Accepted Manuscript Solvent effect on the vibrational spectrum of michler’s ketone. experimental and theoretical investigations Marta Sowula, Tomasz Misiaszek, Wojciech Bartkowiak PII: DOI: Reference:

S1386-1425(14)00716-1 http://dx.doi.org/10.1016/j.saa.2014.04.143 SAA 12107

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

29 November 2013 24 March 2014 23 April 2014

Please cite this article as: M. Sowula, T. Misiaszek, W. Bartkowiak, Solvent effect on the vibrational spectrum of michler’s ketone. experimental and theoretical investigations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.04.143

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SOLVENT EFFECT ON THE VIBRATIONAL SPECTRUM OF MICHLER'S KETONE. EXPERIMENTAL AND THEORETICAL INVESTIGATIONS Marta Sowula, Tomasz Misiaszek* and Wojciech Bartkowiak* Institute of Physical and Theoretical Chemistry, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland

ABSTRACT We examined solvent effect on the IR and Raman spectra of MK in several solvents of different polarity and proticity, for understanding of intermolecular interactions, focusing on solvent effect in detail. It has been found that change of solvent polarity has an ambiguous influence on solvatochromism of MK. We have observed that not only vibrations of carbonyl group are affected by the solvent polarity, but also mode ν(C-N) and ν(C-C) in IR and Raman spectra of MK. Experimental investigations have been supported by the quantum-mechanical computations to gain more insight into the solvatochromic behavior of Michler's ketone. Calculations have been carried using Kohn-Sham formulation of Density Functional Theory (DFT) and the Polarizable Continuum Model (PCM) was employed to account for solute solvent interactions.

I. INTRODUCTION Significant change of position, shape and also intensity of absorption or emission band in electronic spectra, as a result of local inhomogeneous electric field induced by surrounding solvent molecules, is known as solvatochromism [1],[2],[3]. The phenomenon is caused by solute-solvent intermolecular interactions which have an impact on the electron density distribution in the ground and excited state of a chromophore. Due to these interactions band position undergoes either blue- or redshift, so that one could distinguish hipsochromic or batchochromic shift, respectively. Likewise, the change of position, shape and also intensity of the band in the infrared or Raman vibrational spectra might be

*

Corresponding authors. [email protected], [email protected].

1

considered as vibrational solvatochromism [4],[5]. Solvatochromism is currently exploited in manufacturing of environmental sensors for example in molecular switches [6]. Beside polarity of a local environment, hydrogen bonding is a strong inter- or intramolecular interaction having large influence on the intensity and shift of a band. So that it has been examined as an important factor determining changes associated with the vibrational solvatochromism [7],[8],[9],[10]. Although vibrational solvatochromism is an effect which has been extensively studied, there are some aspects of the phenomenon still waiting to be investigated. One of them is the influence of the proticity combined with polarity of a solvent on the vibrational spectra. Solvatochromism can be investigated by the usage of simple IR probe [4], which is a small moiety of a molecule that has IR-active stretching mode sensitive to solvent polarity, hydrogen bonding and is responsive to the local electric field. The polarity sensitivity is this significant that IR probe can even act as polarity indicator [4],[7]. Among other modes that can be used as IR probe, like ν(NC), ν(NCO), ν(NCS), ν(NCSe) or ν(CF)[5],[8],[9], the carbonyl stretching mode, ν(C=O), may be considered as an ideal probe for local solvent environment investigations. For this reason, the ν(C=O) has been intensively studied [11],[12],[13],[14]. In 1953 Puranik [15] has observed that the protic solvents can interact with acetone molecule by intermolecular hydrogen bonding formation. The author examined acetone in admixtures of water, methyl-, ethyl-, n-propyl- and n-butyl alcohols. It has been noted that the hydrogen bond formation between acetone and water or one of the alcohols (C=O...HO), leads to decrease of the ν(C=O) wavenumber in Raman spectra. It has been also observed that although the carbonyl group is a place where hydrogen bond has been created, not only v(C=O) may be affected by it, but also other bands of acetone, particularly ν(C-C) and ν(C-H). And what is more, the C=O bond lengthening corresponds with C-C bonds shortening. The title compound, Michler's ketone (MK), is an aromatic amino ketone, benzophenone derivative, used as an intermediate product in the manufacture of triarylmethane dyes, dry film, waxes, alcoholic solvents, textiles or as a sensitizer [16]. MK is also an interesting subject of the investigation for its photophysical and photochemical properties [17],[18],[19],[20],[21],[22]. It is one of the highest positive solvatochromic compounds [17]. This study is an attempt towards full characterization of solvatochromic properties of MK and it aims at analyzing the solvent influence on the IR and Raman 2

