T H E I N F L U E N C E O F A R O M A T I C F R A G M E N T S

ON T H E I N T E R M O L E C U L A R I N T E R A C T I O N O F

P H O S P H O R Y L C O M P O U N D S W I T H T H E M E D I U M

R . R . S h a g i d u l l i n , V. E . B e l ' s k i i , a n d L . K h . A s h r a f u l l i n a

UDC 541.124:541.6:547.1'118

Molecules containing a r o m a t i c r a d i c a l s man i fes t spec i f ic effects in i n t e r m o l e c u l a r in te rac t ion , which have been inves t iga ted chief ly by the NMR method [1-10], as well as by o ther methods [6, 10-12]. The enthalpy of the in t e rac t ion of p o l a r molecu les with a r o m a t i c solvents has a value - A H ~ 1-2 k c a l / m o l e [7], suff ic ient for the fo rmat ion of s h o r t - l i v e d co l l i s ion c o m p l e x e s w i t h a defini te or ien ta t ion . A p e c u l i a r i t y of the in te rac t ion of p o l a r molecu les with the 7r-electronic s y s t e m of benzene r ings is expla ined by an induced dipole or quadrupole moment [1, 4-7, 9, 13] and by a d o n o r - a e c e p t o r mechan i sm [14-16].

In the inves t iga t ion of the i n t e r m o l e c u l a r i n t e r ac t ion of phosphory l compounds (PC) with the medium by the method of IR spec t ro scopy [17], we noted that the p r e s e n c e of a r o m a t i c f r agmen t s in the PC m o l e - cu les o r solvent mo lecu le s g r ea t l y weakens the influence o f the medium on Up= O. Since a r o m a t i c d e r i v a - t ives a r e widely u s e d in the c h e m i s t r y of o rganophosphorus compounds, we s tudied the in te rac t ion with the medium of a number of PC with phenyl and phen0xyl groups at thr phosphorus a tom. The s e r i e s of i nves t i - gated so lvents was a l so expanded.

E X P E R I M E N T A L M E T H O D

The PC used in the work were syn thes i zed and pur i f i ed by the wel l -known methods . The method of m e a s u r e m e n t of the f requenc ies of the va lence v ib ra t ions of the phosphory l group ~ P=O was analogous to that used in [17]. The m e a s u r e d va lues of up= 0 for a number of PC in va r ious solvents a r e c i ted in Table 1. The band up= 0 for ce r t a in PC s tudied is a doublet . The absence of a pronounced influence of the con- cen t ra t ion of PC on the r a t io of the in tens i t i e s of the doublet bands and the i r change with changing d i e l e c - t r i c p e r m e a b i l i t y of the medium in the case of a c o r r e l a t e d shif t of the f requenc ies p e r m i t s us to conclude that the cause of the doublet c h a r a c t e r of the Up= 0 of the compounds (I)-(III) (see Table 1) is the p r e s e n c e of ro ta t iona l i s o m e r s [18, 19]. The values of the dipole moments (DM) of compounds (II) and (V) were de - t e rmined in benzene accord ing to the method of [20].

TABLE 1. Values of Vp= O (cm -1) of the Compounds Studied in

Var ious Solvents

(PhO),P(O)CI PhOP(O)Ch (EtO)EtP(O)Ph (EtO)~%IeCHP(O)Ph, Solvent (PhO)sPO (I) (if) (III) (IV) (V)

n-C~H14 n-C:HI~ C6H6

C6HsCHa CCh

(CH3)~SO C-.H4C12 CHaCN CHCla

'1300, t3t5 1300, t315 t298, t'313 t298, t313 t297, t3t2 t298, 13t0 1297, t3t0 t296, t3t0 1292, t306

