# IR and Raman Dual Modality Markers Differentiate among Three _bis_-Phenols: BPA, BPS, and BPF
## 3 Results  
### IR and Raman Band Assignment  
The chemical structures of BPA, BPS, and BPF (Figure 1) identifying the difference among the three _bis_-phenol compounds contain CH\({}_{3}\)-C-CH\({}_{3}\), O=S=O, and H-C-H, respectively. The structural difference suggests that bond distance and bond angles among CH\({}_{3}\)-C-phenol, O=S-  
phenolic groups are assigned based on the phenolic group in the article. C-H stretching in CH3 (IR 2965 cm\({}^{-1}\), Raman 2973 cm\({}^{-1}\)) and CH3-C-CH3 scissoring (Raman 1106 cm\({}^{-1}\) asym) assignments are cited as referenced. The wavenumbers which involve symmetrical vibrational modes are most intense in IR, and those which involve asymmetrical vibrational modes are most intense in Raman. \begin{table}
\begin{tabular}{c c c} \hline
**Wavenumber (cm\({}^{-1}\))** & **IR Assignments** & **Raman Assignments** \\ \hline
561 & (C-C-C ip bend) & \\
636 & & C-C-C-OH twist \\
728 & C-C-C ip bend & \\
758 & & C-C-C-O-H wag \\
824 & C-C-C trigonal bend & \\
826 & & C-C-C trigonal bend \\
1013 & C-H oop bend & \\
1083 & C-H twist & \\
1106 & & CH3 scissoring asym \\
1173 & & CH2 twisting \\
1177 & CH2 twisting & \\
1216 & CH2 twist + OH bend & \\
1229 & & C-H ip bend \\
1250 & & C-H bending asym \\
1361 & C-H bending sym & \\
1436 & & OH bend asym \\
1459 & & CH3 deformation asym \\
1508 & (C-H ip bend in-phase) & \\
1592 & & C=C stretch in phenol asym \\
1598 & C=C stretch in phenol sym & \\
1611 & C=C stretch in phenol asym \\
1612 & & C=C stretch in phenol asym \\
2965 & & C-H str in CH3 asym \\ \hline \end{tabular}
\end{table} 
Table 1: Vibrational mode assignments of BPA. Figure 4: Normalized IR and Raman spectrum measurements on 10 replicates of BPF. The full-range IR and Raman spectra of BPS (Figure 3) show vibrational modes characteristic of its structure. The vibrational modes for O-S-phenol enable access to the tilt of the phenolic ring relative to the O=S- moiety. In this data set, the relative intensity of corresponding wavenumbers is the major difference between IR and Raman spectra. The IR wavenumbers (1601 cm\({}^{-1}\), 1582 cm\({}^{-1}\), 1497 cm\({}^{-1}\), 1281 cm\({}^{-1}\), 1221 cm\({}^{-1}\), 1335 cm\({}^{-1}\), 1099 cm\({}^{-1}\), 835 cm\({}^{-1}\), and 813 cm\({}^{-1}\)) reasonably match Raman wavenumbers (3070 cm\({}^{-1}\), 1596 cm\({}^{-1}\), 1580 cm\({}^{-1}\), 1495 cm\({}^{-1}\), 1284 cm\({}^{-1}\), 1219 cm\({}^{-1}\), 1335 cm\({}^{-1}\), 1099 cm\({}^{-1}\), 826 cm\({}^{-1}\), and 823 cm\({}^{-1}\)). The two highest intensity IR peaks are 544 cm\({}^{-1}\) and 1099 cm\({}^{-1}\), the first of which has no corresponding Raman peak. The three largest peaks unique to Raman (3070 cm\({}^{-1}\), 1067 cm\({}^{-1}\), and 628 cm\({}^{-1}\)) have virtually no corresponding IR peaks at a similar wavenumber. These five peaks confirm BPS identity. The assignment of wavenumbers to IR and Raman vibrational modes referenced in the literature is shown in Table 2. [PERSON] et al. [19] used DFT to calculate the wavenumber of BPS which enabled assignments of structurally unusual C-S stretching in C-SO2 moiety (near 685 cm\({}^{-1}\)) and S-O stretching (near 1099 cm\({}^{-1}\)) [20]. Comparisons with wavenumbers and assignments for BPA were also reported. CH\({}_{3}\)-C-CH\({}_{3}\) scissoring asym (Raman 1106 cm\({}^{-1}\) asym) appears in the same spectral range as S-O stretching. The analogous vibrational mode O-S-O scissoring and/or C-S-C (in phenol-S-phenol moiety) scissoring was not specifically assigned or identified. In addition in IR, three sets of paired similar-intensity peaks are present (1497 cm\({}^{-1}\) and 1441 cm\({}^{-1}\); 1281 cm\({}^{-1}\) and 1221 cm\({}^{-1}\); and 721 cm\({}^{-1}\) and 688 cm\({}^{-1}\)). No comparable equal-intensity sets of pairing was observed in Raman. One explanation for the IR pairing in BPS is that the vibrational modes site to site on the two phenolic groups are symmetrical, of nearly equal intensity, and in sync in wavenumber but 180 degrees out of phase.