R O T A T I O N A L I S O M E R I S M O F D I C H L O R I D E S OF

C E R T A I N A L K Y L T H I O P H O S P H O R I C A C I D S

R. R. S h a g i d u l l i n , I . A. V a n d y u k o v a , a n d O. A. R a e v s k i i

UDC 54L62:547.1'I18

This communicat ion presents the resu l t s of an investigation of the s ter ic s t ructure of the compounds of the ser ies : ROP(S)CI2, where R = C[~-I 5 (I), Call 7 (II), iso-CsHT: (III), C4H 9 {IV), C6H 5 (V). According to [1], compound {I) exists in the liquid and in solutions as a mixture of rotational i somers ; however, the authors of [1] did not identify the confo rmers . For compounds (II) and (V), there is no information on spectral in- vest igat ions.

We obtained the IR and Raman spec t ra of (I)-(V) in var ious phase states -- gas, liquid, c rys ta l -- as well as in the case of variat ion of the dielectr ic permeabi l i ty of the medium and the tempera ture . In addi- tion, the dipole moments of (I)-(V) in solutions of CC14 at 2 9 8 4 were determined.

For the investigated compounds, in the spec t ra of the liquid and solutions, a doublet nature of the number of bands is distinctly observed. The ratio of the intensities of their components va r i es depending on the dielectr ic permeabi l i ty of the solvent and tempera ture , which may be evidence of thermodynamic equil ibrium of the s ter ic fo rms . In the molecules of ROP(S)C12 rotational i somer i sm is possible, due to rotation around the P - -O bond and in the hydrocarbon residue R. Since our investigations are associated with i somer i sm due to rotation in the phosphorus f ramework, for the investigation we selected the bands of the so-ca l led valence vibrat ions of the p = Sand P- -CI bonds (Table 1). I s o m e r i s m in the hydrocarbon portion will not be considered. The ass ignments of the f requencies of the vibrat ions of the p =S and P- -CI bonds in Table 1 are based on the available data [1, 2] and on our calculation of the f requencies and fo rms of the normal vibrat ions of the methyl dichlorothiophosphate molecule (VI) [3].

In the spec t ra of solutions in nonpolar medium (n-hexane, CCI 4) and in the gas phase of compounds ff)-(V), an equilibrium of two s ter ic fo rms is observed, with a c lea r predominance of the conformer de- noted in Table 1 as i somer b. In the more polar medium [solutions in (CH3)2CO , CH3CN], the equilibrium is shifted in the direction of the i somer a. Consequently, in accord with [2] for (I)-(V) the conformer a

TABLE 1. Frequenc ies of the Valence Vibrations (cm -1) of P--C1 and P =S Bonds of the Molecules ROP(S)C12

Compound Isomer

(i)

(ii)

(iii)

(iv)

(v)

"~(PGI~)

IR Raman

470 476 486 490 446 437 484 486 487 49t 504 507 474 477 488 49O

447 4~ 460

Vas(PClD

IR Raman

528 535 550 558 528 535 550 555 527 530 548 555 529 532 554 558 533 537 570 572

~(P=s)

IR

725 699 7i4 695 7t8 682 712 697 7t4 703

Raman

725 702 7ig 697 722 690 715 699 715 705

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Branch of theAeademy of Sci- ences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1527-1531, July, 1975. Original article submitted August 6, 1974.

�9 76 Plenum Publishing Corporation, 22 7 West 17th Street, New York, N. Y. 10011. No part o f 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.

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Z S L ~ ~, , I } - , : ~" . . . . . . ~ .

75 ~

I x t ~ ~ . , . . _ _ L

5g "

., 25

g 50g 500 7~70 ]2gO 15gg 20DO

b

J

C

2r 280o 3oo0-~ cra 11

3100 2903 lqg~ 7ZO0 ;'DDD 8DD 500 qDD 200 u, cm --~

Fig. 1. IR and Raman s p e c t r a of compound (I): a) gas phase; b, d) liquid; c, e) c rys t a l l i ne phase .

p o s s e s s e s a l a r g e r dipole moment (DM). In the Raman spec t r a the i s o m e r a has both po la r i zed ~nd de- po la r i zed lines; for i s o m e r b all the l ines a re po la r ized to the same degree . This g ives a ba s i s for b e - l i e v i n g t h a t t h e i s o m e r a p o s s e s s e s a more s y m m e t r i c a l f r a m e w o r k of C12P(S)OC than the i s o m e r b.,

