PROTON

MAGNETIC

ORGANIC

RESONANCE

COMPOUNDS

GERMANIUM

AND

SUBSTITUENTS A. A.

WITH THE

FOR N. I.

SPECTRA SILICON

AND

RELATIVE d~

Egorochkin, Burov, and

--p~ N. S. S. Ya.

OF

ABILITY

OF

INTERACTION Vyazankin, Khorshev

UDC 543.42+ 538.113 + 547.245/246

It is known that d~r - p ~ i n t e r a c t i o n between the d - o r b i t a l s of elements of group IVB (Si, Ge, Sn) and u n s h a r e d p - e l e c t r o n s i m p o s e s a substantial imprint upon the chemical and physical p r o p e r t i e s of h e r e t o organic compounds. Thus, we have r e c e n t l y shown by the method of IR s p e c t r o s c o p y that the ability of substituents f o r dTr -PTr interaction with the d - o r b i t a l s of silicon and g e r m a n i u m i n c r e a s e s in the periods of the p e r i o d i c s y s t e m f r o m left to right, and in the groups f r o m the bottom up [1]. This conclusion a g r e e s with the p h y s i c o c h e m i c a l data on the indicated question [2] and is also c o n f i r m e d by the t h e o r e t i c a l concepts of d~ - p ~ interaction [3]. In this work the method of proton magnetic resonance (PMR) was used to e v a l uate the r e l a t i v e ability of e l e m e n t s of group IVB, silicon and g e r m a n i u m , and substituents for d~r -PTr inte faction. According to the m o d e r n t h e o r e t i c a l concepts [4], the chemical shift of a c e r t a i n unchanged f r a g m e n t of the molecule in the PMR s p e c t r a is influenced by the following factors: 1) the inductive effect of the v a r i able substituent; 2) the effect of a n i s o t r o p y of the magnetic susceptibility of the bonds of the substituents; 3) the effect of the i n t r a m o l e c u l a r e l e c t r i c field. F r o m this it follows that the information on d~r -PTr int e r a c t i o n obtained f r o m a d i r e c t c o m p a r i s o n of the e x p e r i m e n t a l chemical shifts is r e l a t i v e l y unreliable. We had e a r l i e r p r o p o s e d a method for evaluating the d Tr -pTr interaction in methyl d e r i v a t i v e s of Si, Ge, and Sn, consisting of an e m p i r i c a l consideration of f a c t o r s 2 and 3, f r o m the PMR s p e c t r a of analogous c a r b o n compounds [5]. The data obtained in this c a s e , while not contradicting the available l i t e r a t u r e m a t e r i a l on dTr -PTc interaction, do need additional verification. In [6] it was shown that a consideration of the t h r e e f a c t o r s e n u m e r a t e d above, influencing the c h e m i c a l shift in the PMR s p e c t r a of methyl d e r i v a t i v e s of silicon and g e r m a n i u m , p e r m i t the contribution to the c h e m i c a l shift introduced by dTr -PTr interaction to be isolated. The p u r p o s e of this work was to develop [6] for a study of the relative ability of substituents in methyl and ethyl d e r i v a t i v e s of silicon and g e r m a n i u m for d~r -PTr interaction and to c o m p a r e the data with the r e s u l t s obtained by the method of IR s p e c t r o s c o p y . Let us c o n s i d e r s u c c e s s i v e l y the f a c t o r s influencing the c h e m i c a l shifts of the protons of the methyl groups (TCH3) in c e r t a i n methyl d e r i v a t i v e s and the CH 2 protons of the ethyl groups (TCH2) in the ethyl d e r i v a t i v e s (Tables 1 and 2). Inductive Effect of Substituents. In m e t h y l s i l a n e s and m e t h y l g e r m a n e s (CH3)a_nMR n (M=Si, Ge; R r e p r e s e n t s substituents of the type of (CH2)mX, where r e = l - 3 , while X = H a l , OH, NAIk 2, SCN, etc.), the substituents R of which a r e incapable of d~r -PTr interaction, ~-CH3 a r e related to the s u m s of the Taft induction constants Y cr~t by linear equations [6] TCH 3

t0.00

TCH~

9.90 -- 0.t46 ~ ' a~ (for methylgermanes)

-

-

0.t40 ~

(~R (for methylsilanes)

L a b o r a t o r y of P o l y m e r Stabilization, A c a d e m y of Sciences of the USSR. T r a n s l a t e d f r o m I z v e s t i y a Akademii Nauk SSSR, Seriya K h i m i c h e s k a y a , No. 6, pp. 1279-1285, June, 1970. Original a r t i c l e submitted D e c e m b e r 23, 1968.

