Abstract
The following selectivities are reported for partitioning of the α-(N,N-dimethylthiocarbamoyl)-4-methoxybenzyl carbocation 1+ between nucleophilic addition of π-nucleophiles and a solvent of 50:50 (v:v) acetonitrile/water at 25 °C (nucleophile, kNu/ks): pyrrole, 23 M-1; 2-methoxythiophene, ≈2 M-1. No nucleophile adducts (<2% of total products) were detected from the reaction of this carbocation in the same solvent containing the following carbon nucleophiles: thiophene (0.10 M), furan (0.10 M), ethyl 1-propenyl ether (0.10 M), amd 1-cyclohexenyl trimethylsilyl ether (0.01 M). These results show that only π-nucleophiles with Mayr nucleophilicity parameters greater than N ≈ 6 are sufficiently reactive to compete with nucleophilic aqueous solvents for addition to 1+, and they provide support for a simple relationship between the Ritchie N+ scale of nucleophilicity in water and the Mayr N scale of nucleophilicity in weakly polar nonnucleophilic solvents.2,3 Our data require a large effective molarity for th...
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