Polarizabilities and dipole moments of benzaldehyde ...

Chemical Physics 300 (2004) 239–246 www.elsevier.com/locate/chemphys

Polarizabilities and dipole moments of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents Nalan Tekin a

a,*

, Mustafa Cebe b, C ß elik Tarımcı

c

Physicochemistry Section, Department of Chemistry, Science and Art Faculty, Balikesir University, 10100 Balikesir, Turkey b Physicochemistry Section, Department of Chemistry, Science and Art Faculty, Uludag University, 16100 Bursa, Turkey c Engineering Physics Department, Faculty of Engineering, Ankara University, 06100 Ankara, Turkey Received 22 May 2003; accepted 21 January 2004

Abstract The purpose of this report is to calculate the orientation polarizability of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents. The calculations are based on the knowledge of permanent dipole moment of the solutions. Other important physical quantities such as refractive index, density, specific volume, dielectric constant, molar polarization and molar refractivity are also calculated. Dipole moments of the solutions are calculated by using measured dielectric constants of the solutions. The dielectric constant measurements were made at 100 kHz. Relationships between the polarizability and concentration, specific volume, dielectric constant and dipole moment of the solutions are suggested. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Refractive index; Orientation polarizability; Specific volume; Dipole moment; Dielectric constant

1. Introduction The determination of polarizabilities in the low frequency range for the investigated solutions (especially hydrogen-bonded systems in liquid phase) requires the precise knowledge of the dipole moments of the relevant solutions [1–4]. Because the dipole moment ðlÞ and the polarizabilities ðaÞ give information about the molecular shape, the electronic charge distribution in the molecule, etc., it is therefore considered as important in characterizing and in elucidation of the molecular structure of various substances [1,2,4]. The aim of this paper is to measure some thermodynamic and physical properties for the relevant solutions and then to find orientation polarizability and to determine relationships between polarizability and specific volume, dielectric constant and dipole moment. The orientation polarizability depends upon the molecular size, shape, intra- and intermolecular interactions. To do this, * Corresponding author. Tel.: +902662-493358; fax: +902662493360. E-mail addresses: [email protected], [email protected] (N. Tekin).

0301-0104/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2004.01.022

density, refractive index, dielectric constant, dipole moment and specific volume were measured in solutions. Benzaldehyde, benzoic acid and oxalic acid were chosen to their different H-bonding capabilities. The orientation polarizabilities of studied systems were changed by polar/H-bonding interactions. The strength of H-bonding between the solute and solvent depends on the hydrogen bond donor and acceptor capacities of the solute and solvent. Determination of the role of Hbonding on orientation polarizability was also aimed. The toluene and cyclohexane should provide an environment where H-bonding is at a minimum whereas the presence of the methyl alcohol, ethyl alcohol, n-propyl alcohol and iso-propyl alcohol should provide a medium that is far more polar and with which the H bonds on the orientation polarizability can interact.

2. Experimental The compounds were obtained from Riedel-de Haen and E. Merck, Germany, Messrs. Fluka A.G. and of purum grade used as such.

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N. Tekin et al. / Chemical Physics 300 (2004) 239–246

Thermostatically controlled pycnometer is used to measure the density at 20.0 0.5 °C. The refractive indices at selected wavelength (Na 589.6 nm (D-line)) in the VIS region were obtained with a Bellingham + Stanley model 60/ED high accuracy Abbe Refractometer at 293 K (0.1 K). The average accuracy of the measurement of the refractive index is 0.00004 (as stated by the producer) but a reproducibility ranging from 0.00001 to 0.00004 (depending on the wavelength used) was achieved in our measurements. The dielectric constant e was measured at 20 °C at the 100 kHz with a HP 4192 A Model Empedance Analyzer with a home-made liquid cell; a parallel plate geometry with a guard ring was used; the liquid volume required is small (about 5 ml). The cell was carefully cleaned and then the calibration of the cell was performed by measuring the capacity under vacuum.

