Ionization potentials table

Pyridine has practically the same ionization potential as benzene it does not, however, necessarily follow that the flrst ionization potentials (Table 9) relate to an electron of the highest occupied 7r-orbital. These compounds are bases, though weaker than aliphatic amines, and parallels have been noted between base strength and ease of ionization (Nakajima and Pullman, 1958 Krishna and Chowdhury, 1963), which might indicate that the flrst ionization potential is that of a lone-pair... 

Fluorescence of PDC is also quenched by amines. The ordering of reactivity is tertiary > secondary > primary, which follows inversely the ionization potential (Table 9.13). The results are explained as indicating that PDC undergoes photoreduction by amines, thereby forming triplet charge-transfer intermediates as the primary step in quenching. Therefore, the mechanism of the PDC reaction is not the same as the proposed mode of reaction of PDC, which involves direct formation of an yhde intermediate by electrophilic attack on the lone-pair electrons of the amine (Table 9.13). ... 

Further indication of the minor contribution of charge-transfer to the stability of t-l-diene or alkene exciplexes is provided by the relative insensitivity of fluorescence quenching rates to donor ionization potential (Table 8). A plot of log kq versus Pip for quenching of t by dienes and vinyl ethers is shown in Fig. 6. Data for the two families of quenchers fall on different lines, both of which have slopes which are less steep... 

Cso is a strong electron acceptor capable of taking on as many as six electrons and the photoexcited Cgo is an even stronger acceptor than the Cgo in the ground state. On the other hand, strained Si—Si bonds can act as the source of electrons which shows low oxidation potentials and high ionization potentials (Table 2). 

A comparison of EH and CNDO with experimental data has been made by Baetzold (30) for other metal homonuclear diatomic molecules. This work has employed the orbital exponents of Clementi et al. (10,11) and experimental atomic data for ionization potentials. Table III lists representative data for transition metal molecules calculated by CNDO and EH. No one procedure is universally superior to another. 

The overall result is a 1-electron reduction of the metal oxidant with concomitant formation of the substrate radical (R ) and is the same in both processes. The ease of electron transfer oxidation of hydrocarbons by a particular oxidant is related to their ionization potentials (Table VII). However, the ease of elec-... 

However, it is difficult to reconcile the observed relative reactivities of hydrocarbons with a mechanism involving electron transfer as the rate-determining process. For example, n-butane is more reactive than isobutane despite its higher ionization potential (see Table VII). Similarly, cyclohexane undergoes facile oxidation by Co(III) acetate under conditions in which benzene, which has a significantly lower ionization potential (Table VII), is completely inert. Perhaps the answer to these apparent anomalies is to be found in the reversibility of the electron transfer step. Thus, k-j may be much larger than k2 for substrates, such as benzene, that cannot form a stable radical by proton loss from the radical cation [Eqs. (224) and (225)]. With alkanes and alkyl-substituted arenes, on the other hand, proton loss in Eq. (225) is expected to be fast. 

The effect of benzenoid annulation is to lower ionization potentials (Table 31). Perhaps the most noteworthy feature is that the ionization potentials of the benzole] heterocycles are lower than those of the benzo[b isomers. Koopmans ... 

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 above categorization emphasizes the similarities of the reactivity patterns of radical anions and radical cations. On the basis of the bond and fragment electron affinities (Table 1) or ionization potentials (Table 2), we can now devise systems that should undergo, for example, facile bond cleavage. As a prerequisite the a (or cr) orbital representing the scissile bond has to be made a major contributor to the LUMO (or HOMO). 

The effect of solvation on the IPs of nucleotides has been investigated by Le-Breton and coworkers using a combination of photoelectron spectroscopy and computational methods. They conclude that the first and second ionization potentials of the nucleotides deoxycytidine 5 -phosphate (CMP) and deoxythymidine 5 -phosphate (TMP) arise from ionization of the negatively charged phosphate group and nucleobase, respectively, both in the gas phase and in solution. The difference in the calculated first and second ionization potentials is smaller for the hydrated versus gas phase nucleosides as a consequence of the larger solvation energy for the zwit-terion formed upon ionization of the nucleobase versus the neutral radical formed upon ionization of the phosphate. The calculated adiabatic ionization potentials for the hydrated nucleobases CMP and TMP are 5.8 and 6.0 eV, respectively, considerably lower than the gas phase nucleobase ionization potentials (Table 1). 

Photoionization studies of rare gas dimers have been carried out . Photoionization efficiency curves for the vdW molecules (Ar. .. Ar, Kr. .. Kr, Xe. .. Xe) were obtained by means of molecular beam techniques. The dissociation energies of the ions were calculated from the measured first ionization potentials (Table 6) and the dissociation energies of the parent vdW molecules. As the dissociation energy of vdW molecules is neghgible compared the dissociation energy of the rresponding cations, the latter energies (available from other sources) can be used to estimate first ionization potentials of vdW systems which have not yet been studied (values in parentheses in Table 6). 

In accordance with the variation observed in their successive ionization potentials. Table 2-1, the (3+) oxidation state is a common characteristic chemical feature of the lanthanoid series. With a few exceptions, typically associated with elements having a relatively low fourth ionization potential (Ce, Pr, Tb), Table 2-1, the (3+) oxidation state exhibits a high stability. In the case of the three elements mentioned above, the (4+) oxidation state is very relevant as well. In particular, higher oxides, i.e. dioxides and mixed-valent (+3/+4) compounds are well known for... 

In many cases, the choice of just where to localize the odd electron and charge is arbitrary, however. This is especially true if there are only carbon—carbon and carbon—hydrogen single bonds, as in propane. When possible, though, we write the structure showing the molecular ion that would result from the removal of one of the most loosely held valence electrons of the original molecule. Just which valence electrons are most loosely held can usually be estimated from ionization potentials (Table 9.3). The ionization potential of a molecule is the amount of energy (in electron volts) required to remove a valence electron from the molecule. 

Additionally to the relativistic calculations one may see the nonrelativistic results for the ns ionization potentials (Table 1.5) and KLl, KMl and KNl excitation energies (Table 1.6) of Kr and Xe, whieh show the importance of the relativistic effects on the calculated values. The main relativistic effeet is obviously associated with the deepest core level and varies from about 245 eV in Kr (total Is lOTC IP is about 14351 eV) to 1396 eV in Xe (total Is lOTC IP is about 34657 eV). However, for... 

---