CCSD(T) CALCULATION OF NMR CHEMICAL-SHIFTS - CONSISTENCY OF CALCULATED AND MEASURED C-13 CHEMICAL-SHIFTS IN THE 1-CYCLOPROPYLCYCLOPROPYLIDENEMETHYL CATION

The source of conspicuous disagreement between theory and experiment f or the chemical shift of C-alpha in the 1-cyclopropylcyclopropylidenem ethyl cation is identified as an inadequate treatment of electron corr elation effects in a previous theoretical study. When the sophisticate d CCSD(T) method is used, all calculated C-13 chemical shifts agree wi th the experimental values to within 2.2 ppm, These findings undermine the basis of an earlier suggestion that the selectively poor performa nce of theory for the C-alpha nucleus can be attributed to environment al effects in which solvent interactions significantly perturb the geo metrical structure of the cation.