Vibrational spectrum and force field of trimethyl- methoxysilane

Journal of Molecular Structure, 37 (1977) 173-166 QI%evier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

VIBRATIONAL SPECTRUM METIIOXYSILANE

AND

T. F. TENISHEVA, A. N. LAZAREV I. V. Grebensl;chikov 199164 Nabereznaya

FORCE FIELD OF TRIMETHYL-

and R. 1. USPENSKAYA

Institute for Silicate Chemrstry. Makaroua 2, Leningrad (USSR

Academy )

of Science of the U.S.S.R.,

(Received 21 May 1976)

ABSTRACT The IR and Reman spectra of (CH,),SiOCH,, (CH,),SiOCD,, (CD,),SiOCH, and (CD,),SiOCD, are presented together with results of normal coordinate calculations. Numerical values of certain force constants and effects of mechanical coupling between Sii0-C bridge vibrations and some of internal vibrations of (CH,),Si and OCH, groups are briefiy discussed INTRODUCTION

Spectroscopic characteristics of the Si-0 bond in the trimethylmethoxy silane molecule are of special importance since this molecule can serve as a reference point if the influence of substituents at silicon and oxygen on the properties of silicon-oxygen bonds in R&-OR’ moiecules is compared. The normal coordinate analysis for this molecule was first attempted in the paper of Lazarev et al. [l] using valence force model and experiment& data on the spectra of (CH3)3SiOCH3(I) and (CH&SiOCD3 (II). In recent calculations by Marchand and Fore1 [2] the force field has been determined in symmetry coordinates. The experimental data used in these calculations included the spectra of I [3], II fl] and (CD3)3SiOCH3 (III) described in ref. 4. The results of the recent refinement of band assignments and force constants of the ~e~yls~yl group on the basis of the spectra in the series (CH&, (CD&-, SiCl (n = 0,1, 2, 3), which are published in detail separately, make possible a more rigorous treatment of spectral assignments and of force constant estimations for trimethylmethoxysilane. EXPERIMENTAL

The IR z+ndRaman spectra of alI practically accessible isotopic species including (CD&SiOCD~ (IV), which has never been studied before, were rek~estigated; special attention was paid to the spurious bands not identified previously (e.g., the‘strong IR band of (CD&SiOSi (CD3)3 at 680 cm-’

174

erroneously treated as a fundamental of III in refs. 2 and 4). Liquid samples at room temperature were used for the Raman study with 6328 A polarized excitation. Amorphous solid samples prepared by rapid condensation of vapors on the surface of a stainless steel mirror cooled by hquid nitrogen were used in the IR study for better resolution of numerous closely spaced_ bands in certain frequency intervals. CALCULATIONS

The normal coordinate calculations have been carried out using the space configuration with C, symmetry (Rig. 1). The following bond lengths were acce@ed: rsc. = 0.168 nm, r,, = 6.142 em, rso = 0.163 nm, ran = 0.199 nm. Valence angles CSiC, OSiC, HCH, HCSi and HCO were assumed to be exactly tetrahedral; the value of 125” selected for the SiOC ar@e is in accordance with modem electron diffraction data and deviates slightly from values used in earlier calculations (113” in ref. 1 and 117“ in ref. 2): Vibrational coordinates relating to the internal rotations of CHJ(CDJ) groups and of the OCHs group (“skeletal” torsion around Si-0 bond) were not taken into account since corresponding frequencies were not identified. Mechanical coupling between these and other internal degrees of freedom is scarcely of significant value. The initial set of force constants of the (CHJ)XSi group has been transferred from the results obtained for the (CH&SiCl molecule, whereas for the 0CH3 group the data of numerous calculations for CHsOH, CH,OCH, and other similar molecules were accessible. On the variation of the initial set of force constants to achieve the best coincidence between calculated and experimental frequencies, mainly the force constants relating to the Si-0 bond, CSiO angles, and to their interactions with adjacent bonds and

Fig. 1. The space configuration of the (dH,)$KKXi~ mokcule adogted for normal coordinate cakuhhion and bond numbering The bonds 1.&S; 14; i5 are i&g in the symmeixy plane_ The bonds Z3.4 -and 5,6:7 -lying in uy planes of pa+ groupC,, describing the local awnmetry of the (CH,),SiG group.