3.1. Permanent dipole moment Dipole moments of molecular systems are calculated by dielectric constant measurement of solutions which were prepared in nonpolar solvents. The total molar polarization can be obtained by applying the Clausius– Mosotti equation [5–7]: ðes 1Þ ðM1 X1 þ M2 X2 Þ Ps ¼ ; ð1Þ ðes þ 2Þ qs where es is dielectric constant of the solution, X2 is mole fraction of solute, X1 is mole fraction of solvents, M1 and M2 are molecular weight of solvent and solute, respectively, and qs is density of the solution. A solution may be considered to be a mixture of two (or more) materials, each contributing to the polarization. Assuming a dilute solution in which the properties of the solution are sums of the properties of the components, one may write a molar property of the overall solution in terms of the mole fraction of each constituent and the effective molar polarizations of each component. For a binary solution the molar polarization is

e01 1 M1 ; e01 þ 2 q1

0 ¼ lim Pm2 : Pm2

ð5Þ

x2 !0

where X1 is mole fraction of solvent, X2 is mole fraction of solute, n is refractive index of the solutions, M1 and M2 are molecular weight of solvent and solute, respectively, and qs is the density of the solutions [8–10]. The different R2 values were plotted against X1 . While mole fraction of solvent led to one at limiting position, R2 , limit molar refraction also can be extrapolated. R2 , molar refraction of the solute was obtained by using extrapolation equation. Dipole moment (l) of solute in Debye was calculated by P2 molar polarization and R2 molar refractivity term [5,11,12]. P2 and R2 values, used in dipole moment equation, are shown in Tables 1–3. l ¼ 0:0128½ðP2 R2 ÞT

1=2

ð7Þ

: 18

esu cm. In this Physical means of 1 Debye is 10 study, obtained dipole moment is known as permanent dipole moment. If a molecular system has polar atomic groups and asymmetric geometry, dipole moment of the molecular system can be calculated by above equations [5,12].

ð2Þ

where X1 is mole fraction of solvent and X2 is the mole fraction of solute. Knowledge of the molar polarization of either component allows one to calculate the other from the measurement of the total polarization through Eq. (2). If the solution is sufficiently dilute, one approximates the molar polarization of the solvent, Pm1 , as that of the 0 pure solvent, Pm1 , particularly if it is nonpolar and has only induced polarization, using Eq. (1) 0 pm1 ¼

For an ideal solution, one expects Pm2 to be independent of concentration, it is a quality only of the molecular structure. For nonideal solutions, Pm2 depends on concentration due to strong solute–solvent interactions. The quantity often reported for a solute is its molar polarization extrapolated to infinite dilution, 0 Pm2 ;

From Lorenz–Lorentz equations, R2 molar refractivity value of solute was obtained. It is given by 2 ns 1 X1 M 1 þ X2 M 2 Rs ¼ ; ð6Þ n2s þ 2 qs

3. Theory

P s ¼ P 1 X1 þ P 2 X2 ;

where the qualities of the pure solvent are indicated by the superscript Ô0Õ and the subscript Ô1Õ. With this approximation, one may determine the solute molar polarization at each concentration from a measurement of the measured molar polarization of the solution 1 0 0 þ ðPm Pm1 Þ : ð4Þ Pm2 ¼ Pm1 X2

ð3Þ

3.2. Orientation polarizability Three contributions to the polarization must be considered: orientation polarization, electronic polarization and vibrational polarization. Orientation polarization is due to the partial alignment of permanent dipoles [5,13,14]. The mean polarizability is the average taken over all possible orientations of the molecule with respect to the field. The orientation polarizability, a0 , has the units of dipole moment divided by electronic field strength, that


241

Table 1 Physicochemical properties of benzaldehyde solutions in different solvents at 20 °C Concentration (mol/l)

Physicochemical properties of benzaldehyde at 20 °C q (g/ml)

Vspe (ml/g)

e

n

P2 (cm3 mol1 )

Methyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8715 0.8713 0.8713 0.8698 0.8694 0.8692 0.8690 0.8682

1.1474 1.1477 1.1477 1.1497 1.1502 1.1504 1.1507 1.1518

39.37 38.85 37.57 35.27 34.76 34.18 33.92 33.13

1.3565 1.3563 1.3563 1.3561 1.3561 1.3560 1.3560 1.3555

34.061 34.032 33.944 33.830 33.804 33.763 33.749 33.710

Ethyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8082 0.8082 0.8080 0.8079 0.8078 0.8077 0.8075 0.8071

1.2373 1.2373 1.2376 1.2377 1.2379 1.2380 1.2384 1.2390

19.45 19.22 18.23 17.54 15.89 15.19 15.15 12.69

1.3903 1.3903 1.3902 1.3902 1.3901 1.3901 1.3900 1.3900

48.963 48.873 48.491 48.198 47.397 47.013 47.001 45.355

n-Propyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8057 0.8056 0.8053 0.8052 0.8047 0.8045 0.8042 0.8042

