I N T R A M O L E C U L A R H B O N D I N V O L V I N G T H E P = S G R O U P

R . R . S h a g i d u l l i n , N . I . R i z p o l o z h e n s k i i , UDC 539.124:547.1'118 F . S . M u k h a m e t o v , I . P . L i p a t o v a , :541.57:546.11 a n d L . I . V a c h u g o v a

The thiophosphoryl group is capable of taking pa r t in the fo rmat ion of i n t e rmolecu la r hydrogen bonds. However , in this r e s p e c t it exhibits l e s s bas ic p r o p e r t i e s than the phosphoryl group [1, 2]. We were un- a b l e to find any informat ion in the l i t e r a tu re regard ing i n t r amolecu l a r hydrogen bonds (IHB) that involve the P=S group. In o r d e r to answer this question we synthes ized d i -n -p ropy l (a-hydroxycyclopentyj) th iono- phosphonate (II) [3], diethyl (~-hydroxyisopropyl) th ionophosphonate (IV) [3] and 2 -e thy l -2 - th iono -3 ,5 ,5 - t r i - m e t h y l - l , 2 - o x a - 3 - p h o s p h o l a n o l (V) [4], and studied the tR spec t r a of dilute solutions of these compounds in CC14.

P r e v i o u s l y it w a s r epo r t ed [5] that a -hydroxyphosphory l compounds each contain two absorpt ion bands in the IR s p e c t r a of dilute solut ions in the region of the s t re tching v ibra t ions of the OH grot~p; this was explained by the exis tence of the compounds in question under these conditions as two rotat ional i so - m e r s , in one of which an IHB is r ea l i zed with the phosphoryl oxygen, while in the other an IHB is r ea l i zed with the P~r e lec t rons of the subst i tuent a t tached to the P a tom. During the cour se of the p re sen t study we es tab l i shed that the IR s p e c t r a of dilute solut ions of (II) and (IV) in CC14 (C ~ 10-4-10 -5 M) a lso each con- tain two absorp t ion bands in the reg ion of the s t re tch ing v ib ra t ions of the OH group, while (V) contains one absorp t ion band in this region. The spec t r a l p ic ture r e m a i n s unchanged on fu r the r dilution. The f requen- c ies of the m a x i m a of these bands a re given in Table 1, together with the cor responding values for the phosphoryl analogs.

F r o m Tab le 1 it follows that a -hydroxyth ionophosphoryl compounds, like the i r phosphoryl analogs [5], ex is t in dilute solutions as two rota t ional i s o m e r s . In ha rmony with the p rev ious ly made ass ignment [5], the sl ight d i f fe rences between the values given in the second column tes t i fy to the exis tence of i so - m e r s with an IHB between the OH group and the e s t e r oxygen ( i somer a).

H H ." \ .-" \

R - - O 0 S 0

P--C-- a b

(o)s / \ \ / \ \

In con t ras t to this, the values given in the fourth column for the thiophosphoryl and phosphoryl com- pounds differ subs tant ia l ly . This gives r e a son to bel ieve that the studied thiophosphoryl compounds also exis t as i s o m e r s , in which an ' IHB is accompl i shed between OH and S ( i somer b). The given data also make it poss ib le to a r r i v e at a definite conclusion regard ing the s t ruc tu re of (V). Compound (V) is an i s o m e r in which an IHB is r ea l i zed between the OH and P=S groups . Consequently, the OH and P=S groups a r e found in the c i s -o r i en t a t ion with" r e s p e c t to the plane of a f i v e - m e m b e r e d r ing. A lower value of ~OH for (V) tes t i f ies to a s t rengthening of the IHB, i .e. , to a m o r e p lanar s t ruc tu re of the r ing that is fo rmed by the IHB. In turn, it i s na tura l to a s soc ia t e the la t te r with the cyclic s t ruc tu re of the molecu le .

A c o m p a r i s o n of the va lues given in Table 1 d i sc loses that in the fo rmat ion of the IHB the P=S group is r espons ib le for a g r e a t e r shift of A~Ot t than the P =O group. The r e v e r s e si tuat ion when going f r o m in t e rmo lecu l a r H bonds to IHB was ment ioned e a r l i e r [6-9]. A conclusive explanation of this phenomenon has apparent ly not been obtained as yet . In [6] it was ment ioned that the subst i tuents , which include SR and

A. E . Arbuzov Inst i tute of Organic and Phys ica l Chemis t ry , Academy of Sciences of the USSR. T r a n s l a t e d f r o m Izves t iya Akademii Nauk SSSR, Ser iya Khimicheskaya, No. 12, pp. 2800-2801, D e c e m - ber , 1972. Original a r t i c le submit ted January 10, 1972.

�9 1973 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th 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.

