ISSN:
0192-8651
Schlagwort(e):
Computational Chemistry and Molecular Modeling
;
Biochemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Informatik
Notizen:
Calculations of 13C chemical shifts in some simple hydrocarbons have been carried out using the GIAO approach in the MINDO/3 semiempirical formalism. In order to achieve reasonable agreement with experiment it is necessary to modify (increase) the vacant orbital energies in the MINDO/3 calculation in order to reduce the magnitude of the paramagnetic contribution, and to also modify this dominant term by generally reducing it as a function of the number of hydrogen and carbon atoms bonded to the resonant nucleus in question. For a set of 34 resonant nuclei of the simpler hydrocarbons, agreement with experiment of the order of 7.8 ppm is attained; however, pathological cases such as cyclopropane and some simple allenes continue to cause problems, increasing the standard deviation of the full set to 12.5 ppm. Our results indicate that the MINDO/3 approach is as viable for 13C chemical shift calculations as other semiempirical approaches, all of which seem currently to be limited to a standard deviation of the order of 10 ppm.
Zusätzliches Material:
2 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jcc.540090417
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