B. Shoulders, S. C. Welch, "A Very Brief, Rapid, Simple, and Unified Method for Estimating Carbon-13 NMR Chemical Shifts," J. Chem. Ed., 1987, 64(11), 915-918.
Thanks to Peter Ertl, Novartis Institutes for Biomedical Research, and Bruno Bienfait for the use of their JSME molecular editor.
Colby College Chemistry, T. W. Shattuck, 2/15/16