FULL H-1 AND C-13 NMR CHEMICAL-SHIFT ASSIGNMENT OF 1-PYRENYL SUBSTITUTED OLIGOSILANES AS A TOOL TO DIFFERENTIATE BETWEEN INTRAMOLECULAR THROUGH-SPACE AND THROUGH-BOND GROUND-STATE INTERACTIONS

A detailed analysis strategy is developed to realize a full proton and carbon NMR chemical shift assignment of a series of substituted 1-pyr enylsilane derivatives mainly based on direct and long-range proton-ca rbon chemical shift 2D-correlation spectroscopy. The proton and carbon chemical shifts of two dimethylaniline substituted 1-pyrenylsilane de rivatives (P2D and P3D) and a pentafluorophenyl substituted 1-pyrenyls ilane derivative (P2F) are compared to nonsubstituted 1-pyrenylsilane derivatives of different silane chain lengths (P2, P3, and P6). Accura te C-13 shifts Of these compounds are shown to be an important tool to study the character of the ground state interactions in these compoun ds. They are more sensitive than H-1 shifts, and the interpretation is more straightforward since there is no confusion with possible chemic al shift anisotropy effects. The analysis leads to the conclusion that changes in local electron density, caused by a donor group as dimethy laniline or by an acceptor group as pentafluorophenyl, are transferred to the pyrene moiety primarily via ''through space'' electrostatic po larization effects rather than donor-acceptor effects. The observed ch anges in chemical shift point to the presence of a significant contrib ution of folded conformations in the ground state for the alpha,omega- substituted silane derivatives.