Theory of the influence of the second co-ordination sphere on the chemical shift

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Abstract
Starting from a description of a molecular wave function using bond orbitals a general formula was derived describing the change of an expectation value of a one electron operator with bond polarization. This equation leads to a bond additive scheme for the description of bond polarization effects containing matrix elements of the Fock-operators. For these matrix elements simple formulae were derived for the case of a point charge approximation. In a second part of the paper this formalism is used for the interpretation of the influence of the second co-ordination sphere on the chemical shift. This scheme is used for a discussion of the 1H chemical shifts of selenites. The variation of the chemical shifts in dependence of the geometry of the hydrogen bond can be understood. Furthermore the theory proved to be useful for the interpretation of the bond angle dependence of 29Si chemical shifts in silica polymorphs. Finally it is possible to study π-bond polarization of various substituents and its influence on 13C chemical shifts. Especially vinyl and cyclohexene derivatives are investigated. In the case of propenyl compounds an explanation for the cis-trans differences in chemical shifts can be given.

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