Van der Waals Forces and Shielding Effects

The usefulness of solvent effect studies on NMR chemical shifts need not be elabo­ rated here; many applications of solvent effects continue to be published in great profusion. Quite a few intermolecular phenomenae may contribute to solvent shifts, but there is always the ubiquitous Van der Waals effect ow. Contrary to such other effects as neighbour anisotropy 0a, reaction field contribution 0E or complexation effects 0e, no major direct use has yet been found for the Van der Waals effect. So far the role of the Van der Waals effect has been that of a nasty, disturbing phenom­ enon, something to be eliminated at all costs. But it is precisely in this latter respect where almost all solvent effect studies fall short. Not only is Ow usually large (larger than 0a and 0E even in 1 H NMR and probably the dominating term with heavier nuclei), but it is strongly variable from one solute to another and even from one nu­ clear site to another in the same solute molecule. No referencing technique, however cleverly devised, will be capable of eliminating the Ow contribution from the other, presumedly more interesting contributions. It appeared quite recently that mathematical trickery by the name of "factor analysis" could achieve the sought-for separation of contribuants.

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and Foreword.- 1. Historical Development (Up to 1961).- 2. Continuum Models.- 2.1. The Continuum Model of Linder.- 2.2. The Continuum Model of De Montgolfier.- 2.3. The McRae Formula.- 3. Pair Interaction Models ?w.- 3.1. The Binary Collision Gas Model of Raynes, Buckingham and Bernstein.- 3.2. The Cage Model.- 3.3. Kromhout and Linder's Quantum Mechanical Model.- 3.4. A Preliminary Comparison of the Various Models Suggested for ?w.- 4. Other Experimental Proton ?w Data.- 5. The Physical Nature of the Field $$ \ overline {{F^{2}}} $$ and of the Associated Excitation Energy.- 5.1. The Bothner-By Method.- 5.2. The Raynes-Buckingham-Bernstein (RBB) Method.- 5.3. Linder's Model.- 5.4. De Montgolfier's Method.- 5.5. The Method of Kromhout and Linder.- 5.6. An Empirical Test.- 6. The Site Factor.- 6.1. The Solute Site Factor of Rummens et al..- 6.2. The Solute-Solvent Site Factor of Raynes.- 6.3. The Solute Site Factor of De Montgolfier.- 7. The Repulsion Effect.- 7.1. The Repulsion Formulation in the Binary Gas Collision Model; Application to Effects on Protons.- 7.2. Repulsion Effects in 19F ?w Shifts.- 7.3. Repulsion Effects in 129Xe.- 7.4. Pressure Effects on ?w.- 8. The Effects of Higher Order Dispersion Terms.- 9. The Parameters B.- 9.1. Marshall and Pople's Calculation of B for an H Atom.- 9.2. Calculation of B for H Atoms and Rare-gas Atoms According to Jameson, Jameson and Gutowsky.- 9.3. ?w of Two Interacting H Atoms According to Marshall and Pople.- 9.4. The Perturbation Calculations of Yonemoto.- 9.5. Kromhout and Linder's Calculation.- 9.6. Empirical Determinations of B for Atoms and Non-polar Molecules.- 10. ?w in Dense Media.- 10.1. The Effects of Higher Order Collisions in Gases.- 10.2. The Gas-Liquid Transition.- 11. The Temperature Dependence of ?w.- 11.1. The Intramolecular Temperature Effect.- 11.2. d?w/dt in Gases.- 11.3. d?w/dt in Liquids.- 12. Factor Analysis.- 12.1. Introduction to the Formalism.- 12.2. Medium Effects as Product Functions.- 12.3. Applications of Factor Analysis.- 12.4. Criticism of the Factor Analysis Method.- 13. 19F ?w Studies.- 14. ?w of Nuclei other than 1H and 19 F.- 14.1 ?w of 13C and 29Si.- 14.2. ?w of 31P.- 14.3. ?w of 129Xe.- 15. Alternate Referencing Systems.- 15.1. Internally Referenced ?w Data.- 15.2. Externally Referenced Measurements.- 15.3. ?M and the Bulk Susceptibility Correction ?b.- 16. On the Required Molecular Parameters and Physical Constants.- 16.1. Bulk Properties.- 16.2. Molecular Properties.- 16.3. The Lennard-Jones (6-12) Force Constants ?/k and r0 and the Functions ?6(y) and S6g.- References.- Author Index Vol. 1-9.