# IR and Raman Dual Modality Markers Differentiate among Three _bis_-Phenols: BPA, BPS, and BPF
## 3 Results
### IR and Raman Dual Modality  
Spectroscopic data provide critical structural information on _bis_-phenol compounds. The simplest value of dual modality is that relevant wavenumbers can be present only in IR or only in Raman. The bis-phenol moiety contains two ring hydroxyl groups; yet compelling evidence of OH stretching in the IR region is absent. Because the oxygen atom is in the same plane as the ring, asymmetric OH stretching corresponds to H stretching above or below the ring, and symmetric OH stretching is H stretching in plane with the ring. Two symmetrical OH stretching modes in sync (and 180 degrees out of phase) can explain the absence of OH stretching in the IR spectra of BPA, BPS, and BPF; the corresponding Raman peaks (3066 cm\({}^{-1}\), 3070 cm\({}^{-1}\), and 3056 cm\({}^{-1}\)) are different from each other. We found other wavenumbers which are even stronger unique fingerprints for distinguishing among these three compounds (Figure 5). In BPA, the IR peak at 1508 cm\({}^{-1}\) has a very high normalized intensity versus the corresponding Raman peak. The ratio is 10.6 times larger in BPA in IR than in Raman; in BPF, the ratio is only 2.8 times larger; in BPS, the ratio is 0.57 (i.e., the Raman peak instead is 1.8 larger). In BPS, at 721 cm\({}^{-1}\), the ratio is 7.4 times larger than in Raman. In contrast with BPA, the ratio is 1.7 times larger, and in BPF, the ratios are similar (0.93). In BPS, also at 1099 cm\({}^{-1}\), the ratio is 1.9 times larger than in Raman. In BPA, the ratio is 0.37 (the Raman peak is 2.7 times larger) and in BPF, the ratio is 5.1 times larger. In BPF, the Raman signal at 845 cm\({}^{-1}\) is 6.3 times greater than in the IR spectrum. In BPA and BPS, the corresponding peaks between Raman and IR are of similar intensity. The specific vibrational modes unique to BPA, BPS, and BPF can be assigned quite precisely. For BPA, 1508 cm\({}^{-1}\) corresponds to 1512 cm\({}^{-1}\) assignable to in-plane in-phase bending at three adjacent sites [3 (C-H ip bend in phase)]. Since the structure is a _bis_-phenol, vibrational modes on each molecule include six molecular sites. For BPF, the normalized relative intensity is 2.8, i.e., C-H ip bend in-phase can be assigned to only one of the phenol rings. For BPS, no peak in that wavenumber indicates that neither of the rings includes 3 (C-H ip bend in phase). The closest wavenumber to a peak in that spectral range corresponds to asymmetric C-C stretching: the intensity of the Raman peak is twice as large as in IR. For BPS, the wavenumbers 720 cm\({}^{-1}\) and 1099 cm\({}^{-1}\) correspond to a set of vibrational modes that can occur concurrently. The first wavenumber C-C-C ip bend (734 cm\({}^{-1}\)) assigns three adjacent carbon atoms (excluding C4) in bending in-plane in sync. Three different C-C-C sites can bend in-plane in the same phenol ring or six per two phenol rings. The second wavenumber (1134 cm\({}^{-1}\)) corresponds to in-phase C-H bending at C4 and occurs only once per ring. The normalized relative intensity ratio of two supports that this vibrational mode is occurring symmetrically and concurrently on both rings. In contrast, for BPA, the normalized relative intensity suggests that the first three-carbon bending mode occurs only once on each ring and the vibrational modes remain symmetrical. For BPF, the ratio IR to Raman is essentially one. \begin{table}
\begin{tabular}{c c c} \hline
**Wavenumber (cm\({}^{-1}\))** & **IR Assignments** & **Raman Assignments** \\ \hline
1596 & & CH ip bend in phase asym \\
1599 & C=C stretch in phenol sym & C=C stretch in phenol asym \\
1608 & & C=C stretch in phenol asym \\
1612 & C=C stretch in phenol sym & C=C stretch in phenol asym \\
2911 & Sym CH str on C-CH\({}_{2}\)-C & \\
3021 & Sym CH str on C-CH\({}_{2}\)-C & Asym CH str on C-CH\({}_{2}\)-C \\
3038 & OH ip str & OH op str \\
3056 & OH ip str & \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._For BPF, the wavenumber 845 cm\({}^{-1}\) can be assigned to 840 cm\({}^{-1}\) C-C-C trigonal bending which is a Raman frequency.