1.2411 1.2413 1.2417 1.2419 1.2427 1.2430 1.2435 1.2435

15.00 14.33 14.11 13.34 12.23 12.01 11.84 11.79

1.4120 1.4120 1.4118 1.4118 1.4115 1.4115 1.4110 1.4110

Iso-propyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8664 0.8664 0.8660 0.8660 0.8656 0.8654 0.8652 0.8649

1.1542 1.1542 1.1547 1.1547 1.1552 1.1555 1.1558 1.1562

13.12 13.12 12.14 12.04 11.13 10.94 10.93 10.90

Cyclohexane 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.7793 0.7780 0.7775 0.7774 0.7767 0.7760 0.7725 0.7663

1.2832 1.2853 1.2861 1.2863 1.2875 1.2886 1.2945 1.3049

2.250 2.240 2.210 2.200 2.190 2.190 2.150 2.130

l (D)

a (1040 ) (C2 m2 J1 )

1.1181 1.1175 1.1156 1.1129 1.1123 1.1114 1.1111 1.1103

11.4167 11.4044 11.3657 11.3107 11.2985 11.2803 11.2742 11.2579

13.503 13.502 13.502 13.504 13.502 13.503 13.504 13.510

1.3050 1.3034 1.2963 1.2908 1.2759 1.2686 1.2684 1.2367

15.5525 15.5143 15.3458 15.2158 14.8666 14.6970 14.6923 13.9671

61.426 60.891 60.725 60.034 58.932 58.698 58.524 58.465

18.559 18.561 18.559 18.562 18.561 18.566 18.553 18.552

1.4348 1.4258 1.4231 1.4113 1.3924 1.3883 1.3856 1.3845

18.8001 18.5650 18.4948 18.1893 17.7054 17.6013 17.5329 17.5051

1.4040 1.4040 1.4038 1.4038 1.4035 1.4032 1.4032 1.4030

55.601 1.3623 1.3622 1.3457 1.3438 1.3258 1.3220 1.3229

16.964 16.963 16.963 16.963 16.959 16.952 16.956 16.954

1.3623 1.3622 1.3457 1.3438 1.3258 1.3220 1.3229 1.3215

16.9482 16.9457 16.5377 16.4910 16.0522 15.9603 15.9820 15.9482

1.4520 1.4518 1.4518 1.4515 1.4515 1.4512 1.4512 1.4510

31.765 31.274 31.111 30.931 30.774 30.802 30.189 30.049

29.135 29.172 29.191 29.177 29.204 29.213 29.345 29.571

0.3554 0.3177 0.3037 0.2902 0.2746 0.2762 0.2013 0.1515

1.1534 0.9217 0.8423 0.7691 0.6886 0.6967 0.3701 0.2096

is, C2 m2 J1 . In low frequencies, orientation polarizability is an important feature of the molecule due to it gives information about the molecular shape and the electronic charge distribution in the molecule [5,15,16]. The orientation polarizability of the molecule are calculated by following equation [5,15,17] l2 a0 ¼ ; ð8Þ 3kT

R2 (cm3 mol1 ) 8.0342 8.0312 8.0311 8.0407 8.0422 8.0439 8.0457 8.0430

where l is permanent dipole moment of the molecules (1 D ¼ 3:336 1030 C m), k is the Boltzmann constant (1.3807 1023 J K1 ) and T is temperature (K). The orientation polarizability values are based on accurate values of dielectric constant and dipole moment. The polarizability can provide some information on the bonding and geometrical features of the studied systems.

242


Table 2 Physicochemical properties of benzoic acid solutions in different solvents at 20 °C Concentration (mol/l)

Physicochemical properties of benzoic acid at 20 °C q (g/ml)

Vspe (ml/g)

e

n

P2 (cm3 mol1 )

Methyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.7916 0.7913 0.7904 0.7902 0.7900 0.7899 0.7895 0.7884

1.2632 1.2637 1.2652 1.2655 1.2658 1.2659 1.2666 1.2684

72.44 61.25 46.44 41.27 32.86 26.42 25.00 23.57

1.3299 1.3298 1.3298 1.3297 1.3297 1.3296 1.3296 1.3295

38.804 38.526 37.982 37.690 37.022 36.235 36.029 35.826

Ethyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8072 0.8060 0.8060 0.8060 0.8054 0.8045 0.8043 0.8035

