Farkas, R.

Hencsei, P.

Nagy, J.

English

Periodica Polytechnica (Budapest University of Technology and Economics)

MEASUREMENT AND CALCULATION OF DIPOLE MOMENTS FOR PHENOXYSILANES By P. HENCSEI, R. FARKAS and J. NAGY Department of Inorganic Chemistry, Technical University, Budapest Received March 7, 1979 Introduction Few papers have been published on the experimental and calculated dipole moments of phenoxy si lanes with composition XC6H40Si(CHah. MAURET et al. have dealt with the dipole moments of phenoxysilanes in two papers [1, 2]. They gave the experimental values for derivatives X=H and X=4-CI (1.21 and 1.24 D; 2.38 and 2.39 D) and explained the increase of the SiOC bond angle on the basis of vectorial calculations by the formation of dn-por bond. In our earlier paper [3] the experimental dipole moments and vectorial calculations using group moment values were presented for derivatives X=H, 0-, m-, p-(CHahSiO. This work deals with the measurements and calculations of dipole moments for the following compounds: X=H, 2-, 3-, 4-CHa, Cl, N02, (CHahSiO, 4-F. Measurement of Dipole Moment The dipole moments of the investigated compounds were determined by ONSAGER'S [4] or by HEDESTRAND'S [5] method, for three compounds the measurements were carried out by both methods. According to Onsager's method the required data for the calculation of the dipole moment of the investigated compound (relative permittivity density and refractive index) were determined by measuring the pure compound. The dipole moment values will be given in Debye units (D) in this paper. The conversion into coulomb meter used in the SI system of units can be carried out by the following equation: 1 ID = - .10-29 Cm. 3 The formula for the calculation of dipole moment is: = V 9kT .yp* f1 40rN 1* 124 P. HESCSEI et al. The expression 1.1 9k~ is constant at a given temperature, its value at 4nlY 25 QC is 0.22123. Since our measurements were performed at this temperature f.L = 0.22123 rp* and where Co is the measured, relative permittivity of the compound, V -- 1\;1 d is the molar volume of the compound 2R+ V Ceff = V-R In latter formula R = PAP e' the sum of atompolarization and electron polarization, assumed to he 1.05 lVIRD • The measured date are summarized in Table 1. Table 1 Dipole moments of phenoxysilanes with formula XC6H40Si(CHab determined by Onsager's method and the measured and calculated quantities required for the calculation (t = 25 cC) x nll di5 (gcm-!J) tefi !L(D) H 1.4753 0.9192 3.395 2.260 1.22 2-CHa 1.4769 0.9158 3.219 2.265 1.17 3-CHa 1.4i6i 0.9124 3.209 2.265 1.17 4-CI 1.4927 1.0416 6.169 2.316 2.15 2-(CHa)aSiO 1.23 [3] 3-(CHahSiO 1.iO [3] According to Hedestrand, the total polarization belonging to infinite di-lution can be determined from data measured in diluted solutions of com-pounds: where lVIl and lVI2 are the molecular mass of thc solvent and the soluted, respectively, d1 is the density extrapolated to infinite dilution, Cl is the relative permittivity extrapolated to infinite dilution, DIPOLE JIO_UE:VTS FOR PHESOXYSILAiVES 125 Table 2 Dipole moments of phenoxysilanes with formula XC6H40Si(CHa)a, determined by Hedestrand's method and the measured and calculated quantities required for the calculation (t = 25 cC) X x:! El,: d,., (gem-a) fL(D) 2-CHa 0.00840 2.025 0.7768 Cl = 2.008 l.l9 0.01135 2.028 0.7783 dl = 0.7750 0.02511 2.051 0.7805 et; = 1.7694 0.04545 2.086 I fJ = 0.2051 3-CHa 0.00239 2.015 0.7759 Cl = 2.011 l.l5 0.01132 0.7767 dl = 0.7741 0.01109 2.032 et; = 1.7647 0.0225,1 0.7794 fJ = 0.2535 0.02280 2.052 0.03371 0.7828 0.03355 2.070 0.04-170 0.7853 0.04430 2.090 4-CHa 0.00231 2.022 0.7746 Cl = 2.008 1.24 0.01113 2.021 0.7767 dl = 0.7744 0.03353 2.086 0.7818 Cl = 1.9230 0.05542 :U11 0.7862 fJ = 0.2142 0.07856 2.149 0.7911 2-Cl 0.00922 2.051 Cl = 2.017 1.92 0.00534 0.7765 d1 = 0.7742 0.01429 2.075 Cl = 4.1660 0.00562 0.7761 D = 0.4440 f1 0.02004· 2.110 0.01022 0.7790 0.02677 2.131 0.02876 0.7867 0.03140 2.146 0.03414 0.7891 3-Cl 0.00804 0.7778 Cl = 2.022 2.20 0.01014 2.076 d1 = 0.7735 0.01415 2.098 0.7799 et; = 5.3748 0.02482 0.7851 fJ = 0.4668 0.02592 2.161 0.02844 2.174 0.7868 126 P. HENCSEI et al. Table 2 cont. x x, Cl.! d,., (gcm-') fL{D) 4-CI 0.00948 2.075 0.7776 81 = 2.018 2.38 0.01682 2.119 0.7807 dl = 0.7744 0.02513 2.154 0.7837 a; = 6.1290 0.03682 2.243 0.7900 {J = 0.4166 0.04714 2.312 0.7937 0.00597 2.114 0.7778 81 = 2.005 4.10 0.00991 2.181 0.7802 dl = 0.7736 0.01347 2.211 0.7829 a; = 17.647 0.01531 2.2B3 {J = 0.6533 0.01759 2.334 0.7850 3-NO~ 0.00553 2.129 0".7758 81 = 2.013 4.50 0.00989 2.22B 0.7782 dl = 0.7724 0.01084 2.24B 0.7791 a; = 21.052 0.01432 2.3111 0.7B14 f3 = 0.6226 0.0174B 2.379 0.7B32 0.00597 2.173 0.77B4 Cl = 2.026 4.86 0.01014 2.253 0.7805 dl = 0.7744 0.01375 2.367 0.7828 a; = 24.687 0.01763 2A60 0.7846 {J = 0.6060 0.01765 0.7854 4-F 0.00161 2.028 0.7735 81 = 2.021 2.14 0.00449 2.042 0.7748 dl = 0.7732 0.00641 2.051 0.7753 a; = 4.810 0.00739 2.056 0.7752 (J = 0.313 0.01378 2.0B7 0.7775 4-(CHahSiO 1.61 [3] IX and fJ are the slopes of straight lines c/xz and d/x2, respectively, X2 is the molar fraction of the solute. In the knowledge of the total polarization, the dipole moment can be calculated by the following equation: {J, = 0.22123 VP", R, where R = P A + P~, approximately taken as 1.05 MRD • DIPOLE l'-fOMEiVTS FOR PHEiVOXYSILAiVES 127 Our measurements were carried out at 25 °C in solutions of the com-pounds, using cyclohexane as solvent. Table 2 contains the measured and calculated data. e1.2 and d1•2 in Table 2 are the relative permittivities and densities of the solutions, respectively. Calculation on the Basis of Group Moments The dipole moment of molecules can be calculated by the vectorial sum-mation of the group moments of substituents. This method is based on the approximation that the group moment of identical groups of atoms is identical in different compounds. As far as the aromatic compounds are concerned, the experimental dipole moment of the monosubstituted benzene derivatives were chosen as group moment values. If a molecule contains two freely rotating polar groups with given group moments, the resultant dipole moment accord-ing to FucHs and TIGANIK [6, 7] is the following: ( 2, 2...L ') e e )1/2 ,U = fl1 -;- ,Uz I ~tLl tLz cos 1 cos 2 cos co where ,Ul and .U2 are the group moments of the polar groups, el and (}2 are the angles between the direction of the rotation axes and the group moment vectors, co is the angle between the two rotational axes, its value is 600 for ortho