Tautomeric conversion, vibrational spectra, and density functional studies on peripheral sulfur derivatives of benzothiazole and benzothiazoline isomers

Accepted Manuscript Tautomeric conversion, vibrational spectra, and density functional studies on peripheral sulfur derivatives of benzothiazole and benzothiazoline isomers Ahmet Altun, Eziz Kulyyev, Naz M. Aghatabay PII: DOI: Reference:

S1386-1425(15)30120-7 http://dx.doi.org/10.1016/j.saa.2015.07.071 SAA 13970

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

16 March 2015 13 July 2015 14 July 2015

Please cite this article as: A. Altun, E. Kulyyev, N.M. Aghatabay, Tautomeric conversion, vibrational spectra, and density functional studies on peripheral sulfur derivatives of benzothiazole and benzothiazoline isomers, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa. 2015.07.071

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Tautomeric conversion, vibrational spectra, and density functional studies on peripheral sulfur derivatives of benzothiazole and benzothiazoline isomers Ahmet Altun

a,b,*

c

c

, Eziz Kulyyev , Naz M. Aghatabay

a

b

Department of Physics, Fatih University, Büyükçekmece, Istanbul 34500, Turkey Department of Genetics and Bioengineering, Fatih University, Büyükçekmece, Istanbul 34500, Turkey c Department of Chemistry, Fatih University, Büyükçekmece, Istanbul 34500, Turkey

Abstract The room temperature structural (tautomerism, dimerization, conformational preference, geometry parameters) and vibrational spectral (IR and Raman) analyses have been performed on benzothiazoline (benzothiazoline-2-thione, 3-methyl-benzothiazoline-2thione) and benzothiazole [2-mercaptobenzothiazole, 2-methylthiobenzothiazole, and bis(benzothiazole-2-ylthio)ethane] derivatives at the B3LYP/6-311++G** level of theory. Although the keto to enol transition barriers are too high over the most stable benzothiazoline isomers, vibrational spectral analyses reveal some major bands of benzothiazole isomers in the present room temperature experimental FT-IR and FT-Raman specta. Therefore, benzothiazole isomers exist at rare amounts in the powdered samples that are mainly composed of benzothiazoline isomers. The benzothiazole isomers have two stable conformations due to the orientation of their SH and SCH3 moieties. The energetic and vibrational spectral analyses suggest that the benzothiazoline-2-thione molecules can be stabilized further through the NH⋅⋅⋅S intermolecular hydrogen bonds in solid phase. All observed fundamental vibrational bands of the molecules have been assigned based on the calculated mode frequencies and IR/Raman intensities. The mode assignments have been expressed in terms of internal coordinates and their percent potential energy distributions. The effects of substitution at the nitrogen and peripheral sulfur atoms have been analyzed for the geometries and vibrational bands of the molecules. Keywords: benzothiazole; benzothiazoline; Infrared; Raman; Density functional theory (DFT); Normal mode *

Corresponding author. Tel.: +90-212-866-3300; Fax: +90-212-866-3402;

E-mail address: [email protected] (A. Altun) 1

1. Introduction Benzothiazole and benzothiazoline are composed of benzene-fused deprotonated and protonated thiazole ring at the ring nitrogen, respectively. When an –SR (R = H and CH3) group is bound to thiazole moiety of benzothiazole, the resulting compound may additionally exist as a benzothiazoline derivative due to the migration of the R moiety from the sulfur (S) substituent to the thiazole nitrogen, known as the keto-enol tautomerism of sulfur (Figs. 1 and 2). However, temperature-dependent NMR measurements between – 90°C to +90°C suggest the presence of only benzothiazoline isomer for R = H [1]. An analogous conclusion is drawn from NMR studies when the ring sulfur atom is replaced with an oxygen atom [2]. In this study, tautomerism of the sulfur derivatives of benzothiazoles and benzothiazolines, which have several potent technological applications [3-5], will be discussed via potential energy surface (PES) scans that connect the two isomeric forms and vibrational spectral analyses. The studied isomers of this purpose (Figs. 1 and 2) are monomeric and dimeric 2-mercaptobenzothiazole (abbreviated as BT-NSH) and

benzothiazoline-2-thione (abbreviated

as BT-NHS) for R = H,

and 2-

methylthiobenzothiazole (abbreviated as BT-NSMe) and 3-methyl-benzothiazoline-2thione (abbreviated as BT-NMeS) for R = CH3. Moreover, substitutional effects on the structures and vibrational spectra of benzothiazole and benzothiazoline derivatives will be investigated. For this purpose, we study also the structure and vibrational spectra of bis(benzothiazole-2-ylthio)ethane that has a chemical formula of C16H12N2S4 and abbreviation of bis(BT-NS)Et (Fig. 1). The geometrical structures and the experimental vibrational spectra of the compounds will be analyzed based on present density functional theory (DFT) calculations. Fig. 1 Fig. 2

2

The studied compounds are chelating agents as they contain one unit of nitrogen and two units of sulfur in their contents. They are thus effective ligands in coordination chemistry and used in pre-concentration of silver ions [6,7], the inhibition of iron and cobalt corrosion [8,9], and cleaning water systems from heavy metals [10]. They are extensively used in rubber industry, such as, in manufacturing tyres and shoes [11]. They are also fungicidal and inhibitors of thyroid hormone [12]. Detailed analyses on structural and spectroscopic features of these compounds that have biological importance and widespread applications in industrial processes will enhance our understanding on their structure-function relations. 2. Experimental details 2.1. Synthesis All chemicals and solvents necessary for the synthesis of BT-NSMe / BT-NMeS and bis(BT-NS)Et were reagent grade and used as purchased without further purification. For synthesizing BT-NSMe / BT-NMeS, methyl bromide (475 mg, 5 mmol) dissolved in ethanol (5 mL) was added to a solution of BT-NSH / BT-NHS (835 mg, 5 mmol) in ethanol (5 mL) containing KOH (336 mg, 6 mmol). The mixture was stirred at 60oC for overnight. The solvent was evaporated under vacuum and the residue was poured into 200 mL of ice-cold distilled water. The white crystaline solid was obtained (720 mg, 80%). M.p 43-45 oC. 1H NMR (CDCl3), δH ppm: 2.68 (s, 3H, CH3), 7.32 (t, H), 7.43 (t, H), 7.81 (d, H), 7.89 (d, H).

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C{1H} NMR (DMSO-d6), δC ppm: 15.88 (CH3), 120.90 (C), 121.38

(C), 124.05 (C), 126.01 (C), 135.15 (C), 153.36 (C), 167.94 (C). For synthesizing bis(BT-NS)Et, sodium benzothiazole-2-thiolate (378 mg, 2 mmol) was mixed well with adsorbent silica gel (350 mg, 60 mesh) in CH2CL2 (2 mL). The mixture was evaporated under vacuum using microwave oven for complete removal of solvent. The powder mixture and 1,2-dibromoethane (188 mg g, mmol) was mixed

3

thoroughly and irradiated at 250 W at pulses of 45 s for 5 min. After completion of reaction (monitored by TLC), the mixture was cooled and the product was extracted with dichloromethane (3 x 5 mL). The extract was dried with anhydrous magnesium sulfate and filtered to remove the solvent. The white solid was crystallized in EtOH (330 mg, 92%). 1H NMR (DMSO-d 6), δH ppm: 3.86 (s, 4H, 2CH2), 7.4−8.0 (m, 8H). 13C{1H} NMR (DMSOd6), δC ppm: 33.04 (2CH2), 121.69 (2C), 122.28 (2C), 125.07 (2C), 126.84 (2C), 135.22 (2C), 153.07 (2C), 166.04 (2C).