1.2388 1.2407 1.2407 1.2407 1.2416 1.2430 1.2433 1.2445

21.17 20.74 20.65 20.57 19.88 19.13 17.29 16.84

1.3634 1.3633 1.3633 1.3632 1.3632 1.3630 1.3630 1.3629

49.618 49.547 49.516 49.488 49.285 49.061 48.298 48.133

n-Propyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8049 0.8047 0.8043 0.8042 0.8038 0.8029 0.8028 0.8013

1.2424 1.2427 1.2433 1.2434 1.2441 1.2455 1.2456 1.2479

31.36 30.81 30.26 29.67 27.08 24.62 12.95 11.94

1.3847 1.3846 1.3846 1.3845 1.3844 1.3844 1.3843 1.3842

Iso-propyl alcohol 0.7861 2.00 103 1.00 103 0.7855 8.00 104 0.7853 0.7853 5.00 104 3.00 104 0.7849 1.00 104 0.7842 0.7841 5.00 105 1.00 105 0.7839

1.2721 1.2730 1.2734 1.2734 1.2740 1.2752 1.2753 1.2757

11.70 11.58 11.51 11.46 11.43 11.43 11.21 10.64

Toluene 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

1.1533 1.1558 1.1559 1.1559 1.1568 1.1583 1.1590 1.1592

0.8671 0.8652 0.8651 0.8650 0.8644 0.8633 0.8628 0.8626

2.510 2.490 2.450 2.430 2.430 2.400 2.360 2.300

l (D)

a (1040 ) (C2 m2 J1 )

1.2114 1.2059 1.1948 1.1890 1.1753 1.1592 1.1548 1.1505

13.4015 13.2801 13.0367 12.9105 12.6147 12.2714 12.1784 12.0879

12.686 12.700 12.700 12.697 12.706 12.714 12.717 12.726

1.3318 1.3303 1.3297 1.3293 1.3254 1.3212 1.3072 1.3041

16.1978 16.1613 16.1468 16.1370 16.0425 15.9410 15.6049 15.5310

67.952 12.023 11.999 11.977 11.949 11.805 11.648 10.082

17.486 17.485 17.493 17.491 17.495 17.515 17.513 17.541

1.5568 1.5553 1.5539 1.5520 1.5427 1.5324 1.4256 1.4086

22.1332 22.0905 22.0508 21.9969 21.7341 21.4448 18.5598 18.1198

1.3769 1.3768 1.3768 1.3767 1.3766 1.3766 1.3765 1.3764

59.711 59.604 59.531 59.466 59.457 59.509 59.232 58.462

17.580 17.588 17.592 17.588 17.592 17.608 17.606 17.606

1.4225 1.4205 1.4192 1.4182 1.4180 1.4186 1.4139 1.4008

18.4792 18.4272 18.3935 18.3676 18.3624 18.3780 18.2564 17.9197

1.5185 1.5184 1.5184 1.5183 1.5183 1.5183 1.5182 1.5182

35.580 35.342 34.706 34.385 34.406 33.959 33.311 32.293

32.228 32.282 32.286 32.295 32.317 32.358 32.382 32.389

0.40121 0.38330 0.34090 0.31682 0.31670 0.27741 0.21123 –

4. Results and discussion 4.1. Permanent dipole moment Ps and Rs of the solutions were calculated by using Eqs. (1) and (6). Tables 1–3 show the calculated values of the molar polarization and molar refractivity of investigated benzaldehyde, benzoic acid and oxalic acid solutions, respectively.

R2 (cm3 mol1 ) 8.2467 8.2466 8.2558 8.2553 8.2572 8.2558 8.2599 8.2691

1.4701 1.3417 1.06128 0.9166 0.9159 0.7027 0.4074 –

For an ideal solution, one expects Ps to be independent of concentration, i.e. it is a quality only of the molecular structure. For nonideal solutions, Ps depends on concentration due to strong solute-solvent interactions [5,14,15]. In our study, we are seen that the values of Ps of the solutions depend on concentrations of investigated solutions (Tables 1–3). Upon the substitution of the determining Ps and Rs of the solutions into Eq. (7) and permanent dipole mo-


243

Table 3 Physicochemical properties of oxalic acid solutions in different solvents at 20 °C Concentration (mol/l)

Physicochemical properties of oxalic acid at 20 °C q (g/ml)