spectra. Some authors have recently reported an almost linear relationship between the electronic and the vibrational frequency shifts corresponding to symmetric NO2 stretching mode for N,N-dimethyl-p-nitroaniline in a variety of solvents [23]. On the other hand, in the case of p-nitroaniline a substantial vibrational solvatochromism of the NO2 stretching mode is not observed. It is interesting to check the relationships between the electronic and the vibrational frequency shifts in the case of MK. Yet another motivation to undertake this study is that the presence of carbonyl group in MK makes it a good infrared molecular probe for polar environment investigations. To the best of our knowledge, the vibrational solvatochromism of MK in its ground electronic state has not been studied yet by means of IR or Raman spectroscopy. In this work, an exploration of the solvent effect on the vibrational spectrum of MK is considered from experimental and theoretical point of view.

II. EXPERIMENTAL AND COMPUTATIONAL METHODS

A. EXPERIMENTAL METHODS Commercially available (Aldrich) Michler's ketone was purified using method described by Tahara and Hamaguchi [18] before use. The FT-IR spectra in the range 400 – 4000 cm-1 of MK in cyclohexane, carbon tetrachloride, chloroform, 2-butanone, acetone, acetonitrile, DMSO and methanol solvents at the concentration of about 5·10-2 M were measured with a Thermo Nicolet spectrometer at 4 cm-1 resolution. The Raman spectra of about 5·10-1M MK solutions in the same solvent as in the IR experiments were recorded with 488 nm line of Spectra Physics Ar-Kr mixed ions laser using Jobin Yvon T64000 spectrograph equipped with a liquid N2-cooled CCD camera in therange 400 - 3500cm-1. During all measurements, performed directly after preparation of solutions at room temperature, spectroscopic grade solvents were used.

B. COMPUTATIONAL DETAILS The molecular geometry and vibrational spectra of MK was calculated using the B3LYP functional and triple zeta 6-311++G(d,p) basis set. The solvent effect was studied by using Polarizable Continuum Model (PCM) [24]. To examine the influence of possible hydrogen bond formation with solvent molecules on the bond length alternation and the 3

wavenumber shift we have built a cluster of MK and explicit solvent molecule (cf. Scheme 1.). Later the combination of previous approaches, the cluster with PCM has been applied. In all instances, the geometry of MK and its complex with solvent molecule was fully optimized without any constraints and followed by evaluation of hessian. All ab initio calculations were performed using the GAUSSIAN 03 suite of programs [25]. The potential energy distribution (PED) was calculated using GAR2PED software package [26].

III. RESULTS AND DISCUSION

A. VIBRATIONAL ANALYSIS

IR SPECTROSCOPY The analysis of experimental IR spectra of MK in different solvents, shows that the absorption bands of ν(C=O), ν(C-N) and ν(C-C) are the most influenced by the nature of a solvent. Table 1 contains vibrational wavenumbers in different solvents. The columns are arranged according to dipole moment (μ), dielectric constant (ε), donor number (DN), Reichardt's polarity parameter, ET(30) [3] and solvent polarity/polarizability (SPP) scale, measured in infrared (IR) [27],[28]. The ET(30) scale is based on the extremely solvatochromic character of pyridinum-Nphenoxide betaine dye. According to Eq. (1) the transition energy of the dissolved betaine is a definition of the ET(30) value for a solvent [3]:

(1 )E T / (kJ⋅ mol− 1 )=h⋅ c⋅ ṽ ⋅ N A= 1 .196⋅ 10− 2⋅ ṽ /cm− 1 Solvents polarity according to Solvent Polarity/Polarizability (SPP) scale is defined as the difference between solvatochromism of 2-dimethylamino-7-nitrofluorene (DMANF) and 2-fluoro-7-nitrofluorene (FAF), which is its homomorph [27][28].

(2 )∆ν (solvent )=ν FNF − ν DMANF The polarity can be determined on given scale form 0 for the gas phase to 1 for DMSO.

