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

COMMUNICATION 2. RAMAN SPECTRA OF A NUMBER OF ESTERS

AND CHLORIDES OF ACIDS OF TRIVALENT ARSENIC

(UDC 543.422+ 661.781)

R. R. S h a g i d u l l i n a n d T. g. P a v l o v a

A. g. Arbuzov Chemical Institute, Academy of Sciences, USSR, Translated from Izvest iya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6,

pp. 995-998, June, 1965 Original a r t ic le submitted May 27, 1963

We had reported ear l ier [1] on data on the IR absorption spectra of a number of organoarsenic compounds. In a continuation of the invest igat ion that we had begun, we studied the Raman spectra of the compounds: (C2HsO)3As

(I) ; (n-C4HgO)3As (II) ; (n-CGHI30)3As (III); CzHs(CeHsO)2As (IV); C6Hs(C~HsO)2As (V); n- C3HTOAsC12 (VI) ;

(n- C4H90)2 As C1 (VII); n- C4HgOAs C12 (VIII).

E X P E R I M E N T A L

ISP-51 spectrographs with photographic and photoelectr ic recording of the spectrum were used to obtain the

spectrograms. The l ight source was a PRK-2 mercury-quar tz lamp, set up in a PS-44 standard i l luminator , The working current of the l amp was kept equal to 3.2 A. The mercury l ine with wave length 4358 A was the excit ing

l ine. A l iquid f i l t e r - a solution of sodium ni trate in dist i l led w a t e r - w a s used to isolate this l ine from the mercury spectrum. The entrance slit of the instrument in the case of photographic recording of the spectrum was equal to 0.040 ram; the entrance and exi t slits of the instrument with photoelectr ic recording were equal to 0.060 and 0.070 ram, respect ively , for the region 200-1600 cm-1, and 0.040 and 0.050 mm for the region of 2600-3200 crn -1. The

procedure for preparing the samples for taking the spectra was described in our preceding communica t i on [1].

D I S C U S S I O N OF R E S U L T S

Below are presented the spectrograms (Fig. 1), frequencies, and intensities in a visual 10-point scale. The letters "b" and "s" here denote "broad" and "sharp," respect ively. It shoutd be kept in mind that, for lack of a

sufficient number of samples, the spectra of the compounds (II), (III), (VIII), (VII) were taken using s m a l l e r - d i a m e - ter cuvettes than for the remaining compounds.

(1) (u, cm-i): 293 (1), 355 (0), 456 (0), 612 (i b), 661 (3 b), 806 (0), 887 (0 b), 990 (0), 1034 (i), 1058 (1), 1098 (4), 1158 (0), 1285 (0), 1356 (i), 1390 (i), 1454 (4), 1477 (2), 2973 (5), 2895 (3), 2934 (3), 2934 (10):, 2976 (7).

(If) (u, cm-1): 402 (0), 425 (0), 475 (i), 600 (i), 660 (3), 737 (i), 802 (i), 818 (2), 870 (0), 880 (0), 935 (i), 994 (i), 1020 (2), 1057 (2), 1107 (3), 1140 (1), 1230 (0), 1250 (0), 1289 (2), 1356 (i), 1375 (I), 1433 (4).

(ItI) (u , em-1) : 359 (0), 494 (0), 611 (0), 664 (2 b), 694 (0), 760 (0), 818 (0), 862 (0), 889 (1), 923 (0), 996(0), 1032 (0), 1071 (1 b), 1120 (1), 1146 (0), 1300 (4), 1377 (0.6), 1485 (4), 1458 (4), 2881 (8), 2905 (10), 2936 (6), 2964 (4).

(IV) (v, cm-l) ,. 304 (3), 314 (2), 355 (1), 557 (i), 580 (7 b), 605 (2), 654 (3 b), 722 (0), 807 (0), 895 (0), 970 (0), 1021 (i), 1040 (I), 1061 (i), Ii01 (3), 1163 (0), 1222 (3), 1285 (i), 1352 (0), 1380 (i), 1407 (I), 1456 (5), 1474 (0), 2878 (0), 2876 (8), 2931 (10), 2970 (7).

(V) (u, cm -I): 260 (3b), 3340 b), 372 (0 b), 487 (0), 546 (0), 607 (0 b), 821 (3), 643 (lb), 671 (3), 702 (0), 739 (0.5), 803 (0 b), 899 (0), 917 (0), 942 (1.5), 998 (i0 s), 1024 (4), 1048 (0), 1082 (2), 1096 (2.5), 1157 (2.5), 1184 (0.5), 1282 (I b), 1386 (0 b), 1439 (i), 1453 (2), 1480 (i), 1524 (0), 1577 (0), 1586 (5), 2868 (4b), 2925 (5 b), 2975 (2.5), 3008 (0).

