Charge Distributions and Chemical Effects: A New Approach to the Electronic Structure and Energy of Molecules

ISBN-13: 9781461255772 / Angielski / Miękka / 2011 / 205 str.

S. Fliszar

Opis

The energy of a molecule can be studied with the help of quantum theory, a satisfactory approach because it involves only basic and clearly identified physical concepts. In an entirely different approach, the molecular energy can be broken down into individual contributions reflecting chemical bonds plus a host of subsidiary "effects," like y-gauche, skew pentane, ring-strain, etc., giving an overall picture in terms of topological characteristics. The latter approach can be successful, particularly if a sufficient number of particular topological situations have been parametrized (which is an empir ical way of "understanding" chemistry), but also contains the seed for difficulties. Indeed, the danger exists of unduly ascribing a physical meaning to corrective terms whose function is primarily to account in an empirical fashion for discrepancies between "expected" and observed results. The link between this type of empirical approach and the knowledge that the ground state energy is uniquely determined by the electron density is lost somewhere along the road, although some of the "steric effects" are here and there vaguely traced back to electronic effects. The approach presented in this monograph goes back to the fundamen tals in that it is exclusively based on interactions involving nuclear and electronic charges. Confining the study to molecules in their equilibrium geometry, the problem of molecular energies is reduced to its electrostatic aspects, explicitly involving local electron populations."

Spis treści

1 Electronic Charge Distributions.- Electron Population Analysis.- Basis Functions.- 2 Charge Analysis of Simple Alkanes.- Inductive Effects of Alkyl Groups.- Back-Calculation of Atomic Charges from the Inductive Effects.- Comparison with Theoretical Population Analyses.- Conclusions.- 3 A Modified Population Analysis.- Criterion for Selecting a Theoretical Method for the Study of Molecular Properties Involving Charges.- A Modified Population Analysis.- Numerical Comparisons of Atomic Charges.- The “Most Even Electron Distribution”.- On the Precision of Theoretical Charges.- Inductive Effects and Charge Distributions.- Conclusions.- 4 Charge Analyses Involving Nuclear Magnetic Resonance Shifts.- Relationships between Nuclear Magnetic Resonance Shifts and Atomic Charges.- Charge-Shift Relationships Involving sp2 Carbon Atoms.- Relationships Involving sp3 Carbon Atoms.- Relationships Involving Oxygen Atoms.- Charge Analyses.- Conclusions.- 5 The Molecular Energy, A Theory of Electron Density.- The Molecule in its Hypothetical Vibrationless State.- Energy Components in Isolated Atoms.- Relationships between Electronic, Orbital, and Total Energies in Molecules.- Binding of an Atom in a Molecule.- Non-Transferability of Bond Energy Terms.- Charge Dependence of Chemical Binding.- Evaluation of the aij Parameters.- Physical Interpretation of the aij Parameters.- Summary.- 6 Energy Analysis of Saturated Hydrocarbons.- The Boat and Chair Forms of Cyclohexane.- General Formulas for Saturated Hydrocarbons.- Definition of Charges Satisfying Eqs. 5.46–5.48.- Numerical Applications: Saturated Hydrocarbons.- Nonbonded Interaction Energies.- Approximate ?Em2Calculations of Saturated Hydrocarbons.- Conclusions.- 7 On the Role of Vibrational Energies.- Outline of Calculations.- Noncyclic Alkanes.- Cycloalkanes.- Ethylenic Hydrocarbons.- Carbonyl Compounds.- Ethers.- On the Quasi-Additivity of Vibrational Energies.- Ring Strain and Vibrational Energies.- Summary.- 8 Unsaturated Hydrocarbons.- Energy Formula for CnH2n Olefins.- Numerical Applications: CnH2n Olefins.- Bond-by-Bond Calculation of Olefins.- Exo- vs. Endocyclic Double Bonds.- Dienes, Allenes, Alkynes and Benzene.- Conclusions.- 9 Energy Analysis of Oxygen-Containing Compounds.- Charge Normalization.- Ethers.- Carbonyl Compounds.- Conclusions.- 10 Conclusion and Assessment.- Charge Distributions.- Molecular Energies.- Appendix Summary of Final Equations and Input Parameters.- Author Index.