9 Consultants Bureau, a division, of Plenum Publishing Corporation, 227 West ]7th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without

permission of the publisher. A copy of this article is available from the publisher for $15,00.

1210

F o r ethyl d e r i v a t i v e s (CH3CH2h_nMR n with R i n c a p a b l e of d~r -PTr i n t e r a c t i o n , the equation t a k e s the f o r m [61: 9cm = 9.47 - - 0.t45

~

rcm = 9.25 - - 0.120

L*~

The p r e s e n c e of a l i n e a r c o r r e l a t i o n b e t w e e n ~ and E ~

(for ethylsilanes)

(for ethylgermanes) is evidenee that the influence of the m a g n e t i c a n i s o H

r

f

t r o p y and the e l e c t r i c field of the group X on ~-CH3 of the f r a g m e n t H - C - M - (CH2)mX and rCH 2 of the f r a g -

H I

I M

1

l

ment - C - M - (CH2)mX is e x t r e m e l y s m a l l .

r

i

M If now we c a l c u l a t e rCH 3 and rCH 2 a c c o r d i n g to the equations cited, f o r compounds with any R c a p a b l e of d~ -PTr i n t e r a c t i o n , the v a l u e s of rin d obtained will c h a r a c t e r i z e only the inductive c o n t r i b u t i o n of R to the c h e m i c M s h i f t s . To p r o e e e d f u r t h e r , r i n d should be c o r r e c t e d for the effective m a g n e t i c a n i s o t r o p y and the e l e c t r i c field of the s u b s t i t u e n t s . The t r a n s i t i o n f r o m the compounds Alk 4 _nM[(CH2)mX]n to Alk 4 _ n 9MX n b r i n g s the X group c l o s e to the CH 3 and CH 2 p r o t o n s of the a l k y l s (CH 3, C2H5). T h e r e f o r e it might be e x p e c t e d that the influence of the m a g n e t i c a n i s o t r o p y and the e l e c t r i c field in the compounds A!k 4 _ n M X n wilt be s u b s t a n t i a l l y g r e a t e r than in A l k 4 _riM[ (CH2)mXln. Effect of the A n i s o t r o p y of the Magnetic S u s c e p t i b i l i t y of the Bonds of the S u b s t i t u e n t s (&ran). The c o n t r i b u t i o n to the c h e m i c a l shifts of Aran was c a l c u l a t e d a c c o r d i n g to the f o r m u l a [4] A r a n _ A)~ / 1 - - 3 c o s 31V \ t~3 w h e r e A• = • I I - x• is the a n i s o t r o p y C1, B r , O), C - O , and C - H bonds; dius v e c t o r R, c o n s t r u c t e d f r o m the m e t e r s of the m o l e c u l e s s t u d i e d a r e

~0 /'

of the m o l a r m a g n e t i c s u s c e p t i b i l i t y of the M - X (M = Si, Ge; X = F , 0 is the angle b e t w e e n the a x i s of s y m m e t r y of t h e s e bonds and the r a c e n t e r of the dipole to the p r o t o n to be s h i e l d e d . The g e o m e t r i c a l p a r a cited in T a b l e 1. It was a s s u m e d that the p o s i t i o n of the c e n t e r of the

d i p o l e c o i n c i d e s with the m i d d l e of the M - X bond. The g e o m e t r i c a l f a c t o r / I - 3cos 2 0 \ \ 1~3 /

