Low electron affinity

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. 

Electron-pair bond extreme Low electron-affinity High bond-forming power for X... 

Amines possess a pair of p-electrons on the nitrogen atom. The nitrogen atom has a low electron affinity in comparison with oxygen. Therefore, amine can be the electron donor reactant in a charge-transfer complex (CTC) in association with oxygen-containing molecules and radicals. It will be shown that the formation of CTC complexes of amines with peroxyl radicals is important in the low-temperature oxidation of amines. 

The 02 superoxide ion possesses a low electron affinity (42kJ/mol in vacuum) and is an active reducing agent. Therefore, it rapidly reacts, in particular, with Fe3+. 

Bare metal cations can be prepared from almost any inorganic source as long as enough energy is given to the sample to allow dissociation, vaporization, and ionization. Metal anions are less well studied due to the low electron affinities of most transition metals. Where M+ and M ions are compared, the M ions are generally less reactive. 

The electrochemical reduction of pure hydrocarbons without functional groups is almost exclusively restricted to unsaturated compounds. The reason is that aliphatic hydrocarbons have extremely low electron affinities that render their reduction impossible, despite a gain of solvation energy within the stability limits of conventional solvent-electrolyte systems. 

Atoms of elements in group 1 (lA) and group 2 (IIA) have low ionization energies and low electron affinities. Atoms of these elements give up electrons easily, hut attract them poorly. Therefore, they form positive ions in ionic compounds. 

Alkanes are among the least reactive classes of compounds they are poor electron acceptors (low electron affinities) as well as donors (high ionization potentials, viz., CH4,12.61 eV C10H22, 9.65 eV). ° The molecular anions of w-alkanes are especially unstable " negative ion yields for simple alkanes are 10" times lower than positive ion yields. Electron attachment results in small fragment ions (CH, CH2, CH3, M-AIkanes can be ionized by electron (MS) or... 

The nearest anionic analogue of H"1 is the F ion. Some of the calculations for it are at first surprising, but parallel those of the proton and are acceptable under closer scrutiny (a) F- forms a stronger covalent bond than Cl" (>Br" > I-) 38 (b) F" is a very strong base with a large transfer of electron density to the acid. This is a result of the low charge capacity (low electron affinity) of fluorine. 

One could aho draw a comparison between the noble gases and the alkali metals based on Ihdr low electron affinities. However, the electron affinities of noble gases appear always to be endothermic whereas the aBcaE metals hove anal hut finite exothermic electron affinities Icadbig lo some chemistry based on acceptance of electrons (Chapter 12). 

It is reasonable to conclude that radicals with a strong tendency to lose an electron will have a rather low electron affinity and, consequently, a relatively low reactivity towards e7r... 

Another case for which ET could be expected as a viable alternative to the SN2 displacement mechanism concerns the reactions of CH3I and CC14 with the nitric oxide anion, NO-263. Because of the extremely low electron affinity of NO (0.024- 0.55 kcalmof1), an ET process to the halo-compounds would be exothermic. However, in neither case was the substrate radical anion observed, despite the fact that both have bound molecular anions. Both reactions yield only the halide ion, a product which can arise via dissociative ET (a) or S 2 (b) (Scheme 38). The mechanism could not be assigned. 

Favoured at cathode materials of low overpotential (Table 6 Pt, Pd, Ni) and with substitutes of low electron affinity... 

The photoanodic dissolution of n-silicon in acidic fluoride media provides an example of the complexity of multistep photoelectrochemical reactions [33, 34]. The reaction requires the transfer of four electrons, but it is clear that not all of the steps involve photogenerated holes because the photocurrent quantum efficiency is between 2 and 4. The explanation of the high quantum efficiencies is that the initial hole capture step can be followed by a series of steps in which intermediates with low electron affinity inject electrons into the conduction band. These intermediates can be assigned nominal oxidation states as shown in the following scheme. 

Metals have very low electron affinities. This is especially true for the Group 1 (IA) and 2 (IIA) elements. Atoms of these elements form stable positive ions. A negative ion that is formed by the elements of these groups is unstable. It breaks apart into a neutral atom and a free electron. 

The units for electron affinity are the same as the units for ionization energy kJ/mol. High negative numbers mean a high electron affinity. Low negative numbers and any positive numbers mean a low electron affinity. 

Group 1 (IA) and 2 (IIA) elements give up electrons readily. They have low or no attraction for electrons. In other words, they have a strong tendency to form positive ions. Thus, they have low ionization energies and low electron affinities. 

Group 18 (VUIA) elements do not attract electrons and do not give up electrons. In other words, they do not naturally form ions. (They are very stable.) Thus, they have very high ionization energies and very low electron affinities. 

The chemical counterpart of the roof will be a set of valence-shell electrons, and we shall look at atomic and molecular architectures that can be hosted under such a roof when bringing in stable nuclei and corresponding core electrons. In order to see what happens with such an idea in a Chemical Aufbau approach, let us start with an octet of electrons under which we place a nucleus with atomic number Z = 10 and a K-shell with two core electrons. The result is a neon atom, an exceptionally stable architecture with spherical (three-dimensional) symmetry. The same result would happen for Z = 18 (argon) with one more "floor", and so on or the following noble gas atoms. Actually, we start with the closed electronic shells allowed by the Pauli Exclusion Principle and the "n ( Rule", and we supply the nuclei corresponding to such shells. The proof for the stability of this architecture is provided by the high ionization potential and the low electron affinity. 

---