(3 )SPP (solvent )= [∆ν (solvent )− ∆ν (gas )]/ [∆ν (DMSO )− ∆ν (gas )] The vibrational spectra of carbonyl containing compounds exhibit significant wavenumber shifts of C=O stretching mode [12],[29],[30],[31]. Our experiment has shown that for mode ν(C=O) in the IR spectrum of MK the biggest wavenumber shift amounts to 4

only 5 cm-1. Such shift is observed between spectra measured in DMSO and cyclohexane, the most polar aprotic and the non polar aprotic of all used solvents, respectively. Spectra measured in polar protic methanol and non-polar aprotic cyclohexane demonstrate shift of 3 cm-1. The latter value is not significant in comparison with the results obtained in previous investigations concerning ν(C=O) in the same solvents [29]. Bellamy and Williams [29] have reviewed the data concerning wavenumber shifts of ν(C=O) of 8 carbonyl containing compounds. The shift amounts to 12 cm-1 for benzophenone (MK's parent molecule), 13 cm-1 for acetophenone, 19 cm-1 for cyclohexanone and 9 cm-1 for dimethyl formamide. Nyquist's investigations, on the other hand, have shown that the differences of vibrational wavenumbers of ν(C=O) in DMSO and non-polar aprotic carbon tetrachloride are from 8 cm-1 to 11 cm-1 for acetone/benzophenone and 4–methoxyacetophenone, respectively [30]. In contrast to the results obtained by these authors, our experiment has shown the shift equal only to 3 cm-1 for MK. Nevertheless, the constant trend in position changes can be observed. Analyzing vibrational wevenumbers received from the experiment (Table 1) one could notice that the ν(C=O) absorption band for MK in aprotic solvents (cyclohexane, carbon tetrachloride, chloroform, acetonitrile and DMSO) shows a redshift transition along with increasing polarity of a solvent, according to polarity parameters (ε, μ, ET(30), SPP). Likewise, the experimental results have been correlated with Kirkwood-Bauer-Maga (KBM) parameter [32] (4) and Buckingham's equations for polar and non-polar solvents [33] (5): (4)

Δv ε− 1 C 0 = , 2ε+1 v

(5)

Δv ε− 1 n2 − 1 C+C +C ε n v0 = 2ε+ 1 2n+1 for polar solvents, Δv 1 ε− 1 C+ (C ε +C n ) 0 = 2 2ε+1 v

for non-polar solvents.

where: ε – dielectric constant, n – refractive index,

Δv v 0− v s 0 v 0 = v 0 , where v is the

vibrational frequency in the gas phase and vs is the frequency in the solvent of dielectric constant (ε). According to all parameters (ε, μ, ET(30), DN and SPP) and correlations mentioned above two trends in v(C=O) wavenumbers have been observed. On Figs. 1-3 it has been shown the results interpreted separately for polar (both protic and aprotic) and non-polar 5

aprotic solvents and DMSO. The purpose of such division is to show that in all polar solvents the mode ν(C=O) in the IR spectrum of MK wavenumber values are the same, while in non-polar aprotic ones and DMSO the differences are noticeable. Chloroform, which is once considered as polar and once as a non-polar solvent (μ= 1.0 D) fits both trends at the same time. The two trends may be caused by intermolecular interactions, mainly by possibility of hydrogen bonding formation. To verify above hypothesis we have calculated ν(C=O) wavenumber using PCM approach for all solvents used in experiments. The results has been shown on Fig. 4 as a dependence of ν(C=O) wavenumber on E T(30) scale. Here, the two trends have been observed as well. It disagrees the influence of hydrogen bonding on wavenumber shift. The similar relationship is observed on the ν(C=O) wavenumber vs. SPP scales or Buckingham equation. It is worth noting that there is not observed the band of the ν(C=O) stretching vibration like in benzophenone in alcohols [34]. The wavenumber shift of mode ν(C-C) in the IR spectrum of MK is significant, the biggest difference between transition in cyclohexane and carbon tetrachloride (1286 cm-1) and in methanol (1294 cm-1), amounts to 8 cm-1. The largest C-N band transition is 10 cm-1 (1359 cm-1 in 2-butanone and 1369 cm-1 in DMSO and methanol). Moreover an attempt to correlate the v(C-N) and ν(C-C) wavenumber shifts with different polarity parameters and functions did not show any clear explanation for their mode of action.

RAMAN SPECTROSCOPY As Raman spectroscopy is complementary to IR spectroscopy, there are many similarities in experimental results for these two. The obvious fact is that modes ν(C=O), ν(C-C) and ν(C-N) in the Raman spectrumof MK are strongly influenced by surrounding solvent. Table 2 shows experimentally measured changes of Raman wavenumbers as a function of polarity parameters (ε, μ, ET(30), DN and SPP). Raman spectroscopy has similar effect on MK's wavenumber shifts as IR spectroscopy. In aprotic solvents, the redshift transitions occur according to increase of aprotic solvent polarity. In polar protic solvents situation has not been found as that clear as in IR experiment. However, with exception of MK in chloroform and methanol, all the ν(C=O) wavenumber transitions are solvent polarity parameters dependent (Fig. 5 and 6). Though, it has been noticed that the MK solvatochromic Raman shift of ν(C=O) wavenumber is much more significant than in IR experiment. The difference in mode 6

