2.3 | DFT Calculations
The bisphenol a was obtained from the reaction of phenol with acetone, but, many by-products can be formed in addition to the target product. In this section, the reaction mechanism is theoretically examined and the energies of the bisphenol a and by-product, TS and intermediate are calculated. Thus, the formation possibilities of products and by-products were investigated theoretically. All molecules were optimized using Density functional theory (DFT)/ B3LYP method (Becke, 1993) and 6-311++G(d,p) basis set. In addition, harmonic frequencies of the structures were calculated at the same method and basis sets to find a local minimum (all positive force constants) or transition states (one imaginary force constant only). All calculations were performed with Gaussian 09 program package (Frisch et al. 2009).