An INDO Molecular Orbital Approach to the Proton Affinity of Oxygenated Compounds

Abstract

The correlation between the gas-phase proton affinities of aliphatic oxygenated compounds (alcohols, acids, and esters and their electronic structures was investigated by means of an INDO-MO theory. There appears to be a satisfactory linear-dependence of the proton affinities with the energy difference between the parent molecule and the energetically most stable protonated species and with the bond energy of the oxygen-proton bond, although the above energies are overestimated in comparison with the proton affinities. The proton affinities are also predicted with a sufficient accuracy using the first ionization potential and the electron density of the oxygen atom (especially, the % p-character in the oxygen lone-pairs) of the parent molecule.

Basicity parameter of weak organic bases, derived from thermodynamic parameters of their reactions with (tetraphenylporphyrinato)zinc(II)

“…Undoubtedly, all the above interactions could affect the spectral pattern, whereas in some cases they can level variations directly induced by axial coordination of a ligand. However, attempts were made to establish a correlation between the shift of the absorption maxima of ZnTPhP (∆λ max ) and various polarity and basicity parameters of solvents, such as proton affinity [6], dielectric constant [8], Kosower parameter [27], Gutmann donor number [18], Kamlet-Taft π* scale, and parameter β [28]. Uno and Kyuno [29] found a correlation between the position of the Soret band in the spectra of MPs and pK a values of structurally similar ligands (such as pyridine and aniline).…”