Electron delocalizaton interactions and NMR spin-spin coupling constants in saturated cage compounds

since the cage substrate of 1-x;3-y-bicyclo[1.1.1]pentanes is notably strained, it is expected that in compounds of this type important trans-cage spin-spin coupling constants, ssccs, could be observed. such ssccs should be dominated to a great extent by the fermi contact, fc, contribution since this term, for long-range couplings, is transmitted by electron-transfer interactions, which in strained compounds are particularly enhanced. in this paper, both theoretically and experimentally, 4j(13ca,1h3) ssccs in 1-x-bicyclo[1.1.1]pentanes, where the a-atom of group x is 13c, are studied. results are compared with similar trans-cage ssccs in analogous compounds. insights into electron delocalization interactions defining the experimental trends are obtained through the study of s-hyperconjugative interactions of cage bonds. these interactions are studied using the natural bond orbital, nbo, method. results suggest that multipath additivity should hold in compounds where trans-cage ssccs are determined by charge transfer interactions.