1302, 13t3 1302, 13t3 t302, t313 1302,13t3 t300, t311

13007t3t0 t302, 1310 t297, 1308

t302, t312 t302, t3t2 t302, 1309 1302, t309 t302, t309

t300, 1308 t300, t308 t298, 1306

t222 t222 t2t8 t2t9 t216 1208 t210 t2tt

1197 tt97 tt89 1190 tt87 il80 |180 ti80

A. E. Arbuzov Inst i tute of Organic and Phys i ca l Chemis t ry , Kazan ' Branch of the Academy of Sc iences of the USSR. T r a n s l a t e d f rom Izves t iya Akademi i Nauk SSSR, Ser iya Khimicheskaya , No. 9, pp. 2034-2038, Sep tember , 1974. Original a r t i c l e submi t ted November 30, 1973.

�9 19 75 Plenum Publishing Corporation, 227 West 17th Street, New York, N.Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher for $15.00.

1952

T A B L E 2. P a r a m e t e r s of Eq. (1) fo r the I n v e s t i g a t e d C o m p o u n d s

Compounds ~, D a ~, cm -1 r * s ~

(1> (1D (IH) (IV) (V)

PhaPO [i71 (VI)

2,89 2,83 3,38 3,8 4,04 4,49

0,272 0,t95 0,244 0,663 0,979 1,I13

I092 1068 93i 385

--37 --134

0,99 0,91 0,95 0,99 0,99 0,99

*r is the coefficient of correlation; S is the standard deviation.

t,0 0,6 0.6 0,8 0,7 I , t

D I S C U S S I O N

It was shown e a r l i e r that the i n t e r v a l of v a r i a t i o n of Up= O of v a r i o u s PC u n d e r the in f luence of d i - p o l e - d i p o l e i n t e r a c t i o n with the m e d i u m d e p e n d s on the va lue of the d ipo le m o m e n t of the PC [17]. A c o m - p a r i s o n of the da t a of T a b l e 1 and [17] fo r PC with c l o s e v a l u e s of the DM shows tha t the i n f luence of the p o l a r i t y of the m e d i u m on Vp= O is g r e a t l y w e a k e n e d fo r PC c o n t a i n i n g a r o m a t i c r a d i c a l s . F o r e x a m p l e , in the t r a n s i t i o n f r o m hexane to a c e t o n i t r i l e vp__ O of (II) (tt ~ 2.83 D) i s p r a c t i c a l l y u n c h a n g e d (An = 3 cm-1) , whi le f o r (MeO)2P(O)Me, con t a in ing no a r o m a t i c g r o u p s , and p o s s e s s i n g a c l o s e va lue of the DM (~ ~ 2.89 D), the sh i f t of vp= O is 1 8 c m -1. The d e g r e e of i n t e r a c t i o n of the s u b s t a n c e wi th the m e d i u m i s c h a r a c t e r i z e d by the s l o p e a of the l i n e a r d e p e n d e n c e s b e t w e e n the f r e q u e n c i e s up= O f o r v a r i o u s PC, which v a r i e s u n d e r the in f luence of the m e d i u m

vi = aVst + b (1)

w h e r e u i and Ust a r e the f r e q u e n c i e s vp= O of the c o n s i d e r e d and s t a n d a r d PC; a and b a r e c o n s t a n t s . A s the s t a n d a r d PC, j u s t a s b e f o r e [17], we took d i m e t h y l m e t h y l p h o s p h o n a t e (DMMP). The t r e a t m e n t of the da ta fo r the PC tha t we i n v e s t i g a t e d a c c o r d i n g to Eq. (1) by the m e t h o d of l e a s t s q u a r e s showed tha t th is d e p e n d e n c e i s c h a r a c t e r i z e d by r a t h e r high c o e f f i c i e n t s of c o r r e l a t i o n (Table 2). F o r c o m p o u n d s (D-(IID, T a b l e 2 c i t e s the p a r a m e t e r s of Eq. (1) fo r the h i g h - f r e q u e n c y c o m p o n e n t s of the o b s e r v e d doub l e t vp= O. The s e l e c t i o n of the h i g h - f r e q u e n c y c o m p o n e n t of the doub le t i s not a c c i d e n t a l . A c t u a l l y , in b e n z e n e s o l u - t ions of the c o m p o u n d s u n d e r c o n s i d e r a t i o n , the i n t e n s i t y of th is c o m p o n e n t of the doub le t i s h i g h e r than that of the l o w - f r e q u e n c y c o m p o n e n t . Thus , the v a l u e s tha t we u s e d b e l o w f o r the m o l e c u l a r DM of PC in b e n z e n e a r e b a s i c a l l y d e t e r m i n e d by the c o n f o r m e r r e s p o n s i b l e fo r the h i g h - f r e q u e n c y a b s o r p t i o n band .