2.2. Instrumentation Melting point was obtained with an Electro-thermal 9100 melting-point apparatus. Routine 1 H (400 MHz) and

13

C (100 MHz) spectra were recorded in DMSO-d 6 at ambient

temperature on a Bruker Ultrashield Plus 400 MHz instrument. Chemical shifts (δ) were expressed as parts per million (ppm) relative to TMS. The FT-IR spectra were recorded with attenuated total reflectance (ATR) method by inserting the sample directly into the Nicolet 6700 FT-IR spectrometer. FT-Raman spectra were recorded from the samples put in a Pyrex tube on a Bruker RFS 100/S spectrometer. The 1064-nm line, provided by a near infrared Nd:YAG air-cooled laser, was used as excitation line. The output laser power was set to 200 mW. 3. Theoretical details Quantum chemical computations were all performed by using Gaussian03 program package with its fine numerical grid and tight SCF convergence criteria [13]. Optimized gas-phase structures and vibrational characteristics were calculated with the hybrid B3LYP [14,15] density functional and the split-valence triple-ζ 6-311++G** basis set [16–18]. The B3LYP/6-311++G** level geometry and vibrational spectra calculations have already been validated to give converged computational results on many molecules [19–22]. The normal

4

modes were expressed in terms of internal motions, i.e., stretching (ν), out-of-plane deformation (γ), and in-plane deformation (β ), with their percent contributions to the potential energy distribution (PED). Since B3LYP overestimates vibrational frequencies systematically, calculated frequencies are in general scaled with the correlation coefficients between the experimental and calculated frequencies in simulating the spectra [20-28]. In this study, the scaling factors were derived on bare BT-NHS as 0.955 for X–H stretchings (X = C, N, or S; frequencies over 2500 cm–1) and as 0.988 for the frequencies below 2500 cm–1 (R2 = 1.000), analogous to the previously obtained factors at the same computational level [20– 22]. The standard deviation S and the mean absolute deviation MAD of the scaled frequencies from the experimental frequencies of BT-NHS are just 10.9 and 8.3 cm–1, respectively. We thus used these two factors to scale computational frequencies of the other compounds, as well. This yielded small S and MAD values of 10.3 and 7.8 cm–1 (R2 = 1.000), respectively. Therefore, the presently derived scaling factors can be used to scale the computed frequencies of analogous molecules. In the following, as the computational frequencies, we will refer to the scaled frequencies. The room temperature IR and Raman spectra were simulated by using pure Lorentzian band shapes with FWHM of 10 cm−1. In these simulations, the scaled computational frequencies, computed IR intensities, and normalized Raman intensities obtained from the computed Raman scattering activities and laser excitation line of 1064 nm (9398.5 cm−1) as described previously [29,30] were utilized.

4. Results and discussion 4.1. Energetics To assess molecular preferences of the compounds, a series of PES scans were performed. During these PES scans, only the reaction coordinates were fixed while all 5

other coordinates were relaxed. To obtain the keto to enol transition barriers connecting the bare benzothiazoline isomers to the bare benzothiazole isomers, the R moieties (H and CH3) of BT-NHS and BT-NMeS were migrated to their peripheral sulfur atoms (S2, see Fig. 1 for the atom labeling scheme) progressively with an increment of 0.2 Å (Fig. 3). These relaxed PES scans reveal that the bare benzothiazoline isomers are 8.73 and 4.41 kcal/mol more stable than the bare benzothiazole isomers when R is taken to be H and CH3, respectively. The keto to enol transition barriers of the bare species are around 40 kcal/mol (Fig. 3). These large energetic separations and barriers suggest that benzothiazoline isomers (BT-NHS and BT-NMeS) are significantly more abundant than the benzothiazole isomers (BT-NSH and BT-NSMe), and, if existed, the benzothiazole isomers are too minor in the gas phase at the room temperature. Fig. 3 To further assess the reliability of B3LYP/6-311++G** energies, we have performed MP2 [31] calculations with a large correlation consistent valence triple-ζ basis set of cc-pVTZ [32] that correct Hartree-Fock (HF) energies for dynamical correlation effects. Analogous to B3LYP/6-311++G** result of 8.73 kcal/mol, HF/cc-pVTZ and MP2/cc-pVTZ calculations find that BT-NHS is 7.07 and 5.86 kcal/mol more stable than BT-NSH, respectively. The approximate transition-state structure with the N...H separation of 1.4 Å is 46.8 and 38.0 kcal/mol above BT-NHS at HF/cc-pVTZ and MP2/cc-pVTZ levels, respectively (B3LYP/6-311++G** result: 37.7 kcal/mol). Therefore, MP2 level dynamical correlation at the top of HF wave function reduces the transition barrier by around 9 kcal/mol and results in very similar barrier with B3LYP (38.0 kcal/mol vs. 37.7 kcal/mol). These computational experiments indicate that the inclusion of dynamical correlation is very crucial in estimating the transition barriers, and both B3LYP and MP2 calculations that include dynamical correlation give similar energy profiles.

6

In crystal phase, BT-NHS molecules are stabilized by two H-bonds between NH and peripheral S moieties of two BT-NHS molecules as shown in Fig. 2. Thus they exist as dimeric units as suggested in the previous X-ray study [33]. Although intramolecular H transfer from N of BT-NHS to its S is quite unlikely in the gas phase (see above), the conversion from BT-NHS to BT-NSH may be possible in the solid phase with the transfer of hydrogen from N in one of the BT-NHS moieties of the dimer to the peripheral S of the other BT-NHS in the dimer (intermolecular H transfer). To reveal if the tautomeric keto to enol conversion is possible in the crystal phase through intermolecular R transfer, we constructed dimeric BT-NHS and BT-NMeS as in Fig. 2 based on the crystal structure [33]. Then, we performed relaxed PES scans on them by migrating one R substituent (H and CH3) in the dimer to its neighboring peripheral S atom progressively with the increment of 0.2 Å (Fig. 4). Fig. 4 BT-NSH dimer lies energetically too high from BT-NHS dimer (22.8 kcal/mol, Fig. 4a). Moreover, the keto to enol transition state is just 0.7 kcal/mol above the BT-NSH dimer. Therefore, if the BT-NSH dimer was formed despite large energetic separation between the benzothiazoline and benzothiazole dimers, even the lattice vibrations could overcome the flat transition barrier, resulting the structure down to the BT-NHS dimer. This is already apparent from the calculated vibrational spectra of BT-NSH dimer, which has one imaginary frequency due to the mode that describes relative motion of the two BTNSH molecules in the dimer (see Supplementary Data). These analyses exclude thus the presence of BT-NSH dimer that has H-bonds between N and peripheral S atoms in the crystal phase. The initial structures of BT-NMeS and BT-NSMe dimers were constructed by replacing the R = H moieties with R = CH3 moieties, which is the most appropriate conformation for the keto-enol transition (Fig. 2). As in the bare structure, the keto to enol 7

