NMR spectroscopy is a key method for characterizing molecular structures . In this study, four DFT functionals, B3PW91, PBEPBE, CAM-B3LYP, and M06-2x ---combined with the aug-cc-pVTZ basis set, were employed to calculate the carbon NMR chemical shifts in the gas phase and in CHCl3 solvent, as the available NMR measurements in the literature were conducted in this solvent. The carbon NMR chemical shifts were referenced to tetramethylsilane (TMS) with a shielding value (δC) of 182.47 ppm for 13 C chemical shifts. In accordance with these recommendations, our NMR calculations utilized gauge-invariant atomic orbitals (GAIOs). This method has yielded accurate solution NMR chemical shifts for resveratrol in our previous study . All quantum mechanical calculations were performed using the Gaussian 16 computational chemistry packages and the Amsterdam Density Functional (ADF) suites of programs [36].