Geometry Effects in NMR Spectra - the y-gauche Effect

As can be seen from Eq. (2.28), the chemical shift is a general 2 rank tensor. In NMR spectra, only the symmetric part 

When comparing experimental and theoretical data, it is essential to note that theoretical calculations yield absolute values with respect to the bare nucleus in vacuo whereas experimental data refer to a reference (Tetra-Methyl-Silane (TMS) for ). The experimental scale 6 is related to the theoretical scale G via 

The most important geometrical effect on NMR spectra of chain molecules is the y-gauche effect and has already been discussed in the Introduction. The experimental effect has been parametrized by a phenomenological theory 

2 Notions and Concepts in Chain Molecules and Quantum Chemistry 

The Y g( tiche constants yXi are empirical parameters and have to be adjusted by comparison with experiment. 

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