A c c o r d i n g to [17], the va lue of a d e p e n d s on the d ipo l e m o m e n t of PC, which was a s s o c i a t e d with the d i p o l e - d i p o l e m e c h a n i s m of the i n t e r m o l e c u l a r i n t e r a c t i o n . F o r the PC i n v e s t i g a t e d in t h i s work , c o n t a i n - ing pheny l and phenoxy l g r o u p s , t h e r e a r e s u b s t a n t i a l d e v i a t i o n s f r o m the p r e v i o u s l y found [17] d e p e n d e n c e f o r a l i p h a t i c PC (Fig . 1). The v a l u e s of a f o r PC wi th a r o m a t i c r a d i c a l s a r e l o w e r than fo r the a l i p h a t i c PC c o r r e s p o n d i n g to t hem in DM. T h i s m a y be a s s o c i a t e d with the c o m p e t i n g r o l e of the s u p p l e m e n t a r y i n t e r a c t i o n due to the a r o m a t i c r a d i c a l s . C o m p l e t e s u p p r e s s i o n of the d i p o l e - d i p o l e m e c h a n i s m of the i n t e r a c t i o n does not o c c u r in th is c a s e , which i s i n d i c a t e d by the c o n s e r v a t i o n of l i n e a r r e l a t i o n s h i p s (1) b e t w e e n the f r e q u e n c i e s of the c o m p o u n d s i n c l u d e d in T a b l e 1 and the f r e q u e n c i e s of o t h e r PC [17] in the c a s e of a change in Vp= O u n d e r the in f luence of the m e d i u m .

TABLE 3. Values of Exvp= O (MeO)2P(O)Me in Various Solvents Relative to the Gas Phase*

. ~ ~o ~.~

t 2 g 4 5 6 7 8 9

10

Solvent

n-C,~H14 n-CTHI~ (C~HsbN (C~HshO (C~H~)~O (CH~hO (C2H~O)aP C~HsCHs C~H~ C~HsC1

AVp=O, cm-l"

12 t2 t6 17 18 20 20 20 21 24

t l t2 i3 t 4 t5 t6 t7 t8 t9 20 2t

Solvent

(CHahCO (CH,.)~CO (C2H40)~ C~H5 N (CH~) C6H~NO~ HC(O)N(CH3)~ CGHsCN C6H~C(O)CH~ CHaCN (CHahSO CHINO2

A~p= O, cm -I

25 25 25 26 26 27 27 28 30 31 32

* The values of •v were estimated for the low-frequency component of the doublet Vp = O' using the data of [17].

1953

,,o! I

! O f - -

x r

2 • ! •

Fig. 1

'~I ] " 18x i?__._ dU x M

I I I i I

0 t 2 3 ~,D

Fig. 2

Fig. 1. Dependence of the value of a f rom Eq. (1) on the dipole moments of PC. 1) (I); 2) (II); 3) (III); 4) {IV). 5) (V); 6) (VI); 7)C13PO; 8) (MeO)2P(O)Me; 9) (MeO)2P(O)H; 10) (BuO)3PO; 11) (EtO)2P(O)Cl; 12)Et2P(O)OEt; 13) (Me2N)3.PO; 14) Et3PO. The data for compounds 7-14 were taken f rom [17].