Vspe (ml/g)

e

n

P2 (cm3 mol1 )

Methyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.7944 0.7940 0.7935 0.7926 0.7917 0.7913 0.7907 0.7902

1.2588 1.2594 1.2602 1.2616 1.2631 1.2637 1.2647 1.2655

53.08 34.83 27.46 25.36 23.15 17.89 17.21 15.73

1.3297 1.3295 1.3295 1.3295 1.3294 1.3294 1.3292 1.3292

38.097 37.024 36.224 35.949 35.599 34.341 33.150 33.644

Ethyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8116 0.8107 0.8105 0.8104 0.8101 0.8095 0.8090 0.8089

1.2321 1.2335 1.2338 1.2339 1.2344 1.2353 1.2361 1.2362

50.61 44.18 28.89 24.74 21.50 21.06 21.03 16.39

1.3631 1.3630 1.3630 1.3629 1.3629 1.3629 1.3628 1.3628

53.456 53.456 53.060 51.247 50.396 49.536 49.433 49.454

n-Propyl alcohol 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

0.8180 0.8072 0.8065 0.8063 0.8062 0.8060 0.8053 0.8044

1.2225 1.2388 1.2399 1.2402 1.2404 1.2407 1.2417 1.2432

42.00 41.58 26.06 19.23 13.25 12.21 8.900 8.460

1.3844 1.3843 1.3843 1.3842 1.3842 1.3842 1.3840 1.3840

Iso-propyl alcohol 0.7892 2.00 103 1.00 103 0.7883 8.00 104 0.7874 0.7874 5.00 104 3.00 104 0.7873 1.00 104 0.7865 0.7865 5.00 105 1.00 105 0.7856

1.2671 1.2685 1.2700 1.2700 1.2702 1.2714 1.2714 1.2729

11.84 11.06 10.90 10.81 10.26 8.000 7.890 7.670

Toluene 2.00 103 1.00 103 8.00 104 5.00 104 3.00 104 1.00 104 5.00 105 1.00 105

1.0394 1.0395 1.0414 1.0475 1.0526 1.0534 1.0630 1.0675

2.720 2.700 2.700 2.700 2.690 2.680 2.640 2.630

0.9621 0.9620 0.9602 0.9546 0.9500 0.9493 0.9407 0.9368

l (D)

a (1040 ) (C2 m2 J1 )

1.1980 1.1763 1.1598 1.1539 1.1464 1.1197 1.0938 1.1045

13.1066 12.6361 12.2841 12.1595 12.0019 11.4494 10.9258 11.1406

12.608 12.617 12.620 12.618 12.623 12.632 12.637 12.638

1.4007 1.3937 1.3621 1.3470 1.3315 1.3295 1.3297 1.2957

17.9171 17.7385 16.9432 16.5696 16.1905 16.1419 16.1468 15.3316

68.462 69.324 66.546 63.997 59.873 58.814 54.081 53.277

17.194 17.419 17.433 17.433 17.435 17.439 17.446 17.466

1.5692 1.5789 1.5358 1.4954 1.4277 1.4096 1.3265 1.3115

22.4872 22.7660 21.5401 20.4217 18.6145 18.1455 16.0691 15.7078

1.3766 1.3765 1.3765 1.3764 1.3764 1.3763 1.3763 1.3763

59.646 58.722 58.571 58.445 57.649 53.482 53.226 52.759

17.499 17.513 17.533 17.528 17.530 17.544 17.544 17.564

1.4228 1.4068 1.4039 1.4018 1.3881 1.3138 1.3091 1.3001

18.4870 18.0735 17.9991 17.9453 17.5962 15.7629 15.6503 15.4359

1.5185 1.5184 1.5183 1.5182 1.5182 1.5181 1.5181 1.5180

34.901 34.645 34.709 34.913 34.949 34.842 34.619 34.626

29.023 29.029 29.084 29.258 29.405 29.426 29.700 29.829

0.53140 0.51930 0.51982 0.52111 0.51603 0.51004 0.48610 0.48002

2.5788 2.4627 2.4674 2.4798 2.4315 2.3753 2.1579 2.1041

ments of the solutions were calculated [5]. Tables 1–3 show the calculated permanent dipole moments of benzaldehyde, benzoic acid and oxalic acid solutions, respectively. According to the results of this study, oxalic acid molecules are more polar than benzoic acid and benzaldehyde molecules. Hydrogen bonding between molecules of a aldehyde compound is not possible, since there is no readily available acidic proton. Thus, calculated

