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Solvent effect on Raman spectra of conformational key bands of chloroacetone and bromoacetone
Spectrochimica Acta Part A 55 (1999) 2659 – 2670 www.elsevier.nl/locate/saa
Solvent effect on Raman spectra of conformational key bands of chloroacetone and bromoacetone Yosuke Shiratori, Minoru Kato *, Yoshihiro Taniguchi Department of Chemistry, Faculty of Science and Engineering, Ritsumeikan Uni6ersity, Kusatsu, Shiga, 525 -8577, Japan Received 15 December 1998; accepted 6 April 1999
Abstract Raman spectra were measured for chloroacetone and bromoacetone in various solvents at 20°C. The authors recorded the C–X (X:Cl and Br) stretching modes for both chloroacetone and bromoacetone and the CO stretching mode for bromoacetone. In each spectrum for aqueous solutions, an additional band appeared on the lower frequency side of the band of the syn conformer. These bands are assigned to the syn conformer which forms a hydrogen bond between each halogen atom of haloacetones and water molecule. From solvent effects on peak frequencies, half band widths and band profiles, the authors discussed local hydration structures of haloacetones. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Raman spectroscopy; Haloacetone; Solvent effects on peak frequency; Hydrogen bond; Hydration structure
1. Introduction Conformational equilibrium is one of the simplest chemical equilibria and an essential molecular property. Conformational equilibria, especially in liquids can be affected occasionally by medium environments such as temperature, pressure and solvent. A shift of conformational equilibrium by medium effects is closely related to a difference in solvation structures between conformers. Thus medium effects are important subjects for studies of liquid structures and their properties. * Corresponding author. Tel.: +81-775-612761; fax: + 81775-612659. E-mail address: [email protected] (M. Kato)
Vibrational spectroscopies have been powerful methods for investigating conformational equilibria since the pioneer study by Mizushima [1]. To study conformational equilibria of a certain liquid compound in various environments, we need to assign its conformational key bands and understand the origins of spectral shifts because they reflect solvation structures. Mizushima et al. [2] have studied the conformational equilibrium of chloroacetone (Fig. 1) using Raman and infrared spectroscopies. They assigned vibrational modes and suggested that the gauche and the syn conformers are predominant in the vapor and the solid phases, respectively. Since their study, there have been some works on chloroacetone [3–6] that should be cited.
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Taniguchi et al. [7] measured infrared spectra of the C–Cl stretching region in carbon disulfide at various pressures. They discussed pressure effect on the frequency shifts and the conformational equilibrium, and solvent effect on the frequency shifts with Bauer and Magat theory [8]. Durig et al. [9] reported the vibrational assignments and the detail of each conformer structure on the basis of the results of Raman and infrared measurements, and ab initio calculations. A recent Raman work by Kato et al. [10] was the first to report about the conformational behavior of chloroacetone in aqueous system. They found the presence of a new species of chloroacetone relating to a hydrogen bond with water molecule, and named it syn% conformer. As for bromoacetone (Fig. 1), no systematic research has been done. Crowder and Cook [11] measured infrared spectra in the vapor and the liquid phases and reported that bromoacetone has a conformational equilibrium similar to chloroacetone. Since this work there was no notable report except a recent work by Durig [12], which determined the vibrational assignments and the structure of each conformer via Raman and infrared measurements, and ab initio calculations. As described above, conformational equilibria of haloacetones have been investigated mainly from the viewpoint of structural chemistry. However, solvent effects on their equilibria have not been reported sufficiently; there have been no studies, particularly, for aqueous solution except the study by Kato et al. [10]. In this work, the authors measured Raman spectra of chloroacetone and bromoacetone in
various solvents at 20°C, and observed additional Raman bands for the C–Br and the CO stretching modes of bromoacetone in water and heavy water, similarly to chloroacetone [10]. The origins of these additional bands and of the spectral shifts for various solutions are discussed.
2. Experimental Chloroacetone (\ 95%, Tokyo Kasei) was distilled under reduced pressure. Impurities of bromoacetone (\ 90%, Tokyo Kasei) were drained off through a membrane filter. Spectra-grade nhexane, cyclohexane, tetrachloroethylene, diethylether, tetrahydrofuran (Nakarai Tesque) and acetonitrile (Wako) were used without further purification. Water distilled after ion exchange and deuterium oxide from CEA with a purity of 99.9% were used. Raman spectra were recorded using a JEOL 400D spectrometer equipped with a cooled HTV-R649 photomultiplier and photon counting detector. Samples were exited with 90° scattering of 514.5 nm radiation from an argon ion laser (NEC GLG3300) with 250 500 mW output. The spectral slit width, scanning speed and the number of scanning were: 4.2; 100 cm − 1 min − 1 and 5–10 times, respectively. All measurements have been done at 20°C. Temperature of samples was controlled within an error of 9 0.3°C by thermostated water circulating around the glass cell. The observed spectra were analyzed by GRAMS/386 software (Galactic Industries) and were fitted with Voigt functions to determine peak frequencies and integrated intensities of bands. The authors measured the C–X (X:Cl and Br) stretching modes for chloroacetone and bromoacetone, respectively, and the CO stretching mode for bromoacetone in various solvents.
3. Results and discussion
3.1. Chloroacetone
Fig. 1. Conformers of chloroacetone and bromoacetone.
Raman spectra in the C–Cl stretching region for various solvents are shown in Fig. 2. The strong bands at higher and lower frequencies are
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Fig. 2. Raman spectra of the C–Cl stretching modes of chloroacetone at 20°C (a) in cyclohexane (mole fraction of solute, x =0.12); (b) in tetrachloroethylene (x= 0.05); (c) in tetrahydrofuran (x =0.05); (d) neat liquid; (e) in acetonitrile (x =0.05); (f) in heavy water (x=0.02) and (g) in water (x= 0.02). Spectra (a) and (c) were obtained after subtraction of solvent scatterings. A peak around 750 cm − 1 of the spectrum (e) comes from acetonitrile.