transition barrier of the dimer with R = CH3 is too high (over 40 kcal/mol, Fig. 4b). Therefore, the intermolecular methyl transfer from the BT-NMeS dimer to the 11.2 kcal/mol higher-lying BT-NSMe dimer is unlikely. The optimized structures of BT-NMeS and BT-NSMe dimers have also imaginary frequencies as a result of the relative motion of the two units of molecules in the dimer irrespective of the methyl conformations (see Supplementary Data). Therefore, the methyl group and the nitrogen or peripheral sulfur atom must not be directed to each other in the solid phase BT-NMeS / BT-NSMe. The relaxed PES scans find (Fig. 5) that the benzothiazoline isomers have two stable rotamers (Rot1 and Rot2; Fig. 1) due to the orientation of R moieties at the room temperature. The R moiety is closer to the nitrogen atom in Rot1 and to the ring sulfur atom in Rot2. The Rot1 rotamers are the ones obtained from the PES scans that connect benzothiazole and benzothiazoline isomers and thus served as the initial structures of the rotational PES scans about the C7–S2 bond. Rot1 rotamers of the bare BT-NSH and BTNSMe are just 0.74 and 1.92 kcal/mol more stable than the Rot2 rotamers, respectively. Zero-point energies calculated using the scaled vibrational frequencies do not change this energy separation. The energy barriers that connect Rot1 to Rot2 are also very small (2.95 and 4.07 kcal/mol, respectively). Previous MP2/6-31G* find the energetic separation of Rot1 and Rot2 of bare BT-NSH around 2 kcal/mol (slightly higher than the present value of 0.74 kcal/mol) with the same transition barrier of this study (2.95 kcal/mol). Combining these PES results with the too high keto to enol barriers, it can be concluded that the Rot1 to Rot2 rotamers can only exist with rare amounts in the gas phase and powdered samples at the room temperature. Fig. 5 4.2. Geometrical Structures Optimized geometry parameters of the investigated molecules and the previous X-

8

ray data of BT-NHS (or, BT-NSH) [33] and bis(BT-NS)Et [34] are as given in Table 1. The computational structures of monomeric BT-NSH, BT-NHS, BT-NSMe, and BTNMeS have only plane symmetry in addition to the identity. Therefore, they belong to Cs point group. However, the dimeric structures have C2h and Cs symmetry for R = H and CH3, respectively. In the X-ray study [33], compared with the geometry data of analogous compounds, it is concluded that the existed isomer is BT-NHS rather than BT-NSH. Consistently, all the X-ray geometry parameters [33] are closer to the present computational geometry parameters of BT-NHS rather than those of BT-NSH. However, the X-ray study [33] finds a structure that slightly deviates from planar symmetry. The deviation from planarity in the X-ray structure can be attributed to noncovalent interactions among BT-NHS molecules that are not considered in the calculations or to insufficient experimental settings like its low resolution. The most significant structural changes moving from the monomeric to dimeric structures occurs for the N–R and S–R bond lengths that amount to ±0.2 Å. The other geometry parameters are almost the same in the monomeric and dimeric computational structures. The X-ray data of the crystalline bis(BT-NS)Et indicate a molecular structure deviated slightly from centrosymmetry. Gas-phase geometry optimization initiated from the X-ray structure of bis(BT-NS)Et causes very slight changes in the geometry parameters and results in fully centrosymmetric structure belonging to the Ci point group. As in BTNHS, the slight distortions in the X-ray geometry of bis(BT-NS)Et may arise from the packing effects in the solid state or low resolution used in the measurements. The most significant deviations in the geometry parameters of bis(BT-NS)Et with geometry optimizations are for C–H bonds, which are ~0.14 Å. However, this arise from a technical problem of X-ray measurements that consistently find contracted C–H bond lengths (~0.98 Å) due to smallness of the scattering of X-rays over H atoms [35]. Neutron diffraction measurements are known to obtain more accurate C–H bond lengths that are ~1.09 Å [35], 9

similar to the present computational results. Table 1 When the R substituents are transferred from the N to the S2 atom, the most important geometry parameter changes occur for the N–C7–S2 moiety: S–C7 bond is stretched by 0.11 Å while N–C7 bond is contracted by 0.08 Å. Bond angles involving N, C7, and S2 atoms vary also up to 9° (Table 1). Therefore, the most important distinctions on the vibrational spectra of the present isomers are expected for the internal coordinates involving N, C7, and S2 atoms.

4.3. Vibrational Spectra The experimental and simulated IR and Raman spectra of BT-NSH, BT-NHS, BTNSMe, BT-NMeS, and bis(BT-NS)Et are shown on Figs. 6–10. The experimental and calculated (unscaled and scaled) vibrational frequencies, symmetry species, and assignments of the normal modes in terms of percent PED of internal coordinates are given in Tables 2–4 while IR intensity (IIR), Raman scattering activity (S Ra), normalized Raman intensity (IRa) of the modes are mostly given in Supplementary Data for the sake of simplicity. Among the dimeric structures, here only vibrational spectra of BT-NHS dimer are given (Figs. 6 and 7; Table 2) since all of its vibrational frequencies are real. The plot of the spectra and the lists of the vibrational characteristics are given for the other dimers in Supplementary Data. The experimental vibrational bands were assigned in comparison with the computed (scaled) frequencies, and computed IR/Ra intensities. The normal modes of BTNSH were labeled with the numbers 1–39 (Table 2). They were then correlated with the modes of the other compounds (Tables 2–4) to make the realization of the substitutional effects clearer. Since the simulated vibrational spectra of Rot1 and Rot2 isomers are indistinguishable to each other, one of those (Rot1) is demonstrated on Figs. 4–7. 10

Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Table 2 Table 3 Table 4 The normal modes with the in-plane and out-of-plane vibrations transform, respectively, with the A' and A'' symmetry types for the molecules that have Cs symmetry (the bare BTNSH and BT-NHS; the bare and dimeric BT-NSMe and BT-NMeS). The normal modes of the BT-NHS and BT-NSH dimers with C2h symmetry transform with Au and Bu for IR-only active modes, and with Ag and Bg for Raman-only active modes. Since bis(BT-NS)Et has a center of symmetry with Ci symmetry, its normal modes are either IR-only active or Raman-only active, known as the rule of mutual exclusion. The IR-only and the Ramanonly active modes transform with Au and Ag symmetry types, respectively. The IR-only and the Raman-only active modes that involve the same type of vibrations have almost the same frequencies. Thus, they are given at the same rows in Table 4. IR and Raman spectra of the bare BT-NSH and BT-NHS have already been studied with B3LYP and several other density functionals but with smaller basis sets and mostly with approximate mode descriptions [1,36–39]. The present calculations with the larger 6311++G** basis set, which have already been shown to give converged vibrational frequencies [19], result in modified assignments for the modes that involve vibration of mostly hydrogen atoms. The frequencies of the majority of the modes with the same definitions have been calculated almost the same for different molecules. However, it is quite typical for the 11

corresponding experimental frequencies (for example, see the modes 11–14) to vary from those of BT-NSH or BT-NHS by about ±10 cm-1. This can be attributable to environmental differences in the solid phase. In terms of the intensity patterns, the calculated vibrational spectra of the benzothiazoline isomers (BT-NHS and BT-NMeS) are more consistent with the experimental spectra than those of benzothiazole isomers (BT-NHS and BT-NMeS) (Figs. 6–9), consistent with the present calculated energetics and previous NMR analyses [1]. However, several calculated bands for the benzothiazole isomers exist also in the experimental spectra as listed in Tables 2 and 3 in addition to those for benzothiazoline isomers. Therefore, although benzothiazole isomers can be present at the room temperature only at very rare amounts, the vibrational measurements are able to detect some of their major vibrational bands. The most significant difference in the computed vibrational spectra of the monomeric and dimeric species is due to stretching frequencies of N–H and S–H bonds. The computed frequency (scaled) of N–H stretching shifts from 3445 cm-1 (medium) in the monomeric BT-NHS to 3116 and 2084 cm-1 (very strong) in the BT-NHS dimer. The corresponding band is at 3109 cm-1 (medium) in the experimental IR spectrum of BT-NHS, being more consistent with the spectra of the dimer structure. Similarly, the computed frequency (scaled) of S–H stretching shifts from 2556 cm-1 (very weak) in the monomeric BT-NSH to 2295 and 2266 cm-1 (very strong) in the BT-NSH dimer. The corresponding IR band appears in experimental spectra at 2573 cm-1 (very weak), which is consistent with the monomeric BT-NSH. In addition, the in-plane C–C deformation band at 867 cm-1 (IR) and out-of-plane C–H deformation band at 849 cm-1 (IR) are too weak too appear in the calculated IR spectrum of monomeric BT-NHS but appear at the calculated IR spectrum of BT-NHS, as in the experimental IR spectrum. The vibrational spectra of the monomeric and dimeric vibrational spectra plotted with real frequencies are almost the same for BT12

NMeS and BT-NSMe since repulsions between methyl groups in the dimer make the intermolecular interactions very weak. The stretching frequencies are found for the CH3 and CH2 groups of the present molecules in the range of 2890–3040 cm-1 while the ring CH and NH stretchings are all found above 3000 cm-1 (Tables 2-4), as observed for analogous compounds [40]. The stretching frequencies of the CH3 group are dependent on its position (at S or N). When the CH3 group is at N rather than at S, its stretching frequencies are estimated at lower frequencies (up to 23 cm-1). The position and type of the R moiety affect the frequencies of not only the R group but also several ring vibrations, like the C–S1 stretchings (modes 26 and 27). For BT-NHS, BT-NSH, BT-NMeS, and BT-NSMe, mode 26 appears at 607, 706, 939 (calc.), and 1005 cm-1, while mode 27 has the frequencies of 667, 632, 527, and 656/646 (Rot1/Rot2) cm-1, respectively.

Similar to BT-NSMe, modes 26 and 27 of

bis(BT-NS)Et appear at 1006 and 636

cm-1, respectively, since the substituents of

peripheral S atoms are similar (CH3 vs CH2-). 5. Conclusions The geometry parameters, tautomerism, dimerization, conformational preference, and vibrational spectra (IR and Raman) of peripheral sulfur derivatives of benzothiazoline (BT-NHS and BT-NMeS) and benzothiazole (BT-NSH and BT-NSMe) have been investigated in terms of DFT calculations using the B3LYP functional and 6-311++G** basis set. The structure and vibrational spectra of bis(BT-NS)Et have been also calculated and compared with the previously available X-ray structure. Each normal mode in the present experimental vibrational spectra of the presently investigated molecules was assigned based on the present vibrational spectral calculations. The effects of substitution at the nitrogen and peripheral sulfur atoms have been discussed on the structures and vibrational spectra. PES scans find the keto to enol transition barriers too high over the

13

most stable benzothiazoline isomers. However, the room temperature vibrational spectra contain some major bands of benzothiazole isomers. Therefore, benzothiazoline isomers are the main species while benzothiazole isomers exist at rare amounts. Dimer formation through H-bonds connecting the ring nitrogen and peripheral sulfur was obtained possible only for BT-NHS, as suggested by the previous X-ray study. The dimeric structures of the other molecules are not equilibrium geometries as they contain imaginary frequencies. Acknowledgments This work is supported by the Scientific Research Fund of Fatih University under the project numbers of P50011102_Y (1679) and P50031301_G (3285). Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version.

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J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A. Pople, (2004) Gaussian 03, Revision C.02, Gaussian, Inc., Wallingford, CT. [14] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [15] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1998) 785–789. [16] R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, J. Chem. Phys. 72 (1980) 650–654. [17] M.J.S. Dewar, C.H. Reynolds, J. Comp. Chem. 2 (1986) 140–143. [18] K. Raghavachari, J.A. Pople, E.S. Replogle, M. Head-Gordon, J. Phys. Chem. 94 (1990) 5579–5586. [19] M.P. Andersson, P. Uvdal, J. Phys. Chem. A 109 (2005) 2937–2941. [20] V. Kucuk, A. Altun, M. Kumru, Spectrochim. Acta, 85A (2012) 92–98. [21] A. Altun, N.M. Aghatabay, Vib. Spectrosc. 64 (2013) 68–77. [22] M. Kumru, V. Küçük, M. Kocademir, H. M. Alfanda, A. Altun, L. Sarı, Spectrochim. Acta 134A (2015) 81-89. [23] A. P. Scott, L. Radom, J. Phys. Chem. 100 (1996) 16502. [24] S.S. Panikar, B.S. Deodhar, D.K. Sawant, J.J. Klaassen, J. Deng, J.R. Durig, Spectrochim. Acta 103A (2013) 205–215. [25] G.A. Guirgis, J.J. Klaassen, B.S. Deodhar, D.K. Sawant, S.S. Panikar, H.W. Dukes, J.K. Wyatt, J.R. Durig, Spectrochim. Acta 99A (2012) 266–278. 16