F igure 1 c i t e s as an example the s p e c t r a of compo~mds (D in va r ious phase s ta tes . A compar i son of the s p e c t r a of compounds (I)-{V), as well as the p rev ious ly studied (VI) [3] in the liquid and solid ph ase s g ives evidence of s tabi l izat ion of the i s o m e r a in the c r y s t a l for (V[) arid {i). F o r ([H) and (V) the s p e c t r a in the c rys ta l l ine phase a re m o r e complex in compar i son with (I) and (~TI), and we a re not in te rpre t ing them at the p r e s e n t t ime. As fo r {iI) and {IV) we were unable to obtain a c rys ta l l ine phase under the e x p e r i m e n - tal conditions (cooling to l l0~

The ra t io of Lhe absolute in tegra l in tens i t ies of the bands belonging to di f ferent c o n f o r m e r s , d e t e r - mined by analogy with [2, 4], p e r m i t s an es t imat ion of the re la t ive amounts of the Conformers p a r t i c i p a t - ing in the equi l ibr ium. Table 2 c i t e s the re la t ive contents of the i s o m e r s in solutions of the inves t igated compounds in CC14 and CH3CN, found in th is way.

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T A B L E 2. Rat io of the C o n f o r m e r s in Solut ions

I " GCI, b" CIt~CN om-j - V poun~isomel: a [isomer isomer a isomer

(I)[ 0,2 0,8 0,4 (H.)[ 0,2 0.8 0,4

(IH)[ 0,2 018 0,4 (iv) I 0,3 o,7 o,5 (v)l 0,~ 0,s 0,3

(vI)[ 0,., o.7 0.4

0,6 0,6 0,6 0,5 0,7 0,6 [3]

T A B L E 3. E n e r g y and En t ropy D i f f e r ences of Rota t ional I s o - m e r s

AHb- a (~'50), cal ASb-a (~ 0.3) cal Corn- I/mole (liquid) " /too1 .deg

pound ]

(i) ( i i )

([ii) 0v) (v)

IR Raman

--450 --550 --600 --~0 --400 --400

--450

--3,02 --4,06 --3,04 --2,51 --3,50

T A B L E 4. Coe f f i c i en t s of Equat ions fo r Calcula t ion of the Dipole M o m e n t s in CCI 4 Solut ions [6]

C o r n - v P0, C m s ix, D pound

(II) (IlI) (Ix) (V)

10,500 9,357

10,357 9,071 6,885 9320

0,370 0,t43 0,228 0,291 0,502 0,249

i90,465 187,885 206,646 191,9t6 152,747 164,172

3,04 3,02 3,i6 3,04 2,72 2,82 in1

The change in the in tens i t i es in the c a s e of va r i a t ion of the t e m p e r a t u r e p e r m i t t e d an e s t ima t ion of the d i f f e r - ence of the in te rva l e n e r g i e s (AH) and en t ropy (AS). The va lues of AH and AS of ro ta t iona l i s o m e r s , ca lcu la ted a c - co rd ing to the well known f o r m u l a [4, 5] f o r the compounds s tudied a r e given in Table 3.

As has a l r e ady been ment ioned, the data obtained a r e ev idence of a p r e d o m i n a n c e of the l e s s po la r n o n s y m - m e t r i c a l f o r m -- i s o m e r b - - in nonpo la r med ium at 298~ fo r all the c o m p o u n d s of the inves t iga ted s e r i e s , a l though the o the r i s o m e r is e n e r g e t i c a l l y p r e f e r r e d . This

ind ica tes a l a r g e r s t a t i s t i ca l weight of the b - f o r m . Table 4 p r e s e n t s the expe r imen t a l va lues of the DM of c o m p o u n d s (I)-(V) in so lu t ions of CCI 4 at 298~ Since the m o m e n t of the h y d r o c a r b o n r e s idue is taken as cons tan t , ca lcu la t ion l eads to the s a m e va lues of the DM of compounds (I)-(V) and the p r e v i o u s l y ca l cu la t ed (VI) [3]�9

As poss ib le c o n f o r m a t i o n s we c o n s i d e r e d f o r m s with ro ta t ion of the O--R g roup r e l a t ive to the P = S g roup by 0 ~ - - c i s , 60 ~ - - gauche , 120 ~ -- sh ie lded (from the P--C1 bond), and 180 ~ - - t r ans . In the c a l - cu la t ion we used the m o m e n t s of the bonds a c c o r d i n g to [7].