175

angles were varied Thus, it was found possible to fix the following force constants of the (CHa)BSi group aiming the more objective estimates of the force constants mentioned above* 5.2 8.75 0.75 0.96 1.542 0.1 0.15 0 0.2 0

a:*' bs-28

a2 2.5 b;q9 02 2.3 12.5 5.8 12.5

1::; 1314 2.3

0.1 0 0.4 -9.06 0.5 0.035 0.09 0.02 0.05

The suggested model of valence force field for trimetbylmethoxysilane contains approximately the same number of parameters as more provisionally determined potential functions in previous investigations [ 1, 21. The more rigorous nature of this model enables more precise separation between kinematic and purely dynamic (electronic) effects affecting the vsio frequency shifts in the spectra of (CH,)$3iOR type molecules if these are analyzed by means of normal coordinates. A set of force constants relating to the (CH3)3Si[O] group proved to be transferable on the normal coordinate analysis for (CH&SiOH and (CHJ)$iONa which indicates an increase of Si-0 stretch force constant to 8.6 (X lo6 cmm2)and 9.5, respectively. The same sequence of bond orders in the series (CHJ)3SiOCH3, (CH3)3SiOH, (CH3)3SiONa has been found by Dr. B. F. Shchegolev by MO (CND0/2) calculations performed in sp basis. The use of the same set of force constants for (CH,),Si[O] group in the normal coordinate analysis for (CH,),SiOCH = CH? and (CH3)3SiOC(H) = 0 reveals a decrease of Si-0 force constant in the (CH3)3SiOR’ molecules with strongly electron accepting radicals R’. A similar decrease of Si-0 bond orders follows from MO calculations in sp basis. Thus, the general trends in the dependence of Si--O force constant upon the nature of substituents at the oxygen atom can be at least semiquantitatively described in terms of sp-bonding without an appeal for the hypothesis on (p -+ d) R interaction. *The diagonal force constants are denominated by a subscript indicating the bond number or the numbers of bonds forming the corresponding valence angle (see Fig. 1 for the numeration of bonds). The non-diagonal force constants are denominated by subscript and superscript which indicate the interacting coordinates. Ail force constants are given in units x 10’ cm_?, the dimensionaiity enabling the dimensionless values of G-matrix elements. It should be bornein mind that, unlike the Soviet literature on the spectra of hydrocarbon which u&for the force constants the scale where the unit of length is equal to the *H bond length (0.109 nm) and the unit of mass is equal to the “spectroscopic” hydrogen mass (1.988 a-u.), here we use 1 A as the unit length and 1 a-u. as the unit mass (*Wescale).-The Gmatrix elements have been calculated as usual with spectroscopic masses of H and D aIiproximately correcting the frequencies for anharmonicity.

176 It is worth adding tbat the transferability of the force field for (CH&Si[O group to more complex molecules has been proved by the normal coordinate analysis of the spectrum of hexamethyldisiloxane. The more detailed description of these investigations is planned to be given in the book “Vibrations of Simplest Siloxane Molecules”. Several force constants, although not fmed in the process of variation, retained the numerical values characteristic for the (CH3)$Xl molecule

0.1 0.7 -0.1

h: a:*' 13 bz*

I’= 1.2 n!f

0.2 0.3 (in different planes)

Cut of 25 force constants given below the first three refer to the internal coordinates of the (CH3)3Si group but their values differ from the corresponding values for the (CHa)3SiC1 molecule; all other constants relate to the bonds and groupings lacking in that molecule.

b:a4 m22:S nS:5 kl k I4 k 1.2 k 1.14 a ‘2 5

0.2 0.1 (in the same plane) 0.4 (in different planes) 7.3

k IS k14_,5 k,4,,6

9.4

h” f2 al* b:s3

1.5

1.0

0.15

&.I 5

0.05 (in the same plane) 0.07 1.0

ait*16

0.9

ml:7

h”15

aL41.14

=at4j-17

0.4

kls.16= k 16.17

14.15 mi.l4

m i:L

r3 :4’ ~‘h6 14.13 ifs’-:6’ .

