QUANTUM-CHEMICAL

STUDY OF DIMERIC ASSOCIATES OF

PHOSPHORUS ACID AMIDES V. E. Klimenko,

G. Peine!, and V. V. Pen'kovskii

UDC 539.196.3

A study of an electrostatic field near reaction centers of molecules of the amides of phosphoric acid(I) and O,O-dimethyl hydrogen phosphate(II) [i, 2] showed that electrostatic interaction of phosphoryl and amide groups makes it possible for these molecules to undergo self-association. There are no corresponding experimental proofs, although direct proofs of self-association have been obtained for more complex phosphorus acid amides. Thus, dimeric cyclic-type associates have been identified in the solid phase of N-substituted amides of O,0-dialkyl hydrogen phosphates by IR spectroscopy [3] and x-ray diffraction analysis [4]. In solutions of the same compounds, according to the results of an investigation of their IR spectra [5, 6] and isopiestic determination of the molecular weight [7], dimers that are assigned a cyclic structure are also formed [5]; for a solution concentration of 0.01 M, the relative content of the dimers is 50% and increases with increasing concentration [5, 6]. In the present paper, we give the results of a quantum-chemical investigation of dimerization of the molecules of I and II, which was carried out by a method taking into account configurational interaction plotted on localized orbitals according to perturbation theory (the usual abbreviation is PCILO) [8]. This method has been used to study interactions in polyatomic molecular systems, in particular, in complexes with hydrogen bonds [9, I0], because of the effectiveness of its computer implementation. We should also note that the concepts underlying the PCILO method are closely related to the usual chemical description of electron pairs in molecules. The structures of the investigated dimers are shown in Fig. i. In all the cases, the geometric parameters of the monomers were the same as in [I] and [2], with the exception of dimer 9, in which for the formation of a symmetric structure the P--N--H valence angles were decreased by 7.25 ~ The lengths of the intermolecular hydrogen bonds and also the values of the angles in the O ... H--N fragments and between the P==O and N--H bonds were optimized in each dimer. For plotting of the model Hamiltonian by the PCILO method, we used the atomic orbitals of valence shells of types s and p with standard CNDO/2 parametrization. Dimers 1 and 3 were also calculated by the SCF MO LCAO method in a 3G basis according to the GAUSSIAN70 (QCPE No. 236) program. All the calculations were carried out on the EC 1040 computer of the Computer Center of Leipzig University. The hydrogen bonds in dimers 1-9 were found to be practically linear (
Institute of Theoretical Physics, Academy of Sciences of the Ukrainian SSR, Kiev. Karl Marx University, Leipzig, GDR. Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 19, No. 5, pp. 612-615, September-October, 1983. Original article submitted April 14, 1983.

0040-5760/83/1905- 0565507.50

9 1984 Plenum Publishing Corporation

565

Ir o = p~.o-,'/

\

H \ /H \p~

#\

fl" y( #

0. ' /

14-0/10-#

#_0/ {

O-H r

IV~2 ~ N~O -

)

O-H H/N-P%0

2

3

H .y.. lr

OCtl

\

~'o

P = 0 ~- # 1,10--# .~/_O/I ---"~-p,~ . O-H H" 0 "

H\ i #

~-/'oc5 \

o

o=

Y\

/' =O =--'-"~IV"H 3" /! ~co/PC//

~

s

\

,.

A,~~ o-__::J'e

e\

~c-o/I

0 -C//s

. t e = 0/

~'c-o ,.o-c~ ,~-~

14" /

".~ ,, ,H

.-J'~

..e__ o" o-c~

%c_o. ~= o

8

9

H~C-O I 7

\ K"I'L R

~co 'o%

c-o o =~/.-o-c~/ ~

~ c~ o

e/--~M, 0%

/Y ~4 ,. R

o'-ces

Fig. i. Schematic representation of the dimers of the molecules of phosphoramidic acid in trans-trans configurations (1-4) and O,O-dimethyl phosphoramidate in trans-trans (5-6) and gauche-gauche configurations (7-9). TABLE i.

Interatomic Distances in the Dimers, nm m

Dimer

1

2

3

4

5

6

7

I

8

9

I

/~O...H Ro...H

0,173 0,273

0,229 0,281

0,143 0,243

0,229 0,271

0,200 0,259

0,191 0,200 0,190 0,143 0,291 0,259 0,280 0,243

TABLE 2. Stabilization Energies and Their Components for the Investigated Dimers, kJ/mole AE2