assigned to the C – Cl stretching mode of the syn and the gauche conformers, respectively [2,9]. The weak bands at ca. 805 and 830 cm − 1 are assigned to the C –C – C symmetric stretching and the CH2 rocking modes of the syn conformer, respectively [2,9]. Observed frequencies of the C – Cl stretching modes of chloroacetone for various solvents are summarized in Table 1. An additional band appears around 750 cm − 1 in each Raman spectrum for the aqueous solutions (Fig. 2 f and g). In the previous work [10], this additional band has been assigned to the C – Cl stretching mode of the syn
conformer which forms a hydrogen bond between the chlorine atom and water molecule (syn% conformer). The frequencies of the syn and the gauche conformers are considerably higher in water and heavy water than in n-hexane. The observed blue shifts by the solvent changes from n-hexane to water and heavy water were explained by the hydrophobic hydration around the chlorine atom [10]. On the other hand, red shifts by the solvent changes from n-hexane to polar solvents except water and heavy water were observed. This im-
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plies an increase in attractive interactions between the solute and the solvent molecules in polar solvents [15]. According to Bauer and Magat theory [8], the frequency shift in a dielectric continuum medium is expressed by the following equation: Dn 8
1 o−1 · a 3 2o+ 1
(1)
where Dn, o and a are vapor–liquid frequency shift (nl − nv), relative permittivity of a solvent and radius of a solute, respectively. Fig. 3 shows the relationships between the frequencies of the C–Cl stretching modes and (o− 1)/(2o + 1). All the data except the data for water and heavy water were fitted using a linear function. Satisfactory linear correlations between the frequencies and (o−1)/ (2o + 1) suggest that the solvent effects on fre-
Table 1 Peak frequencies of the CCl stretching modes of chloroacetone in various solvents Solvent
CCl stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Vapore Nonpolar sol6ents n-C6H14 n-C6H14d cyclo-C6H12 cyclo-C6H12d cyclo-C6H12 cyclo-C4H8O2d C2Cl4 C6H6d CS2f
nG
DnG b
nS%
DnS%b
nS
0.05 B0.03 0.05 B0.02 0.12 B0.02 0.05 B0.02 0.05
728.0 728.5 727.5 727 728.7 726 729
Polar sol6ents (C4H9)2Od cyclo-C4H8O (CH3)2COd Neat Neatc Neate Neath CH3CN
3.08 7.52 21.2 30.0g 30.0g 30.0g 30.0g 37.5
B0.03 0.05 B0.02 1.0 1.0 1.0 1.0 0.05
Water and hea6y water D2O D2Oh H2O H2Oh
79.8 79.8 80.1 80.1
0.02 0.02 0.02 0.02
IR IR Raman
728.4 −0.4 +0.1 −0.9 −0.6 +0.3 −2.4 +0.6
764.9 765 764.3 763.5 763.6 762.5 764.4 762.5 764
+0.1 −0.6 −1.4 −1.3 −2.4 −0.5 −2.4 −0.9
Raman IR Raman IR Raman IR Raman IR IR
727 726.3 726 727.1 724 728 726.4 726.2
−1.4 −2.1 −2.4 −1.3 −4.4 −0.4 −2.0 −2.2
763 762.2 762 762.1 764 763 761.3 762.4
−1.9 −2.7 −2.9 −2.8 −0.9 −1.9 −3.6 −2.5
IR Raman IR Raman Raman Raman Raman Raman
731.6 730.5 732.3 730.2
+3.2 +2.1 +3.9 +1.8
768.1 768.6 768.8 767.3
+3.2 +3.7 +3.9 +2.4
Raman Raman Raman Raman
747.2 746.9 752.2 750.2
−17.7 −18.0 −12.7 −14.7
Relative permittivity, at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C), data from [13]. Dn=n (solvent)−n (n-hexane). c [2]. d [4]. e [9]. f [7]. g [14], at 19°C. h [10]. b
DnS b
731 731 730 1.89 1.89 2.02 2.02 2.02 2.22 2.27 2.28 2.63
a
Method
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Fig. 3. Solvent dependence of the frequencies for the C – Cl stretching modes of chloroacetone (: this work; : [2]; : [4]; ": [7]; 2: [9]; +: [10]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o− 1)/(2o+ 1)= 0.186], cyclohexane (0.202), dioxane (0.224), tetrachloroethylene (0.229), benzene (0.230), carbon disulfide (0.261), dibuthylether (0.291), tetrahydrofuran (0.406), chloroacetone (0.475), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
quencies except the aqueous solutions agree with the dielectric continuum model. It is noticeable that the deviations of the data for water and heavy water from the linear lines are significant. This indicates that the hydration structures around the chlorine atoms of the syn and the gauche conformers are unusual from the viewpoint of a dielectric continuum model. In general, intermolecular repulsive forces along a bond of a molecule induce a blue shift [15]. The present result agrees with a previous conclusion by Kato et al. [10] that hydrophobic hydration is formed around the chlorine atoms of these conformers.
3.2. Bromoacetone Figs. 4 and 5 show Raman spectra of the C–Br and the CO stretching modes, respectively, of bromoacetone in various solvents. In
the C–Br stretching region for organic solvents, the bands at higher and lower frequencies are assigned to the C–Br stretching mode of the syn and the gauche conformers, respectively [12]. Although Durig et al. [12] observed a weak band at 729 cm − 1, which was assigned to the C–C–C symmetric stretching mode of the gauche conformer, the authors could not observe this band. Observed frequencies of the C–Br stretching modes for various solvents are summarized in Table 2. As for the C= O stretching mode, the band splitting is not related to a Fermi resonance, and consequently the higher and the lower frequency bands are assigned to the syn and the gauche conformers, respectively [12]. To discuss whether the CO stretching mode is appropriate as a conformational key band, we compare the integrated intensities of the C–Br and the CO stretching modes. The ratios of the integrated intensities between the syn and the gauche bands:
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r=
IS aScS = IG aGcG
(2)
and their relative values to the value of the neat liquid: r IS /IG = r(neat) IS (neat)/IG (neat) =
(aS /aG )(cS /cG ) {aS (neat)/aG (neat)}{cS (neat)/cG (neat)} (3)
are summarized for the C–Br and the C=O stretching regions in Table 3. Here, I, a and c indicate Raman intensity, an unknown coefficient and the concentration of each conformer, respectively. The subscripts indicate the conformers. Assuming that aS /aG does not depend on the solvent, Eq. (3) leads to the following equation: r cS /cG = r(neat) cS (neat)/cG (neat)
(4)
Fig. 4. Raman spectra of the C–Br stretching modes of bromoacetone at 20°C; (a) in n-hexane (mole fraction of solute, x = 0.05); (b) in tetrachloroethylene (x = 0.02); (c) in diethylether (x =0.05); (d) in tetrahydrofuran (x =0.05); (e) neat liquid; (f) in acetonitrile (x = 0.05); (g) in heavy water (x = 0.01) and (h) in water (x= 0.01). Spectra (a); (b) and (d) were obtained after subtraction of solvent scatterings. A peak around 750 cm − 1 of the spectrum (f) comes from acetonitrile.