substitution, 1200 for meta substitution and 1800 for para substitution (Fig. 1). Values of tL2 and ez characteristic of the particular substituents were taken from the literature [8] and are summarized in Table 3. el value of the {CH3hSiO group was calculated from the experimental dipole moments. The : X I I I I a, Fig. 1. Calculation of dipole moment from group moments 128 P. HE;'\CSEI et a1. above mentioned equation was applied for p-bis-(trimethylsiloxy)-benzene assuming the free rotation of the (CH3hSiO groups and 69° was obtained for ()1 [3]. Table 3 Yalues of group moments X-(e,R,) .u,(D) 6, !,,(D) I 8, (CllahSiO 1')') 69' '-'------'1 Clla 0.37 I 0 Cl -1.59 i 0 :'\O~ -4.01 I 0 F -1.47 I 0 Quantumchemical Calculations Del Re and iterative PPP methods were used for the calculation of the charge distribution of the investigated compounds. The applied equations and the parameters of the calculations were described in our previous paper [9]. The geometry data of the calculations were chosen on the basis of electron diffraction measurements of CoHsOSiH3 [10]: RSi_o: 164.8 pm, Rc_o = 135.7 pm, SiOC bond angle = 121". The calculation of the :r systems was carried out on planar models, in the case of the ortho and meta substitution the silicon atom was in trans position. FOl' the C2 and Co as well as for the C3 and Cs carbon atoms of the para substituted compounds, the mean values of the corresponding calculated partial charges 'were taken. The reason of averaging the charges mentioned "was that the same results (charge distribution, dipole moment, electronic transitions) were provided in the calculations 'with planar model and with the silicon atom in perpendicular position, respectively. The partial charges G and :r ohtained in the calculations are summarized in Table 4. The dipole moments of molecules can he calculated from the partial charges given by the quantumchemical calculations. In the calculations it ,vas assumed that the (CH3hSiO group could freely rotate along the Car-O axis, the rest of the molecules was fixed and characterized by a constant vector. The average value of the dipole moment for a freely rotating molecule was calculated by integration from the summation of the constant and rotating vector: 2:r -~ 1 f[ ~ ,a~ = -, (a cos 'Y.. cos q; - x)~ 2:r • (a sin 'Y.. - y)2 + (a cos 'Y.. sin cp)2]dcp. o X~H A193 -A·211:1 .0711 -.0204--·.03119 . -.04·05 -.03:H X=2-Cl .0155 .0'1.24 .04·10 . 0;1·09 A200 .'1.239 .1072 .OB53 .0003 .0369 ... 0331 - .0162 .J 56.1 . OB3,j· .015;; • ();l.tj.o .01tl2 .01111 .O,j.27 X=:~-NO" .;1.19:1 A2BO .0727 .01:17 .10 IJ .0309 .. 0379 --.0200 . OB50 .00HO - .OB:J!I. .0155 .0439 .04.17 .Oltll . (H2 I j. -.12:H .2191 -.0:169 .0270 .0017 -.0032 ·-.124:1 .:llBB -.04.B3 -- .0412 -.012,1 -.004B .0006 ....• 0221 .0342 -.1153 .2199 -··.0261 -·.OOBB . - .051·3 .0109 .OBB -.0062 .54M . -.290,1. Partial charp;cH a and :7 of phwoxysilancs XC"JI.IOSi(CIla)a er X=2-CHa .'1.194. ·-A27t j. .07H .... 0·\.00 .0:120 --.0396 .0:IB9 . (Jl9,j· - .0B3<I-.0155 .()171 .020B .0,1.16 .lH09 .(H]\) .()tI2'1 X-=3-Cj .'1.19:1 -- A27B .0774-.0IBB .06B6 .0016 ·-.0:15.1 -.019B .... 1590 .OB:H .0155 .Olj.53 .(H:IB .0·\.1:1 '(H25 X=·1,-NO" .'1.19:1 ·A2B2 .0712 -.OIBO .. - .OISS .050:~ --.0723 --.0]65 -.OB:H .OISS .