[26] N. M. Aghatabay, A. Altun, M. U. Gürbüz, M. Türkyilmaz, C. R. Chimie, 17 (2014), 905–912. [27] A. Altun, K. Gölcük, M. Kumru, J. Mol. Struct. (Theochem), 637 (2003) 155–169. [28] A. Altun, K. Gölcük, M. Kumru, J. Mol. Struct. (Theochem), 625 (2003) 17–24. [29] P.L. Polavarapu, J. Phys. Chem. 94 (1990) 8106. [30] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta 49A (1993) 2007–2017. [31] M. H.-Gordon, J.A. Pople, M.J. Frisch, Chem. Phys. Lett., 153 (1988) 503–506. [32] Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007−1023. [33] J.P. Chesick, J. Donohue, Acta Cryst. B 27 (1971) 1441–1444. [34] Q. Liu, D. Shi, C. Ma, F. Pan, R. Qu, K. Yu, J. Xu, Acta Cryst. C59 (2003) o219– o220 [35] M.F.C. Ladd, R.A. Palmer, Structure Determination by X-ray Crystallography, 4th ed. Kluwer Academic/Plenum Publishers, N.Y. 2003. [36] A.K. Rai, R. Singh, K.N. Singh, V.B. Singh, Spectrochim. Acta 63A (2006) 483– 490. [37] H. Böhlig, M. Ackermann, F. Billes, M. Kudra, Spectrochim. Acta 55A (1999) 2635–2646. [38] L. Xiao-Honga, T. Zheng-Xina, Z. Xian-Zhou, Spectrochim. Acta 74A (2009) 168– 173. [39] R. Sun, J. Ge, J. Yaoa, S. Li, H. Shena, R. Gua, Spectrochim. Acta 71A (2008) 1535–1539. [40] K. Golcuk, A. Altun, M. Kumru, Spectrochim. Acta, 59A (2003) 1841–1847.

17

FIGURE CAPTIONS Fig. 1. Monomeric forms of the studied compounds and their atom numberings. Fig. 2. Dimeric forms of the studied compounds arranged suitable for the migration of the R moiety. Fig. 3. Relaxed PES scans that connect the bare (a) BT-NHS to Rot1 of BT-NSH, and (b) BT-NMeS to Rot1 of BT-NSMe. Fig. 4. Relaxed PES scans that connect the dimeric (a) BT-NHS to Rot1 of BT-NSH, and (b) BT-NMeS to Rot1 of BT-NSMe. Fig. 5. Relaxed PES scans that connect Rot1 and Rot2 of the bare (a) BT-NSH (b) BTNSMe. Fig. 6. Experimental and simulated IR spectra of BT-NSH and BT-NHS at the room temperature. Fig. 7. Experimental and simulated Raman spectra of BT-NSH and BT-NHS at the room temperature. Fig. 8. Experimental and simulated IR spectra of BT-NSMe and BT-NMeS at the room temperature. Fig. 9. Experimental and simulated Raman spectra of BT-NSMe and BT-NMeS at the room temperature. Fig. 10. Experimental and simulated IR and Raman spectra of bis(BT-NS)Et at the room temperature.

18

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Table 1 Geometry parameters of the investigated molecules. Parametersa

BT-NHS

Interatomic distance (Å) S2-C7 1.651 S2-H/S2-C8 N-H/N-C8 1.011 S1-C2 1.766 S1-C7 1.780 N-C1 1.389 N-C7 1.367 C1-C2 1.403 C1-C6 1.394 C2-C3 1.391 C3-C4 1.394 C4-C5 1.398 C5-C6 1.393 C-H (ring)e 1.083 C8-H (meth.)e C8-C8’ NH⋅⋅⋅S2 / S2H⋅⋅⋅N Bond angle (°) C7-S2-H (C8) C7-N- H (C8) C2-S1-C7 C1-N-C7 N-C1-C2 N-C1-C6 C2-C1-C6 S1-C2-C1 S1-C2-C3 C1-C2-C3 C2-C3-C4 C3-C4-C5 C4-C5-C6 C1-C6-C5 S1-C7-S2 S2-C7-N S1-C7-N

BT-NSH Rot1

BT-NSH Rot2

1.766 1.349

1.767 1.349

1.758 1.779 1.388 1.288 1.413 1.399 1.394 1.392 1.403 1.389 1.083

1.757 1.782 1.387 1.286 1.414 1.399 1.394 1.392 1.403 1.389 1.083

93.5 118.5 92.1 118.0 111.8 127.3 120.8 110.2 129.2 120.7 118.6 120.7 121.0 118.3 125.6 126.5 107.9

88.0 111.0 115.4 125.2 119.5 109.3 129.1 121.7 118.0 120.9 121.0 119.0 118.6 125.0 116.4

Calculated (Monomer) BT-NMeS BT-NSMe Rot1 1.657 1.459 1.759 1.775 1.396 1.374 1.403 1.396 1.391 1.394 1.397 1.394 1.083 1.091

96.1 88.1 111.2 115.4 125.2 119.4 109.1 129.2 121.7 118.0 120.9 121.0 119.0 122.6 121.3 116.1

BT-NSMe Rot2

bis(BT-NS)Etb

1.758 1.825

1.760 1.826

1.761 1.840

1.758 1.784 1.388 1.290 1.413 1.399 1.394 1.392 1.402 1.389 1.084 1.089

1.756 1.790 1.384 1.288 1.413 1.400 1.394 1.391 1.403 1.388 1.084 1.090

1.758 1.782 1.389 1.290 1.412 1.399 1.394 1.392 1.402 1.389 1.084 1.089 1.523

100.0 122.5 92.1 116.0 112.9 126.7 120.3 110.0 129.1 121.0 118.6 120.5 121.0 118.5 122.9 128.0 109.0

88.0 111.2 115.4 125.2 119.4 109.3 129.1 121.6 118.1 120.9 121.0 119.0 118.3 125.7 116.1

102.4 88.0 111.5 115.4 125.2 119.4 109.3 129.0 121.7 118.0 120.9 121.0 119.0 123.3 121.0 115.7

Calculated (Dimer)b BT-NHS BT-NSH Rot1

BT-NHS dimerc

1.671

1.754 1.372

1.662

1.744 1.822

1.742 1.819

1.030 1.764 1.773 1.390 1.352 1.403 1.395 1.392 1.393 1.400 1.391 1.083

1.756 1.777 1.390 1.295 1.412 1.400 1.393 1.391 1.402 1.389 1.083

1.740 1.732 1.380 1.353 1.387 1.391 1.386 1.395 1.384 1.353

1.729 1.751 1.399 1.293 1.406 1.384 1.389 1.374 1.389 1.378 0.930 0.970 1.494

1.734 1.753 1.396 1.297 1.405 1.393 1.389 1.378 1.386 1.379 0.930 0.969

2.356

2.040

101.1

100.7

88.8 110.1 114.9 125.4 119.7 109.6 129.5 120.9 118.3 121.2 120.6 119.3 116.1 127.3 116.6

88.7 109.7 115.5 125.2 119.3 109.4 129.2 121.5 118.2 120.8 121.5 118.7 116.8 126.5 116.7

100.6 88.1 111.2 115.3 125.2 119.5 109.3 129.1 121.6 118.0 120.9 121.0 119.0 118.1 125.9 116.0

96.2 120.7 91.7 117.1 112.2 126.9 120.9 109.9 129.3 120.8 118.3 120.8 121.1 118.1 123.5 127.5 109.1

88.5 111.5 115.1 125.5 119.4 109.3 129.0 121.7 118.1 120.8 121.0 119.0 118.0 126.4 115.6

92.3 116.4 112.0 127.5 120.5 110.0 129.1 120.9 117.6 120.6 121.6 118.6 123.4 127.4 109.2