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Fig. 5. Raman spectra of the CO stretching modes of bromoacetone at 20°C; (a) in n-hexane (mole fraction of solute, x=0.05); (b) in tetrahydrofuran (x= 0.05); (c) neat liquid and (d) in acetonitrile (x=0.05). Spectrum (a) was obtained after subtraction of solvent scattering.
All the values of r/r (neat) for the C – Br stretching mode are close to the corresponding values for the CO stretching mode. Hence, this supports that the CO stretching mode is appropriate as a conformational key band. Next, we discuss solvent effects on the C–Br stretching modes (Fig. 4 and Table 2) in detailed. An additional band was observed at 685 cm − 1 for each aqueous solution (Fig. 4 g and h), similarly to the case of chloroacetone [10]. This band may
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be assigned to the C–Br stretching mode of the syn conformer that has a hydrogen bond between the bromine atom and water molecule (syn% conformer). The peak frequencies for the syn conformer are higher in water and heavy water than in n-hexane. On the other hand, the peak frequencies for the gauche conformer are lower in water and heavy water than in n-hexane, which is different from the case of chloroacetone. All the Dn values [n (solvent)-n (n-hexane)] for the polar solvents are negative. This suggests an increase in attractive interactions between the solute and the solvent molecules in polar solvents. Fig. 6 shows the relationships between the frequencies of the C–Br stretching modes and (o− 1)/(2o +1) for various solvents. The authors fitted all the data except the data for water and heavy water using a linear function. As for the syn conformer, the correlation between the frequency and (o− 1)/(2o +1) is similar to that for both conformers of chloroacetone (Fig. 3). The deviations from the linear line for water and heavy water suggest the presence of the hydrophobic hydration around the bromine atom. In contrast, the data of the gauche conformer for water and heavy water are on the linear line. This is different from the cases of both conformers of chloroacetone (Fig. 3) and the syn conformer of bromoacetone. This implies that the hydration structure around the bromine atom of the gauche conformer is significantly different from those cases. Hydrophobic hydration does not seem to be formed around the bromine atom of the gauche conformation. The half band width and the band profile of a stretching mode are also influenced by solute–solvent interactions [15,16]. A change in the band width induced by a change in the interaction is known to correlate with the frequency shift [15,16]. The relationships between the half band widths of the C–X stretching modes and (o−1)/ (2o +1) for various solvents are shown in Fig. 7a for chloroacetone and Fig. 7b for bromoacetone. The authors fitted all the data except the data for water and heavy water using a linear function. The half band widths for the syn bands of chloroacetone and bromoacetone decrease linearly with increasing (o− 1)/(2o + 1), whereas the
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Table 2 Peak frequencies of the C–Br stretching modes of bromoacetone in various solvents Solvent
C–Br stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Nonpolar solvents n-C6H14 cyclo-C6H12 C2Cl4
Method
nG
DnG b
nS%
DnS%b
nS
Dn bS
669 668
IR IR
1.89 2.02 2.27
0.05 0.02 0.02
665.9 665.6 665.9
−0.3 90
702.0 702.5 703.2
+0.5 +1.2
Raman Raman Raman
Polar solvents (C2H5)2O cyclo-C4H8O Neat Neatc Neatd CH3CN
4.27 7.52 – – – 37.5
0.05 0.05 1.0 1.0 1.0 0.02
663.4 661.2 659.8 660 662 660.1
−2.5 −4.7 −6.1 −5.9 −3.6 −5.8
700.4 699.2 699.7 697 702 700.0
−1.6 −2.8 −2.3 −5.0 +1.6 −2.0
Raman Raman Raman IR Raman Raman
Water and heavy water D2O H2O
79.8 80.1
0.01 0.01
660.0 659.9
−5.9 −6.0
705.1 703.8
+3.1 +1.8
Raman Raman
685.0 685.2
−17.0 −16.8
a
[13], at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C). Dn=n (solvent)−n (n-hexane). c [11]. d [12]. b
data for the aqueous solutions [(o − 1)/(2o + 1)= 0.491] deviate from the linear lines. These results seem to correlate with the results of the frequency shifts (Figs. 3 and 6). As for the gauche conformation, the band widths of both haloacetones increase with increasing (o − 1)/(2o + 1), and the change for bromoacetone is much larger. In this case there seems to be no correlation between the behaviors of the band width and the frequency. However, for the aqueous solutions the data for chloroacetone deviate from the linear line, whereas the data for bromoacetone are very close to the linear line. These behaviors are in agreement with the behaviors of the frequencies shown in Figs. 3 and 6. In addition, the band profiles of the gauche conformer of chloroacetone in the aqueous solutions are Lorentzian-like [Fig. 2f and g, (Lorentzian width)/(Gaussian width)= 5.1 for water and 1.7 for heavy water], whereas those of bromoacetone are Gaussian-like [Fig. 4g and h, (Lorentzian width)/(Gaussian width): 0]. The band profile of an isotropic Raman spectrum is
given by a convolution of Lorentzian and Gaussian functions. If an attractive (repulsive) intermolecular force along a bond is dominant, its band profile becomes Gaussian- (Lorentzian-) like [15]. Since the depolarization degrees of the C–Cl stretching mode of liquid chloroacetone and the C–Br stretching mode of liquid bromoacetone are very small (0.07 and 0.12, respectively), the curTable 3 The ratios of the integrated intensities between the syn and the gauche bands for various solutions and their ratios to the value for neat liquid C−Br stretching
CO stretching
Solvent
r =IS /IG
r/r (neat)
r =IS /IG
r/r (neat)
n-C6H14 cycloC4H8O Neat CH3CN
0.10 0.33
0.19 0.63
0.13 0.37
0.24 0.67
0.52 0.64
1.00 1.23
0.55 0.66
1.00 1.20
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Fig. 6. Solvent dependence of the frequencies for the C – Br stretching modes of bromoacetone (: this work; : [11]; : [12]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o −1)/(2o+1) =0.186], cyclohexane (0.202), tetrachloroethylene (0.229), diethylether (0.343), tetrahydrofuran (0.406), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
rent C–X stretching band profiles are approximately the same with isotropic band profiles [17]. Therefore, these results for the gauche conformation are consistent with the conclusion led by the results for the frequency shifts. Fig. 8 shows Raman spectra in the C= O stretching region for the aqueous solutions, indicating that no additional band is seen on the lower frequency side of each syn band. Curve fittings were done by using two Voigt functions (Fit 1) or using three Voigt functions (Fit 2). Table 4 indicates the ratios of the integrated intensities between the syn and the gauche bands (IS /IG ) and their relative ratios to the value for the neat liquid [r/r (neat)] for the C – Br and the CO stretching modes. There are large differences in the ratios between the C – Br and the CO stretching modes for Fit 1, whereas the values are close to each other for Fit 2. Since the ratios correspond to the free energy changes by the solvent changes from the neat to waters, Fit 2 is reason-
able in terms of thermodynamics. Hence, an additional band is considered to be present in the CO stretching region. Each additional band in Fig. 8(a-2) and (b-2) could correspond to each syn% band of the C–Br stretching mode for the aqueous solutions. The present work also supports the existence of the new species syn% in the aqueous solutions, which has been reported by Kato et al. [10]. Finally, observed frequencies of the CO stretching modes for various solvents are listed in Table 5. Fig. 9 shows the relationships between the frequencies of the CO stretching modes and (o− 1)/(2o + 1) for various solvents. The authors fitted all data except the data for water and heavy water using a linear function. As for water and heavy water, the data deviate from the corresponding linear lines and their directions are opposite to the cases of the C–Br stretching mode of the syn conformer (Fig. 6) and the C–Cl stretching modes of both chloroacetone conformers (Fig.
