Proton polarizability

Wang, J., El-Sayed, M.A., Time-resolved Eourier transform infrared spectroscopy of the polarizable proton continua and the proton pump mechanism of bacteriorhodopsin, Biophys. J, 2001, 80, 961-971. 

Lindemann R, Zundel G (1977) Polarizability, proton transfer and symmetry of energy surfaces of carboxylic acid W-base hydrogen bonds—infrared investigations. J Chem Soc Faraday Trans 2(73) 788-803... 

The atomic unit (AU) of dipole moment is that of a proton and electron separated by a distance equal to the first Bohr orbit, oq. Similarly, the au of polarizability is Oq [125]. Express and o for NH3 using both the cgs/esu and SI approach. 

An effective polarizability, reflecting the stabilization of a positive charge on the protonated nitrogen atom through polarizability, is calculated by Eq, (16). 

The contribution of an atomj to the polarizability effect is attenuated by the number of bonds, H , between this atom and the site of protonation, i. 

Thus, the values calculated for effective polarizability at the nitrogen atom for a series of 49 amines carrying only alkyl groups was correlated directly with their proton affinities, a reaction that introduces a positive charge on the nitrogen atom by protonation (Figure 7-7) [40. ... 

Fundamental enthalpies of gas-phase reactions such as proton affinities or gas-phase acidities can be correlated with the values of the Inductive and the polarizability effect. 

Quantum chemical descriptors such as atomic charges, HOMO and LUMO energies, HOMO and LUMO orbital energy differences, atom-atom polarizabilities, super-delocalizabilities, molecular polarizabilities, dipole moments, and energies sucb as the beat of formation, ionization potential, electron affinity, and energy of protonation are applicable in QSAR/QSPR studies. A review is given by Karelson et al. [45]. 

The asymmetrical anhydrobase (20) constitutes the first step of the formation of trimethine thiazolocyanine when a 2-methylthiazolium salt reacts either with a benzothiazolium or its opened form [which is bis-o-(formylmethylamino)(diphenyl disulfide] (Scheme 26). In a second step, 20 is protonated by a second molecule of 2-methylthiazolium. It results in cleavage of the benzothiazoline ring, which gives 21 together with the formation of the monomeric anhydrobase (22). Cleavage of the C-S bond of 20 can be explained by the important electronic desaturation of the C atom observed in NMR spectrum and the great polarizability of the C-S bond in this type of ring (48). 

The presence of the zeolite cavity dramatically lowers the activation energy for the protonation of toluene. It is mainly due to screening of the charges in the transition state due to the polarizable lattice oxygen atoms. In the transition state, a positive charge develops on protonated toluene. 

X Benzene 80.1 0.03-0.1 Prinarily dispersion with weak proton -acceptor properties. Polarizable in induction Interactions. 

The solvent triangle classification method of Snyder Is the most cosDBon approach to solvent characterization used by chromatographers (510,517). The solvent polarity index, P, and solvent selectivity factors, X), which characterize the relative importemce of orientation and proton donor/acceptor interactions to the total polarity, were based on Rohrscbneider s compilation of experimental gas-liquid distribution constants for a number of test solutes in 75 common, volatile solvents. Snyder chose the solutes nitromethane, ethanol and dloxane as probes for a solvent s capacity for orientation, proton acceptor and proton donor capacity, respectively. The influence of solute molecular size, solute/solvent dispersion interactions, and solute/solvent induction interactions as a result of solvent polarizability were subtracted from the experimental distribution constants first multiplying the experimental distribution constant by the solvent molar volume and thm referencing this quantity to the value calculated for a hypothetical n-alkane with a molar volume identical to the test solute. Each value was then corrected empirically to give a value of zero for the polar distribution constant of the test solutes for saturated hydrocarbon solvents. These residual, values were supposed to arise from inductive and... 

Kornyshev et al.76 proposed several models of the interface, including both orienting solvent dipoles and polarizable metal electrons, to calculate the position of the capacitance hump. Although it had been shown32,79 101 that this was one of the features of the interfacial capacity curves that should depend on the nature of the metal, available calculations did not give the proper position of the hump. The solvent molecules in the surface layer were modeled as charged layers, associated with the protons and the oxygen atoms of molecules oriented either toward or away from the surface. These layers also carried Harrison-type pseudopoten-... 

The significance of the values calculated for the effective polarizability was first established with physical data, among them relaxation energies derived from a combination of X-ray photoelectron and Auger spectroscopy, as well as N-ls ESCA data53, 54). From our point of view, however, the most important applications of effective polarizability are to be found in correlating chemical reactivity data. Thus, the proton affinity (PA) of 49 unsubstituted alkylamines comprising primary, secondary and tertiary amines of a variety of skeletal types correlate directly with effective polarizability values (Fig. 22). 

The proton affinities (PA) of two restricted subsets of amines were correlated directly with inductive and polarizability effect parameters, respectively (Figs. 19 and 22). These can be combined with data on other hetero-substituted amines to give a set of 80 amines of different skeletal and substitution types (e.g. Fig. 24). In this and all other systems (below), a residual electronegativity value, %l2, (Eq. 5) derived from those of the atoms of the first, 1, and second, 2, sphere neighbors of the nitrogen atom is preferred as a measure of the inductive effect49). 

The signs of the coefficients in this equation are consistent with the interpretation of the two factors the negative sign of the coefficient for the x12 parameter indicates that an increase in the inductive effect destabilizes the corresponding ammonium ion and thereby leads to a decrease in the proton affinity. On the other hand, an increase in the effective polarizability, ad, stabilizes the ammonium ion and therefore... 

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