The expe r imen ta l va lues of the DM p r o v e d i n t e rmed ia t e in c o m p a r i s o n with the ca lcu la ted va lues , which a l so c o n f i r m s the ex i s t ence of an equ i l ib r ium of the c o n f o r m e r s . Using the equat ion #2ex p = #2x + #~ �9 ( l - -x) , wr i t ing the e x p e r i m e n t a l DM and the n u m b e r of c o n f o r m e r s , and taking into account c o n s i d e r a t i o n s on t he i r s y m m e t r y , s t a t i s t i ca l weights , and AS, we can c o n s i d e r tha t in a CC14 solut ion an equ i l ib r ium of the t r a n s - and g a u c h e - f o r m s is r e a l i z e d . Th i s a g r e e s with the shape of the c u r v e of the van de r Waals in- t e r a c t i o n s of the unbonded a t o m s [8].

A c o m p a r i s o n of the data of Table 2 with the expe r imen t a l DM leads to an apparen t con t rad ic t ion : with s o m e d e c r e a s e in the amount of the t r a n s - f o r m in nonpo la r m e d i u m in (III) in c o m p a r i s o n with (VI), t he re is no d e c r e a s e in the DM. An ana logous phenomenon was de tec ted in [9] and expla ined by an i n c r e a s e in the t w o - f a c e d angle c~ in compounds with a b r a n c h e d h y d r o c a r b o n r e s idue on account of an i n c r e a s e in the s t e r i c i n t e r ac t i ons with the (thio) phospho ry l g roup

s

C1 1

The m a t e r i a l obtained in th is work is a suppIementa ry conf i rmat ion of this explanation.

EXPERIMENTAL

The IR spectra were obtained on a UR-10 instrument, the Raman spectra on a Coderg instrument.

The capacitance of the solutions was measured on an IDM instrument [i0]. The indices of refraction were

determined on an IRF-23. The experimental conditions were described earlier [3]. The constants of the

substances corresponded to the literature data.

The authors would like to express their gratitude to V. K. Khairullin for his attention to the work and

f o r p rov id ing the inves t iga ted s e r i e s of compounds , a s well a s V. I . Kova lenko f o r h i s d i s cus s ion of the r e -

sul ts .

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CONCLUSIONS

I. The question of the steric structure of the compounds- ROP(S)CI 2, where R ~ C2H 5, C3H ~, iso- C3H7, C4H9, C6H5, is discussed on the basis of the vibrational spectra and dipole moments.

2. The relative amounts of the conformers participating in the equilibrium are estimated. In non- polar medium at room temperature, the less polar nonsymmetrical gauche-form (80%) predominates, with energy preference for the more polar trans-isomer.

3. An increase in the two-faced angle SPCR in the transition from CH3OP(S)CI 2 to compounds with a more branched hydrocarbon residue is suggested for the gauche-form.

LITERATURE CITED

i. R.A. Nyquist, W. W. Muelder, and M. N. Wass, Spectrochim. Acta, A26,769 (1970). 2. A.F. VasiITev, Zh. Prikl. Spektroskopii, 6, 485 (1967). 3. R.R. Shagidullin, O. A. Raevski[, and I. I. Vandyakova, Izv. Akad. Nauk SSSR, Ser. Khim.~ 80

(1975). 4. S. Midzusima, The Structure of Molecules and Internal Rotation [Russian translation], IL (1957). 5. Yu. A. pentin and V. M. Tatevskii, Izv. Akad. Nauk SSSR, Set. Fiz., 26, 1241 (1962). 6. E. Guggenheim and J. pru, Physicochemical Calculations [Russian translation], IL (1958). 7. O.A. Raevskii, Fo Ko Khalitova, and T. A. Zyablikova, Izv. Akad. Nauk SSSR, Ser. Khim., 348

(1972). 8. E. El[el, N. All[nger, S. Angyal, and Go Morrison, Conformat[onal Analysis [Russian translation],

Mir (1969). 9. O.A. Raevskii, in: Problems of Stereochemistry [in Russian], Izv-vo Kievskogo Un-ta (1975), p. 5.

i0. R. Sh. NigmatulIin and M. R. Vyaselev, Zavod. Lab., 300, 500 (1964).

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