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3). Therefore, this result shows that hydrophilic hydration is formed around the oxygen atom of bromoacetone in the aqueous solutions. In this work, the authors measured the C–Cl stretching mode of chloroacetone and the C–Br and the CO stretching modes of bromoacetone in various solvents at 20°C. In the spectra of bromoacetone in aqueous solutions, an additional band appeared on the lower frequency side of each syn band of the C–Br and the CO stretching modes, similarly to the C–Cl stretching mode of chloroacetone [10]. These bands have been assigned to the syn conformer which forms a hydrogen bond between the bromine atom and water molecule. From the solvent effects on frequency shifts, half band widths and band profiles, the authors have obtained the following information about the hydration structures of haloacetones: (1) repulsive force caused by hydrophobic hydration acts on the chlorine atoms of both chloroacetone conformers and the bromine atom of the syn bromoacetone; (2) hydrophobic hydration is not formed around the bromine atom of the gauche bromoacetone; (3) hydrophilic hydra-
Fig. 7. Solvent dependence of the half band widths of the C – X stretching modes for (a) chloroacetone and (b) bromoacetone. Data ( for the syn conformation; for the gauche conformation) except water and heavy water are fitted by a linear function.
Fig. 8. Raman spectra of the CO stretching modes of bromoacetone (a) in water and (b) in heavy water at 20°C. (a-1) and (b-1): curve fittings were done by using two Voigt functions. (a-2) and (b-2): curve fittings were done by using three Voigt functions.
Fig. 9. Solvent dependence of the frequencies for the CO stretching modes of bromoacetone (: this work; : [11]; : [12]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o − 1)/(2o+1) = 0.186], tetrachloroethylene (0.229), tetrahydrofuran (0.406), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
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Table 4 The ratios of the integrated intensities between the syn and the gauche bands for the aqueous solutions and their ratios to the value for neat liquid CBr stretching
CO stretching
Solvent
r =IS /IG
r/r (neat)
Neat D2O
0.52 1.21
1.00 2.33
H2O
1.27
2.44
a b
Curve fit
Fit Fit Fit Fit
1a 2b 1 2
r =IS /IG
r/r (neat)
0.55 0.48 1.22 0.53 1.26
1.00 0.97 2.21 0.96 2.29
Curve fittings were done by using two Voigt functions. Curve fittings were done by using three Voigt functions.
Table 5 Peak frequencies of the CO stretching modes of bromoacetone in various solvents Solvent
CO stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Nonpolar solvents n-C6H14 C2Cl4
nG
Method DnG b
nS%
DnS%b
nS
DnS b
1740 1738
IR IR
1.89 2.27
0.05 0.02
1724.7 1721.5
−3.2
1747.1
Polar solvents cyclo-C4H8O Neat Neatc Neatd CH3CN
7.52 – – – 37.5
0.05 1.0 1.0 1.0 0.02
1718.6 1712.5 1716 1714 1716.9
−6.1 −12.2 −8.7 −10.7 −7.8
Water and heavy water D2O H2O
79.8 80.1
0.01 0.01
1704.1 1705.8
−20.6 −18.9
1710.2 1710.0
−36.9 −37.1
Raman Raman
1738.2 1734.3 1738 1734 1738.0
−8.9 −12.8 −9.1 −13.1 −9.1
Raman Raman IR Raman Raman
1727.2 1728.8
−19.9 −18.3
Raman Raman
a
[13], at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C). Dn=n (solvent)−n (n-hexane). c [11]. d [12]. b
tion is formed around the oxygen atom of each bromoacetone conformer.
(Mitsubishi Chemical) for helpful works on the earlier stage of this study.
Acknowledgements
References
This work has been supported in part by the Ritsumeikan Academic Research Grant for Young Researches. The authors thank Y. Nanba
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[12] J.R. Durig, J. Lin, H.V. Phan, J. Raman Spectrosc. 23 (1992) 253. [13] Chapter 6, in: D.R. Lide, H.P.R. Frederikse (Eds.), CRC Handbook of Chemistry and Physics, 76th ed., CRC Press, 1995, p. 159. [14] Kagaku Binran Kiso-hen 24th ed., in: The Chemical Society of Japan (Ed.), Maruzen, Tokyo, 1993, Chapter 13, p. 498. [15] K.S. Schweizer, D.J. Chandler, J. Chem. Phys. 76 (1982) 2296. [16] G.J. Remar, R.A. MacPhail, J. Chem. Phys. 103 (1995) 4381. [17] S.M. George, H. Auweter, C.B. Harris, J. Chem. Phys. 73 (1980) 5573.
