I N V E S T I G A T I O N O F T H E H Y D R O G E N B O N D I N G

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

C H L O R O F O R M BY I R S P E C T R O S C O P Y

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

UDC 541.57:546.11: 547.1' 118 :

547.412.123 : 543.422.4

The ability of phosphoryl compounds to form H bonds with weak proton donors such as HCC13 has scarce ly been studied [1, 2], although a quantitative evaluation of this proper ty is of in teres t for the study of the in termolecular interact ions between phosphoryl compounds and HCC13. As a continuation oi [3, 4], we have undertaken a study of the IR spect ra of several sys tems of phosphoryl compounds with HCC13 and CC14 in the region of the stretching (VCH) and overtone of the deformation (25CH) vibrations of the C--H group of chloroform. The absorption region of the stretching vibration of the P = O group (~ p = O) in solu- tions of phosphoryl compounds in CC14 and HCC13 has also been considered.

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

The phosphoryl compounds were synthesized by the usual methods. The solvents were tested for the absence of mois ture according to their IR spect ra in the region of the stretching vibrations of the hydroxyl group. The IR spect ra were recorded on a UR-20 spectrometer . The reproducibil i ty of the frequencies was + 1 cm -i. Cuvettes made f rom NaC1 with optical paths of 0.005 and 0,011 cm and phosphoryl concen- t ra t ions of ~ 0.1 M were employed for the work in the absorption region of vp = O o The vCH region was recorded with optical paths equal to 0.06 and 0.109 cm and HCC13 concentrat ions equal to 2.5 and 0.05 M, respectively. In determining the association constants Kas s = Cc/C a �9 Cd 2, where C c, Ca, and C d are, respectively, the equilibrium concentrat ions of the complex, the acceptor, and the proton donor, the value of C d was measured with the aid of a calibration curve of the optical density of the 25CH band as a function of the concentration in binary mixtures with CC14 at various temperatures . The dielectr ic constant of the (Me2N)3PO + HCC13 + CC14 sys tem was determined by the "zero-beat" method.

DISCUSSION OF RESULTS

In a prexrious study of hydrogen bonding in phosphoryl compound + weak proton-donor systems [i], the VCH band of the proton donor served as the working band. We also considered this vibration in several

TABLE 1

up = O in up ~ O in Shift of the K~s / Compound. CC14, HCC13, 25 CH~ (liter2/ l --all,

..... tone o~ ~ 2 kcal/mole cm "l cm't IHCCI~,em- I mole)

EtaPO (Me~N)3PO PhEtOP(O)Et (EtO)2P(O)Et (MeO)~P(O)Me (PrO):P(O)SMe (Et O)~P(O)CH-2CI (EtO)~P(O)C1 (PhO)aPO (EtO)P(OICI2 PhOP(O)C12 CI~PO

1i76 t 209 t2i6 1250 1249

t250, 1260 t265

t280, t293 1297, i3t2 t293, t313 t302, 1309

t305

1i52

t242 t242, 1250

1256 1278, i288 1292, t306 i288, t307 i298, i306

i296

83 83 75 70 6t~ 64 64 54 5O 49 4O 39

4,t4

0,t9

oS

2,5

2,2

t,2 1,2

05

A. E. Arbuzov Institute of Organic and Physical Chemistry, Academy of Scier~ces of the USSR, Kazan' Branch. Transla ted f rom Izvest iya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 798- 801, April , 1976. Original art icle submitted April 29, 1975.

�9 Plenum Publishing Corporation, 227 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 o f the publisher. A copy o f this article is available from the publisher for $15.00.

778

2qoo 2500 v, cm -1

8

q, 0

310

/

I I I I ~

1 2 ? (fVl6zN)a PO:HCCI, a

Fig. 1 Fig. 2 Fig. 1. Inf rared spec t ra in the region of the 26CH overtone of ch loro- form: 1) HCC13 + CC14; 2) HCC13 + CC14 + (MeO)2P(O)Me; 3) HCC13 + CC14 + (Me2N)3PO. CHCC13 "~ 2M, CpC ~ 0.2-0.5 iYi.