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(Vl) (~, cm-1): 173 (6), 304 (0), 335 (i), 363 (8), 389 (I0), 435 (i), 503 (0), 546 (0), 610 (i), 659 (2), 700(I), 790 (i), 823 (0), 866 (i), 892 (0), 952 (0), 987 (0), 1030 (i), 1037 (0), 1086 (0), 1115 (I), 1142 (0), 1171 (0), 1208 (0), 1247 (0), 1275 (i), 1295 (i), 1341 (0), 1374 (0), 1442 (2), 288] (5), 2912 (4), 2936 (6), 2964 (4).

(VII) (v, cm-~): 253 (0), 285 (0 b), 339 (8), 353 (i), 386 (I), 482 (0), 531 (0), 613 (0), 665 (3), 696 (0), 748 (1), 813 (i), 832 (2), 880 (0), 904 (I), 944 (0), 963 (0), i001 (00), 1023 (0), ].062 (3), 1118 (3), 1145 (0), 1230 (0), 1258 (0), 1298 (3.5), 1385 (0), 1433 (2), 1448 (4), 1469 (2.5), 2869 (I0), 2906 (8), 2937 (7), 2967 (5).

(VIII) (u, cm-1): 163 (8), 190 (i), 287 (0), 352 (8 b), 385 (i0 b), 412 (3), 483 (0), 528 (0), 661 (3), 698 (0.5), 750 (0.5), 814 (0), 831 (I), 882 (0), 905 (5), 946 (0), 1057 (2), 1118 (2), 1150 (0), 1230 (0), 1258 (0), 1299 (3), 1383 (0), 1431 (0), 1449 (4), 1465 (2), 2871 (8), 2907 (6), 2935 (6), 2968 (4).

The following conclusions may be drawn from a comparison of the spectra : the frequencies of the va lence vibrations of the C - H bonds bas ica l ly possess the usual values. A comparison of the intensities permits us to re la te the lines ~2965 and 2935 c m - t to the CH s group and 2908 cm -! to the CH z group with assurance. The first two lines may belong to degenerate vibrations, split as a result of the Fermi resonance, with the overtones of the frequencies

~(CH) [2]. The third belongs to Uas CH 2. The lines u s CHs and u s CH z evident ly are not resolved by the instrument and blend into one max imum at ~2875 cm -1. It may be noted that Uas CH s in the C2HsOAs group is somewhat over- es t imated, but less than is observed in C~HsOP.

In the region from 1350 to 1480 cm -1, in contrast to the IR spectra, a more complex picture can be traced. In

general , four lines are observed here. In accord with the l i tera ture data , the lines ~s CHz at ~1385 cm -1 are very weak. The lines 5 CH2, within the interval from ~1480 to ~1460 cm -1, which are strengthened as the length of

the carbon chain is increased, are of low intensity. Rather intense are the lines 6as CH~ at ~1455 cm-~; finally, the l ine at ,-4440 cm "1 is interesting in that its intensity increases with increasing number of carbon atoms of the sub- stituents. In view of this, it may be assigned to the vibrations of the CH 2 group. A new l ine at 1407 cm -1, charac-

ter izing the CH 2 - As group, appears in the spectrum of (IV).

The following frequencies may be isolated within the region 1050-1350 cm -1. The l ine ~1300 cm -1 exhibits

a c lear relationship to the number of methylene groups. Its intensity increases from one in compounds (IV) and (V), which each contain four CH2, to four in (III) with 15 CH 2. By analogy with hydrocarbons [3], this frequency should

be assigned to the fanlike vibrations of the CH z group. The l ine with frequency 1100 cm - i in compounds (I), (IV),

and (V) is striking. Its presence has also been noted for organophosphorus compounds, containing an ethoxy group

(IV). This l ine is distinguished by its intensity and its distinctness in a l l the spectra and, consequently, is a good

ana ly t ica l character is t ic of the EtOP and EtOAs groups. This l ine and the lines ~1120, ~1060 cm -1, with intensity differing from zero in the spectra of al l the remaining compounds, may be due to the pendulum vibrations of the

CHz groups (planar and nonplanar).

We assigned the strong bands at 1020 and 1070 cm -1 in the IR spectra to the vibrations of the A s O - C bond [1].

In the Raman spectra, the lines in this region are only negl ig ible intensity, indicat ing a polar character of the bond.

The very strong l ine at ~1000 cm -1 in the spectrum of compound (V) belongs to the pulsation vibrations of

the ring.