a.423 1.68 1.57 0.85 0.7 0.75 GE5 0.1 -0.06 -0.045 -6.06

Thus, the force field of the (CH3)3SiOCH3 molecule and of its deutero derivatives has been described by 46 non-zero force constants. The estimated value of the diagonal Si-0 stretch force constant is in good agreement with correlation between the SF-0 force constant and bond length suggested in ref. 6 if the latter equals 0.1639 nm according to the last electron diffraction data [ 53. It is worth mentioning that only the relatively large interaction term between the Si-0 stretch and t$e CSiO bending allows the reproduction on calculation of the strong interaction (coupling) between z&i0 and &H3(Si) vibrations (see below) which has been found experimentally. The comparison of calculated and experimental values of fundamental frequencies for all four &topic species is given in Tables l-4. The forms of vibrations are described_qualitatively in terms pf internal g@up~vib&idns for (0)CHS, Si-0-C and (O)Si(CH,),, in the last ca&_t& ‘-‘genet+$lL ‘- ,connections with correspt+ding vibrations of (CH&Si groups in (C&j&X molecules of Clv symmetry beiig indicated. *The “motig forces?ftir each

117 normal coordinate are characterized by potential energy distribution (PED) which is of particular interest in the case of strong coupling (“mixing” of group vibrations). Only brief comments to the assignments accepted in Tables l-4 and to some of the coupling effects in the spectra are given below. The precise coincidence of calculated f’requencies with experimental ones was not aimed at in the case of (O)C-H stretching vibrations because of perturbation of their frequencies by well known Fermi resonance between Y,CH~ and 26 C&(u,CD3 and 26CD3) and, probably, between Y,,CD, and 2&O (mixed with 6CDx) in the molecules II and IV. In view of these complications it seemed unreasonable to improve coincidence in the &H(O) frequency interval by means of assuming dynamic asymmetry in the OCH, group (the lack of Local three-fold symmetry of the force field). The experimental values of 6CHa (6CD3) vibrations of the methoxy group could be reproduced rather satisfactorily without this assumption. Thus, the dynamic asymmetry of the methoxy group has been taken into account only on calculation of pCH3(0) vibrations. This asymmetry was def$r$ed Fatp,e simplest way by assuming k,4,15 f k 14.16, h16.1~ and ait"' f 014' , lJr4'

.

vCO vibration is strongly coupled with p CH,(O), species A ' in molecules I and UI (see PED in Tables 1 and 3) which is probably the reason for comparable IR intensities of the bands near 1190 and 1080 cm-‘. The intensi@ of pCH,(O) vibration species A" remains low. On transition to the molecules containing the 0CD3 group the eigen-frequency of pCD, reduces; nevertheless the lowering of 6CDj(0) frequencies leads to considerable mixing between these vibrations and vC03, thus exciting an increase of 1R intensities of KDJ(0) vibrations belonging to species A' and complicating the pattern of spectral changes on deuteration in the interval 1200-1050 cm-‘. It is worth adding that on the base of relative IR intensities of bands at 1060 and 1050 cm-’ their assignment to 6.,CD3(0) vibrations species A' and A", respectively, can be reversed. The Si-0 stretching movement contributes mainly to the vibrations at 72G c’rn-’ in I and at 700 cm-’ in II. However, this motion contributes also to thp puCHA(Si) vibration (species A') near 870-860 cm-‘. This contribution incrr-sasesthe p ,,CH3(Si){AI ) frequency in comparison with p ,,CH,(SiKE] vibration or with p,,CH#i){A,) in (CHJ)JSiX molecules with low &ix freo,uency_ In molecules III and IV the “unperturbed” (by mechanical coupling)frequencies of uSi and p ,,CDJ(Si){A I} * nearly coincide. The strong interaction causes considerable “resonance repulsion” of two frequencies, the @.ential energy of the Si-0 stretch being located mainly in the more high frequency vibration (800 cm-’ in III and 780 cm-’ in IV). The contribution of uSi( to tie low -fiiequency vibration is manifested experimentally by the partial pcdarization (arid enhanced intensity) of the Raman band at 640-630 cm-‘. The

WI5

c-my

in (CD;

hSiCl.