Fig. 2. Dependence of the dielectr ic constant (~) on the rat io of the mola r concentrat ions (Me2N)3PO : HCC13 in CC14 solutions. The total concentrat ion of the components in CC14 was 1 mole / l i t e r .

systems. When (Me2N)3PO is added to an HCC13 + CC14 solution, a broad band, whose position is at 2974 in the presence of a large excess of HCC13 and at 2967 em -i in the presence of equal (1VIe2N)3PO and HCC13 concentrat ions, appears on the low-frequency side of the vCH band of HCC13 (3020 cm-i). Similar changes are also observed in this region of the spect rum for other phosphoryl compounds. Because of the strong absorption in the 2800-3000-cm -1 region by the C--H groups and the small difference between the f re - quencies of the free and bound C--H groups of chloroform, in many cases it is difficult to use the VCH vibration fc r a quantitative evaluation of the hydrogen bonding. Irt these cases it is more convenient to use the 26CH overtone [5]. The 25CH band of chloroform in CC14 at 2400 cm -i has a shoulder at 2432 cm -1, L e., it appears in a region usually f ree of absorption. The frequency of the 25CH band remains unchanged within the accuracy of the experiment as the HCC13 concentrat ion in CC14 is var ied f rom 0.05 to 4.5 lVI. This indical:es that the effect of the se l f -associa t ion of HCCI 3 on this band is small. This is consistent with the insignificant effect of the se l f -associa t ion of HCC13 on the chemical shift of HCC13 in the P1VIR spec t ra [6].

When phosphoryl compounds are added to a solution of HCC13 in CC14, a new absorption band appears in the regio:~ of the 25CH band of the f ree C--H groups of chloroform on the high-frequency side (Fig. 1). The shift of the 25CH band is accompanied by a decrease or an increase in intensity, in agreement with the data in [7]. These spect ra l changes depend on the nature of the substituents on the P = O group (see Fig. 1). 1Vioreover, the shift of the 25CH band (as in the case of vCH) depends on the rat io of the HCC13 and phosphoryl concentrat ions in the CC14 solution. The 25CH shift is somewhat smal le r in the presence of excess HCC13 than in the presence of an excess of the phosphoryl compound. This may be due to the formation of hydrogen-bonding complexes of different composit ions.

It has previously been concluded that 1 : 1 and 2 : 1 complexes exist in the case of the HCC13 + (CH3)2CO system [8]. The shape of the dependence of the dielectr ic constant of the (Me2N)3PO + HCC13 + CC14 sys tem on the composition (Fig. 2) conf i rms the formation of two associate species, viz., PC.HCC13 and PC-

2HCC13 (where PC is the phosphoryl compound}. The f irs t causes a slightly g rea te r shift in the 25CH~ The data in Table 1 re fe r to an experiment with excess HCC13, i.e., mainly charac te r i ze the P C . 2HCC13 c o m - plexo The measured values of Kas s a n d - A H for a number of sys tems are listed in the table. The enthal- pies of formation of the complexes were found from the dependence of In Kas s on the tempera ture (in the 20-80 ~ range) with considerat ion of the composition of the PC ~ 2HCC13 and were recalculated per one H bond. An analysis of the data in Table 1 leads to the conclusion that there is a corre la t ion b e t w e e n - A H and the 25Ct t shift, v i z . , - A H = 0~ , r = 0~176

A plot corresponding to this equation does not pass through the coordinate origin, i . e . , the equation is violated in the case of very weak H bonds with HCC13 (--zkI-I < 0.5 kcal/mole) . The 25Ct t shift, Kass, and --AH vary as functions of the nature of the substituents on the phosphorus atom. Nuclear magnetic resonance has revealed [4] that the following dependence holds for solutions in CC14: --AI-I(+ 0.2) = --0o25Zz* + 3.0. The following s imi lar relat ionship follows f rom our data: --AH = -- 0.272:~* + 2.9. It is obvious that this equation also does not apply to the --L~I < 0.5 kca l /mole region.