X-Ray bis(BT-NS)Etd

S2-C8-H (C8’) e H-C8-He S2-C8-C8’ Torsional angle (°) C1-N-C7-S2 C8 (H)-N-C7-S2 C2-S1-C7-S2 N-C7-S2-H (C8) S1-C7-S2- H (C8) C7-S2-C8-C8’ S2-C8-C8’-S2’ a

180.0 0.0 180.0 0.0 180.0

180.0 0.0 180.0 0.0 180.0

180.0 0.0 180.0 180.0 0.0

109.6

108.7 110.2

109.3 109.5

112.5 109.8 112.5

180.0 0.0 180.0 0.0 180.0

180.0 0.0 180.0 0.0 180.0

180.0 0.0 180.0 180.0 0.0

179.2/0.7 ±0.4 ∓179.4 ∓0.7 ±178.8 ±77.5 180.0

180.0 0.0 180.0 0.0 180.0

180.0 0.0 180.0 0.0 180.0

, When the same atom type is involved in the parameter due to dimeric composition of bis(BT-NS)Et, one of these is shown with a prime sign. The parameters of one of the benzothiazole moieties are written since they are identical. c Taken from ref. 28. d Taken from ref. 29. e Averaged values that belong to the same type of internal coordinates. b

112.2 107.9 112.2

112.2 107.9 112.2

179.1 2.4 -179.4 -3.7 175.6 84.4 178.6

-178.5 0.5 179.0 -0.8 -179.4 -83.0

Table 2 Experimental and calculated vibrational frequencies and mode definitions of BT-NSH and BT-NHS. Monomeric Species No

Experimental

Dimeric BT-NHS

BT-NSH (Rot1)

BT-NSH (Rot2)

BT-NHS

Calc.

Calc.

Calc. Scaled

PED(%)a

IR

Raman

Calc.

Scaled

Calc.

Scaled

3070 m

3070

s

A'

3200 3056

3200 3056

3199 3055

Bu

3201

3057

Ag

3201

3057

100 CH

2

3038 m

3041

m

A'

3193 3049

3193 3049

3190 3047

Bu

3195

3051

Ag

3195

3051

100 CH

A'

3182 3039

3182 3039

3182 3038

Bu

3186

3042

Ag

3186

3042

100 CH

3173 3031

Bu

3175

3032

Ag

3175

3032

100 CH

3607 3445

Bu

3263

3116

Ag

3229

3084

100 NH

1633 1613

Bu

1636

1616

Ag

1638

1618

43 CC; 43/38/43 CH; {14 NH}

3022

w

Scaled

Ra-only active modes

1 3

Scaled

IR-only active modes

4

3020 m

A'

3171 3028

3171 3028

5

2573 vw

A'

2677 2556

2676 2556

5

3109 m

A'

6

1611 vw

A'

1631 1612

1632 1613

7

1582 m

1582

s

A'

1598 1578

1597 1578

7

1596 m

1598

m

A'

1620 1601

Bu

1622

1603

Ag

1622

1602

39 CC; 40 CH; 10 NH

8

1495 s

1496

m

A'

1520 1502

1532 1513

1514 1495

Bu

1545

1526

Ag

1541

1523

48/45/45 CH; 40/42/- CN; {21 CC; 27 NH}

9

1456 s

1458

m

A'

1486 1468

1486 1468

1493 1475

Bu

1492

1475

Ag

1493

1475

62/63/61 CH; 25/28/28 CCC

A'

1463 1445

1462 1445 1443 1426

Bu

1465

1448

Ag

1463

1445

48 CH; 16 CCC; 28 NH

10

100 SH

42/42 CC; 47/47 CH

62/63 CH; 25/25 CCC

10

1423 vs

1424

m

A'

11

1319 vs

1318

s

A'

1343 1326

1342 1326

1350 1334

Bu

1358

1341

Ag

1353

1336

43/42/44 CC; 40/41/33 CH

12

1283 s

1286

m,sh

A'

1301 1286

1302 1287

1295 1280

Bu

1295

1279

Ag

1300

1284

73/71/65 CH; 16/17/15 CCC

13

1244 vs

1253

vs

A'

1261 1246

1263 1247

1271

s

A'

1286 1271

Bu

1283

1267

Ag

1284

1268

51 CH; 35 CN

1185 1170

Bu

1185

1171

Ag

1185

1171

85/84/84 CH; 9/9/10 CCC

13 14

1154 m

1157

w

A'

1184 1170

1184 1170

15

1128 m

1131

m

A'

1144 1130

1144 1130

15

1142 m

A'

16

1088 m

A'

1089 1076

1091 1078

16

1076 s

1075

m

A'

17

1032 vs

1030

m

A'

1052

w

A'

17

1041 1029

18

1012 vs

1013

m

A'

19

998

m

999

w,sh

A" 989

19

982

vw,sh 976

vw

A"

20

939

m

933

vw

A" 951

940

883

vw,sh

A'

891

21

1030 1017

901

977

59/58 CH; 30/29 CN

77 CH; 15 CCC Bu

1152

1138

Ag

1151

1138

1092 1079

Bu

1095

1082

Ag

1092

1079

1052 1039

Bu

1051

1039

Ag

1048

1035

43 CH; 48 CS2

1031 1018

Bu

1031

1019

Ag

1027

1014

52/53/55 CCC; 44/44/42 CS1

983

971

Au

985

973

Bg

985

974

88CH; 11 CC

937

926

Au

942

931

Bg

942

931

82 CH; 18 CCC

78/78 CS1

990 951

86 CH; 14 CC

978 940

84 CS1 45/45 CH; 43/42 CS2

1046 1033 1036 1024

76 CH; 17 CCC

1150 1137

82 CS2H

21

916

vw

21

A'

930

83 CS2H

919

A'

21

Bu

22

859

m

22

867

m

866

23

849

m

850

24

A'

866

856

866

855

w

A'

vw

A" 861

851

861

851

757

vw

A" 765

756

765

756

24

748

vs

745

vw

A"

25

718

m

718

w,sh

A" 724

715

725

716

26

706

s

706

m

A'

703

712

703

26

607

m

A'

27

632

vw

A'

27 28

667

vs

712 640

632

643

A' 572

A" 593

586

596

588

A'

586

589

582

29

A' 522

w

vw

593

A" 525

1312

1296

Ag

1312

1297

518

527

521

82 CN 52/54 CCC; 36/37 NC

876

865

Bu

876

866

Ag

877

867

56 CCC; 38 NC

851

840

Au

857

847

Bg

857

846

82 CH; 16 CCC

753

744

Au

756

747

Bg

756

747

83 CH; 15 CCC

713

705

Bu

716

707

Ag

716

707

57/51/57 CH; 41/46/42 CCC

644

637

Bu

621

614

Ag

621

613

620

612

Bu

658

650

Ag

654

647

82 CS1

559

552

Au

567

561

Bg

569

562

54/54/51 CNC; 42/41/44 CCC

714

706

Au

713

704

Bg

713

705

80/79 CH; 16/17 CCC

58/56 CS1; 37/37 CCC 54 CS1; 40 CCC 82 CS1

635

29 30

43 NH; 27 CH; 17 NC

1239 1225

40/38 CS1; 35/38 CCC; 20/23 SH 48 CCC; 46CS1 64/63 CCC; 24/27 SCS

30

A"

517

511

Au

526

520

Bg

527

521

47 NH; 24 SCS; 18 CCC

31

A'

507

501

507

501

499

493

Bu

503

497

Ag

502

496

56/58/50 CS1C; 39/38/38 CCC; {10 NH}

32

A" 435

430

436

431

425

420

Au

428

423

Bg

429

424

86/83/82 CCC

33

A'

388

383

385

380

397

393

Bu

397

393

Ag

396

392

100 breath.

