Indirekte Kernspinkopplung in den Tetramethylverbindungen der IV. Gruppe

Abstract

The indirect nuclear spin-spin coupling between protons, C¹³ and the spin ½ isotopes of the group IV elements (Si²⁹, Sn¹¹⁹ and Pb²⁰⁷) were investigated in the tetramethylcompounds X(CH₃)₄. Substances enriched in C¹³ were used. The absorption of the most sensitive nucleus H¹ was observed directly while the resonances of the other nuclei were located by a double resonance technique. The normalized coupling constants between directly bonded nuclei were found to be positive in all cases while their magnitudes are in good agreement with a semi-empirical estimate using the contact mechanism. All normalized two-bond X—C—H coupling constants are negative while the three-bond C—X—C—H coupling constants are positive as well as the four-bond H—C—Si—C—H coupling constant. Using these results it is shown that the sign of the normalized X—H coupling constants in the analogous hydrides XH₄ are positive confirming a theoretical prediction made in previous work.