7&s I 746 s

836 vs

1188 8 1161 w 1079~vs 864 vs

124Svs

’ ‘1266 sh

I 1404 1416 w

293 6 sh 2831 m 1470 sh 1464 m 1’

2936(2) P 283014.5) p

1467 (1) dp

2902 m

29OO(Q.,6)p

a

2969, m

2961 (4) dp

P

IR (-190” ) w (cm-‘)

Raman (liquid) ij (cm-l)

Experimental data

1

I

A', A" A' A" A' A' A" A' A' A' A" A' A" A"

2A’, 2A”

A’

A”

A' A

A’

iI

A', A' A' A" A", A" A' A" A' A’, A”

764 I 732

1267 1268 1266 1 1176 1144 1086 868 841 840 I

2862 1477 1464 t 144s 4 x 1407 2 x 1406

2951 2924 2 x 2923

2962

2 x 2970 2968 I

2969 2971

bsCH,(Si)

6,CH,(Si)

GH,(O)

a&H,(O)

63 OCH, 26 HCH(O), 13 CO, 7 SiO 73 OCH, 27 HCH(0) 77 CO, 10 OCH, 6 HCH(O), 6 SiO 66 SiCH, 24 SiO, 5 CSiO 67 SiCH, 20 Sic, 11 CSiC 68 SiCH, 19 SIC, 12 CSiC 139SiCH, 6 CSiO, 3 Sic 90 SiCH, 6 CSiO, 3 Sic 99 SiCH

63 HCH(Si), 46 SiCH

99 HCH(Si)

99 CH(0) 66 HCH(O), 33 OCH 73 HCH(O), 27 OCH 63 OCH, 39 HCH(0)

100 CH(Si)

dX(Si 1 2&H,(O) * I$H,(O) I&H,(O) - 2aCH,(O)

99 CH(0)

100 CH(Si)

Q$H,(O)

u,CH,(Si)

Band sssignments and rcsulte of normnl coordinate analyais -_ -PED (%) Forms of vibrations Symmetry wcalc species (cm-‘) __--_._-w---w

Experimental and calculated frequencies of the (CH,),SiOCH, molecule ____-.__ -- _ -- --

TABLE 1

)Ir 2

721s ‘090m I 883m 606 w ’

%l ’ 21 A’ A” A’ A i A” A’ A”

716 689 689 I 604 326 285 238 216 213 162 {A, 1

6SiOC [pSiC,] r&l?

6,SiC, {E}

GG

v,SiC,(Ej

uSiO[pllCH,(Si))

47 SiO, 34 SiCH, 11 SIC, 6 CO 75 SIC, 26 SiCH 79 Sic, 23 SiCH 87 Sic, 10 SiO 48 SiOC, 35 CSiO, 8 CSiC, 4 SiO 79 CSiC, 16 CSiC 66 CSiO, 34 CSiC 73 CSiC, 8 CSiO, 8 SiOC, 6 SiCH 7 1 CSiC, 18 CSiO, 7 SiCH 68 CSiO, 39 SiOC

?he,freq$enciee of impurity bands and weak bands corresponding to the overtones and combinations are not included. The forms of vibrations~are described in terms of group vibrations; in the cases of considerable coupling one of interacting vibrations (with lesser contribution) is indicated in square brackets. The symmetry species of (CH,),SiO group vibrations for local C,v symmetry are given in braces. The cases of excitation due to Fermi resonance are indicated by the symbol “.+” *Were not obsemed on the background of uCH,(Si) ban& (see Table 3).

-170(1.6) pp -fv?

~OQU$)PP?

602(26) p 321,(2) PP 2KV2)‘dp 24U2.6) PP

iss(Q) dp

7lQtQ) PP

,

VB

’1758i’ 746 8

75011) do’

V8

838

1071 V8 1064 sh, 8 10638hb 928 m 903 w 856 sh, VS

1121

1250,~s

1

1261 sh

,840(1‘S) dp

1$12(Z) dp, I< ;:I,.:’ / I

A”

A’

;:,

A’

A $,,’

A A’ A”

;’

A’

2A’ 2A” A, ‘A,, I

A’ A’

2,:

IA 2088 4 x 1407 2x 1406 1268 1267 1266 1120 1089 1065 1046 926 901 852 841 840 I 763 I 763

2230

I

;;;[ “,h 2135 w 2067 m

2;;;;) (1.5) dp 2132(X6) p ;

2242sh

2247(l) pp?

1;;;;

2902 w

2901(g) p

vyq?