ν(C=O) in the Raman spectrum of MK wavenumber amount to 20 cm-1, measured in isooctane and hexane, where ν(C=O) is 1605 cm-1 and in methanol, where ν(C=O) is 1585 cm-1. Elenewski and Hackett, using Raman spectroscopy, have presented solvent effect on benzophenone (MK's parent molecule) [34]. It has been shown that the biggest Raman shift for the molecule is amount to 20 cm-1, as a difference between ν(C=O) wavenumbers in hexane and methanol. What is in exact agreement with our investigations concerning MK, where the shift of the ν(C=O) wavenumber for the same solvents is identical. An attempt to classify experimental Raman results according to categories proposed by Elenewski and Hackett, in the same work, have been made. The categories are the alcohol hydrogen bonding, alcohol bare shifts, halogen bonding/aromatic and general polar/nonpolar solvents. Although the experimental results that have been obtained seem to fit the division into four proposed groups, there not enough of them to confirm it with absolute confidence. It has been noticed that Raman shifts of ν(C-C) and ν(C-N) exist, but no correlation connecting them with polarity parameters has been found. The situation may be caused by the fact that the Raman spectroscopy experiment did not expose enough wavenumbers that could be possibly examined and assigned to any order. Exemplary spectra are available in supplementary materials.

B. MOLECULAR STRUCTURE The results of calculations performed in continuous dielectric environment (PCM approach) of geometric parameters for MK in different solvents are presented in Table 2. Analysis of this data allow to draw a conclusion that in aprotic solvents, i.e. in the cyclohexane, carbon tetrachloride, chloroform, acetonitrile and DMSO, bond length changes are monotonous not only with respect to ε but also to DN, μ and SPP scale. Similar trend has been also observed in the case of two other set of parameters in Table 2, acceptor number (AN) [35], and ET(30). In the case of AN and ET(30) scales, the results of calculations do not fit the trend for chloroform and acetonitrile, respectively. In the case of MK in methanol and water solvents, such dependence does not exist for all of polarity parameters but SPP scale, where only water does not fulfill the observed trend. Bond length changes of MK are computed directly based on the data collected in 7

Table 3. The changes, defined as the difference between bond length in gas phase and in a solvent, are displayed in Figure 1. At first glance the most solvent influenced bonds are C=O (bond index 11), C-N (index 3 and 19) and C-C (index 10 and 12). This is in line with the experimental results. For the C=O (C-N) (C-C) bond the differences amount to 0.012 Å (-0.013 Å) (-0.008 Å) for polar solvents (acetonitrile, DMSO, methanol and water), 0.008 Å (-0.009 Å) (-0.005 Å) for non-polar chloroform and about 0.004 Å (-0.005 Å) (-0.003 Å) for other non-polar solvents (cyclohexane and carbon tetrachloride). Analysis of the changes in bonds lengths allows to observe constant trend in bond alternation. In each solvent length of the bonds with bond index 1, 2, 4, 6, 7, 9, 11, 13, 15, 16, 18, 20 and 21 increase while length of bonds with bond index 3, 5, 8, 10, 12, 14, 17 and 19 decrease. Scheme 2 pictures the trend. Since not only solvent polarity but also its proticity is an expected factor contributing to the overall solvent effect, we have performed additional calculations using the supermolecular approach. In order to account for the intermolecular hydrogen bonding effect, our model includes a single solvent molecule placed in the vicinity of C=O moiety (cf. Scheme 1). Similar approach was adopted by Choi et al. [7] and Choi and Cho [10] who studied other IR probes. The bond lengths computed within supermolecular approximation are presented in Table 4. Analysis of the data assembled in the table has shown the relation between polarity of a solvent, C=O bond length and ET(30) scale values. The relation exists only for polar solvents, so the 2-butanone, acetone, acetonitrile, DMSO and methanol. Non-polar chloroform does not fit this trend. All solvents polarity parameters are shown in Table 4. It should not be overlooked that both employed approaches, i.e. implicit and explicit solvent representation, predict bond length changes in a similar manner (cf. Figure 2). However, in the most cases the changes in bond lengths predicted by the supermolecular model are about two times smaller than these predicted employing the PCM method. The largest changes in bond lengths are found for the same bonds (bond index 3, 10, 11, 12 and 19). A complex composed of a single MK and single DMSO molecule shows different properties than all other supermolecules. The differences in bond lengths are the least significant when compared to MK with other molecules, i.e. the difference between C=O bond length in complex with methanol is equal to 0.008 Å and with DMSO to 0.004 Å. It has been also observed that opposite trend in bonds alternation occurs, i.e. in complex with methanol bond no. 10 (cf. Scheme 2.) length is -0.005 Å and with DMSO 0.001 Å. 8

Third model is a combination of the two previous ones. The supermolecule is surrounded by continuous dielectric environment (PCM approach). The differences in bond length changes in this model can be seen in the Fig. 3-6. It has been observed that this model is the one according to which the biggest bond length changes occur. They are 0.0127 Å for C=O bond -0.0082 Å for one of C-C bonds and -0.0119 Å for DMSO. The trend in bond length alternation appears in all instances. To sum up, the bond length changes are dependent of both solvents polarity and its ability of H-bonding formation. It should be emphasized that neglecting the hydrogen bond between MK and a solvent while concerning changes in bond lengths is a too crude approximation.

