INTERPRETATION OF SUBSTITUENT-INDUCED CHEMICAL-SHIFTS IN C-13 NMR-SPECTRA OF 2-SUBSTITUTED NORBORNADIENES - INFLUENCE OF HOMOCONJUGATION

Complete signal assignments and an interpretation of the C-13 NMR spec tra of bicyclo[2.2.1] hepta-2,5-diene and of 12 of its 2-substituted d erivatives are presented, The substituent effects observed at C-l, C-2 and C-3 are very similar to those reported for 2-substituted propenes and monosubstituted benzenes, Transmission of those effects on C-5 an d C-6 may be at least partially attributed to the homoconjugative inte raction between the double bonds in the systems investigated, The rela tive importance of the field and the resonance effects at particular p ositions have been evaluated by the dual substituent parameter analysi s of the chemical shift data, Relationships between substituent-induce d chemical shifts and electron densities, calculated by the PM3 method , have been found.