R2 (cm3 mol1 ) 8.2132 8.2118 8.2167 8.2258 8.2327 8.2366 8.2383 8.2435

dipole moment of oxalic acid is greater than the others (Table 3). However, charge density of oxalic acid molecule also has a greater value. The carbonyl oxygen atom can, however, be a Lewis base receptor for hydrogen bonding with alcohol. When solutions of three molecules are compared with each other, it can be seen that dipole moments of prepared solutions with n-propyl alcohol are much greater than the other solvents (Tables 1–3). H-bonding can be reveal at this solutions. Weak

244


energy interactions caused by the geometric structure of molecular systems are changed and system has asymmetric structure [2,14]. It is determined that dipole moments of benzaldehyde–cyclohexane and benzaldehyde–toluene systems are lower than the other systems (Table 1). According to the results, interactions are weak in this systems and the solvents have nonpolar property. 4.2. Orientation polarizability Polarizability, refractive index and specific volume depend on geometry of the molecule [1,2,6]. These quantities are effected by interactions in the solutions. If the geometry of the molecule changes with interactions

in the solutions, polarizability, refractive index and specific volume also change [1,2,15]. The orientation polarizabilities of benzaldehyde, benzoic acid and oxalic acid solutions were calculated by using Eq. (8) [5,12] and are shown in Tables 1–3, respectively. For benzaldehyde–n-propyl alcohol system has the biggest dipole moment, polarizability of the system is the bigger than other systems (Fig. 1(a)). The polarizability changes with square of matrix component of electric dipole moment of molecular system [6,11,15]. Although benzaldehyde–methyl alcohol system has the bigger dielectric constant than the other systems, polarizability of the system is less than the other systems (Fig. 2(a)). Interaction between benzaldehyde and methyl alcohol is strong but at result of the interaction,

20

15

α0 (C2m 2/J)

α0(C 2m 2/J)

20

10 5

0

0,3

0,6

0,9 µ (D)

1,2

1,5

0

1,8

0

5

10

15

25

25

20

20

15 10 5

20

25

30

35

40

45

ε

(a)

α0 (C2m 2/J)

α0(C 2m 2/J)

(a)

15 10 5

0

0

0

0,3

0,6

(b)

0,9 µ (D)

1,2

1,5

1,8

0

20

40 ε

(b)

25

25

20

20

α0 (C 2m 2/J)

α0(C 2m 2/J)

10 5

0

15 10 5

80

60

15 10 5

0

0

0 (c)

15

0,3

0,6

0,9

1,2

1,5

1,8

µ (D)

Fig. 1. Relationships between orientation polarizabilities (a0 1040 C2 m2 J1 ) and dipole moments of the solutions. (a) Benzaldehyde, (b) benzoic acid, and (c) oxalic acid solutions in different solvents at 20 °C. The compositions are methyl alcohol (r), ethyl alcohol (j), n-propyl alcohol (N), iso-propyl alcohol (x), cyclohexane (d).

0 (c)

10

20

30 ε

40

50

60

Fig. 2. Orientation polarizabilities (a0 1040 C2 m2 J1 ) of the solutions as a function dielectric constants. (a) Benzaldehyde, (b) benzoic acid, and (c) oxalic acid solutions in different solvents at 20 °C. The compositions are methyl alcohol (r), ethyl alcohol (j), n-propyl alcohol (N), iso-propyl alcohol (x), and cyclohexane (d).


α0 (C2m 2/J)

20

iso-propyl alcohol

between solvent and solvent or solute and solvent are very strong and thus geometry of molecular system can be changed by this interactions [5,19]. The refractive index is a useful optical property reflecting ionic or molecular behavior in a solution. The calculated orientation polarizability values of molecules are plotted in Fig. 4 as a function of the refractive index. It is shown that the orientation polarizabilities increase with increasing probability of interactions between species in the solutions [6,14,15]. In the solutions, geometry of the molecules are changed by this interactions. Refractive index changes at same direction with density of medium and polarizability. It has been established that there is a general trend of increasing the orientation polarizability of the studied molecules with 20

