Ton pair

Figure 2. General ton-pair scheme for the addition of bromine to phenylacetylene in acetic acid (33).

The "bond strength" thus obtained refers, of course, to the dissociation of the ton pair to the separated ions. M X- - M h X- tt is somewhat easier to dissociate an ion pair into the uncharged constituent atoms, M X - M + X. because the ionization energy of Ihe metal is greater than the electron affinity of the nonmctal. 

The choice of counterions (anions) in the cationic polymerization of heterocyclic monomers can be almost as wide as in anionic polymerization, but only for the most nucleophilic monomers (i. e. cyclic amines). Unfortunately, in the polymerization of cyclic ethers, this choice is much more restricted. Thus, the small anions like F or OH cannot be used because, due to their high nucleophilicity and ability to form covalent bonds, they give rise to fast termination. In order to suppress or even to eliminate termination by collapse within an ton pair (cf. Sect. 5.1.), it is necessary to use complexed anions having large ionic radii. These are shown below (rctyst)-... 

The coordination numbers of metal ions range from I. as in ton pairs such as Na CI in the vapor phase, (o 12 in some mixed metal oxides. The k>v limit, 1. Is barely within the realm of coordination chemistry, since the Na Cr km pair would not normally be considered a coordination compound, and there are few other examples. Likewise, the upper limit of 12 is not particularly important since k is rarely encountered in discrete molecules, and the treatment of sohd crystal lattices such as hexagonal BaTiOj and perovskite> as coordination compounds is not dc ie frequently. The lowest and highest coordination numbers found in typical coordination compounds are 2 and 9 with the intermediate number 6 being the most important. 

Brandstrom. A. Gustavii. K. Ton pair extraction in preparative organic chemistry. A convenient method for the preparation of salts of amines. Acta Chem. Scand. 1969, 23. 1215-1218. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

Positrons cannot be observed directly because, as Figure 22-6a illustrates, when a positron encounters an electron, the two particles annihilate each other, converting their entire mass into a pair of photons. The occurrence of positron emission can be inferred from the observation of such a pair of photons. Each photon produced in this process has a specific energy Epi ton = 9.87 X lO kJ/mol. Photons with such high energy are called y rays. 

Fig. 4.19 Polarization effects (a) idealized ion pair with no polarization, (b) mutually polarized ton psir, (c) polarization sufficient to form covalent bond. Dashed lines represent hypothetical unpdarized tons...

Available lone pairs of the bound fluorine group are attracted to the hydrogen ton, leading to the formation of a weak acid. The rate constant for the overall reaction is 6.2 x 10-,° s-1 in neutral solution, bul 1.4 x Iff s in acid solution. When... 

The reaction of propargylic alcohols and sc C02 in the presence of a trialkylphosphine as a catalyst gave cyclic carbonates in an excellent yield (Ikariya and Noyori, 1999). Dixneuf reported that the reaction proceeded without solvent, but not in nonpolar solvents such as toluene. The reaction efficiency in sc C02 was superior to that in solution phase (Fournier et al., 1989 Journier et al., 1991). The TON reached 1200 and the TOF exceeded 400. The sufficient concentration of C02, as well as the high reactivity of the ion-pair intermediate in sc C02, is responsible for such high efficiency. 

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