was a v e r a g e d ,

c o n s i d e r i n g f r e e r o t a t i o n of the CH 3 and C2H s g r o u p s a r o u n d the M - C bonds and a s s u m i n g that all p o s s i b l e c o n f i g u r a t i o n s a r i s i n g d u r i n g r o t a t i o n a r e e q u a l l y p r o b a b l e . Computations i n d i c a t e d that f o r M - X (M = Si, Ge; X= F, C1, B r , C) and G e - O bonds, the g e o m e t r i c a l f a c t o r has v a l u e s of the o r d e r of (1-10).102~ cm -3, which in the i n t e r v a l of A)~ f r o m 1 to 10.10 -6 em3-mole -1 l e a d s to v a l u e s of Aran < 0.01 ppm. [n the c o m pound (CH3)3SiOCH3, Aran f r o m S i - 0 , C - O , and C - H bonds of the SiOCH 3 f r a g m e n t a r e equal to - 0 . 0 1 , +0.02, and +0.01 ppm, r e s p e c t i v e l y . The c o n t r i b u t i o n of AZan f r o m the C - H bonds of the f r a g m e n t GeOCH 3 in (CH3)3GeOCH 3 is equal to +0.01 ppm. The v a l u e s of A~ of the C - O and C - H bonds w e r e a s s u m e d equal to 1.48 and 0.90.10 -6 cm3-mole -1 [4]. The value of A• of the S i - b o n d , equal to 0.8-10 -6 cm3-mole -1, was c a l c u l a t e d a c c o r d i n g to the D o r f m a n method [13] f r o m the m a g n e t i c s u s c e p t i b i l i t y of (CH3)SiOCH3 (X = - 7 8 . 8 910 -6 c m L m o l e -1 [14]) and the m o l a r r e f r a c t i o n s of the bonds. F o r phenyl d e r i v a t i v e s ( t r i m e t h y l p h e n y l s i l a n e and d i m e t h y l d i p h e n y t g e r m a n e ) we c a l c u l a t e d the c o n t r i b u t i o n s due to the ring c u r r e n t s of the a r o m a t i c r i n g s . In this c a s e it was a s s u m e d that the ring c u r r e n t s have the s a m e value as the c u r r e n t in b e n z e n e . A s s u m i n g the p o s s i b i l i t y of f r e e r o t a t i o n of the m e t h y l g r o u p s a r o u n d the M - C H a bonds, we found A~-an a c c o r d i n g to the method of [15], equal to - 0 . 2 1 and - 0 . 3 4 p p m f o r (CH3)3SiC6H 5 and (CH3)2Ge(C6Hs)~, r e s p e c t i v e l y . Effect of the I n t r a m o l e c u l a r E l e c t r i c F i e l d of the Substituents (ATeL). The c a l c u l a t i o n of the c o n t r i bution t o t h e c h e m i c a l Shifts due to the influence of the e l e c t r i c field of the M - X (M =Si, Ge; X= F, CI, B r , C, O), C - O and C - H d i p o l e s , was p e r f o r m e d a c c o r d i n g to the f o r m u l a ATel -~ --3.1.10-1~E~ - - t .05. t 0-18.E ~ ,

1211

TABLE 1. G e o m e t r i c a l P a r a m e t e r s , Dipole Moments of the M - X Bonds, and ATeI of the Compounds Studied Bond length, A Compound

(CHa)a SiF (CHa)3 GeF (CH3)s SiOCtt3* (CH~)3 GeOCHs (~H~)~ SiC1 (CHs)~ SIC12 CH3 SiCI~ (CH~)a GeCl (CHa)~ GeCl~ CH~ GeCl~ (CH3)3 SiBr (CH@3 GeBr

~--X

1Vi-: C

1,57 [7] 1,65 [7] i,63[81 t,85191 2,03 [91 2,03 [91 2,03 [9[ 2,t5191 2,15 [91 2 ,t5 [9t 2,21 [91 2,30[9]

1,80 [7] t,98 ]91 i,8819 S 1,9819I 1,88 ]9] t,88 [91 i ,88 [91 t,98 [91 1,98 I9l t ,98 [9] 1,88 [9[ 1,98 [91

~,.(~- x), D

~:el' ppm

~t,91"

--0,29 --0,36 --0,30 --0,26 --0,33 --0,64 --0,93 --0,39 --0,76 --t,12 --0,35 --0,37

2,80 [iit

t ,23 [12I

2,oo [12i

2,29 [121 2,2i [t2] 2,t3112] 3,t7112] 3,07 [121 3,03 [t2| 2,56 $ 3,09 $

* The length of the C - O bond = 1.43 A; p(C-O) = 0.7 D;
E z is the c o m p o n e n t

of the electric field E of the dipole in the direction of the C - H

~cos 0 \ value obtained from electrostatics, E z = 2 # B~ / , the a n g l e b e t w e e n the a x i s of s y m m e t r y of M - X t h e dipole to the s h i e l d e d p r o t o n .

b o n d [6]. In the

w h e r e # i s the dipole m o m e n t of the M - X

bond; 0 i s

a n d the r a d i u s v e c t o r It, c o n s t r u c t e d f r o m the c e n t e r of