IV. SUMMARY AND CONCLUSIONS Michler's ketone has been investigated in a variety of solvents with the aid of IR and Raman spectroscopy as well as using quantum-chemistry methods (at the DFT/B3LYP/6311++G(d,p) level), to study the solvent effect on the vibrational spectrum. The theoretical and experimental results prove that the solvatochromism of MK is dependent both on polarity of a solvent and its ability of hydrogen bonding formation. Two trends between the wavenumber shifts of mode ν(C=O) in the IR spectrum of MK and polarity parameters (ε, μ, ET(30), DN and SPP) or Buckingham's equations and KBM have been observed. One for polar and second for non-polar aprotic solvents and DMSO. Only the wavenumber shift of mode ν(C=O) in the IR spectrum of MK in the chloroform solvent fits both trends and because of its low but non-zero polarity, chloroform behaves as polar and as non-polar aprotic solvent at the same time. The ν(C-N) and ν(C-C) wavenumber shifts also appeared to be very solvent sensitive. Unfortunately the simple systematization of ν(C-N) and ν(C-C) have not been possible neither for IR nor Raman spectroscopy, according to any polarity parameters or correlations mentioned above. The mode ν(C=O) in the IR spectrum of MK has shown a small solvatochromic shift. Since investigations concerning benzophenone, MK's parent molecule, did not show any abnormalities regarding this molecule [11],[36],[37]. Raman experiment on the other hand has shown relatively big wavenumber red shift for the mode ν(C=O) in the spectrum of MK. However, the Raman spectra shows the same dependence of mode ν(C=O) wavenumber shift for non-polar aprotic solvents and 9

chloroform as in IR experiment. Nevertheless the Raman shifts of mode ν(C-N) and ν(C-C) wavenumbers have been observed, in range of used solvents, no correlations for them occur. Moreover, the mode ν(C=O) in the Raman spectrum of benzophenone and MK shows exactly the same wavenumber shift, while IR wavenumber shift in the case of benzophenone is four times larger than that corresponding to MK. In analogy to Puranik's work [15], the C=O bond length increases in all solvents, while the C-N and C-C bond lengths decrease in all solvents but DMSO in supermolecular model. PCM technique have not perfectly captured the solvent effect found in the experiment, which is a result of both, solvents polarity and its possibility of hydrogen bond creation. What suggests that the model is to simple to render the mentioned effect, still, it is at least in qualitative agreement with the experiment. In this work we have made an attempt to analyze the ambiguous solvent effect on the vibrational spectrum of MK. Almeida and Santos [38] have presented spectra of 2,3-diphenyl-cycloprop-2-enone (DPC) measured in few solvents and revealed similar problem to ours. In their investigations the mode ν(C-C) from aromatic ring was the one more solvent sensitive than the carbonyl group ν(C=O) mode. In the work the solvent effect on the mode ν(C=O) in the Raman and IR spectra of DPC could be understood by the complex composition of the mode, also affected by the presence of a Fermi resonance. MK's stretching modes can not be explained in this way. The question, why the wavenumber shift is that much different for complementary spectroscopies, still remains open. In our future work we are going to try facing solvent effect of other molecules, which structures are based on benzophenone molecule as a root.