(H25 .0127 n._I - .12:17 .2U19 . (}Ij,OO - .0226 .0023 .0077 .0019 .021,5 .12:15 .219B --.0:11,0 ····.043,j. ·-.0.1 1.9 --.0220 .OO!),t, -.0271 .0:167 -.1126 .2222 -.0175 .016,j. .01S9 -.0501 .5426 .29lH A19:1 .42B2 .0716 -.0133 .0575 --.0334, ..... 03H'I, - .0202 --.OB:H .Ol55 -.0191 .0207 .O,t,29 .(};I,I,j, .(HII .(H2It .'1.19:1 - A2B2 .0716 -- .0]66 .0 .0672 -.IS92 --.OB:\;!. .0155 .O,j,27 .0439 ---X= •• 2~OSi(CH!l)!l 11' Si Al 96 ° .'1·259 Cl '()901 Ca .. OIB2 C,·.03B6 CSi ·····.OB:H, H(CSi) .0155 Ha .01,26 H,I .O,tll Si o (' I C. f'~i H(CSi) Il" .'\.193 A2B2 .071,j, .OIB'!. ···.OB3'j, .0] 55 '(H2S -..12:15 .219:1 .0:16:1 ··-.0:126 .OOH .0117 .00:10 -.0256 .- . .1 2,J,B .2193 -·.03BB -- .02:16 -.OIlB .0209 .0:J60 Si o Cl C. C; C.I Cr. Cn N ON CS; H(Cs;) Ha HI Hr. X=~,t-CHa AI9:l A2B2 .0710 - .0197 .03IB .0590 - .OB:\;\. .0155 ·-.019:1 .0207 .O,t2,j . .O,t15 AI9Cl --A261 .0900 .OB07 .(JIBB ---J IIG -.O:IB7 _ ... (J:W,I, .0 I H2 .Onl, . (11 (,() .OB:H, .0155 .(H,26 .(HIJ .(HIO .O,J.2S -- .126B .217] .0624 0.233 .0011.6 - .1277 .220B -.(H4:1 .()2,\.4 Si () Cl C .• C~ Cr. x :1-OSi(CHah AJ9:1 A2BO .0727 .000:1 .0199 - .0,170 Cs; II(CSi) 11 .. -.OB34, .0155 .fH39 .(142,1, .(HI2 11; 11;, .'1.193 .'1.282 .07H ··.0177 --.OJl6 .1609 -.22.1:1 -.OB:H .0155 .(H2Ct .().I.30 .12:~7 .2192 .O:IH .026'1, .00]7 .0020 .109B .2266 .021'\, .0727 .OIM .00'1,0 .0227 .OH.1-.511,24 . ·.2969 .12S0 .220B .0359 .06();I. .0321 . ()(HB .1226 .2197 .0:n6 .0235 .OO!7 .0,1,73 .0274 DIPOLE }IO.llESTSFOR PHEIVOXYSILA1"ES 129 y ----- -;p-----",_ 7O.(OSiR3) _______ '~-~~~·/c(~\~ __ ----X z ----~ ---.x Fig. 2. Calculation of dipole moment from charge distribution, assuming free rotation The positions of the vectors are illustrated in Fig. 2. In the calculations, the charge distribution of the molecules was regard as constant during rotation. The dipole moments of phenoxysilanes, calculated on the basis of group moments and from the charge distrihutions are summarized in Tahle 5. Table 5 Dipole moments of phenoxysilanes (XCsHPSi(CHah) calculated from group moments Pm and charge distribution ,liD [in Debye units] X ,Urn ,H?; H 1.089 2-CHa 1.332 1.123 3-CHa 1.206 1.074 4-CHa 1.137 1.051 2-CI 2.166 1.767 3-Cl 1.822 2.017 4-Cl 2.319 2.098 2-:XO~ 3.978 3.990 3-:XO~ '!.392 4.253 4-:NO~ 4.585 4.611 4-F 2.215 2.414 2-(CH3)3SiO 1.772 1.503 3-(CH3)3SiO 1.663 1.477 4-(CH3)3SiIO 1.606 1.431 Discussion In Fig. 3 the dipole moments calculated on the basis of group moments are shown as a function of the experimental dipole moments. A linear regres-sion line is drawn in the figure, the regression coefficient is 0.986. In Fig. 4 130 pm :DJ 3 2 2 P. HENCSEI et o\. " " 3 /. I" I" .-I" I" I" I" I" 1"' I" I" h I" / r = 0.986 jlexp. [DJ Fig. 3. Dipole:moments of phenoxysilanes calculated from group moments vs. experimental values pS' [DJ 3 2 2 3 r = 0..991 OSi(CH3h @ X Fig. 4. Dipole moments of phenoxysilanes calculated from charge distribution vs. ex per mental values the connection between the dipole moments calculated from the charge distri-butions and the experimental dipole moments is illustrated, regression coeffi-cient r = 0.991. The agreement between the experimental and the calculated dipole moment is good in both cases: the standard deviation is 0.156 D (8.61%) in the