Literature, Software, Books and Websites 455

and 3 should largely cancel out energy differences due to ring strain. The two magnetic properties calculated [33] arise from the presence of a diatropic ring current [27], which tends to push an aromatic molecule out of a magnetic field (calculated property: magnetic susceptibility, and which exerts NMR shielding on a proton at or above the ring center (calculated property: nucleus-independent chemical shift, NICS). NICS values are obtained from the calculated NMR shielding (section 5.5.5) of a “ghost nucleus” [34] with no charge, electrons or basis functions, placed at or above [35] the ring center. Calculation of the changes in and in NICS along the reaction coordinate for the known reaction, the isomerization of diademane to triquinacene (Fig. 8.9), showed that the transition state, but neither the reactant nor the product, was aromatic. Homoaromaticity in a few neutral, ground-state molecules has been claimed [36].

The absence of homoaromaticity in triquinacene is probably due to the three pairs of nonbonded carbons being too far apart, 2.533 Å, from X-ray diffraction; in the transition state (Fig. 8.9), in contrast, the nonbonded CC distance has been reduced to 1.867 Å according to a calculation (section 7.2.3.4c).

Significantly, the measured C–C length, 1.319 Å, is close to the normal C–C length (calculated and measured parameters of triquinacene are cited in [33]).

8.2 TO THE LITERATURE

A feast of information on computational chemistry is available, a small selection of which is given below.

8.2.1Books

Listed in chronological order; readers should use their judgement to decide in which order to read them.

Essentials of Computational Chemistry. Theories and Models, C. J. Cramer, Wiley, New York, 2002.

Covers a wide range of topics. The level is sometimes quite advanced. Critical discussions of the literature.

Computational Chemistry: A Practical Guide for Applying Techniques to Real World Problems, D. Young, Wiley, New York, 2001.

computational chemistry programs. The material of this book is available at http://server.ccl.net/cca/documents/dyoung/

A Chemist’s Guide to Density Functional Theory, W. Koch and M. C. Holthausen, Wiley-VCH, New York, 2000.

Detailed introduction to the theory and applications of DFT.

Quantum Chemistry, 5th edn, I. N. Levine, Prentice Hall, Upper Saddle River, NJ, 2000.

Chapters 15, 16, and 17 give many references to the original literature, to books, to programs, and to websites. Enormously useful book on quantum chemistry in general.

Series of books from Wavefunction, Inc, makers of the Spartan computational chemistry program 2000 and earlier. For available books contact Wavefunction, http://www.wavefun.com/

These books, oriented toward Wavefunction’s Spartan program, are very useful introductions to the practice of computational chemistry.

Introduction to Computational Chemistry, F. Jensen, Wiley, New York, 1999. Good general introduction. Goes fairly deeply into theory.

Computational Thermochemistry, K. K. Irikura and D. J. Frurip, Eds., American Chemical Society, Washington, DC, 1998.

Useful source of information on the calculation of energy quantities: heats of formation, reaction energies, bond energies, activation energies, high-accuracy methods (G2, CBS, etc.), energies of solvation.

The Encyclopedia of Computational Chemistry, 5 volumes, P. von R. Schleyer, Ed., Wiley, New York, 1998.

A convenient source of information, but pricey (ca. $3000).

Molecular Mechanics Across Chemistry, A. K. Rappé and C. J. Casewit, University Science Books, Sausalito, CA, 1997.

Detailed presentation of the applications of MM, particularly in biochemistry and drug design.

Exploring Chemistry with Electronic Structure Methods, 2nd edn, J. Foresman and Æ. Frisch, Gaussian, Inc., Pittsburgh, PA, 1996.

Very useful hands-on guide; oriented toward Gaussian 94, but very useful for Gaussian 98 too.

Molecular Modelling. Principles and Applications, A. R. Leach, Longman, Essex, England 1996.

Good general introduction. Goes reasonably deeply into theory.

Modern Quantum Chemistry. Introduction to Advanced Electronic Structure Theory,

A. Szabo and N. S. Ostlund, 1st edn, revised, McGraw-Hill, New York, 1989.

A detailed, very advanced introduction to basic Hartree–Fock, CI, and MP theory.