2960 m

2959(4) dp A'A’, A”

2 x 2970 2969 2971 2 x 2968 I 2924 2 x 2923 I 2231

A’, A’ A’ A” A”. A”

-

WC& (cm-‘)

Symmetry species

IR (-190’) w (cm-‘)

Raman (liquid) rs (cm-‘)

plCH,(Si){E)

PiiCH,(Si){E)

:$$$){A,~

[uSiO]

uCO[ aCD,(O)] 6,CD,(O)[uCO, uSiO] &CD,(O) 6,CD,(O)[uCOl pCD,(O)

6,CH,(Si)

6,CH,(Si)

u,&D,(O) 2uCO[ 6CD, (O)] - u&D,(O) +&D,(O) 26&D,(O) - u&D,(O) u&D,(O) .+ 26&D,(O)

v,CH,(Si)

u,CH,(Si)

Forma of vibrations

Band assignmentsand resultaof normal coordinate analysis

Experimental data

Experimental and calculated frequencies of the (CH,),SiOCD, molecule

TABLE 2

45 CO, 24 OCD, 23 DCD(0) 48 OCD, 30 DCD(O), 10 CO, 118iO 74 DCD(O), 26 OCD 56 DCD(O), 21 CO, 19 OCD 46 OCD, 23 Wb(O), 14 CO, 8 8i0 72 OCD, 26 DCD(0) 59 SiCH, 13 OCD, 10 SiO, 5 CSiO 67 SiCH, 20 Sic, 11 CSiC ’ 68 SiCH. 19 SiC. 12 @Sic 89 SiCH; 4 CSiC, 3 Sic 90 SiCH,’ 5 CSiO, 3 8iC

63 HCH(Si), 46 SiCH

99 HCH(Si)

98 CD(O) 98 CD(O) 98 CD(O)

100 CH(Si)

100 CH(Si)

PED (%)

A’ A’ A A’ I A” A’

;:

:I A

732 700 088 689 I 699 314 283 237 213 212 I 162 SSiOC[pSiC,]

&JiC, {E}

v,SiC, {A, 1 pSiC, {E} [GiOC] pSiC,@) WC, IAt 1

u,SiC, {E )

&iO[p$H,(Si)]

~~CH,(Si){A~~ 99 SiCH 42 Sid, 26 SiCH, 20 Sic, 7 OCD 72 SIC, 27 SiCH 79 Sic, 23 SiCH 81 SIC, 14 SiO 41 SiOC, 39 CSiO, 10 C&C, 4 SiO 78 CSiO, 17 CSiC J 66 CSiO, 36 CSiC 71 CSiC, 10 CSiO, 7 SiOC, 6 SiCH 70 CSiC, 19 CSiO, 7 SiCH 62 CSiO, 46 SiOC ’

See rimarks to Table’ 1: ‘The eklstence of polarized bands near the high- and low-frequency edges of broad band with unresolved structure can be supposed. %‘h$brindkm be (at least partially) attributed to the admixture of (CH,),SiOSi(CH,),. &la&d shoulder of depolarized band at 688 cm-‘.

1690) PP?

209(11J dp

699(@) P 326(21 P’P ?92(2) dp 239(3)PP~

$89(4) dp

-a!?@ pp

703 m 689ni 1 082 ah 601 w

I,

‘j$$

(1.5) dp

A’ A”

737 sh, VB

726 +a

I

903 i 191 vs

1ool; vs

dP

,,_/> 1.11. , qw) P 797i(~S)P1

lfQ(;l.s’)

A” A! A”

A

A’ A” A’ A’, A”

A

A A" A’ A’

1028 sh, s

,

1168 w 1079 vs 1042 m

1190 9’

2121 w 1470 sh ,1463 w. 14’5kjsh

lQzo(swip

,I

2216 m

2216(7.5) dp

/ -.

2831 m

2x

2x

3x

2x

A

2902m A” A’ A’, A” A’ A’ A’ I A” 2A’,A” A’ A”

2938 m

2936’(1.6) p 2900 ? ’ 2S,30(3.6) p 2862 2236 2234 2231 2231 2229 2121 1477 1464 1 1446 1176 ’ 1144 1086 1042 1039 1036 1036 I 997 997 994 1 802 717 716 I

2961

2962

A’

2968 m

‘;;5:)

(9.5) dp

Symmetry wCdc species (cm-‘) -_-_--

IR (-190”) w (cm-‘) _--_

p,SiC, @I [@USi)

uSiO[@D,(Si)]

a,CD,(Si)

6,CD,(Si)

&$H,(O) PCH,(ON~COI &H,(O) ~WP~H,(O)I

h&H,(O)

u&D,(a)

u,CD,(Si)

2aCH,(O) *. I&H,(O) QCH,(O) u,CH,( 0) n 26CH,( 0)

qdX(O)