first case and 0.188 D (9.88%) in the second case. Prominent difference between the calculated and measured values is observed only for one com-pound: for the ortho-bis(trimethylsiloxy)-benzene. This significant de"iation can be explained by the hindered rotation structure of the compound. The good agreement in other cases shows that in the series of phenoxysilanes the group moment of the same substituents is nearly identical for substitutions in differ-ent positions and the effect of the substituents on the n systems of the mole-cules is not significant. The effect of the nitro group is more marked, specially DIPOLE MOi-.fENTS FOR PHENOXYSILANES 131 in the case of para substitution. The good agreement of the dipole moments calculated from the charge distribution with the experimental values proves the free rotation structures of the compounds "With the exception of the above mentioned ortho-bis-(trimethylsiloxy)-benzene. The greater deviation observed for the para-fluoro derivative can be explained by the enhanced effect of the fluor atom on the charge distribution. At the same time the good agreement between experimental and calcu-lated data proves the applied quantumchemical methods, parameters and geometrical data to be adequate and the choice of planar model to be reasonable. Acknowledgement The authors wish to express their thanks to Dr. FERENCZI-GRESZ, S. for the measure_ ment of the dipole moment of p-FCGH40Si(CH3h Summary In this paper the experimental and calculated dipole moments of phenoxysilanes with formula XCsH40Si(CHs)s (X = H, 2-, 3-, 4-CHs' Cl, NO!, (CHahSiO, 4-F) are given. The measurements of dipole moments were carried out at 25°C in liquid state by ONSAGER'S method and in cyclohexane solutions by HEDESTRAND'S method. The calculated values were determined on the basis of the group moment method and from the charge distribution provided by Del Re and IPPP methods. Based on the good agreement between experimental and calcu-lated data, the (CHa)sSiO groups were found to freely rotate along the Car-O axis in phenoxy-silanes (with the exception of the ortho-bis-(trimethylsiloxy)-benzene). References 1. MAURET, P.-ABADIE, A.-CALAS, R.-yALADE, J.: Bull. Soc. Chim. Fr. 1221 (1967) 2. BORDEAu, M.-DEDIER, J.-FRAINNET, E.-FAYET, J.-P.-M . .u;RET, P.: J. Organometal. Chem. 59, 125 (1973); 61, 91 (1973) 3. NAGY, J.-HENCSEI. P.-FERENCZI-GRESZ. S.-GABOR. T.: Acta Chim. (Budapest) 69, 411 (1971)· .4.0NSAGER, L.: J. Am. Chem. Soc. 58, 1486 (1936) 5. HEDESTRA.."iD, G.: Z. Phys. Chem. B 2, 428 (1929) 6. FUCHS, 0.: Z. Phys. Chem. B 14, 339 (1931) 7. TIGANIK, L.: Z. Phys. Chem. B 14, 135 (1931) 8. MIl'I"KlN, V. I.-OSIPOV, 0. A.-ZHDANOV, Y. A.: Dipole Moments in Organic Chemistry. Plenum Press, New York, 1970. p 91. 9. HENCSEI, P.-NAGY, J.: Z. Phys. Chem. (Leipzig) 258, 1013 (1977) 10. GLIDEWELL, C.-RANKIN, D. W. H.-RoBIETTE, A. G.- SHELDRICK, G. M.-BEAGLEY, B.-FREEMAN, J. M.: J. Mol. Struct. 5, 417 (1970) Dr. PAL HENCSEI I Dr. Renata, FARKAS H-1521 Budapest Doe. Dr. Jozsef NAGY 

MEASUREMENT AND CALCULATION OF DIPOLE MOMENTS FOR PHENOXYSILANES

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MEASUREMENT AND CALCULATION OF DIPOLE MOMENTS FOR PHENOXYSILANES

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