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References [1] A. Hantzsch, Ber. Dtsch. Chem. Ges. 55 (1922) 953-979. [2] W. Liptay, Angew. Chem., Int. Ed. 8 (1969) 177-188. [3] Ch. Reichardt and T. Welton, Solvents and Solvent Effects in Organic Chemistry, 4th ed., VCH, (1988). [4] H. Lee, J.-H. Choi and M Cho, J. Chem. Phys. 137 (2012) 114307-114321. [5] M. Cho, J. Chem. Phys. 130 (2009) 094505-094520. [6] A. B. S. Elliot, R. Horvath and K. C. Gordon, Chem. Soc. Rev. 41 (2012) 1929-1946. [7] J.-H. Choi, K.-I. Oh, H. Lee, Ch. Lee and M. Cho, J. Chem. Phys. 128 (2008) 134506- 134514. [8] G.-J. Zhao, K.-L. Han, J. Phys. Chem. 113 (2009) 14329-14335. [9] H. Lee, G. Lee, J. Jeon and M. Cho, J. Phys. Chem. 116 (2012) 347-357. [10] J.-H. Choi and M. Cho, J. Chem. Phys. 134 (2011) 154513-154525. [11] P. Sett, T. Mistra, S. Chattopadhyay, A. K. De and P. K. Mallick, Vibrational Spectroscopy 44 (2007) 331-342. [12] R. D. Pensack, K. M. Banyas and J. B. Asbury, Phys. Chem. Chem. Phys. 12 (2010) 1414414152. [13] N. Tekin, H. Pir and S. Sagdinc, Spectrochimica Acta A. 98 (2012) 122-131. [14] H. Wang, L. Wang, S. Shen, W. Zhang, M. Li, L. Du, X. Zheng and D. L. Phillips, J. Chem. Phys. 136 (2012) 124509-124520. [15] P. G. Puranik, Proc. Indian Acad. Sci., Sect. A 37 (1953) 499-503. [16] National Toxicology Program, Report of Carcinogenics: carcinogen profiles/U.S. Dept. of Health and Human Services 12 (2011) 270-271. [17] Ch. Reichardt, Chem. Rev. 94 (1994) 2319-2358. [18] T. Tahara, H. Hamaguchi, Chem. Lett. 21 (1992) 17-20. [19] P. Suppan, J. Chem. Soc., Far. Trans. 1 71 (1975) 539-547. [20] L. C. T. Shoute, Chem. Phys. Lett. 195 (1992) 255-261. [21] M. Hashino and M. Kogure, J. Phys. Chem. 92 (1988) 417-420. [22] S. Spange, M. El-Sayed, H. Müller, G. Rheinwald, H. Lang and W. Poppitz, Eur. J. Org. Chem. 2002/24 (2002) 4159-4168. [23] Y. Kimura, T. Hamamoto and M. Terazima, J. Phys. Chem. A 111 (2007) 7081-7089. [24] S. Miertuš, E. Scrocco and J. Tomasi, Chem. Phys. 55 (1981) 117-129. [25] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Rob, J. R. Cheeseman, J. A. Montgomery Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson,

H. 11

Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, 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. PiskorzI. 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 and J. A. Pople, Gaussian 03, Gaussian, Inc., Wallingford, CT, 2003. [26] J.M.L. Martin, C. Van Alsenoy, GAR2PED, A Program to Obtain a Potential Energy Distribution from a Gaussian Archive Record, University of Antwerp, Belgium, 2007. [27] J. Catalán, ed. G. Wypych, 10.3. Solvent Effect Based on Pure Solvents Scales, Hanbook of Solvents, ChemTec Publishing (2001) [28] J. Catalán, V. López, P. Pérez, R. Martín-Villamil and J.-G. Rodriguez, Liebigs Ann. 1995 (1995) 241-252. [29] L. J. Bellamy and R. L. Williams, Trans. Faraday Soc. 55 (1959) 14-18. [30] R. A. Nyquist, V. Chrzan and J. Houck, Applied Spectroscopy 43 (1989) 981-983. [31] B. Jović, A. Nikolić and S. Petrović, J. Mol. Struct. 1044 (2013) 140-143. [32] J. G. Kirkwood, in W. West and R. T. Edwards, J. Chem. Phys. 5 (1937) 14-22. [33] A. D. Buckingham, Proc. Roy. Soc. London, Ser. A 248 (1958) 169-182. [34] J. E.Elenewski and J. C. Hackett, J. Chem. Phys. 138 (2013) 224308-224316. [35] V. Guttmann, The Donor - Acceptor Approach to Molecular Interactions, Springer (1978). [36] T. Kolev, B. Nikolova, B. Jordanov and I. Juchnovski, J. Mol. Structure 129 (1985) 1-10. [37] T. M. Kolev and B. A. Stamboliyska, Spectrochimica Acta A 56 (1999) 119-126. [38] L. C. J. Almeida and P. S. Santos, Spectrochimica Acta A 58 (2002) 3139-3148. [39] J. A. Dean, Lange's Handbook of Chemistry, 13th ed, McGraw - Hill Book Company (1972).

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Scheme 1. Supermolecule model of Michler's ketone and single solvent molecule (here water molecule), showing the definition of angle Θ.

Wavenumbers [cm-1]

Fig. 1. Dependence of the experimental ν(C=O) wavenumber (in cm-1) on the values of ET(30) scale.