.
Solvent effect on Raman spectra of conformational key bands of chloroacetone and bromoacetone Yosuke Shiratori, Minoru Kato *, Yoshihiro Taniguchi Department of Chemistry, Faculty of Science and Engineering, Ritsumeikan Uni6ersity, Kusatsu, Shiga, 525 -8577, Japan Received 15 December 1998; accepted 6 April 1999
Abstract Raman spectra were measured for chloroacetone and bromoacetone in various solvents at 20°C. The authors recorded the C–X (X:Cl and Br) stretching modes for both chloroacetone and bromoacetone and the CO stretching mode for bromoacetone. In each spectrum for aqueous solutions, an additional band appeared on the lower frequency side of the band of the syn conformer. These bands are assigned to the syn conformer which forms a hydrogen bond between each halogen atom of haloacetones and water molecule. From solvent effects on peak frequencies, half band widths and band profiles, the authors discussed local hydration structures of haloacetones. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Raman spectroscopy; Haloacetone; Solvent effects on peak frequency; Hydrogen bond; Hydration structure
1. Introduction Conformational equilibrium is one of the simplest chemical equilibria and an essential molecular property. Conformational equilibria, especially in liquids can be affected occasionally by medium environments such as temperature, pressure and solvent. A shift of conformational equilibrium by medium effects is closely related to a difference in solvation structures between conformers. Thus medium effects are important subjects for studies of liquid structures and their properties. * Corresponding author. Tel.: +81-775-612761; fax: + 81775-612659. E-mail address: [email protected] (M. Kato)
Vibrational spectroscopies have been powerful methods for investigating conformational equilibria since the pioneer study by Mizushima [1]. To study conformational equilibria of a certain liquid compound in various environments, we need to assign its conformational key bands and understand the origins of spectral shifts because they reflect solvation structures. Mizushima et al. [2] have studied the conformational equilibrium of chloroacetone (Fig. 1) using Raman and infrared spectroscopies. They assigned vibrational modes and suggested that the gauche and the syn conformers are predominant in the vapor and the solid phases, respectively. Since their study, there have been some works on chloroacetone [3–6] that should be cited.
1386-1425/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 - 1 4 2 5 ( 9 9 ) 0 0 0 8 6 - 4
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Taniguchi et al. [7] measured infrared spectra of the C–Cl stretching region in carbon disulfide at various pressures. They discussed pressure effect on the frequency shifts and the conformational equilibrium, and solvent effect on the frequency shifts with Bauer and Magat theory [8]. Durig et al. [9] reported the vibrational assignments and the detail of each conformer structure on the basis of the results of Raman and infrared measurements, and ab initio calculations. A recent Raman work by Kato et al. [10] was the first to report about the conformational behavior of chloroacetone in aqueous system. They found the presence of a new species of chloroacetone relating to a hydrogen bond with water molecule, and named it syn% conformer. As for bromoacetone (Fig. 1), no systematic research has been done. Crowder and Cook [11] measured infrared spectra in the vapor and the liquid phases and reported that bromoacetone has a conformational equilibrium similar to chloroacetone. Since this work there was no notable report except a recent work by Durig [12], which determined the vibrational assignments and the structure of each conformer via Raman and infrared measurements, and ab initio calculations. As described above, conformational equilibria of haloacetones have been investigated mainly from the viewpoint of structural chemistry. However, solvent effects on their equilibria have not been reported sufficiently; there have been no studies, particularly, for aqueous solution except the study by Kato et al. [10]. In this work, the authors measured Raman spectra of chloroacetone and bromoacetone in
various solvents at 20°C, and observed additional Raman bands for the C–Br and the CO stretching modes of bromoacetone in water and heavy water, similarly to chloroacetone [10]. The origins of these additional bands and of the spectral shifts for various solutions are discussed.
2. Experimental Chloroacetone (\ 95%, Tokyo Kasei) was distilled under reduced pressure. Impurities of bromoacetone (\ 90%, Tokyo Kasei) were drained off through a membrane filter. Spectra-grade nhexane, cyclohexane, tetrachloroethylene, diethylether, tetrahydrofuran (Nakarai Tesque) and acetonitrile (Wako) were used without further purification. Water distilled after ion exchange and deuterium oxide from CEA with a purity of 99.9% were used. Raman spectra were recorded using a JEOL 400D spectrometer equipped with a cooled HTV-R649 photomultiplier and photon counting detector. Samples were exited with 90° scattering of 514.5 nm radiation from an argon ion laser (NEC GLG3300) with 250 500 mW output. The spectral slit width, scanning speed and the number of scanning were: 4.2; 100 cm − 1 min − 1 and 5–10 times, respectively. All measurements have been done at 20°C. Temperature of samples was controlled within an error of 9 0.3°C by thermostated water circulating around the glass cell. The observed spectra were analyzed by GRAMS/386 software (Galactic Industries) and were fitted with Voigt functions to determine peak frequencies and integrated intensities of bands. The authors measured the C–X (X:Cl and Br) stretching modes for chloroacetone and bromoacetone, respectively, and the CO stretching mode for bromoacetone in various solvents.
3. Results and discussion
3.1. Chloroacetone
Fig. 1. Conformers of chloroacetone and bromoacetone.
Raman spectra in the C–Cl stretching region for various solvents are shown in Fig. 2. The strong bands at higher and lower frequencies are
Y. Shiratori et al. / Spectrochimica Acta Part A 55 (1999) 2659–2670
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Fig. 2. Raman spectra of the C–Cl stretching modes of chloroacetone at 20°C (a) in cyclohexane (mole fraction of solute, x =0.12); (b) in tetrachloroethylene (x= 0.05); (c) in tetrahydrofuran (x =0.05); (d) neat liquid; (e) in acetonitrile (x =0.05); (f) in heavy water (x=0.02) and (g) in water (x= 0.02). Spectra (a) and (c) were obtained after subtraction of solvent scatterings. A peak around 750 cm − 1 of the spectrum (e) comes from acetonitrile.