Within the interval of frequencies from 600 to 700 cm -I, where we should expect the appearance of the

vibrations of the A s - O bond [1], lines of apprec iable intensity are observed. After an a t tent ive examinat ion, it

may be concluded that in general this is a t r iplet with a more intense middle and less intense ext reme l i n e s - "shoulders," which are at t imes diff icult to separate: 650-665, 600-610, 690-700 cm -i . The three components under considerat ion may be due, as has a l ready been noted [1], to the presence of symmet r ica l and ant i symmetr ica l [de- generate for (RO)sAs] vibrations, as well as various rotat ional isomers. The middle l ine at 660 cm -1 may be related to symmetr ica l vibrations of the atoms. It is observed with great constancy in the spectra of a l l the investigated

compounds, independent of the number of alkoxy substituents.

In the case of compound (IV), the strong l ine at 580 cm - i belongs to the vibrations of the A s - C bond [1]. In compound (V), the A s - C bond at the benzene ring should possess a higher vibrat ional frequency.

The monosubstituted benzene ring also gives several lines in this region; a whole series of compounds possess a strong l ine with frequency 610-620 cm -1 [5]. Thus, for compound (V), it may be considered that the line at 616 cm -I is re la ted to the ring, while the l ine at 672 cm -1 belongs to the A s - C bond at the ring. The l ine of A s - O is

superimposed upon them.

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0 3uo'r

200 ~00 1000 1~00 Z600 300~

II |I II

I, 200

200

I, 1

" ~ , , 4 P . . 1oo /ooo ,~'oo z6oo 3'ooo

I I I I

B00 1000 /q00 g600 3000 CITl -I

6 5

II"

2oo ~oo 1be 1~oo boo bo ~oo 1ooo

8

1ooo ~/oo 26oo s'0oo ~oo zeoo 5OO 1000 300~ fqO0 s ),, orn-1

I~80 2500 6000 ~CIII - I

Fig. 1. Raman spectra: 1) (C2HsO)3As; 2) C6Hs(C2HsO)2As; 3) (n-C4HgO)3As; 4) n- C3HTOAsCI2; 8) (n-C6HI30)3As; 8) (n-C4HgO)2AsC1; 7) C2Hs(C~HsO)2As; 8) n-C4HgOAsCi2; ve r t i ca l l ines-- l ines of mercury.

Very intense lines, which according to [6] should be assigned to the vibrations of the As-C1 bond, are observed in the spectra of the acid chlorides in the region of 300-400 cm -t . In the spectrum of the monochloride, in accord with the structure of the compound, there is only one l ine. For dichlorides, on the other hand, a doublet is observed, with m a x i m a at 360 and 390 cm "1. As our measurements showed, the l ine at 390 cm -1 is highly polar ized and

should be assigned in view of this to the symmet r ica l vibrations of the two chloride atoms. In the spectra of c o m - pounds (VI) and (VIII), an intense l ine at 170 cm -I is not iceable ; it may be re la ted to 6(AsCt2).

CONCLUSIONS

I. The Raman spectra of a number of esters and chlorides of trivalen~ arsenic acids were studied in the region

up to 3200 cm -I, and a general interpretation of them was give n.

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2. The characteristics of the AsO-C, As-OC, As--C, As-C1 and As--C12 groups were discussed.

LITERATURE CITED

I. P~ R. Shagidullin and T. E. Pavlova, Izv. AN SSSR, Ser. Khim., 1963, 2117. 2. M.V. Vol'kenshtein, M. A. El'yashevich, and B. I. Stepanov, Vibrations of Molecules [in Russian], Vol. 1,

GITTL, Moscow-Leningrad (1949), p. 512. 3. Application of Spectroscopy in Chemistry [Russian translation], Editor West, IL, Moscow (1959), p. 282. 4. I~ l~ Shagidullin, Izv. Kazanskogo Filiala AN SSSR, Ser. Khim., 6, 123(1961). 5. K. Kohlrausch, Raman Spectra [Russian Translation], IL, Moscow (1952), p. 319. 6. A.W. Reitz and P,. Sabathy, Z. Phys. Chem. Abt., B41, 151 (1938).

Al l a b b r e v i a t i o n s o f p e r i o d i c a l s in the a b o v e b i b l i ography are l e t t e r - b y - l e t t e r t rans l i t er -

a t i o n s of t h e a b b r e v i a t i o n s as g i v e n in the or ig ina l R u s s i a n journal . S o m e or al l o f th i s per i -

o d i c a l l i t e r a t u r e m a y we l l b e a v a i l a b l e in E n g l i s h t rans la t ion . A c o m p l e t e l i s t o f the c o v e r - t o -

c o v e r E n g l i s h t r a n s l a t i o n s a p p e a r s at the b a c k of th i s i s s u e .

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