The g e o m e t r i c a l f a c t o r / \

cos0 /~3 /\ was c a l c u l a t e d c o n s i d e r i n g f r e e r o t a -

lion of the CH3 groups around the M - C bonds. It was assumed that the center of the dipole coincides with the middle of the M - X bonds. The quadratic factor was neglected. The dipole moments of the M - X bonds in the ethyl derivatives were assumed to be the same as in

r the methyl derivatives. It should be mentioned that the geometrical parameters of the fragment -CH 2- M

i

f

- X practically do not differ from the parameters of CH3 - M - X . Therefore the contributions of ATel (just

f like the contribution of A%n) to TCH of the methyl derivatives should be the same as those to ~-CH2 of the '~ 3 ethyl derivatives. As we go from the compounds Alk4_nM[(CH2)mX]n to AIk3MX, AIk2MX2, and AIkMX3, one, two, or three M--X bonds, respectively, are removed from the molecule. We took this fact into con-

I I

I I

sideration by calculating A~-elfrom the M-- C bond in the fragments CH3- M - C - and -CH 2- M - C. It was

I t

I I

found that for one S i - C bond A~'el=--0.09 ppm, while for G e - C ATel=--0.08 ppm. The chemical shift ~-calc= Tind+ A'ran + ATel contains a correction for the three factors cited, which influence 7-. Therefore, the comparison of 7cale with the experimental chemical shift (Texp) yields informamarion on the contribution of d~ - p ~ interaction to T. Relative Ability of Substituents for d~ -PTr Interaction. Summarizing the aforementioned, we can conclude that in the expression for ~'cale' the value of ~'indwas calculated with great accuracy. However, in the calculation of A'ran and ATel, several assumptions were made (the center of the dipole was taken as the center of the M - X bond, and the calculations of A~" were performed in the dipole approximation), in view of which the values of these quantities should be considered as approximate. Therefore Tcalc cannot pretendto any high accuracy, and consequently, the conclusions of d~ - p ~ interaction that can be drawn on the basis of the deviations of 7calc from ~-expare qualitative.

i

l

It is clear a priori that in the fragments CH3- M - X and -CH 2 - M - X the effect of d~

I

-p~-inter-

l

action between M and X, leading to an increase in the negative charge on M, act in the direction opposite to the inductive effect of X. As a result of this, Texp should have higher values in comparison with ~'calc,

1212

T A B L E 2. E x p e r i m e n t a l a n d C a l c u l a t e d C h e m i c a l Shifts (ppm) i n the PlV[R S p e c t r a of the C o m p o u n d s Studied M --Si

Compound

(CH3)aMF (CHa)>MF= (CHa) a~IOCHa (CHa)aMC[ (CHQ~ (CICH2) MCI (CHa)~M CI2 (CHa) (CICH2)MCh CHa-YICIa (CHa)~MCGHa (CHa)2M (C~Hs)z (CHa)aMBr (C..,H~)aMC1 (C~Hs)~MCI= (C~HsMCIa (GaH~)aMBr

M=Ge

rexp

rcalc

~"r

9,80 l~6i 9,681161 9,94 [17 l 9,58[~61 9,45 [18] 9,20 ['1.6] 9,08 * 8,86 Ii6l 9,7,6 *

9,37 8,66 9,65 9,35 9,2i 8,73 8,58 8,t2 9,7t

0,43

9,29 [19] 9,22 [20] 8,93 [20[ 8,60 [20[ 9, ~4 [20[

8,84 8,t8 7,56 8,83

9~5

,02

0,29 0,23 0,24 0,47 0,50 0,74 0,08 --0~6 0,38 0,75 i ,04 0,31

rexp

rcalc

Av

9,49 [t9]

9,17

0,32

9,661211 9,33 [221 9,18 [t81 8,82 [22]

9,49 9,t7 9,01 8,45

077

8,33 [22~

7,75

0,58

9,38 * 9,18 122] 8,89 [23[

9,38 9,20 8,67 7,97 7,33 8,65

0,0O --0,02 0,22 0.49 0,fi4 0, t~

8,46 1231 7,97 [231 8,81 [23]

0,16 0,I7 0,37

* Data of this work.