α0 (C2m 2/J)

geometry of the molecular system changes less. Polarizability depend on geometry of the molecule and polarization of the studying bonding is effected with perturbation by geometric structure [2,6,15]. The relationship between specific volume values and orientation polarizability values of the solutions were illustrated in Fig. 3. The orientation polarizabilities increase with increasing specific volume in the solutions which are prepared with polar solvents [5,6,17,18]. In the solutions which is prepared with a particular solvent, it is shown that the specific volume decreased and orientation polarizability increased with increasing concentration of the solution at a given temperature (Tables 1–3). Because, the interaction between solute and solvent increased with increasing concentration of the solution. For the solutions which are prepared with different solvents at a particular concentration, polarizabilities of the solutions which are prepared with npropyl and iso-propyl alcohol are the bigger than the other systems (Fig. 3). In this solutions, interactions

245

n-propyl alcohol

15 10 5

15

0 1,34

ethyl alcohol

10

methyl alcohol

1,36

1,38

(a) 5

1,4 n

1,42

1,44

1,46

1,45

1,5

1,55

1,45

1,5

1,55

cyclohexane

25 1,1

1,15

1,2

1,25

25

α0 (C2m 2/J)

1,3

1,35

Vspe (ml/g)

(a)

n-propyl alcohol

α0 (C2m 2/J)

0

20 15 10

iso-propyl alcohol

20

5

15

ethyl alcohol

10

0

methyl alcohol

1,3 5

1,35

1,4

(b)

toluene

n

0 1,1

1,15

1,2

1,25

α0 (C2m 2/J)

25

n-propyl alcohol

20 ethyl alcohol

iso-propyl alcohol

α0 (C2m 2/J)

Vspe (ml/g)

(b)

20 15 10

15

5

10

methyl alcohol

0

toluene

5

1,3

0

(c) 1

(c)

25

1,3

1,05

1,1

1,15

1,2

1,25

1,3

Vspe (ml/g)

Fig. 3. Orientation polarizabilities (a0 1040 C2 m2 J1 ) dependence on specific volume. (a) Benzaldehyde, (b) benzoic acid, and (c) oxalic acid solutions in different solvents at 20 °C.

1,35

1,4 n

Fig. 4. Orientation polarizabilities (a0 1040 C2 m2 J1 ) of the solutions as a function refractive index. (a) Benzaldehyde, (b) benzoic acid, and (c) oxalic acid solutions in different solvents at 20 °C. The compositions are methyl alcohol (r), ethyl alcohol (j), n-propyl alcohol (N), iso-propyl alcohol (x), cyclohexane (d).

246


increasing the refractive index. In this study, the results have been closest to the other studies [1,2,20].

5. Conclusions According to the results, polarizability, refractive index and specific volume depend on geometry of the molecule. These quantities are effected by interactions in the solutions. If the geometry of the molecule changes with interactions in the solutions, polarizability, refractive index and specific volume also changes. The results shows that the effect of solvent is not the same for orientation polarizabilities in three systems. In the non-H-bonding (with toluene and cyclohexane) medium, polarizabilities of the three molecules are very smaller than H-bonding medium. Oxalic acid is the notable exception. In the polar medium of alcohols Hbonding there are marked differences between the orientation polarizabilities. The larger the monocarboxylic guest molecule the greater is its ability to disintegrate the infinite H-bonded aggregate of the dicarboxylic host. There are intramolecular hydrogen bonding between the hydroxy hydrogen and the carbonyl oxygen atoms. The carboxylic acid moiety is considered to be a highly polar organic functional group. This polarity results from the presence of a strongly polarized carbonyl (C@O) group and hydroxyl (OAH) group. Recall that oxygen is a relatively electronegative atom and when covalently bound to carbon and particularly hydrogen, a strong permanent dipole is created. In the case of carboxylic acids, the OAH group is even more strongly polarized than the OAH group of alcohols due to the presence of the adjacent carbonyl moiety. The dipoles present in carboxylic acids allow these compounds to participate in energetically favorable hydrogen bonding (H-bonding) interactions with alcohols. The total energy of H-bonding interactions for carboxylic acids is greater than that observed for other organic compounds containing OH or C@O dipoles

such as aldehydes. Carboxylic acids have a greater number of dipoles and stronger dipoles than these other organic compounds, and thus can form more and stronger H-bonds with other substances capable of Hbonding interactions. The nature of the reaction medium influences the dissociation of acids. Alcohols are favorable medium for the ionization process because they have high dielectric constant and the ability to solvate anions and cations. By contrast, nonpolar solvents are poor media for acid dissociation.

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