Forms of vibrations

Band assignments and results of normal coordinate analysis

Raman (liquid) w (cm-‘)

Experimental data

Experimental and calculated frequencies of the (CD,),SiOCH, molecule

TABLE 3

64 DCD(Si), 33 SiCD, 11 Sic 64 DCD(Si), 33 SICD, 11 Sic 62 ~DCD(Si),37 SiCD, 8 Sic 69 SiO, 18 &CD, 8 CO, 4 DCD(Si) 46 SIC, 38 MD, 9 DCD(Si), 8 CSiC 46 Sic, 39 SiCD, 9 DCD(Si), 8 CSiC

100 DCD(Si)

’ 99 CH(0) 99 CH(0) 99 CD(Si) 99 CD(%) 99 CD(Si) 100 CD(Si) 100 CD(Si) 100 CD(Si) 66 HCH(O), 33 OCH 73 HCH(O), 27 OCH 63 OCH, 39 HCH(0) 53 OCH, 26 HCH(O), 13 CO, 7 SiO 73 OCH, 27 HCH(0) 77 CO, 10 OCH, 6 HCH(O), 6 SiO 91 DCD(Si), 6 SiCD, 2 CSiC 96 DCD(Si), 2 SiCD 99 DCD(Si)

99 CH(0)

PED (410)

E

w

In

h

I

i

2130(l) P 2119(19) p 2063 (9) P 1123(l) p ,~1077? / b .ioeq( ’ (1)dp

22i’6(7.6) dp

w

Raman (liquid) (cm-l)

Experimental data

A

2246 eh

A’, A” A’ i216 m A” A A” 2200 eh A” 2137 w A !&I’,A” 2123 w 2067 m A’ 1121 V8 A’ A’ 1073 VI ‘1066 Bh, 8 A” 106Sc sh A’ A’ 1041 m 1A” A’ A” 1027 8h, m A ( A” A’ 1901 vp i ‘A” A’ 99i 8 A’ 926 m A” 903 w ’ A’ 774 VB

Symmetry epeciee

IR (-190”) td (cm-‘)

3 x 2121 2088 1120 1090 1066 1048 1041 1042 1039 1036 1036 1036 i 998 997 993 924 901 774

2 x 2236 2234 2231 2231 2229 I 2230

2231

WCJO (cm-‘)

uSiO[PIICD,(Si)]

PCD,W PCDAO)

a&D,(&)

WWW

26&D,(O) +. @D,(O) $D,(8i) @D,(O) .+ %.&D,(O) vCO[6CD,(O)] a,CD,(O)[uCO, uSiO] &CD,(O) @D,(O)WOl

~,CWW

u,CD,(Si)

+,PWV

Forms of vibrations

Band awignmenta and results of normal coordinate analysis

Experimental and calculated frequencies of the (CD,),SiOCD, molecule

TABLE 4

100 CD(Si) 98 CD(O) 46 CO, 24 OCD, 23 DCD(0) 48 OCD, 30 DCD(O), 11 SiO, 10 CO 73 DCD(O), 26 OCD 62 DCD(O), lS,OCD, 13 CO 37 sDCD(Si), 4 SiCD, 3 DCD(0) 92 DCD(Si), 4 SiCD 96 DCD(Si), 2 SiCD 99 DCD(Si) ’ 98 DCD(Si), 1 DCD(0) 100 DCD(Si) ’ ,63 DCD(Si), 33 SiCD, 11 Sic 64 DCD(Si),,SS SiCD, 11 Sic 62 DCD(Si), 36 SiCD, 3 Sic 61 OCD, 26 DCD(O), 12 CO, 6 610 72 OCD, 26 DCD(0) ’ 43 SiO, 22 SiCD, 14 OCD, 6 SIC, 6 CO

99 CD(a) 99 CD(SI) 99 CD(SI) 76 CD(Si), 23 CD(0)d 100 CD(Si) 93 CD(O)

76 CD(O), 24 CD(Si)d

PED (%)

P

E

A’ I A” A’

A’ A” A’ A” A

( $r’

614vw

663~ 636 VW?

