EFFECTS OF SUBSTITUENT GROUPS ON SPIN-SPIN COUPLING IN NUCLEAR MAGNETIC RESONANCE.
Final rept. 27 Feb 63-15 Jun 66,
STEVENS INST OF TECH HOBOKEN NJ
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The initial phases of this investigation were motivated by the observation that certain spin-spin coupling constants are directly additive whereas others are pairwise additive with respect to the substituent groups. During the study it has been found that the directly bonded C-F, Si-H and Sn-H and nondirectly bonded Sn-H couplings are pairwise additive. Furthermore, the C13 and proton shifts of substituted methanes of the form CHXYZ are pairwise additive with respect to substituents X, Y and Z. The methyl proton shifts of substituted ethanes having the form H3C-CXYZ were found to be directly additive. In light of the above observations a theoretical study was made. By the use of McWeeny group functions and the popular Ramsey formulation of NMR it was possible to account for all of these experimental findings concerning spin-spin couplings and chemical shifts. Furthermore, symmetry considerations were shown to play an important role in the theoretical aspects of spin coupling. It has been found that the approximate, zero-order, ground-state wave-function must lie below the true energy of the first excited state for second-order energy calculations. This condition is rarely met for molecules more complicated than hydrogen. A simple model consisting of two, noninteracting electrons confined to a one-dimensional square-well potential was used to test the perturbation method employed in spin coupling calculations. This study showed that the Ramsey theory correctly treats the Fermi contact mechanism, at least for this simple case. Author
- Nuclear Physics and Elementary Particle Physics