Prediction of the 13C NMR Chemical Shifts of Fluorenone Analogues by the GIAO Method

After the geometry optimization at B3LYP/6-31+G(d,p) level, the NMR calculations of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31+G(d) level and B3LYP/6-311G+(2d,p) level, respectively. The 13C NMR chemical shifts calculated at HF/6-31+G(d) level show better agreement with the observed values. By a series of linear correction equations (δpred = a + bδcalc), accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound. The linear correlation of δpred with δexptl is excellent, and the square of correlation coefficient, r2, is up to 0.994. The maximum absolute difference between δpred and δexptl, △δ, is 4.6 ppm, and the root-mean-square error between δpred and δexptl is only 2.6 ppm.