assigned to the C – Cl stretching mode of the syn and the gauche conformers, respectively [2,9]. The weak bands at ca. 805 and 830 cm − 1 are assigned to the C –C – C symmetric stretching and the CH2 rocking modes of the syn conformer, respectively [2,9]. Observed frequencies of the C – Cl stretching modes of chloroacetone for various solvents are summarized in Table 1. An additional band appears around 750 cm − 1 in each Raman spectrum for the aqueous solutions (Fig. 2 f and g). In the previous work [10], this additional band has been assigned to the C – Cl stretching mode of the syn
conformer which forms a hydrogen bond between the chlorine atom and water molecule (syn% conformer). The frequencies of the syn and the gauche conformers are considerably higher in water and heavy water than in n-hexane. The observed blue shifts by the solvent changes from n-hexane to water and heavy water were explained by the hydrophobic hydration around the chlorine atom [10]. On the other hand, red shifts by the solvent changes from n-hexane to polar solvents except water and heavy water were observed. This im-
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plies an increase in attractive interactions between the solute and the solvent molecules in polar solvents [15]. According to Bauer and Magat theory [8], the frequency shift in a dielectric continuum medium is expressed by the following equation: Dn 8
1 o−1 · a 3 2o+ 1
(1)
where Dn, o and a are vapor–liquid frequency shift (nl − nv), relative permittivity of a solvent and radius of a solute, respectively. Fig. 3 shows the relationships between the frequencies of the C–Cl stretching modes and (o− 1)/(2o + 1). All the data except the data for water and heavy water were fitted using a linear function. Satisfactory linear correlations between the frequencies and (o−1)/ (2o + 1) suggest that the solvent effects on fre-
Table 1 Peak frequencies of the CCl stretching modes of chloroacetone in various solvents Solvent
CCl stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Vapore Nonpolar sol6ents n-C6H14 n-C6H14d cyclo-C6H12 cyclo-C6H12d cyclo-C6H12 cyclo-C4H8O2d C2Cl4 C6H6d CS2f
nG
DnG b
nS%
DnS%b
nS
0.05 B0.03 0.05 B0.02 0.12 B0.02 0.05 B0.02 0.05
728.0 728.5 727.5 727 728.7 726 729
Polar sol6ents (C4H9)2Od cyclo-C4H8O (CH3)2COd Neat Neatc Neate Neath CH3CN
3.08 7.52 21.2 30.0g 30.0g 30.0g 30.0g 37.5
B0.03 0.05 B0.02 1.0 1.0 1.0 1.0 0.05
Water and hea6y water D2O D2Oh H2O H2Oh
79.8 79.8 80.1 80.1
0.02 0.02 0.02 0.02
IR IR Raman
728.4 −0.4 +0.1 −0.9 −0.6 +0.3 −2.4 +0.6
764.9 765 764.3 763.5 763.6 762.5 764.4 762.5 764
+0.1 −0.6 −1.4 −1.3 −2.4 −0.5 −2.4 −0.9
Raman IR Raman IR Raman IR Raman IR IR
727 726.3 726 727.1 724 728 726.4 726.2
−1.4 −2.1 −2.4 −1.3 −4.4 −0.4 −2.0 −2.2
763 762.2 762 762.1 764 763 761.3 762.4
−1.9 −2.7 −2.9 −2.8 −0.9 −1.9 −3.6 −2.5
IR Raman IR Raman Raman Raman Raman Raman
731.6 730.5 732.3 730.2
+3.2 +2.1 +3.9 +1.8
768.1 768.6 768.8 767.3
+3.2 +3.7 +3.9 +2.4
Raman Raman Raman Raman
747.2 746.9 752.2 750.2
−17.7 −18.0 −12.7 −14.7
Relative permittivity, at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C), data from [13]. Dn=n (solvent)−n (n-hexane). c [2]. d [4]. e [9]. f [7]. g [14], at 19°C. h [10]. b
DnS b
731 731 730 1.89 1.89 2.02 2.02 2.02 2.22 2.27 2.28 2.63
a
Method
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Fig. 3. Solvent dependence of the frequencies for the C – Cl stretching modes of chloroacetone (: this work; : [2]; : [4]; ": [7]; 2: [9]; +: [10]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o− 1)/(2o+ 1)= 0.186], cyclohexane (0.202), dioxane (0.224), tetrachloroethylene (0.229), benzene (0.230), carbon disulfide (0.261), dibuthylether (0.291), tetrahydrofuran (0.406), chloroacetone (0.475), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
quencies except the aqueous solutions agree with the dielectric continuum model. It is noticeable that the deviations of the data for water and heavy water from the linear lines are significant. This indicates that the hydration structures around the chlorine atoms of the syn and the gauche conformers are unusual from the viewpoint of a dielectric continuum model. In general, intermolecular repulsive forces along a bond of a molecule induce a blue shift [15]. The present result agrees with a previous conclusion by Kato et al. [10] that hydrophobic hydration is formed around the chlorine atoms of these conformers.
3.2. Bromoacetone Figs. 4 and 5 show Raman spectra of the C–Br and the CO stretching modes, respectively, of bromoacetone in various solvents. In
the C–Br stretching region for organic solvents, the bands at higher and lower frequencies are assigned to the C–Br stretching mode of the syn and the gauche conformers, respectively [12]. Although Durig et al. [12] observed a weak band at 729 cm − 1, which was assigned to the C–C–C symmetric stretching mode of the gauche conformer, the authors could not observe this band. Observed frequencies of the C–Br stretching modes for various solvents are summarized in Table 2. As for the C= O stretching mode, the band splitting is not related to a Fermi resonance, and consequently the higher and the lower frequency bands are assigned to the syn and the gauche conformers, respectively [12]. To discuss whether the CO stretching mode is appropriate as a conformational key band, we compare the integrated intensities of the C–Br and the CO stretching modes. The ratios of the integrated intensities between the syn and the gauche bands:
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r=
IS aScS = IG aGcG
(2)
and their relative values to the value of the neat liquid: r IS /IG = r(neat) IS (neat)/IG (neat) =
(aS /aG )(cS /cG ) {aS (neat)/aG (neat)}{cS (neat)/cG (neat)} (3)
are summarized for the C–Br and the C=O stretching regions in Table 3. Here, I, a and c indicate Raman intensity, an unknown coefficient and the concentration of each conformer, respectively. The subscripts indicate the conformers. Assuming that aS /aG does not depend on the solvent, Eq. (3) leads to the following equation: r cS /cG = r(neat) cS (neat)/cG (neat)
(4)
Fig. 4. Raman spectra of the C–Br stretching modes of bromoacetone at 20°C; (a) in n-hexane (mole fraction of solute, x = 0.05); (b) in tetrachloroethylene (x = 0.02); (c) in diethylether (x =0.05); (d) in tetrahydrofuran (x =0.05); (e) neat liquid; (f) in acetonitrile (x = 0.05); (g) in heavy water (x = 0.01) and (h) in water (x= 0.01). Spectra (a); (b) and (d) were obtained after subtraction of solvent scatterings. A peak around 750 cm − 1 of the spectrum (f) comes from acetonitrile.
