol ether. For example, although the conversion of methyl vinyl ether to 1,1-dimethoxyethylene results in a 4.3 times increase in rate, in line with the 0.2 — 0.3 eV decrease in IP, the 1,2-dimethoxyethylenes are 13 to 25 times less reactive than methyl vinyl ether, even though the IPs of these molecules are much lower... 

The proximity of the diffusion limit also inhibits a detailed discussion of the data in Table 7, but a significant difference to the substituent effects discussed in Section III.D.4 is obvious. Whereas the reactivities of terminal alkenes, dienes, and styrenes toward AnPhCH correlate with the stabilities of the new carbenium ions and not with the ionization potentials of the 7r-nucleophiles [69], the situation is different for the reactions of enol ethers with (p-ClC6H4)2CH+ [136]. In this reaction series, methyl groups at the position of electrophilic attack activate the enol ether double bonds more than methyl groups at the new carbocationic center, i.e., the relative activation free enthalpies are not controlled any longer by the stabilities of the intermediate carbocations but by the ionization potentials of the enol ethers (Fig. 20). An interpretation of the correlation in Fig. 20 has not yet been given, but one can alternatively discuss early transition states which are controlled by frontier orbital interactions or the involvement of outer sphere electron transfer processes [220]. 

The slow rate of the methane reaction could then be ascribed to the exceptionally high ionization potential of the methyl radical (10.0 ev.) In turn, the high rate of the Si-H reaction might be explained by the... 

The nature of the lithium surface is important. Varying the particle size of the lithium dispersion from 25 pm with a surface area of 2782 cm to 150 pm with a surface area of 464 cm reduced the optical purity of the resulting acid by nearly 50%. It was also demonstrated that the amount of sodium impurity in the lithium dispersion had a significant effect not only on the stereochemical results of the metallation reaction but also on the reactivity of the metal surface itself. For example, reaction of chiral l-iodo-2,2-diphenylcyclopropane with 25 pm lithium dispersions containing 0.002 %, 0.02 % and 1 % sodium yielded after carbonation l-methyl-2-cyclopropanecarboxylic acid (99) with optical purities of 13 %, 16% and 36%, respectively. The increase in optical purity with increase in sodium content may be a consequence of lowering the ionization potential of the metallic surface . ... 

Selective synthesis of 2-methyl naphthalene has been studied over HZSM-5, HZSM-11, HSABO-11, HZBS-11, Zn-ZSM-11, Ga-ZSM-11, HY and HZSM-20 type zeolites. The nature of the naphthalene-methanol interaction has been investigated in order to elucidate the reaction mechanism. According to the data obtained by FT-IR, TPD of naphthalene, ionization potential and proton affinity of different aromatic rings, zeolites with medium pores and with sites of medium or high acid strength are necessary for the reaction. The results seem to be consistent with the Rideal type mechanism. 

Using the indirect method it is not necessary to make the difficult measurement of the ionization potential of the radical, and also the heat of formation of the radical is found more directly. Under the impact of electron bombardment, propane can dissociate into ethyl ions and method radicals. Ethane can dissociate to produce ethyl ions and hydrogen atoms, so that the difference between the energies of these two processes corresponds to that for the reaction between propane and a hydrogen atom to give ethane and a methyl radical. The heats of these processes are< ... 

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