FTIR (400–4000 cm⁻¹) spectra of “Bisphenol A” are presented. Absorption peaks (400–4000 cm⁻¹) are assigned on the basis of Density Functional Theory (DFT) with configuration as B3LYP 6-311G++ (3df 3pd). Calculated absorption peaks are in reasonable reconciliation with experimental absorption peaks after scaling with scale factor of 0.9679 except C-H and O-H stretching vibrations.

Bisphenol "A" is a widespread environmental hormone. After the prohibition on the use of BPA in some applications, it is progressively replaced by its variants. However, these variants of Bisphenol "A" are also noxious. It is therefore of the utmost importance to find the similarity among these materials and put all of them under restriction to avoid harmful effects. Therefore, Bisphenol "A", "AF", "E", and "S" are studied by Terahertz spectroscopy (0.5-2.5 THz). Various molecular vibrations are found and assigned based on density-functional-theory calculations. Refractive Indices are calculated as well. The principal component analysis reveals the critical vibrational frequencies for their detection and shows the correlation between them.

Bisphenol “S” (BPS), a common replacement for bisphenol “A” (BPA) after its ban in food contact applications, is studied by Fourier transform infrared (FTIR) spectroscopy ($400–6800{\mathrm{cm}}^{-1}$). Identified molecular vibrations are assigned based on density functional theory calculations. As BPS is suspected to be as toxic as BPA, principal component analysis is used to find possible correlations among their molecular vibrations. We have found frequencies showing a connection between these two materials via molecular vibrations, helping not only to categorize such materials but also to find the origin of their toxicity.