34

A'

368

363

369

365

382

377

Bu

389

385

Ag

386

381

68/70/68 CC S1; 24/24/28 SCS

35

A" 290

286

293

290

278

274

Au

286

282

Bg

284

281

82/82/89 NCCC (torsion)

36

A" 210

207

131

101 551

545

Au

802

793

Bg

781

771

89 NH

36

538

vw

A"

96 SH

37

A'

195

192

194

192

210

208

Bu

235

232

Ag

217

214

82/82/80 CS2

38

A" 187

185

192

129

186

184

Au

189

186

Bg

188

186

82/82/89 CCS1C (torsion)

39

A" 103

101

103

190

91

90

Au

97

95

Bg

96

94

90/90/- NCS2H; {88 HNCS2 } (torsion)

Bu

48

47

Ag

100

99

100 NHS2

Ag

53

52

100 NHS2

Bg

46

45

100 CNH-S2

a

Au

33

32

Au

11

11

100 NHS2C (torsion)

The contributions separated by “/” belong to Rot1 and Rot2 of BT-NSH, and BT-NHS, respectively. The contributions present only in BO-NHS are expressed inside {}. Due to the similarity between the mode definitions of the monomeric and dimeric BT-NHS, PEDs of the modes are given based on the monomeric BT-NHS.

Table 3 Experimental and calculated vibrational frequencies and mode definitions of monomeric BT-NSMe and BT-NMeS. No Experimental IR

Raman

3053 m

3057

BT-NSMe (Rot1)

BT-NSMe (Rot2)

BT-NMeS

Calc.

Scaled

Calc.

Scaled

Calc. Scaled

PED(%)a

3197

3054

3200

3056

3203 3059

A'

100 CH

2

3191

3048

3192

3049

3195 3052

A'

100 CH

3

3181

3037

3181

3038

3185 3042

A'

100 CH

3169

3027

3170

3027

3175 3032

A'

100 CH

3158

3016

3138

2996

1

4

3026 vw

3026

s

m

2990 w 3007 w

3009

m

3150

3008

3133

2992

2927 m

2927

s

3059

2922

3047

2910

2910 w,sh 6

1622 w

7

1586 w

1590

m

8 9 10

1477 vw 1455 vs

1460

vs

A" 100 CH3 (asym.) 3098 2959

A" 100 CH3 (asym.)

3149 3007

A'

100 CH3 (asym.)

A'

100 CH3 (sym.)

3035 2899

A'

100 CH3 (sym.)

1630

1611

1631

1611

1625 1605

A'

49/49/52 CC; 43/43/41 CH

1598

1579

1596

1577

1619 1599

A'

50/49/51 CC; 47/47/45 CH

1513

1495

1518

1500

1511 1493

A'

41/51/53 CH; 30/39/- CN; 29/9/7 CH3; {28 CC}

1485

1468

1486

1468

1495 1477

A'

58/49/50 CH; 31/26/30 CCC; 9/24/18 CH3

1474

1456

1481

1464

1484 1466

A'

81/77/62 CH3; 11/15/36 CH

1463

1446

1463

1445

A'

56/59 CH; 27/29 CCC

A'

38 CH; 32 CN; 23 CCC

10

1374 1358 1424 vs

1429

vs

1455

1438

1465

A" 100 CH3

1448 1499 1481

1350 vw

1359

1343

1366

A" 100 CH3 A'

91/94 CH3

1450 1432

A'

92 CH3

1350

11

1308 vs

1308

m

1342

1326

1342

1326

1348 1332

A'

50/51/66 CCC; 38/39/21 CH; {17 CN}

12

1273 s

1274

m

1300

1285

1302

1286

1292 1276

A'

70/70/62 CH; 21/22/11 CCC; {28 CN}

13

1234 vs

1238

vs

1260

1245

1263

1248

A'

58/60 CH; 35/34 CNC

13

1153 w

1158

vw

A'

42 CH; 36 CNC; 18 CCC

14

1162 w

A'

85 CH; 12 CCC

14

1177 vw

1188 1174

A'

86 CH; 13 CCC

15

1121 w

1124

m

1143

1130

1144

1130

1146 1132

A'

78/78/32 CH; 20/20/54 CCC; {12 NCH3}

16

1074 w

1075

w

1084

1071

1084

1071

A'

49/49 CS1; 47/46 CCC

16

1050 w,sh

A'

38 CS1; 40 CCC; 18 N-CH3

17

1020 m

A'

62/67 CH; 24/22 CCC

A'

70 CCC; 13 CH

A'

48/48 CS1; 49/49 CH3 68 CS1; 27 N-CH3

17 26

1005 vs

1164 1150 1183

1169

1183

1169

1069 1056 1040 1043

vw

1010

s

1027

1040

1028 1048 1035

1013

1001

1022

1010

26 19

973 971

vw

s

984

973

988

976

982

970

973

961

1110 vw,sh 959

s

20

936

w

22

853

vw

962

851

vw

w

23 755

vs

25

722

s

29

705

5

678

5

939

A'

981

969

A" 77/84/90 CH; 13/14/8 CC

1126 1112 981

969

972

961

948

936

950

939

867

857

868

858

22 24

950

A'

43/47 CH3; 38/30 CS2

A'

74 CH3; 14 CS2

A"

83/79 CH3

1147 1134

A" 92 CH3

935

924

A" 82/80/91 CH; 17/17/9 CCC A'

37/39 CCC; 35/37 CH; 16/17 NC

835

825

A'

46 CCC; 44 NC

859

849

861

850

851

840

A" 82/81/93 CH; 17/18/4 CCC

764

755

764

755

755

746

A" 79/78/80 CH; 18 CCC

761

w

725

716

725

717

721

713

A" 60/58/57 CH; 37/37/39 CCC

s

707

s

713

704

713

704

718

709

A'

55/55/52 CCC; 38/38/41 CS1

s

680

w

699

691

705

697

A'

93/81 SCH3

A'

68 NCH3; 26 CH

1341 1325

27 18

597

w

664

656

654

646

607

600

593

585

18

534

527

A'

78 CS1

A'

55/56 CCC; 42/40 CS1 58 CCC; 38 CS1

653

645

A'

595

588

596

588

573

566

A" 56/56/52 CNC; 41/41/45 CCC

528

521

526

520

529

523

A" 62/62/60 CCC; 36/37/37 SCS

507

501

506

500

511

504

A'

32

436

431

437

431

431

426

A" 91/90/88 CCC

34

406

401

400

396

418

413

A'

70/71/69 CC S1; 25/25/29 CH3-S/N

33

366

362

370

366

A'

56 breath.; 44 CS2 100 breath.