the more capable the substituentXfordrr -Prr interaction. Analyzing the data of Table 2, in which A7 = rex p - rcalc, from this standpoint, we can arrive at the following conclusions. For the same X, the quantities Ar in the series (CH3) 4_nSiXn have larger values than in the series (CH3) 4_nGeXn. This indicates a greater ability of silicon than germanium for d~r -P~r interaction. In the series (CH3)aMX, the values of AT decrease when X is varied in the sequence F > OCH 3 > Cl > C6H 5 > Br. This sequence reflects the decrease in the ability of the substituents for dTr -Pr~ interaction. The data on AT in ethyl derivatives also indicate a greater drr -Prr interaction with chlorlne than with bromine. Thus, the sequence of decreasing ability of substituents for drr -p~ interaction obtained in this work confirms the series found earlier by the PMR method - F ~ OCH 3 > CI ~ C6H 5 > Br [5] and I!g spectroscopy - R > O > C1 > Br [i]. A characteristic feature of the spectra of the compounds under consideration is the larger AT in the ethyl derivatives than in the methyl derivatives. We observed a similar pattern in the fIR spectra of trisubstituted silanes [24]. In this work we showed that the value of Av = Vcale - ~exp is a measure of the dr~ -PTr interaction of the substituent X with silicon in the silanes Alk~ _nSiH. In this expression Vcalc is the frequency of the valence vibration of the Si-H bond in the absence of the effects of de-P~r interaction. Let us note that in the I!q spectra of silanes, Vcalc > Vex p, while in the PMR spectra considered above, ~'exp > rcalc. In Table 3, which summarizes the data for chlorosilanes, it is evident that there is a profound analogy between the variation of Ar and that of Av. Thus, as we go from (CH3)3SiCI to CH3SiCI 3, and from (CH3) 2 9(CI)SiH to CI3SiH, the values of A'r and Av more than triple. In ethyl derivatives, the transition from compounds with one chlorine atom to compounds with three chlorine atoms leads to an increase in AT and Av of less than doubling. In this case, a large Av corresponds to a larger AT. The values of Ar and Av in the methyl derivatives are substantially lower than in the ethyl derivatives. The cause of the difference of AT and Av in the methyl and ethyl derivatives is not the larger inductive effect of the methyl group than of the ethyl group, as it follows from a comparison of Ar in compounds with the chloromethyl group - (CH3)2(C[ 9CH2)MCI and (CH3)(CICH2)SiCI 2. The values of Ar in these compounds differ little from those in (CH3) 3 9MCI and (CH3)2SiCI 2. The peculiarity of the spectra of methyl and ethyl derivatives noted, in our opinion, can be explained on the b a s i s of or,o - - c o n j u g a t i o n ( h y p e r c o n j u g a t i o n ) . In the c a s e of a , o - - e o n j u g a t i o n t h e r e i s a d i s p l a c e m e n t of the ( r - e l e c t r o n s of the C - H b o n d to the n e i g h b o r i n g bond H

Hy

I;

T h i s r e s u l t s i n a d e c r e a s e in the e l e c t r o n d e n s i t y on the p r o t o n s of the m e t h y l g r o u p , i . e . , the o b s e r v a t i o n of a P M R s i g n a l i n m e t h y l d e r i v a t i v e s at l o w e r v a l u e s of r, with a l l o t h e r c o n d i t i o n s e q u a l . It i s known that the ethyl g r o u p p o s s e s s e s c o n s i d e r a b l y l e s s a b i l i t y f o r h y p e r c o n j u g a t i o n t h a n the m e t h y l g r o u p . In view of t h i s , the v a l u e s of A r = rex p - Tcalc i n m e t h y l d e r i v a t i v e s a r e s m a l l e r t h a n i n e t h y l d e r i v a t i v e s on a c c o u n t of the d e c r e a s e in rex p a s a r e s u l t of h y p e r c o n j u g a t i o n . At the s a m e t i m e , the e f f e c t s c o n s i d e r e d

1213

TABLE 3. Values of AT (PMR s p e c t r a of m e t h y l - and ethylehlorosilanes) and A~ (IR spectra) of Trisubstituted Silicon Hydrides

Compound I~,ppl-n (CH3)aSiC1 (CHa)~SiCl= CH3SiCla (C=Hs)aSiC1 (C~Hs)2SiCI~ C~H~SiCla

0,23 0,47 0,74 0,38 0,75 1,04

Compound (CHa)~(C])SiH (CHa) (C1)2Sitt ClaSiH (C=Ha)~(Cl)SiH (C=Hs)(C1)2SiH ClaSiH

AV, cln -I

act in the direction opposite to the effect of dTr -PTr interaction between Si and C1. T h e r e f o r e , the electronegativity of chlorine f o r m a l l y i n c r e a s e s . However, in the computation of Vcalc in the IR s p e c t r a of chlorosilanes, we did not take this c i r c u m stance into consideration, which led to a d e c r e a s e in the values of Vcalc. F o r this reason, Av= V c a l c - ~exp in methyl d e r i v a tives also p o s s e s s lower values than in ethyl derivatives.