Y. Shiratori et al. / Spectrochimica Acta Part A 55 (1999) 2659–2670
Fig. 5. Raman spectra of the CO stretching modes of bromoacetone at 20°C; (a) in n-hexane (mole fraction of solute, x=0.05); (b) in tetrahydrofuran (x= 0.05); (c) neat liquid and (d) in acetonitrile (x=0.05). Spectrum (a) was obtained after subtraction of solvent scattering.
All the values of r/r (neat) for the C – Br stretching mode are close to the corresponding values for the CO stretching mode. Hence, this supports that the CO stretching mode is appropriate as a conformational key band. Next, we discuss solvent effects on the C–Br stretching modes (Fig. 4 and Table 2) in detailed. An additional band was observed at 685 cm − 1 for each aqueous solution (Fig. 4 g and h), similarly to the case of chloroacetone [10]. This band may
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be assigned to the C–Br stretching mode of the syn conformer that has a hydrogen bond between the bromine atom and water molecule (syn% conformer). The peak frequencies for the syn conformer are higher in water and heavy water than in n-hexane. On the other hand, the peak frequencies for the gauche conformer are lower in water and heavy water than in n-hexane, which is different from the case of chloroacetone. All the Dn values [n (solvent)-n (n-hexane)] for the polar solvents are negative. This suggests an increase in attractive interactions between the solute and the solvent molecules in polar solvents. Fig. 6 shows the relationships between the frequencies of the C–Br stretching modes and (o− 1)/(2o +1) for various solvents. The authors fitted all the data except the data for water and heavy water using a linear function. As for the syn conformer, the correlation between the frequency and (o− 1)/(2o +1) is similar to that for both conformers of chloroacetone (Fig. 3). The deviations from the linear line for water and heavy water suggest the presence of the hydrophobic hydration around the bromine atom. In contrast, the data of the gauche conformer for water and heavy water are on the linear line. This is different from the cases of both conformers of chloroacetone (Fig. 3) and the syn conformer of bromoacetone. This implies that the hydration structure around the bromine atom of the gauche conformer is significantly different from those cases. Hydrophobic hydration does not seem to be formed around the bromine atom of the gauche conformation. The half band width and the band profile of a stretching mode are also influenced by solute–solvent interactions [15,16]. A change in the band width induced by a change in the interaction is known to correlate with the frequency shift [15,16]. The relationships between the half band widths of the C–X stretching modes and (o−1)/ (2o +1) for various solvents are shown in Fig. 7a for chloroacetone and Fig. 7b for bromoacetone. The authors fitted all the data except the data for water and heavy water using a linear function. The half band widths for the syn bands of chloroacetone and bromoacetone decrease linearly with increasing (o− 1)/(2o + 1), whereas the
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Table 2 Peak frequencies of the C–Br stretching modes of bromoacetone in various solvents Solvent
C–Br stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Nonpolar solvents n-C6H14 cyclo-C6H12 C2Cl4
Method
nG
DnG b
nS%
DnS%b
nS
Dn bS
669 668
IR IR
1.89 2.02 2.27
0.05 0.02 0.02
665.9 665.6 665.9
−0.3 90
702.0 702.5 703.2
+0.5 +1.2
Raman Raman Raman
Polar solvents (C2H5)2O cyclo-C4H8O Neat Neatc Neatd CH3CN
4.27 7.52 – – – 37.5
0.05 0.05 1.0 1.0 1.0 0.02
663.4 661.2 659.8 660 662 660.1
−2.5 −4.7 −6.1 −5.9 −3.6 −5.8
700.4 699.2 699.7 697 702 700.0
−1.6 −2.8 −2.3 −5.0 +1.6 −2.0
Raman Raman Raman IR Raman Raman
Water and heavy water D2O H2O
79.8 80.1
0.01 0.01
660.0 659.9
−5.9 −6.0
705.1 703.8
+3.1 +1.8
Raman Raman
685.0 685.2
−17.0 −16.8
a
[13], at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C). Dn=n (solvent)−n (n-hexane). c [11]. d [12]. b
data for the aqueous solutions [(o − 1)/(2o + 1)= 0.491] deviate from the linear lines. These results seem to correlate with the results of the frequency shifts (Figs. 3 and 6). As for the gauche conformation, the band widths of both haloacetones increase with increasing (o − 1)/(2o + 1), and the change for bromoacetone is much larger. In this case there seems to be no correlation between the behaviors of the band width and the frequency. However, for the aqueous solutions the data for chloroacetone deviate from the linear line, whereas the data for bromoacetone are very close to the linear line. These behaviors are in agreement with the behaviors of the frequencies shown in Figs. 3 and 6. In addition, the band profiles of the gauche conformer of chloroacetone in the aqueous solutions are Lorentzian-like [Fig. 2f and g, (Lorentzian width)/(Gaussian width)= 5.1 for water and 1.7 for heavy water], whereas those of bromoacetone are Gaussian-like [Fig. 4g and h, (Lorentzian width)/(Gaussian width): 0]. The band profile of an isotropic Raman spectrum is
given by a convolution of Lorentzian and Gaussian functions. If an attractive (repulsive) intermolecular force along a bond is dominant, its band profile becomes Gaussian- (Lorentzian-) like [15]. Since the depolarization degrees of the C–Cl stretching mode of liquid chloroacetone and the C–Br stretching mode of liquid bromoacetone are very small (0.07 and 0.12, respectively), the curTable 3 The ratios of the integrated intensities between the syn and the gauche bands for various solutions and their ratios to the value for neat liquid C−Br stretching
CO stretching
Solvent
r =IS /IG
r/r (neat)
r =IS /IG
r/r (neat)
n-C6H14 cycloC4H8O Neat CH3CN
0.10 0.33
0.19 0.63
0.13 0.37
0.24 0.67
0.52 0.64
1.00 1.23
0.55 0.66
1.00 1.20
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Fig. 6. Solvent dependence of the frequencies for the C – Br stretching modes of bromoacetone (: this work; : [11]; : [12]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o −1)/(2o+1) =0.186], cyclohexane (0.202), tetrachloroethylene (0.229), diethylether (0.343), tetrahydrofuran (0.406), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