28 30 31

506

s

33

397

392

A'

57/59/60 CS1C; 38/39/38 CCC

35

295

291

289

286

302

298

A" 79/79/82 NCCC (torsion)

21

267

264

268

265

300

296

A'

38

189

187

190

188

206

204

A" 85 CCS1C (tors.)

80/80/- S-CH3; {85 N-CH3}

140

138

176

174

124

123

A" 91/91/88  CH3 (twist)

37

137

136

147

145

225

222

A'

39

95

94

98

97

83

82

A" 89/89/- NCS2C {92 CNCC } (torsion)

36

57

56

37

37

137

135

A" 95/95/90  CH3 –S/N

a

72/72/82 CS2; 17/17/- S-CH3

The contributions separated by “/” belong to Rot1 and Rot2 of BT-NSMe, and BT-NMeS, respectively. The contributions present only in BO-NHS are expressed inside {}.

Table 4 Experimental and calculated parameters for the vibrational spectra of bis(BT-NS)Et. No

Experimental IR

Raman

1 3

3054 3056

3 4

m

w 3042

m

Raman-only Active Modes (Ag)

Calc.

Scaled

IIR

Calc.

Scaled

SRa

IRa

3198

3054

20.64

3198

3054

594.82

0.027

100 CH

3192

3048

28.05

3192

3049

236.24

0.011

100 CH

3182

3039

11.70

3182

3039

286.20

0.013

100 CH

3170

3028

100.02

0.005

100 CH

3140

2998

63.02

0.003

3083

2945

259.72

0.013

100 CH2 (sym.)

3024

vw

3170

3028

1.83

3003

vw

3157

3015

2.41

3009 2952

vw

vw

3093 2938

vw

PED(%)a

IR-only Active Modes (Au)

2954

100 CH2(asym.) 100 CH2 (asym.) 100 CH2(sym.)

3.50

6

1623

vw

1630

s

1630

1610

5.68

1630

1610

119.68

0.024

49 CC; 42 CH

7

1589

vw

1591

vs

1598

1579

5.05

1598

1579

74.44

0.015

50 CC; 48 CH

1504

w

1510

1492

262.85

1511

1493

870.05

0.197

31 CN; 25 CH2; 23 CH; 17 CC

1462

vw

1485

1467

29.97

1485

1467

76.33

0.018

61 CH; 33 CCC

1463

1445

158.84

1463

1446

179.23

0.043

56 CH; 26 CCC

8 9

1462

s

10

1450

m

1426

vs

11

12

1424

vw

1452

1435

23.38

1450

1432

227.12

0.055

85/80 CH2

1332

w,sh

1342

1326

17.35

1342

1326

13.42

0.004

50 CC; 38 CH

1236

w

1318

m

1256

1241

4.17

1334

1318

65.87

0.018

55/91 CH2; 39/6 CH

1156

vw

1303

m

1179

1165

3.99

1316

1300

43.17

0.012

70/86 CH2; 23 CH

1270

w

1272

vw

1301

1285

23.44

1301

1285

121.21

0.035

71/69/ CH; 19 CCC

1258

vw

1263

1248

92.91

1261

1246

303.26

0.093

53/58 CH; 40/-CH2; -/29 CCC;

13 14

1176

vw

1160

m

1183

1169

1.97

1183

1169

8.19

0.003

72/86CH; 10/12 CCC; 16/- CH2

15

1127

m

1136

vs

1144

1130

14.60

1144

1130

68.81

0.025

78 CH; 20 CCC

16

1073

m

1094

m

1082

1069

31.63

1084

1071

32.01

0.013

45 CS1; 36 CCC

17

1020

m

1029

vw

1039

1027

7.86

1040

1027

44.84

0.019

70 CH; 26 CCC

1038

1026

13.20

0.006

67 CH2-CH2; 30 CH

1002

990

53.25

0.023

46 CS1; 44 CH2-CH2

983

971

0.03

0.000

86 CH; 14 CCC

971

959

41.10

0.019

74 CH2-CH2

26

1006

26

992

vs

19

965

m

968

w

953

w

993

981

430.27

983

971

0.01

51 CS1; 38 CCC

947

935

3.22

947

935

0.46

0.000

82 CH; 17 CCC

vs

867

857

3.48

867

856

35.02

0.019

60 CCC; 31 NC

s

859

849

1.71

859

849

0.19

0.000

82 CH; 17 CCC

vs

763

753

125.10

763

754

2.10

0.001

78 CH; 18 CCC

m

738

729

31.28 727

718

88.20

0.062

76 S-CH2

20

943

m

22

863

w

842

23

828

vw

822

24

754 732

5

715

25

722

s

29

702

m

5

670

m

27

w

688 636

w w m

18

78 CH2

722

713

21.03

724

715

4.77

0.003

59 CH; 38 CCC

712

704

11.64

713

704

47.42

0.034

44 CCC; CS1

682

674

16.14

664

656

38.15

665

657

10.26

0.008

77 CS1

606

599

5.58

606

599

12.15

0.011

69 CC; 29 NCS1

79 S2-CH2

28

564

m

595

588

1.03

595

588

0.42

0.000

54 CNC; 40 CCC

30

540

w

526

520

0.37

526

520

0.32

0.000

36 CCC; 40 SCS

31

508

w

507

501

0.39

507

501

21.68

0.026

60 CS1C; 39 CCC

32

453

w

433

428

9.42

433

428

0.13

0.000

91 CCC

34

413

w

409

404

3.40

415

410

7.16

0.011

69 CCS1; 25 CH2-S

33

372

m

369

365

8.93

368

364

4.81

0.009

56 breath.; 44 CS2

21

339

vw

342

338

3.23

0.007

65 C-S-CH2; 34 CCS1

21 35

298

vs

281

278

11.65

292

289

0.10

88 C-S-CH2; 11 CCS1 292

289

1.58

0.004

80 NCCC (torsion)

216

214

82 S-CH2

7.89

227

m

193

191

2.98

0.016

80 CH2 (rock.)

193

m

186

183

2.67

0.015

80 CH2 (rock) 85 CCS1C (torsion)

38

188

186

3.56

37

160

158

3.37

143

142

1.96

0.018

52 CS2; 48 S-CH2

39

104

103

2.76

99

97

3.39

0.060

87 CNCS2 (torsion)

48

47

2.44

0.169

100 S-CH2-CH2 (twist.)

35

35

8.19

1.000

58 SCH2 ; 42 NCS2C (torsion)

36

a

23

23

0.32

89 NCS2C (torsion)

21

20

0.10

100 C-S2-CH2-CH2 (torsion)

12

12

0.10

100 C-S2-CH2-CH2 (torsion)

The contributions separated by “/” belong to the IR-only and Raman-only active modes with the same description, respectively.

Graphical Abstract

• • • •

Mechanism of intramolecular and intermolecular tautomerism Conformational stability The room temperature experimental IR and Raman spectra DFT calculations to investigate structures and vibrational spectra

25