| The premise on which this text is based is that the vast majority of chemical phenomena may be qualitatively understood by the judicious use of simple orbital interaction diagrams. The material borrows heavily from the pioneering work of Fukui [1, 2], Woodward and Ho¨mann [3], Klopman [4], Salem [5], Ho¨mann [6], and many others whose work will be acknowledged throughout including Fleming: Frontier Orbitals and Organic Chemical Reactions [7], from which a number of illustrative examples are extracted. If there is uniqueness to the present approach, it lies in the introduction of the a and b of simple Huckel molecular orbital theory as reference energy and energy scale on which to draw the interaction diagrams, mixing s and s* orbitals and nonbonded orbitals with the usual p orbitals of SHMO theory on the same energy scale. This approach is difficult to justify theoretically, but it provides a platform on which the reader can construct his or her interaction diagrams and is very useful in practice. Numerous illustrations from the recent literature are provided.
The book is intended for students of organic chemistry at the senior undergraduate and postgraduate levels and for chemists in general seeking qualitative understanding of the (often) quantitative data produced by modern computational chemists [8]. All reactions of organic compounds are treated within the framework of generalized Lewis acid Lewis base theory, their reactivity being governed by the characteristics of the frontier orbitals of the two reactants. All compounds have occupied molecular orbitals and so can donate electrons, that is, act as bases in the Lewis sense. All compounds have empty molecular orbitals and so can accept electrons, that is, act as acids in the Lewis sense. The ``basicity'' of a compound depends on its ability to donate the electron pair. This depends on the energy of the electrons, the distribution of the electrons (shape of the molecular orbital), and also on the ability of the substrate to receive the electrons (on the shape and energy of its empty orbital). The basicity of a compound toward di¨erent substrates will be di¨erent, hence a distinction between Lowry±Bronsted basicity and nucleophilicity. A parallel de®nition applies for the ``acidity'' of the compound. |