13

Fig. 2. Dependence of the experimental ν(C=O) mode wavenumber (in cm-1) on the values of SPP scale.

Wavenumbers [cm-1]

Fig. 3. Dependence of the experimental ν(C=O) mode wavenumbers (in cm-1) on the values from Buckingham equations (5).

14

1672

non-polar aprotic and DMSO solvent chloroform polar solvent

1670 1668

wavenumber/cm

-1

1666 1664 1662 1660 1658 1656 1654 1652

30

35

40

45

50

55

ET(30)

Fig. 4. Dependence of calculated (PCM) ν(C=O) mode wavenumbers (in cm-1) on the values of ET(30) scale.

Wavenumbers [cm-1] Dipole moment μ [D]

Fig. 5. Dependence of ν(C=O) Raman shift (in cm-1) on the values of ET(30) scale.

15

Fig. 6. Dependence of ν(C=O) Raman shift (in cm-1) on SPP scale.

The differences between bond length changes [Å]

Fig. 7. The MK's theoretical bond length changes in different solvents according to gas phase. Counted in continuous environment (PCM) as Δl=l(solvent) – l(gas phase), where l(solvent) is the length of a bond in a solvent and l(gas phase) is the length of the same bond in gas phase. Bond index corresponds to the number of a bond from Scheme 2.

16

Fig. 8. The MK's theoretical bond length changes for supermolecular model. Counted as Δl=l(MK with single solvent molecule) – l(gas phase), where l(MK with single solvent molecule) is the length of a bond with substituted single solvent molecule and l(gas phase) is the length of the same bond in gas phase. Bond index corresponds to the number of a bond from Scheme 2.

Fig. 9. Change of MK's bond lengths in three theoretical models for DMSO as a solvent. Diagram with dots shows the bond length changes in PCM, diagram with squares respond to MK's bond length changes in supermoleculer model and diagram with circles to changes of the bonds in supermolecular model in continuous environment, so 17

supermolecule in PCM.

Bond index

Fig. 10. Change of MK's bond lengths in three theoretical models for chloroform as a solvent. Diagram with dots shows the bond length changes in PCM, diagram with squares respond to MK's bond length changes in supermoleculer model and diagram with circles to changes of the bonds in supermolecular model in continuous environment, so supermolecule in PCM.

Bond index

Bond index

Fig. 11. Change of MK's bond lengths in three theoretical models for acetonitrile as a solvent. Diagram with dots shows the bond length changes in PCM, diagram with squares respond to MK's bond length changes in supermoleculer model and diagram with circles 18

to changes of the bonds in supermolecular model in continuous environment, so supermolecule in PCM.

Scheme 2. Michler's ketone structure with the trend of bond lengths alternation shown, where red color means bond lengths shortening and green color means bond lengths increasing.

19

Table 1. Selected experimental IR wavenumbers (in cm-1) in different solvents. calculated

KBr

cyclohexane

carbon tetrachloride

chloroform 2-butanone acetone acetonitrile DMSO methanol

μa

0.0

0.0

1.0

2.8

2.9

3.9

3.9

1.7

εa

2.2

2.2

4.8

18.5

20.7

37.5

46.6

32.7

0.0

0.0

4.0

-

17.0

14.1

29.8

19.0

ET(30)

30.9

32.4

39.1

41.3

42.2

46.7

45.1

55.4

SPPd

0.557

0.632

0.786

0.881

0.881

0.895

1.000

0.962

DNb c

Proposed assignment

1

427

405

-

405

405

403

401

407

405

401

τCC(Ring)

2

435

420

418

-

416

-

-

-

420

420

τCC(Ring)

3

524

513

-

513

511

509

-

515

513

-

4

587

571

573

573

573

573

573

573

571

575

5

658

629

-

631

631

631

-

631

629

-

δCC(Ring)

6

693

646

-

-

648

648

-

648

646

-

τCC(Ring)

7

744

683

683

685

686

686

686

686

683

688

τCC(Ring)

8

786

742

-

-

-

742

742

742

742

742

9

813

768

768

-

-

769

771

771

768

771

γCH(Ring)

10

817

802

-

-

804

806

-

806

-

-

γCH(Ring)

11

834

816

818

-

824

825

825

827

816

825

12

849

829

833

-

835

837

837

839

827

836

γCH(Ring)

13

974

926

926

926

926

926

926

928

926

928

γCH(Ring)

14

986

945

945

946

945

945

947

945

947

947

γCH(Ring)