rent C–X stretching band profiles are approximately the same with isotropic band profiles [17]. Therefore, these results for the gauche conformation are consistent with the conclusion led by the results for the frequency shifts. Fig. 8 shows Raman spectra in the C= O stretching region for the aqueous solutions, indicating that no additional band is seen on the lower frequency side of each syn band. Curve fittings were done by using two Voigt functions (Fit 1) or using three Voigt functions (Fit 2). Table 4 indicates the ratios of the integrated intensities between the syn and the gauche bands (IS /IG ) and their relative ratios to the value for the neat liquid [r/r (neat)] for the C – Br and the CO stretching modes. There are large differences in the ratios between the C – Br and the CO stretching modes for Fit 1, whereas the values are close to each other for Fit 2. Since the ratios correspond to the free energy changes by the solvent changes from the neat to waters, Fit 2 is reason-
able in terms of thermodynamics. Hence, an additional band is considered to be present in the CO stretching region. Each additional band in Fig. 8(a-2) and (b-2) could correspond to each syn% band of the C–Br stretching mode for the aqueous solutions. The present work also supports the existence of the new species syn% in the aqueous solutions, which has been reported by Kato et al. [10]. Finally, observed frequencies of the CO stretching modes for various solvents are listed in Table 5. Fig. 9 shows the relationships between the frequencies of the CO stretching modes and (o− 1)/(2o + 1) for various solvents. The authors fitted all data except the data for water and heavy water using a linear function. As for water and heavy water, the data deviate from the corresponding linear lines and their directions are opposite to the cases of the C–Br stretching mode of the syn conformer (Fig. 6) and the C–Cl stretching modes of both chloroacetone conformers (Fig.
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3). Therefore, this result shows that hydrophilic hydration is formed around the oxygen atom of bromoacetone in the aqueous solutions. In this work, the authors measured the C–Cl stretching mode of chloroacetone and the C–Br and the CO stretching modes of bromoacetone in various solvents at 20°C. In the spectra of bromoacetone in aqueous solutions, an additional band appeared on the lower frequency side of each syn band of the C–Br and the CO stretching modes, similarly to the C–Cl stretching mode of chloroacetone [10]. These bands have been assigned to the syn conformer which forms a hydrogen bond between the bromine atom and water molecule. From the solvent effects on frequency shifts, half band widths and band profiles, the authors have obtained the following information about the hydration structures of haloacetones: (1) repulsive force caused by hydrophobic hydration acts on the chlorine atoms of both chloroacetone conformers and the bromine atom of the syn bromoacetone; (2) hydrophobic hydration is not formed around the bromine atom of the gauche bromoacetone; (3) hydrophilic hydra-
Fig. 7. Solvent dependence of the half band widths of the C – X stretching modes for (a) chloroacetone and (b) bromoacetone. Data ( for the syn conformation; for the gauche conformation) except water and heavy water are fitted by a linear function.
Fig. 8. Raman spectra of the CO stretching modes of bromoacetone (a) in water and (b) in heavy water at 20°C. (a-1) and (b-1): curve fittings were done by using two Voigt functions. (a-2) and (b-2): curve fittings were done by using three Voigt functions.
Fig. 9. Solvent dependence of the frequencies for the CO stretching modes of bromoacetone (: this work; : [11]; : [12]). Data except water and heavy water are fitted by a linear function. The solvents are n-hexane [(o − 1)/(2o+1) = 0.186], tetrachloroethylene (0.229), tetrahydrofuran (0.406), acetonitrile (0.480), heavy water and water (0.491). The o values of solvents were cited from [13].
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Table 4 The ratios of the integrated intensities between the syn and the gauche bands for the aqueous solutions and their ratios to the value for neat liquid CBr stretching
CO stretching
Solvent
r =IS /IG
r/r (neat)
Neat D2O
0.52 1.21
1.00 2.33
H2O
1.27
2.44
a b
Curve fit
Fit Fit Fit Fit
1a 2b 1 2
r =IS /IG
r/r (neat)
0.55 0.48 1.22 0.53 1.26
1.00 0.97 2.21 0.96 2.29
Curve fittings were done by using two Voigt functions. Curve fittings were done by using three Voigt functions.
Table 5 Peak frequencies of the CO stretching modes of bromoacetone in various solvents Solvent
CO stretching mode (cm−1) oa
Mole fraction
Vaporc Vapord Nonpolar solvents n-C6H14 C2Cl4
nG
Method DnG b
nS%
DnS%b
nS
DnS b
1740 1738
IR IR
1.89 2.27
0.05 0.02
1724.7 1721.5
−3.2
1747.1
Polar solvents cyclo-C4H8O Neat Neatc Neatd CH3CN
7.52 – – – 37.5
0.05 1.0 1.0 1.0 0.02
1718.6 1712.5 1716 1714 1716.9
−6.1 −12.2 −8.7 −10.7 −7.8
Water and heavy water D2O H2O
79.8 80.1
0.01 0.01
1704.1 1705.8
−20.6 −18.9
1710.2 1710.0
−36.9 −37.1
Raman Raman
1738.2 1734.3 1738 1734 1738.0
−8.9 −12.8 −9.1 −13.1 −9.1
Raman Raman IR Raman Raman
1727.2 1728.8
−19.9 −18.3
Raman Raman
a
[13], at 20°C except C2Cl4 (at 30°C) and cyclo-C4H8O (at 22°C). Dn=n (solvent)−n (n-hexane). c [11]. d [12]. b
tion is formed around the oxygen atom of each bromoacetone conformer.
(Mitsubishi Chemical) for helpful works on the earlier stage of this study.
Acknowledgements
References
This work has been supported in part by the Ritsumeikan Academic Research Grant for Young Researches. The authors thank Y. Nanba
[1] S. Mizushima, Structure of Molecules and Internal Rotation, Academic Press, New York, 1954. [2] S. Mizushima, T. Shimanouchi, T. Miyazawa, I. Ichishima, K. Kuratani, J. Chem. Phys. 21 (1953) 815.
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