Linear relation between substituted pyridine lone pair vertical ionization potentials and pKa

Abstract

The cation exchange rates in cryptates may be obtained most conveniently from variable temperature 1SC nmr spectra of 1/1 cryptateligand mixtures (forthcoming report). Double probe 13C, 23Na nmr studies may provide detailed information on the electric effects produced by ligand structure, binding sites, ion pairing, and me-dium15 as well as on molecular tumbling. Complexes of other metal cations may also be investigated (lithium and cesium for instance).30 (30) The use of nitrogen-14 as the quadrupolar nucleus allows similar studies to be performed on nitrogen-containing substances of chemical or biological interest.24•25 (31) ERA No. 265 from CNRS.

Substituent effects on imidazole basicity and photoelectron spectroscopy determined ionization energies

“…Photoelectron spectra have been determined for imidazole (1), the substituted 1-methyl-(2), 2-methyl-(3), 1,2-dimethyl- (4), 1-acetyl- (5), and l-(trifluoroacetyl)imidazoles (6), and benzimidazole (7).…”

“…7.v = -1.67ecNDO-7.50eV (1) Substituent effects on imidazole, 7V, and calculated SCF orbital energies, e, are provided in Table I for the x2 and x3 functions.…”

“…The validity of multiparameter correlation equations such as the LD (extended Hammett) equation and the Yukawa-Tsuno equation is in doubt. The former equation in the form (Qx/Qh) = L<T/x + Do*rx (1) was reported by Ehrenson, Brownlee, and Taft2 to be the best choice for the correlation of reactivity of substituted pyridines.…”

Insights into porphyrin chemistry provided by the microperoxidases, the haempeptides derived from cytochrome c

“…The occupied frontier orbitals of pyridines have been identified as the nitrogen "lone pair" orbital, n r , with r symmetry, and the two orbitals, p S and p A , with p-symmetry. 91, 113 We have found that there is a statistically significant correlation between log K for the coordination of substituted pyridines and energy of the p S orbital, but no correlation with the energy of the n r orbital (where orbital energies were computed using a RHF/SCF ab initio method employing a MP2/6-31G** basis set); 106 this supports the notion that p-bonding effects are more significant than r-bonding effects in determining the strength of binding of pyridines by the ferrous centre in Fe(II)-N-AcMP8.…”

The coordination of imidazole and substituted pyridines by the hemeoctapeptide N-acetyl-ferromicroperoxidase-8 (FeIINAcMP8)

“…The occupied frontier orbitals of pyridines have been identified as the nitrogen ''lone pair'' orbital, n r , with r symmetry, and the two orbitals, p S and p A , with p-symmetry [7,79]; p S has the correct symmetry for interaction with the metal orbitals. We have previously shown there is a linear relationship between the energies of n r and p S , determined by ab initio MO calculations, and the magnitude of log K III for the binding of substituted pyridines by Fe III NAcMP8, and concluded that both r and p bonding is important [7]; a re-examination of our data shows, however, that it is likely that the correlation observed for the r component is not statistically significant.…”