Cation-P interactions

Pb, Hg, Cd and Cu due to cation-p interactions. The phenomenon may also reflect the principle of hard and soft acids and bases introduced by Pearson (1963). Furthermore, highest sorption for mercury cation by C[4]BCP is in agreement with previous studies (Yilmaz et al., 2006) where calixarenes bearing nitrile functionalities showed much more affinity toward this cation. 

Murayama K, Aoki K (1998) Resorcin[4]arene dimer linked by eight water molecules and incorporating a tetraethylammonium ion guest-driven capsule formation via cation-p interactions. Chem Commun 607... 

S" " Inorganic precursor cation (P) interacting with anionic surfactants (S ) by Coulomb force ... 

Figure 17.15 The structure of (a) the nonlinear p" cation in laAsFg and (b) the weaker cation-anion interactions along the chain (cf Fig. 17.13). For comparison, the dimensions of (c) the linear 22-electron cation L" and (d) the nonlinear 20-electron cation Te3 are given. The data for this latter species refer to the compound [K(crypt)]2Te3.en in K2Tc3 itself, where there are stronger cation-anion interactions, the dimensions are r = 280 pm and angle = 104.4°).

Lamb, J. D., Izatt, R. M., Christensen, J. J., Eatough, D. J. Thermodynamics and Kinetics of Cation-Macrocycle Interaction, in Coordination Chemistry of Macrocyclic Compounds (ed. Melson, G. A.), p. 145-217, New York, Plenum Press 1979... 

Figure 6.12 Stabilization of the ethyl carbocation, CH3CH2+, through hyperconjugation. Interaction of neighboring C H

Gallivan, J.P. and Dougherty, D.A. (1999) Cation-Tt interactions in structural biology. Proceedings of the National Academy of Sciences of the United States of America, 96, 9459-9464. 

Caldwell, J.W. and Kollman, P.A. (1995). Cation-7t interactions nonadditive effects are critical in their accurate representation. J. Am. Chem. Soc. 117, 4177-4178... 

FIGURE 40. Cation-anion interactions in ethyl(methyl)imidazoIium NNtCM salt-ionic liquid with a m.p. of 35 °C. (distances are in A)... 

We have seen that the ab initio self-consistent quantum mechanical functional methods such as DFT/B3LYP with the chosen 6-31+G(d,p) basis sets are well suited to calculate reasonable molecular ion structures and vibrational spectra of these ions. The results obtained by us or others have indicated that the neglect of the presence of cation-anion interactions is a reasonable approximation for a rather successful prediction of the Raman spectra. Based on such calculations, detailed and reliable assignments of the spectra can be given and information on conformational equilibria can be obtained. 

The Primary Donor. - The radical-cation P+ In the bRC of purple bacteria and also in PS I the primary electron donors have been identified as (B)Chl dimers and EPR/ENDOR clearly showed that the unpaired electron and the positive charge - is (asymmetrically) distributed in a supermolecular orbital extending over both dimer halves (see sections 2.1,3.1). Dimer formation has the important consequence of charge delocalization and this stabilization of the primary donor radical-cation leads to a decrease of the oxidation potential. A fine tuning of the potential is possible through interactions with the environment, e.g. via H-bonds. 

When the guest used is p-nitrophenylcholine carbonate (PNPCC) the Lewis acid zinc(n) activates the well-positioned carbonyl group in the P PCC Zn-cavitand towards reactions with external nucleophiles. The energy minimized structure of the PNPCC Zn-cavitand complex shows that cation-n interactions and C —O -Zn coordination bond occurs simultaneously. 

A comparative study of the variation in the F chemical shift of the P F " resonances of complexes 5 or 27 on addition of increasing amounts of the salt KPFe was carried out. The resonances were compared with those of free RPF. The results are represented in Figure 3.8. A similar study was carried out with the BF4 complexes 6 and 28 and the salt NBU4BF4. For the complexes, the chemical shift of the anion is different to that of the free salts. When an increasing amount of the salt is added the chemical shift changes and it approaches that of the free anion. This observation points to the existence of some cation-anion interaction in solution that modifies the anion resonances. A F, H-HOESY experiment confirmed the existence of these contacts in the case of complex 27. A correlation between the fluorine resonance of the PFg anion and the protons of the pyridazine ring indicates that the counter-anion... 

Figure 10.9 Interaction of the methyl group orbital 4 with the p orbital of the cationic carbon. 4", 4 moves down, stabilizing the structure. Its perturbed form shows delocalization of the electron pair into the cation p orbital. Orbital p moves up, but it is unoccupied and so does not alter the energy.

Heteronuclear correlation (HETCOR) is an experiment establishing a correlation between the chemical shift of proton and that for another nucleus (i.e. C, P, Nor Si). The experiment relies on the heteronuclear dipolar interactions and uses a CP to transfer magnetization from protons to a rare spin.4,6 We have used 2D HETCOR experiment to characterize support/counter-cation/cluster interaction in the supported mesoporous catalysts.21... 

---