779

When we go f rom solutions of phosphoryl compounds in CC14 to solutions in HCCI~, we obse rve a shift of the vp = O band toward lower f requencies (see Table 1). The dec rea se in ~p ~ O in HCC13 cannot be at t r ibuted only to H bonds. In solvents which do not have pro ton-donor p r o p e r t i e s but do have a dipole momen t the re is also a dec rea se in the f requency of the vp = O band of phosphoryl compounds owing to the d ipo l e -d ipo l e in teract ion [3]. The fo rmula der ived for dimethyl methylphosphonate (DMMP) in [4], Avp - - O = 4.76 ~ + 12, where ~ is the dipole momen t of the solvent, can be used to evaluate the shift in vp = O for DMMP in HCC13 due to the d i po l e -d ipo l e in teract ion (Avp _= O = 17 cm-1). The exper imenta l value of Avp = O for DM/VIP in HCCI~ equals 32 cm -1. The dif ference between these values (15 cm -1) ap- parent ly r e f l ec t s the influence of the H bonding. Thus, the change in vp = O under the effect of hydrogen bonding with HCC13 is of the same oJ:der of magnitude as that due to t h e d { p o l e - d i p o l e interact ion. In the genera l case , the &vp ___ O resul t ing f rom the t rans i t ion f rom the gaseous phase to a solution is due to the p re sence in the phosphoryl compound + HCC13 sys t em of s eve ra l types of i n t e rmolecu la r in teract ions; the re fore , i t cannot r e f l ec t the e lec t ron-donor ability of the P = O group, as was a l ready pointed out in [9].

In conclusion, we note that the doublet na ture of the vp = O band of for some phosphoryl compounds is due to rota t ional i s o m e r i s m . The s i m i l a r values of Avp = o f o r the i s o m e r s of thephosphory l c o m p o u n d s - indicates that the na ture of the in terac t ion with HCC13 is the s ame [3].

CONCLUSIONS

1. In phosphoryl compound + HCCI3 + CCI 4 systems, hydrogen-bonding complexes form with chloro- form with 1 : 1 and ~ : 2 compositions.

2. The enthalpy of formation of a hydrogen bond between a phosphoryl compound and HCCI 3 has been evaluated, and it correlates linearly with the shift in the overtone in the range measured~

3. A linear correlation of --AH with the sum of the Taft constants of the substituents on the phosphorus has been found.

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

1. M . W . Hanson andJ . B. Bouck, J . Amer . Chem. Soc., 7._99, 5631 (1957). 2. T. G r a m s t a d and Q. 1Vinndheim, Spectrochim. Acta, 2_88, 1405 (1972). 3. R . R . Shagidullin, V. E. Be l ' sk i i , L. Kh. Ashraful l ina, L. A. Kudryav tseva , and B. E. Ivanov,

Izv. Akad. Nauk SSSR, Ser. Khim., 2502 (1973). 4. R . R . Shagidullin, V. E. Bel ' sk i i , and L. Kh. Ashraful l ina, Izv. Akad. Nauk SSSR, Ser. Khim.,

2034 (1974). 5. W . E . Thompson and G. C. Pimente l , Z. E lec t rochem. , 6._44, 748 (1960). 6. G . R . Wiley and S. J. Mil ler , J. Amer. Chem. Soc., 9_.44, 3287 (1972). 7. G. P imente l and O. McClellan, The Hydrogen Bond, W. A. F r eeman , San F ranc i sco (1960). 8. A . P . Grinyuk, E. V. Belous, and A. D. Krysenko, Ukr. Khim. Zh., 3_.9.9, 922 (1973). 9. L. Bel lamy, Advances in In f ra red Group Frequencies , Methuen, London (1968).

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