15

1078

1007

-

1005

1007

1009

1007

1005

1009

-

δNCH + νCN 3

16

1131

1064

-

1064

1064

1066

1064

1066

-

-

δNCH 3

17

1168

1134

-

-

1128

1128

-

1128

1130

-

νCaromC +

γCaromN + τCC(Ring) δCC(Ring) + δscisNC 2

τCC(Ring) + γCO + γCaromN

γCH(Ring) + γCaromC

20

νCC(Ring) 18

1208

1149

-

1147

1149

1147

-

1149

1149

-

δCH(Ring)

19

1232

1176

1184

1184

1182

1184

1182

1182

1182

1184

δCH(Ring)

20

1262

1209

1215

-

1211

1213

-

-

1209

-

νCN + νCC(Ring)

21

1302

1234

-

-

1232

1232

-

1230

1232

1232

νCaromC

22

1358

1286

1286

1286

1290

1288

1288

1290

1288

1294

νCC(Ring)

23

1380

1321

1321

1321

1325

1321

1321

1323

1321

1327

νNC(Ring)

24

1444

1375

1360

1360

1367

1359

1363

1365

1369

1369

δNCH 3

25

1485

1410

-

1412

1411

-

-

-

1404

1414

δNCH 3

26

1514

1431

-

1429

1431

1430

1423

1433

1429

1432

δNCH 3

27

1529

1444

-

1446

1446

1448

1433

1448

1444

1448

δNCH 3

28

1554

1481

-

1483

1483

1485

1487

1487

1487

-

νNC(Ring)

29

1638

1531

1525

1527

1529

1529

1529

1529

1531

1533

νCO + νCC(Ring)

30

1642

1543

-

-

-

1546

1548

1547

1543

-

νCC(Ring)

31

1685

1599

1604

1602

1601

1601

1601

1601

1599

1601

νCO

32

2974

2818

-

-

2818

-

2819

2815

2816

-

νCH 3

32

3052

2864

-

2862

2866

-

2868

2867

-

-

νCH 3

33

3055

2904

-

2897

2912

-

-

2908

2912

-

νCH 3

35

3128

2983

-

2985

-

-

-

-

-

-

νCH 3

a

Dipole moment – μ [37]

a

Dielectric constant – ε [37]

b

Donor number – DNb [35]

c

Reichardt's Polarity Parameter – ET(30) [3]

d

Solvent Polarity/Polarizability scale – SPP [27]

21

Table 2. Experimental Raman shift (in cm-1)of MK's solutions in different solvents.

Calculated

KM powder

hexane

cyclohexan e

carbon tetrachlorid e

chlorofor

2-

m

butanone

acetone

acetonitril e

DMSO

methanol

μ

0.1

0.0

0.0

1.0

2.8

2.9

3.9

3.9

1.7

ε

1.9

2.2

2.2

4.8

18.5

20.7

37.5

46.6

32.7

DN

0.0

0.0

0.0

4.0

-

17.0

14.1

29.8

19.0

ET(30)

31.0

30.9

32.4

39.1

41.3

42.2

46.7

45.1

55.4

SPP

0.519

0.557

0.632

0.786

0.881

0.881

0.895

1.000

0.962

Assignment

1

343

353

358

-

-

366

-

-

-

-

-

δCC(Ring)

2

478

-

-

-

-

447

-

-

-

-

-

3

587

559

-

-

-

554

-

-

-

-

-

4

693

658

-

-

-

668

-

-

-

-

-

5

786

729

-

-

-

730

-

-

-

-

-

6

813

778

-

776

776

778

776

776

776

776

777

γCH(Ring)

7

817

783

784

-

-

-

-

-

-

-

-

γCH(Ring)

8

1208

1147

-

1149

1149

1150

1148

1148

1150

1150

-

δCH(Ring)

9

1232

1186

-

-

-

1180

-

-

-

-

-

δCH(Ring)

10

1444

1374

-

-

-

1370

-

-

-

-

-

δNCH3

11

1460

1380

-

-

-

-

-

-

-

-

-

12

1514

-

-

-

-

1432

-

-

-

-

-

δNCH3

13

1638

1544

-

-

-

1544

-

-

1541

1539

-

νCO + νCC(Ring)

14

1685

1588

1605

1600

1600

1590

1597

1596

1595

1591

1585

νCO

δrockNC2 + γCaromN δCC(Ring) + δscisNC2 τCC(Ring) τCC(Ring) + γCO + γCaromN

νCC(Ring) + δNCH3

22

Highlights


Solvent effect on vibrational spectra of Michler's ketone was investigated.
Redshift vibrational transition along with increasing polarity of a solvent was observed.
The wavenumber shift of νCO mode can be interpreted separately for polar and non-polar aprotic solvents including DMSO.
Raman shifts of ν(C-C) and ν(C-N) modes did not show any correlation connecting them with polarity parameters.