Computational chemistry, chemical shift

Buhl, M. 1998, NMR Chemical Shift Computation Structural Applications , in Encyclopedia of Computational Chemistry, Schleyer, P. v. R. (Editor-in-Chief), Wiley, Chichester. 

Basis Sets Correlation Consistent Sets Benchmark Studies on Small Molecules Coupled-cluster Theory Gradient Theory M0ller-Plesset Perturbation Theory NMR Chemical Shift Computation Ab Initio Spin Contamination Symmetry in Chemistry. 

The definitive method for determining static structures is X-ray diffraction. Indeed, the 1976 Nobel Prize in Chemistry was awarded to Professor William N. Lipscomb for his work in determining structures of the boron hydrides by diffraction methods. However, it must be remembered that packing forces and solvation effects may change the preferred structure between solid state and solution. Another technique, which combines theory and experiment, has established a reliability on a par with X-ray diffraction for confirming structures. It is called the ab /n/n o/IGLO/NMR method (see NMR Chemical Shift Computation Structural Applications for an extensive discussion of calculated NMR chemical shifts) and combines calculated chemical shifts for a number of possible structures with the experimentally measured chemical shifts in solution. 

Nuclear magnetic resonance (NMR) is one of the major experimental tools in structural chemistry and biochemistry. The prediction of NMR shifts from ab initio calculations has been demonstrated for isolated molecules (see NMR Chemical Shift Computation Ab Initio), but the development of a practical ab initio approach for the calculation on NMR shifts in solids has been accomplished only quite recently. Based on DFT-LDA and a pseudopotential plane wave approach, these authors have presented an approach which promises to be useful in the investigation of NMR shifts in crystalline solids as well as in amorphous materials and liquids. As a demonstration of this approach, Mauri et al. have calculated the H NMR shifts of LiH and HF in the state of isolated molecules and in a crystal. In the case of LiH the results show very little change between the free molecule (a = 26.6 ppm) and the crystal (cr = 26.3 ppm). However, a significant change is found for the crystal at high pressures (65 GPa), where the chemical shift increases to 31.2 ppm. A quite different picture is obtained for the HF molecule, where the theory predicts a shift of 28.4 ppm in remarkable agreement with the experimental value of 28.4 ppm. For the HF crystal, a shift of... 

Infrared Data Correlations with Chemical Structure Infrared Spectra Interpretation by the Characteristic Frequency Approach Neural Networks in Chemistry NMR Chemical Shift Computation Ab Initio NMR Chemical Shift... 

Since about 1990, powerful post-Hartree-Fock approaches for the inclusion of electron correlation in chemical shift calculations have been developed and applied in main group chemistry (see NMR Chemical Shift Computation Ab Initio and NMR Chemical Shift Computation Structural Applications). Unfortunately, these correlated methods are computationally too demanding at present to be applied to transition metal complexes and clusters of chemically relevant size. In particular, the least expensive post-CHF method available, the MP2-GIAO approach, is expected to fail for systems with significant nondynamical correlation effects. 

Density Functional Applications Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Density Functional Theory Applications to Transition Metal Problems ESR Hypeifine Calculations Gradient Theory Metal Complexes Molecular Magnetic Properties NMR Chemical Shift Computation Ab Initio NMR Chemical Shift Confutation Structural Applications NMR Data Correlation with Chemical Structure Relativistic Effective Core Potential Techniques for Molecules Containing Very Heavy Atoms Relativistic Effects of the Superheavy Elements Relativistic Theory and Applications Transition Metal Chemistry Transition Metals Applications. 

Chemometrics Multivariate View on Chemical Problems Combinatorial Chemistry Factual Information Databases Fuzzy Methods in Chemistry Infrared Data Correlations with Chemical Structure Infrared Spectra Interpretation by the Characteristic Frequency Approach Inorganic Chemistry Databases Inorganic Compound Representation NMR Chemical Shift Computation Ab Initio NMR Chemical Shift Computation Structural Applications NMR Data Correlation with Chemical Structure Online Databases in Chemistry Spectroscopy Computational Methods Standard Exchange Formats for Spectral Data Structure and Substructure Searching Structure Determination by Computer-based Spectrum Interpretation Structure Generators Synthesis Design. 

Chemical concepts of catalytic cracking, 4 1 Chemical feedstock, history, 30 161-162 Chemical shift, 42 120-122 anisotropy, 33 204-205, 42 123-124 computational chemistry, 42 129-137 molecular structure and, 42 129-133 tensor, 42 124-125, 133-135 theoretical calculations, 42 133-137 theory, 42 122-129 in XAS, 34 228, 231-232 to describe change in Fermi energy of metal, 34 232... 

Complex reactions, routes of, 28 188-192 Components in Gibbs phase rule, 32 317-319 Computational chemistry chemical shift, 42 129-137 Condensation... 

Ahlrichs R, von Arnim M (1995) TURBOMOLE, parallel implementation of SCF, density functional, and chemical shift modules. In dementi E, Corongiu G (eds) Methods and techniques in computational chemistry. STEF, Cagliary Eichkorn K, Treutler O, Ohm H, Haser M, Ahlrichs R (1995) Chem Phys Lett 242 652 Becke AD (1988) Phys Rev A 38 3098 Perdew JP (1986) Phys Rev B 33 8822 Garrou PE (1985) Chem Rev 85 171 and references cited therein... 

On a more positive note, multimedia enable us to respond pedagogically to the shifting paradigms of science, where, as remarked above, numerical analysis is replacing analytical solutions of equations. Through it, we can present computational chemistry, for instance, and pursue the fascinating complexity that arises from systems of coupled differential equations in chemical kinetics. 

To aid in the analysis of NMR spectra, computer programs have been developed which solve the nuclear-spin secular equation.12 The input to these programs is the observed spectral data and initial guesses for the chemical shifts and coupling constants by an iterative process, accurate parameters are calculated. Programs are available from the Quantum Chemistry Program Exchange (Section 1.21). 

Recent developments in computational chemistry have established the exact structure of carbocations by combining computational and experimental results.78,79 Furthermore, accurate 1H and 13C NMR chemical shifts of carbocations and other organic molecules can be calculated with the application of recent coupled cluster methods, such as GIAO-CCSD(T).80... 

This volume was developed from the second international symposium on NMR chemical shifts. This meeting was organized by the editors at the 216th National Meeting of the American Chemical Society, Boston, Massachusetts, August 23-26,1998, and was cosponsored by the ACS Divisions of Computers in Chemistry and Physical Chemistry. The symposium included four extended lectures by Jameson, Ando, Oldfield, and Nicholas, which are included in this volume as Chapters 1-4, respectively. These lectures provide a convenient review of the current state of the art in the calculation of the NMR chemical shielding (Jameson, Chapter 1), and its application to different areas of chemistry polymers (Ando), biomolecules (Oldfield), and catalysis (Nicholas). 

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