STRETCHING VIBRATIONS OF = C -H BONDS IN PHOSPHOLENES

R. R. Shagidullin, A. V. Chernova, D. F. Fazliev, A. O. Vizel', a n d V . K . K r u p n o v

UDC 541.5:541.124: 547.1'I18

A study was made of the IR spectra of the oxygen- and sulfur-containing derivatives of 2-phospholene and 3-phospholene (I)-(VI) in the region where the stretching vibrations of the -- C -H bonds appear (Table !). The number of u= C-H bands in the spectra of the investigated compounds corresponds to the number of hydrogen atoms at the double bond (see Table i, where (I) has two bands, while (III)-(VI) each have one band). An exception is (If), in whose spectrum above 3000 cm -I is observed only one band at 3060 em-l. * Since the v= C-H frequency, associated with an a-hydrogen [in (Ill) and (V)], is higher than the v= C-H of a fl-hydrogen [in (IV) and (VI)], then the low-frequency band for (i) (3038 cm -i) should be associated pre- ferentially with the ~-hydrogen, and the high-frequency band (3067 cm -I) with the a-hydrogen.

When going from the pure state of the compounds to their dilute solutions in CCI 4 it was established that the position of the v= C -14 in the IR spectrum depends on the distance between the hydrogen taking part in the given vibration and the phosphorus atom. In the case of the A3-isomers the position of the u= C-H(fl) band remains unchanged (Fig. I, Ib and id). The 3038 cm -I band also behaves in a similar manner (Fig. i, la). At the same time, the p=C_H(a) in the A2-isomers are shifted to 3080-3083 em -I, in which con- nection this shift is accompanied by a decrease in the intensity of the bands (Fig. in, b). These changes a re

I b P d -

o i!, //iim

1 I f I ] I I I I I ,

Y##O Y/O# JO~O Y'~O ~,, cm -z

F i g . 1. I n f r a r e d spec t ra o f compounds: a) (I); b) (II); c) (III); d) (IV); 1) pure c o m - pound; 2) solution in CC14 (~1 �9 10 -1 m o l e / l i t e r ) .

mos t dis t inct in the s pec t rum of (I), since the v = C-H(fl) band (3038 em-~)doesno t ch an g e its posi t ion and can s e r v e as an in ternal s tandard . In thei r c h a r a c t e r , the ment ioned changes in ~=C-H(a ) co r r e spond to the signs of the ap -

c pea rance of an i n t e rmolecu la r hydrogen bond [2, 3]. The second p a r t n e r in the fo rmat ion of the H - c o m p l e x can be e i ther the phosphoryl or the

. ~ z x/^~ s thiophosphoryl grouping [4]. As is known, the P a tom, independent of ~ / / / \~ its valence state, exhibits acceptor properties [5]. Consequently, it

may be assumed that the phosphorus-containing fragment of the molecule

, ~ , J r ~_ * Based on the symmetry of the molecule there should be ~To vibrations: A' A" v= C-H and V=C_H, the frequencies of which are apparently very close.

A high value of the u= C-H frequency for (If) when compared with (IV) and (VI) is probably due to the absence of an alkyl substituent at the double bond in compound (II) [I]. t

i

i t I ~ 1 I P i l l _

TABLE I. The Compounds

R--C=fiH. --X R--G--CH2-- ,..X

H~--CH/ \el H~--Cm/-\el (I), (liD, (V) OIL (IV), (u

. o o CH3 CH3 L S

A'- Isomer (~=C--H (.3), ~=C--H (~),

CITI "I)

A a- I S o m e r ("=C--H (~), cm -t)

(i) (3038, 3067) (m) (3o62)

(v) (3063)

(II) (3060) (Iv) (3041) (vD (3039)

A. E. Arbuzov Inst i tute of Organic and Phys ica l Chemis t ry , Kazan 'Branch of the Academy of Sci- ences of the USSR. T r a n s l a t e d f rom Izves t iya Akademi i Nauk SSSR, Ser iya Kh imicheskaya , No. 7, pp. !611-1613, Ju ly , 1974. Original a r t i c l e submit ted Sep tember 30, 1973.

�9 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 an), 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.

].533

by a t t rac t ing the e lec t ron cloud of the double bond, inc reases the labil i ty of the ~-hydrogen. The f l -hydro- gens have a less "acid" cha rac t e r due to the i r g r ea t e r distance f rom the e lect rophi l ic center .

By employing NMR spec t roscopy, the authors of [6] detected a dec rease in the e lec t ron shielding of the P nucleus in the cor responding A2-isomers that contain a t r iva len t phosphorus atom. They deemed this to be proof that d - ; conjugation exis ts between the unshared e lec t ron pair of the P(IH) atom and the multiple bond. In view of the above d iscussed resu l t s it is c l ea r that this explanation is not the sole one. I t is pos - sible to assume that a d e c r e a s e in the e lec t ron density on the P nucleus may be par t ia l ly due to its shift to the hydrogen bond = C - H . . . P(III).

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

The IR spec t ra were taken on a UR-20 spec t rophotometer , using a sl i t p rog ram of 4 and a record ing ra te of 32 c m - i / m i n . Compounds (I)-(IV) were synthesized as desc r ibed in [7]. The A2_ and A3-isomers were isolated as descr ibed in [8, 9]. The sulfur-containing analogs were obtained as descr ibed in [10]. The CC14 was pur i f ied in advance as desc r ibed in [11].

CONCLUSIONS

I. In the IR spectra of the oxygen- and sulfur-containing derivatives of 2-phospholene and 3-phos- pholene the stretching vibrations of the = C -H bond differ in their properties for the ~- and fi-hydrogens.

2. The (~-hydrogens a re more "ac id , " and apparent ly a re capable of forming weak H bonds.

i.

2,

3. 4.

5.

6. 7.

8.

9.

I0. ii.

i . L.

P.

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

L. M. Sverdlov, M. A. Kovner , and E. P. Krainov, Vibrational Spectra of Polyatomic Molecules [in Russian], Nauka (1970), pp. 353, 355. G. C. P imenta l and A. L. McClellan, The Hydrogen Bond [Russian t rans la t ion] , Mir (1964).

V. Iogansen, Dokl. Akad. Nauk SSSR, 164, 610 (1965). J . Bel lamy, New Data on In f ra red Spectra of Complex Molecules [Russian t ranslat ion] , Mir (1971),

308. E. N. Tsvetkov, D. I. Lobanov, and M. I. Kabaehnik, Teor . i l~ksperim. Khim., 1_, 729 (1965). L. D. Quin, J . J . Breen , and D. K. Myer s , J . Org. Chem., 36, 1297 (1971). B. A. Arbuzov, A. O. V ize l ' ,R . S. Giniatullin, and Yu. F. Tar---enko, Izv. Akad. Nauk SSSR, Ser.

Khim., 1848 (1972). B. A. Arbuzov, A. O. Vize l ' ,O . A. Raevskii , Yu. F. Tarenko , and D. F. Fazl iev, Izv. Akad.

Nauk SSSR, Ser. Khim. , 1882 (1968). B. A. Arbuzov, A. O. Vize l ' ,O . A. Raevski i , Yu. F. Tarenko , and L. E. Pe t rova , Izv. Akad.

Nauk SSSR, Ser. Khim., 460 (1969). B. A. Arbuzov, V. K. Krupnov, and A. O. Vize l ' , Izv . Akad. Nauk SSSR, Set. Khim., 1177 (1973). A. I. Serebryanskaya , T. A. Amanchyan, and A. I. Shatenshtein, Zh. Obshch. Khim., 4__00, 880

(1970).

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