Fig. 2. Dependence of the shift Avp= 0 of DMMP on the dipole moments of the solvents. The numbers of the points cor respond to Table 3. The values of ~ in benzene were taken f rom [21].

Data on the influence of a wide c i rc le of solvents on Avp= O of DMMP in turn indicates that the in- fluence of the polar i ty of the medium on the change in vp= 0 is great ly weakened for solvents containing aromat ic f ragments (Table 3). A compar ison of the shift Az, p= O of DMMP with the DM of the solvents is shown in Fig. 2, f rom which the l ineari ty of the dependence Avp= O = 4.76 ~ + 12 for 14 different solvents with corre la t ion coefficient r = 0.98 is evident. The value of the DM of a romat ic solvents has very little influence on the shift Avp= 0. Thus, for example, for benzene (~ ~ 0) and nitrobenzene (~ N 4 D), the values of Avp= O are equal to 21 and 26 cm -1, while for hexane (~ = 0) and nitromethane (~ ~ 3.1 D), Avp= 0 are 12 and 32 cm -1, respect ively . Statist ical t rea tment of the data for a romat ic solvents leads to the equation Avp= O = 1.61 ~ + 21 with r =0.85. As can be seen f rom Fig. 2, in a romat ic solvents the values of Avp= O are higher in compar ison with the aliphatic solvents close in DM (the case of solvents with weak polari ty). This indicates a supplementary interaction, which is not determined by the presence of a DM.

Thus, an investigation of a number of sys tems of PC + solvent by IR spect roscopy shows a pronounced weakening of the dipole-dipole interaction, if the dissolved substance or solvent includes a romat ic f r ag - ments . A considerat ion of the mechanism of this effect is not included within the a ims of the present com- munication. Let us note only that according to [15], in the sys tems (CH3)3PO + benzene, (CH3)3PO + toluene, there is a d o n o r - a c c e p t o r interaction of the a romat ic r ing with the phosphorus atom.

C O N C L U S I O N S

1. The interact ion of a number of phosphoryl compounds containing phenyl and phenoxyl radicals at the phosphorus with the medium was investigated by the method of IR spect roscopy.

2. The presence of a romat ic f ragments , both in phosphoryl compounds and in solvent molecules, weakens the influence of the polar i ty of the medium on the vibrat ion frequency of the P--O bonds. This is explained by a decrease in the role of dipole-dipole interact ions on account of specific interact ions with the a romat ic f ragments .

LITERATURE CITED

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1954

11. M. Tamres , J. Am. Chem. Soc., 7_44, 3375 (1952). 12. C . M . Huggins and G. C. Pimentel, J. Chem. Phys., 2._33, 896 (1955). 13. N. Nakagawa, K. Niki, Y. Takeuchi, and J. Kumagai, Chem. Let ters , 1239 (1972). 14. A . E . Lutskii and E. L Goncharova, Spectroscopy. Methods and Applications [in Russian], Nauka

(1969), p. 149. 15. Yu. P. Egorov, E. V. Ryl ' tsev, and A. S. Tarasevich, Teor . i Eksperim. Khimiya, 8, 169 (1972). 16. L. Andrews and R. Kiefer, Molecular Complexes in Organic Chemistry [Russian translation], Mir

(1967). 17. R . R . Shagidullin, V. E. Bel 'skii , L. Kh. Ashrafullina, L. A. Kudryavtseva, and B. E. Ivanov,

Izv. Akad. Nauk SSSR, Ser. Khim., 2502 (1973). 18. F . S . Mortimer, Spectrochim. Acta, 9, 270 (1957). 19. O . A . Raevskii and F. G. Khalitov, Izv. Akad. Nauk SSSR, Ser. Khim., 2177 (1973). 20. O.A. Raevskii, R. R. ShagiduIIin, I. D. Morozova, L. E. Petrova, and F. G. Khalitov, ibid.,

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1955