Phenols ionization potential

The stability of oxygen-centered radicals has been studied repeatedly in recent years in search of quantitative descriptors of antioxidant activity. The antioxidant activity of phenols is indeed so well correlated with O - H BDEs and the ionization potential that these two energies can be used as the guiding... 

For other substituted phenols, the difference in their ionization potential from that of phenol was calculated, and then their A log A was obtained from Equation 6.10. The log k of substituted phenols was then estimated from Equations 6.9 and 6.13. 

This system of using the van der Waals volume and ionization potential is much simpler than previous systems. It requires only one homologous series of alkyl compounds and one standard such as phenol for substituted phenols. The precision could be improved for polar compounds if / ara-alkylphenols and / ara-alkylbenzoic acids are used however, only a few such compounds are... 

Since phenol has an appreciable dipole moment, and no low energy acceptor orbitals, it should interact best with the donors that have the largest lone pair dipole moment — the oxygen compounds. Iodine has no dipole moment and the interaction with iodine is expected to be essentially covalent. Iodine should interact best with the donors that have the lowest ionization potential, i.e., the ones whose charge clouds are most easily polarized. Similar considerations have been employed to explain the donor strengths of primary, secondary and tertiary amines 35a) and the acid strengths of (35b) ICl, Bt2, I2. CeHsOH and SO2. 

The results for phenolate and naphtholate show that internal transition may lead to solvated electron formation from aromatic anions. The fact that the products are the negatively charged solvated electron and a radical which is neutral (and not a positively charged one) may be partly responsible for the increased efficiency of anions over the undissociated molecules. Primary recombination may decrease in the absence of coulombic attraction. Moreover the ionization potential of the anion is lower. 

Ab initio molecular mechanics calculations have been used to examine the electronic states of selenoxanthene 9 and selenoxanthone 10. These results were used to explain differences in the formation of bromine adducts of these compounds (see Section 7.11.6.1.2) <1998JOC8373>. Bond dissociation enthalpies and adiabatic ionization potentials of phenolic antioxidants containing selenium and tellurium have been carried out using DFT models in an attempt to design novel vitamin E analogues such as 11 <20060BC846>. 

The ionization threshold for each cluster size is lower than the ionization potential of free phenol (Mikami et al. 1987). 

Figure 4-14. Ionization efficiency versus + v2) of phenol(NH3) (n = 1-4) and phenol(MEA) clusters (n = 1-6). The arrow at 8.5 eV represents the ionization potential of free phenol. The ionization thresholds (in eV) are respectively ...

Since the suggestion of the sequential QM/MM hybrid method, Canuto, Coutinho and co-authors have applied this method with success in the study of several systems and properties shift of the electronic absorption spectrum of benzene [42], pyrimidine [51] and (3-carotene [47] in several solvents shift of the ortho-betaine in water [52] shift of the electronic absorption and emission spectrum of formaldehyde in water [53] and acetone in water [54] hydrogen interaction energy of pyridine [46] and guanine-cytosine in water [55] differential solvation of phenol and phenoxy radical in different solvents [56,57] hydrated electron [58] dipole polarizability of F in water [59] tautomeric equilibrium of 2-mercaptopyridine in water [60] NMR chemical shifts in liquid water [61] electron affinity and ionization potential of liquid water [62] and liquid ammonia [35] dipole polarizability of atomic liquids [63] etc. 

The ionization potential (IP) of phenols is a measure of how readily an electron can be donated from the OH group to yield the phenolic cation. As pointed out before, the IP... 

The ionization potential of iodine is sufficiently low for it to form a number of compounds in which it is electropositive. It forms I cations, for example, by reaction of solid silver nitrate with iodine solution, and such cations are sufficiently electrophilic to substitute aromatic compounds such as phenol. Iodine also exhibits the interesting property of forming solutions that are violet colored in non-donor type solvents, such as tetrachloromethane, but in donor solvents, such as ethanol or dioxan, there is a strong iodine-solvent interaction, which gives the solution a deep brown color. Even though iodine solutions were commonly used as antiseptic agents, the element is classified as toxic, and care should be taken to avoid eye intrusions or excessive skin contact. 

The explanation of this effect can be conceived as follows. Phenol has a fairly high dipole moment and has no low-energy acceptor orbitals, whereas iodine has no dipole moment hence interactions with iodine may be expected to have more covalent character than the analogous reactions with phenol. Accordingly, iodine will react more readily with the better polarizable reaction partners possessing lower ionization potentials. Similar considerations may be employed to interpret, for example, the sequence of basic strengths of primary, secondary and tertiary amines [Dr 63], and the sequence of acid strengths of iodine monochloride, elemental bromine, elemental iodine, phenol and sulphur dioxide [Dr 62]. 

Table 3. Quantum mechanical calculation of the ionization potential (IP) of some alkyl substituted phenols (AMI Hamiltonian, MOPAC 93, available from FUJITSU Ltd. together with the interface from CambridgeSoft Corporation information concerning AMI is given in the text below) [52]...

This is the molecular energy difference between each neutral phosphine and its radical cation counterpart the approach has been used as a measure of the 1 Ionization Potential of phenols. ... 

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