Dimer

AE

AEa

AEo

~deloc --76,79 --20,14 --46,73 --44,17 --34,83 --60,04 --40,11 --64,98 --81,14

67,11 --12,39 38,23 --7,45 71,97 --26,46 133,14 39,69 62,13

--107,48 15,16 --56,69 --8,75 --66,24 --5,36 --126,11 --69,21 --114,05

AEcorrI

AEcorr 2

--1,88 --0,80 --1,38 --0,92 4,90 1,21 2,01 --I ,59 --1,47

--7, 08 --1,17 --4,02 --2,55 10,22 9,71 --4,77 --5,90 --7, 29

--27,46 --20,94 --22,87 --24,50 --55,68 --39, 14 --44,38 --27,97

--20,46

energies of dimers i and 3 that we obtained in nonempirical calculations (--78.96 and --50.37 kJ/mole, respectively) practically do not differ from those calculated by the PCILO method. The data of Table 2 show that the cyclic dimers are more stable than the linear ones. In addition, the dimers containing the linear fragment P = O ... H are less stable than the dimer with the linear fragment 0... H--N. For all the cyclic dimers, the angle between the P==O bond and the direction of the hydrogen bond was found to be in the range of 125129 ~ , corresponding to hybridization of the oxygen atom of the phosphoryl group of sp = type (see also [i]). The energy of formation of the dimers from molecules of II in trans-trans configurations (dimers 5 and 6) is 4-5 kJ/mole greater than the energy of their dimerization in the g a u c h e -

566

gauche configurations (dimers 7 and 8); this is significantly less than the energy gain due to the change of the valence angles during dimerization, as is evident from a comparison of dimers 8 and 9. Therefore, the formation of cyclic dimers of phosphorus acid amides can be accompanied by conformational transitions in the monomers. Table 2 also gives the values of the dimerization energy components up to third order (see [8]). The greatest stabilizing contribution is made by the delocalization member; it is comparable with the corresponding theoretical values for other complexes with hydrogen bonds [9, i0]. The third-order correction, which can be considered as the stabilization index of the system due to intermolecular charge transfer, is small, but for systems with low stabilization energy it can be determining. Thus, the formation of dimers I and II is due more to electrostatic interactions than to charge transfer between subsystems. The obtained data make it possible to determine the structure and degree of stability of dimeric associates of phosphorus acid amides, which can be useful in the study of a number of processes determining the reactivity and biological activity of these compounds such as solvation, intra- and intermolecular proton transfer, complexation, passage through membranes, and interaction with antibodies. LITERATURE CITED I.

2.

3.

4.

5.

6.

7.

8.

9. !0. ii. 12.

V. E. Klimenko, G. Peinel, and V. V. Pen'kovskii, "Study of reaction centers of phosphorous acid amides by the molecular electrostatic potential method," Teor. Eksp. Khim., 18, No. 4, 477-481 (1982). V. E. Klimenko, G. Peinel, and V. V. Pen'kovskii, "Effect of conformation states on the electrostatic field of phosphorus acid amides," Teor. Eksp. Khim., 19, No. i, 8687 (1983). B. N. Laskorin, V. V. Yakshin, and B. N. Sharapov, "Study of phosphorus acid amides in the condensed state by IR spectroscopy," Izv. Akad. Nauk SSSR, Ser. Khim., No. 5, 1201-1204 (1978). M. P. Du Plessis, T. A. Modro, and L. R. Nassimbeni, "Structural effects in amides. Crystal and molecular structures of phosphoric and carboxylic anilides," J. Org. Chem., 47, No. 12, 2313-2318 (1982). B. N. Laskorin, V. V. Yakshin, and B. N. Sharapov, "Investigation of intermolecular hydrogen bonds and the steric structure of amides of O,O-dialkyl hydrogen phosphates," Dokl. Akad. Nauk SSSR, 211, No. 2, 350-352 (1973). B. N. Laskorin, V. V. Yakshin, and B. N. Sharapov, "Study of intermolecular hydrogen bonds of phosphorus acid amides in organic solutions," Zh. Obshch. Khim., 4_~7, No. I0, 2370-2375 (1977). B. N. Laskorin, V. V. Yakshin, and B. N. Sharapov, "Study of self-association of phosphorus acid amides by an isopiestic method," Zh. Fiz. Khim., 52, No. 12, 3127-3129 (1978). J.-P. Malrieu, "Method of taking into account the configuration interaction of localized orbitals according to perturbation theory," in: Semiempirical Methods for Calculation of Electronic Structure [Russian translation], Vol. I, Mir, Moscow (1980), pp. 94-138. R. Lochmann and T. Weller, "Calculation of intermolecular interactions within the PCILO framework," Int. J. Quant. Chem., iO, No. 5, 909-916 (1976). R. Lochmann, "PCILO calculations on hydrogen bonded complexes," Int. J. Quant. Chem., 12, No. 6, 841-850 (1977). P. A. Kollman and L. C. Allen, "The theory of the hydrogen bond," Chem. Rev., 72, No. 3, 283-303 (1972). P. Kollman, J. McKelvey, A. Johansson, and S. Rothenberg, "Theoretical studies of hydrogen-bonded dimers," J. Am. Chem. Soc., 97, No. 5, 955-965 (1975).

567