Experimental and DFT evaluation of the 1H and 13C NMR chemical shifts for calix[4]arenes

The density functional theory is employed to determine the efficiency of 11 exchange-correlation (XC) functionals to compute the H-1 and C-13 NMR chemical shifts of p-tert-butylcalix[4]arene (ptcx4, R-1 = C(CH3)(3)) and congeners using the 6-31G(d,p) basis set. The statistical analysis shows that B3LYP, B3PW91 and PBE1PBE are the best XC functionals for the calculation of 1H chemical shifts. Moreover, the best results for the C-13 chemical shifts are obtained using the LC-WPBE, M06-2X and wB97X-D functionals. The performance of these XC functionals is tested for three other calix[4]arenes: p-sulfonic acid calix[4]arene (sfxcx4- R-1= SO3H), p-nitro-calix[4]arene (ncx4, R-1=NO2) and calix[4]arene (cx4 - R-1 = H). For H-1 chemical shifts B3LYP, B3PW91 and PBE1PBE yield similar results, although B3PW91 shows more consistency in the calculated error for the different structures. For C-13 NMR chemical shifts, the XC functional that stood out as best is LC-WPBE. Indeed, the three functionals selected for each of H-1 and C-13 show good accuracy and can be used in future studies involving the prediction of H-1 and C-13 chemical shifts for this type of compounds. (C) 2017 Elsevier B.V. All rights reserved.