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DOI: 10.1039/A902184A (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1999, 1317-1322

Predictions of 13C chemical shifts in carbocations. The use of scaled chemical shifts calculated using GIAO DFT methods[hair space]†

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Valerije Vrček, Olga Kronja and Hans-Ullrich Siehl

Abstract

Accurate prediction of 13C chemical shifts (δpred) for the C+ and the α- and β-carbon atoms in alkyl and cycloalkyl carbocations is achieved through scaling. Abinitio calculated chemical shifts (δcalc) at the GIAO-B3LYP/6-311G(d,p)//B3LYP/6-31G(d) level of theory for 16 different carbocations are scaled using a linear correlation equation (δpred = aδcalc + b). The slope and intercept a and b were determined separately for C+ and the α- and β-carbon positions, and were found to be different for cation structures preferentially stabilized by β-C–H and β-C–C hyperconjugation. A very good correlation of all predicted and experimental chemical shifts is obtained (a = 0.999 ± 0.002, b = 0.231 ± 0.320). Preliminary results indicate that scaling using linear correlations can also be applied to the C+ carbon chemical shift in benzyl type carbocations.

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