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TABLE 1. Frequency of Stretching Vibra t ions of OH Group in Dilute CCt 4 Solutions

Compound ~OH Compound VOl~i

/CH2--CHz (CH30)~ P--C\ 1

II I GH2--CH~ 0 OH

/ C H 3 (CHaO)2P--C< 11 I CH3 0 O H

3597 (I) 3572

(ID 3598 3576

/ C K : - - C H , n-C~H~O)~P--C~ I ~ ( I I )

II I CH2--CH~ S OH

/CH3 (C.~HsO)~P--C( (IV)

11 I \ C H 3 S OiI

/0--G(CH~)~ C,H~O-- P ~ ! (V)

II C--CH~ S / \

GH~ OH

3592 3533

359t 3527

3510

OR groupings, in the 2-subs t i tu ted phenols can be a r r anged on the bas i s of the value of AvOH of the IHB in an o r d e r that is in ha rm ony with the ionizat ion potent ia ls . The authors of [7, 8] be l ieve that invers ion at the IHB is caused by an i nc rea se in the s t r eng th of the H bond involving the S a tom due to i ts g r e a t e r a tomic rad ius . At the same t ime, it was found [9] that, in con t r a s t to the AvOH , the assoc ia t ion constants , and consequently a lso the enthalpies of fo rmat ion of the IHB in compounds of genera l f o rmu la C2Hs-X - ( C H 2 ) n - O H (n = 2, 3, 4; X = O, S) a r e not iceably s m a l l e r for sulfur . Our data, which c o r r o b o r a t e d the phenomenon of invers ion on a new c l a s s of compounds, apparen t ly also tes t i fy in suppor t of the definite ro le of the a tomic rad ius of the proton accep tor in the IHB for the values of A~OH. If the usual values of the bond lengths and angles a r e taken for the molecule of organophosphorus compounds [10], then for a p lanar f i v e - m e m b e r e d r ing, fo rmed because of the IHB, the d is tance (H) O . . . S p roves to be approx i - m a t e l y 0.1 A (AR = 0.1 A) s m a l l e r than the sum of the van der Waals radi i of the O and S a t o m s . For the co r respond ing oxygen analog (containing a P=O bond), under the s a m e assumpt ions , AR is - 0 . 2 ~ i .e. , the d is tance O . . . O is g r e a t e r than the sum of the a tomic rad i i .

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

The IR spectra were taken on a UR-10 instrument. Compounds (1)-(IV) were obtained by the addition of dialkylphosphorous acids to the appropriate ketones [3]. Compound (V) was obtained as described in [4] from diethylthiophosphorous acid and diaeetone alcohol in the presence of sodium ethylate.

CONCLUSIONS

I. Noncyclie c~-hydroxylthionophosphoryl compounds exist in dilute solutions as rotational isomers, in which an intramolecular hydrogen bond is realized.

2. The shift in the frequency of the stretching vibrations of the OH group in the formation of an intra- molecular hydrogen bond with the P=S group in e~-hydroxythionophosphoryl compounds is greater than in the case of the P=O grouping in the a-hydroxyphosphoryl analogs, which is apparently associated with the dif- ference in the radii of the S and O atoms.

1 .

2.

3 .

4. 5.

6.

L I T E R A T U R E C I T E D

L. J . Bel lamy, New Data on the In f r a r ed Spect ra of Complex Molecules [Russian t rans la t ion] , Mir (1971), p. 228. L. I. Vachugova, I. P . Lipatova, S. A. S a m a r t s e v a , and R. R. Shagidullin, Ma te r i a l s of the Scient i - fic Conference of the A. E. Arbuzov Inst i tute of Organic and Phys ica l C h e m i s t r y [in Russian] , Kazan ' (1971), p. 51. A. N. Pudovik, I. V. Gur 'yanova , and E. A. I shmaeva , Reac t ions and Study Methods for Organic Compounds [in Russian] , Vol. 20, Khimiya (1968). N. I. Rizpolozhenski i and F. S. Mukhametov, Izv. Akad. Nauk SSSR, Ser . Khim., 210 (1967). Yu. Yu. Samitov, R. R. Shagidullin, F. S. Mukhametov, and N. I. Rizpolozhenski i , Ma te r i a l s of the Scientific Conference of the A. E. Arbuzov Inst i tute of Organic and Phys ica l C h e m i s t r y [in Russian] , Kazan ' (1970), p. 69. / A. E. Lutskii , Teo re t . i E k s p e r i m . Khim., 95 (1971).

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7. R.A. Nugwist, Spectrochim. Acta, 19, 1655 (1963). 8. L . J . Bellamy and R. J. Pace, Spectrochim. Acta, 25A, 318 (1969). 9. N. Mori, Y. Takahashi, and Y. Tsuzuki, Bull. Chem. Soc. Japan, 40, 2720 (1967).

10. R . E . Sutton (editor), Tables of Interatomic Distances and Configuration in Molecules and Ions, Special Publication No. 11, London (1958).

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