A’ A” A’

736ah,vs 720ve 610 w

717 716 1 611 603 602 I 676 572 t 648 660 299 263 206 184 182 I 141

~.tCDASi)k)

f4 1

6SiOC(pSiC,]

&,SiC, {EE)

@G

pSiC, E) [aSiOC] pSiC, t E)

PLCWO{El u,SG {A,1

46 SC, 38 SiCD,9 DCD(Si),8 CSiC 46 Sic, 38 SiCD, 9 DCD(Si),8 CSiC 64 SiCD, l.7 610,s CSiO,4 CSiC 68 SiCDi 23 Sic, 7 CSiC 64 SiCD, 26 Sic, 7 CSiC 73 SiCD, 19 Sic, 6 CSiO 71 SiCD, 22 Sic, 4 CSiO 80 Sic, 8 SiCD, 7 SiO 100 SiCD 47 SiOC, 33 CSiO, 6 SiCD, 3 CSiC, 4 610 79 CSiO, 10 CSiC 62 CSiO, 31 CSiC, 12 SiCD 69 CSiC, 10 SiCD, 8 SiOC, 7 CSiO 70 CSiC, 13 SiCD, 12 CSiO 66 CSiO, 36 SiOC

to lWe 1. The’u,CD,(O) vibrations are probably involved in Fermi resonance as suggested in Table 2. bThe broad band with unresolved structure probably contains a polarized component near the high frequency edge. aThe’bnnd can (at least partially) be attributed to the admixture of (CD,),SiOSi(CD,),. dComputed forms of two vibrations, V&D,(O) and Y&D, (Si), are mixed because of nccidental coincidence of their calculated frequencies.

$ee &arks

lslr(1.p) pp?

179&5) pp?

2Wl.6) PP 266‘(1.6)dp 206~2)‘PP?

6li2(2$) p

667 (1) dp

6,~4(2)PP $g’(l;S) dp

79 ‘? ?‘81.(1) dp

CONCLUSION

Thus, the assumption on the Fermi resonance between vSi0 and a combination mode in the spectrum of molecule III proposed in ref. 2 is quite unnecessary for understanding the changes in the spectra on transition from I, II to III and IV*. The strong coupling between vSi0 and PUCH3(Si){A,) has been noted on the analysis of the spectrum of (CHJ)3SiOH [7] and is probably characteristic of a number of molecules containhg the (CHS)$iO-group. Similar interaction of vSiF and P,,CH~ occurs in (CH&SiF and (CD3)JSiF molecules and will be described in detail separately. The bending vibration of the Si-O-C bridge is strongly coupled with CSiO bending (psi&), species A’ in the spectra of all four molecules. As a result, the contributions of both degrees of freedom into the normal vibrations near 325-295 cm-’ and 170-155 cm-’ are comparable and both bands are sensitive to the deuteration in both the trimethylsilyl and the methoxy groups. REFERENCES 1 A. N. Lazarev, Chr. Peuker and E. V. Kuhankaya, Neorg. Mat, 3 (1967) 2099. 2 A. Marchand and M.-T_ Forel, Buii. Sot. Chim. Fr., (1975) 72. 3 J. Dedier, A. Marchand, M-T. Fore1 and E. Frainnet. J. Organomet. Chem., 81(1974) 161. 4 N. V. Kozlova. V. P. Bazov, I. F. Kovalev and M. G. Voronkov. Izv. Akad. Nauk. Latv. S.S.R., Ser. Chem, (1971)694. 5 E. Gergb, B. C!&ikviri, P. Giimiiry, L Hargittai, F. C. Mijlhoff, J. Nagy, B. Rowondai, Gy. Schultz and Es. Wagner, The fourth International Symposium on Organosilicon Chemistry, Abstracts, Vol. 1. Part 1. 1975, p. 75. 6 A. N. Lazarev, A. P. Mirgorodsky and L S. Ignat’ev. Kolebatelnye spectry sioznyh okisiov.. Nauka, Leningrad, 1975. 7 Chr. Peuker and A N. Laaarev, Neorg. Mat., 4 (1968) 1716. 8 A N. Laaarev, I. S. Ignat’ev, L. L. Schukovskaya and R I. Pai’chik. Spectrochim. Acta, Part A, 27 (1971) 604.

* A similar assumption on the Fermi resonance involving vSiQh‘as been propos&d in ref. 3 on discussion of the spectrum of (CDj),SiOCHqCH,f in our&pinion, the &imption is unnecessary in this case too, as follows +ib_m our analysis oi&e&iecZ;~& of t.ðil-WV siiylvinyi ether [ 81.