tt 33 55 22 38

On the b a s i s of the aforementioned, still another peculiarity of the data of Table 3 b e c o m e s understandable - the m o r e than tripling of AT and Av f r o m compounds with one chlorine atom 55 to compounds with t h r e e chlorine atoms in the methyl derivatives and the less than doubling of AT and Av in the ethyl derivatives. Considering the low ability of the ethyl group for hyperconjngation, the data on the ethyl derivatives can be i n t e r p r e t e d as an indication of a d e c r e a s e in the dTr -PTr interaction of each of the chlorine atoms when they a r e accumulated in the molecule. In methyl derivatives, when the n u m b e r of chlorine atoms in the molecule is varied, the effect of hyperconjugation evidently also v a r i e s in magnitude, which makes it difficult to obtain data on d~ - p~ interaction. It should be mentioned that hyperconjugation evidently also exists in compounds of the type of (CH3)~-n 9MR n and R3SiH, the substituents R of which are incapable of dTr - P ~ interaction. However, R of this kind exhibit little inductive effect, and t h e r e f o r e hyperconjugation in these compounds is also less pronounced than, for example, in chloroderivatives. In conclusion, let us note that the concept of hyperconjugation has been used in the l i t e r a t u r e to int e r p r e t the IR and PMR s p e c t r a of silanes[25] and starmanes [26]. Thus, it has been noted that the frequency of the valence vibration of Si - H in the IR s p e c t r a of the silanes R3SiH d e c r e a s e s with variation of R in the sequence: CH 3 > i-C4H 9 > n-C~H 7 =n-C4H 9 = C2H5 > i-C3H 7 , while the shielding of the hydride proton in the PMR s p e c t r a i n c r e a s e s in the s e r i e s : CH 3 =i-C4H 9 < n-C3H 7--n-C4H 9 < C2H5 < i-C3H I [25]. Both these sequences have deviations from the scale of the Taft induction constants [27], the cause of which, in the opinion of the a u t h o r of [25], m a y be the effect of hyperconjugation. In the PMR s p e c t r a of stannanes R3SnH, R2SnH 2, and RSnH 3, the shielding of the hydride proton i n c r e a s e s in the s e r i e s i-C3H 7 < n-C4H ~ ~ n-C3H 7 ~ C2H5 < CH 3, while the frequencies of the valence vibrations of S n - H in the IR s p e c t r a of methyl derivatives have a n o m alously high values, close to those for phenyl derivatives. This also is evidence of hyperconjugation, e s pically pronounced for the methyl derivatives [26]. The frequency V G e - H in t r i m e t h y l g e r m a n e is also anomalously high in c o m p a r i s o n with other t r i a l k y l g e r m a n e s [28]. The intensification of the effect of hyperconjugation as we go from organosilicon compounds to o r g a n o g e r m a n i u m and organotin compounds is evidently due to an i n c r e a s e in the polarizability of elements of group IVB f r o m silicon to tin. The influence of hyperconjugation on the chemical shifts of - S H and - S e l l in the PMR s p e c t r a of a l k y l m e r c a p t a n s and alkylselenols was noted in our work [29]. The facts cited confirm the conclusions on hyperconjugation drawn in this work. EXPERIMENTAL The PMII spectra were obtained on a YaMR-5535 spectrometer (40 MHz). The compounds (CH3)(CI 9CH2)SiCI~, (CH~).~SiC6H 5, and (CH3)zGe(C~Hs) 2 were studied in CCI 4 solutions (1:3 by volume) with an addition of a certain amount of eyclohexane as an internal standard. The chemical shifts T were determined with an accuracy of ~:0.2 ppm (TC6HI2 = 8.56 ppm). CONCLUSIONS I. An analysis of the chemical shifts in the proton magnetic resonance (PMR) spectra of (CH3)3MX (M = Si, Ge; X = F, OCH 3, Br, C6H5), (CH3) 4 _ nMCln, (C2H5) 4 - nMCln, and (C2Hs)3MBr, corrected for the effects of magnetic anisotropy and the electric field of the substituent X, showed that the ability of X for d~ - p ~ interaction with the atom M decreases in the series: F > OCH 3 > CI > CGH 5 > Br. Silicon possesses greater ability for d~-P~r interaction than germanium. 2. On the basis of a comparison of the results obtained with data on the IR spectra of silicon hydride, a hypothesis was advanced on the influence of hyperconjugation on the IR and PMR spectra of silanes.

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LITERATURE i. 2. 3. 4. 5. 6. 7. 8. 9. i0. Ii. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

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