STRUCTURE OF ONE-ELECTRON OXIDATION PRODUCTS OF OXlMES

V. E. Turs, A. A. Karelov, N. M. Lyapin, and V. A. Shlyapochnlkov

UDC 541.127:541.6:530.145: 547.288.4:542.943

Various opinions exist on the reaction mechanism for the oxidation of oximes (I), in which connection one-electron oxidation processes are selected as being the most probable [1]:

=C=N--O +X+YH-~ (III)

a I

\C=N--OH -5 XY ~- ~C =N--OH -5 X Y ~- n~ / (I) / (II)

A B

\C=N--O--X (V) /

O

\ c =N /~ (W)

/ \ X

--kC--N=O (vii) c /

x

The character of the end oxidation products of (I) should be determined to a large degree by properties of the intermediate particles [(II) and (III)] and the products of their recombina- tion with the remainder of the oxidizing agent [(V), (VI), and (VII)].

The purpose of the present paper was to make a theoretical study of the structural and energy characteristics of compounds (I)-(III) and the possible protonated forms of the oximes in order to estimate the appearance probability of the various reaction products of (I) with electrophiles. The complexity of a kinetic study of the reaction due to the low stability of the intermediate compounds Justifies the use of quantum chemistry methods to estimate the probable schemes for progress of the process.

In order to estimate the nucleophilic centers in (I) as an approximation of isolated molecules [2] it is necessary to make an adequate calculation of their electronic structure. Among the contemporary semlempirlcal methods the calculation by the CNDO/2 method gives the best agreement with the nonempirical method on the order of alternation of the MO levels of formoxime (la) (Table i). However, the values of the LCAO coefficients in the upper occupied orbital (UO0) of (I), calculated by the CND0/2 method (Table 2), do not permit isolating the reaction center, while the charge distribution indicates the preferableness of electrophilic attack on the oxygen.

Calculation of the protonated (In) as a model of the reaction of (I) with electrophiles by the CND0/2 method, with an optimization of the geometric parameters, leads to the conclu- sion that protonatlon is possible at three centers: oxygen (IVa), nitrogen (IVb), and C=B bond (IVc). The most stable form is (IVc), and the least stable is (IVa). Compounds (IVa) and (IVb) retain the planar structure that is inherent to (Ia), while substantial spatial rearrangement occurs in the formation of (IVc) (Table 3).

Calculations of the cation-radical (IIa) and radical (IIIa) of formoxime by the CND0/2 and PND0 methods within the framework of the unrestricted Hartree-Fock method lead to the conclusion that these radicals are of the o type, with a predominant localization of the spin density on the nitrogen in (IIa) and on the oxygen in (IIIa), which indicates the possible appearance of the N- and O-derlvatives during the recombination of (If) and (III) with the oxidizing-agent fragment. I

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. ii, pp. 2610-2612, November, 1979, Original article submitted March 14, 1979.

0568-5230/79/2811-2425507.50 �9 1980 Plenum Publishing Corporation 2425

TABLE I. Order of Alternation of Five Upper Occupied MO of Formoxime Based on Orbital Energies (eV) and Types of Calcula- tions by MO Methods

ab initio

-12,33g -13,01o -16,75q - 17,67g -i8,98o

MPNDOF3

-9,38o -i0,04~ -12,57o -t3,80~t -14,35o

p ~ o

-i3,18o .13,74~ -16,88o -t9,48o -19,66~

CNDO~W

-ti,32~ -t2,21o -13,79~t -13,84o -14,85o

CNDO/2

- i4,69n -14,86o -t7,25o -20,60n -2t,11o

IEHM

-ii,72o -it ,88g -t4,58o -i4,67n -i4,89o

TABLE 2. LCAO Coefficients in UOO (z-Type) and Charges on Atoms of Oxime Fragment, Calculated by the CNDO/2 Method for Oxlmes with Various Substituents on the Carbon Atom (I)

Substituents LCAO coefficients in UO0 Charges on atoms, atomic units

R ' R 2 C N O C N O

H H 0,58 0,49 -0,65 +0,04 -0,02 -0,20 CH, H 0,52 " 0,54 -0.55 +0,09 =0,05 -0,21 CH~ CH3 0,49 0,56 -0152 +0,t2 -0,07 -0,20 CH~ NHz 0,38 0,63 -0145 +0,24 -0A5 -0,22 CH~ CN 0,50 0,54 -0,5i +0,il -0,04 -0,20 H Ph 0,39 0,49 -0,38 +0,07 -0,04 -0A9

TABLE 3. Geometric Parameters and Energy of Compounds, Calculated by MO Methods (CNDO/2 and PNDO)

MO method

CNDO/2 CNDO~ CNDO$ CNDO#2 PNDO PNDO PNDO

Compound

(Ia) (Ira) (IVb) (IVc) (Ia) (IIa) (IIIa)

Bond lengths,

C=N N--O

CNO ]Total ener-

Ideglang le, g y , eV

t ,29 t,29 t ,30 i,36 t,29 1,27 1,29

t,28 1,30 t,28 t,24 1,28 t ,25 t,23

1t6 114 12i 1t7 it6 i50 135

-t07i,89 -1083,t9 -1084,66 -t085,42 -i027,94 -t0t7,78 -t005,52

A theoretical estimate (by the PNDO method with an optimization of the geometry) of the relative stability of (la)-(llla) shows that the decomposition of (lla) 3 which is formed by the reaction of (la) with Cla by the scheme A + B (AEAB = 197.3 kcal/mole), is improbable by the direction B + C (AEBC = 292.4 kcal/mole). The energy characteristics of the C12 and HCI molecules were taken from [3]. The validity of the relative energy estimates of (la)-(llla) is confirmed by the fact that a calculation of the value of the vertical ionization potential of (la) by the PNDO method, with an optimization of the geometry of (la), is in agreement with the experimental value (11.02 and 10.63 eV [4], respectively).

A comparison of the geometric parameters of (la) and (lla) (see Table 3) makes it pos- sible to assume that a bathochromic shift of vC--N during the ionization of (Ia) arises due to the kinematic effect, and not due to a weakening of the ~ system, as is assumed in [4] (the z orders of the C=/q bonds of (Ia) and (IIa) are respectively equal to 0.96 and 0.94). Based on the calculation data, (Ia)-(IIIa) have a planar structure, in which connection the value of the C=N-O valence angle in (IIIa) (see Table 3) is in agreement with that obtained from the EPR spectra of oximes [5]. Projection based on the spin failed to introduce notice- able changes in the calculation results.

The authors are indebted to O. Yu. Dolgunicheva for supplying the results of the non- empirical calculation of (Ia).

CONCLUSIONS

i. According to the calculations based on the CNDO/2 and PNDO, the radicals and cation- radicals of oximes retain a planar structure and are radicals of the a type, in which the spin density is predominantly localized on the oxygen and nitrogen atoms, respectively.

2426

2. An e s t i m a t e of the nucleophilic centers in oximes (CON, =~--, -O-) disclosed that on the basis of the values of the LCAO coefficients in the UOO and the cha~ge distribution (CNDO/ 2 calculation) is is difficult to make an unequivocal conclusion regarding the direction of , electrophilic attack. The protonation of oximes is most favorable at the ~ bond and least favorable at the oxygen.

1.

2. 3.

.

5.

LITERATURE CITED

I. P. Freeman, Chem. Rev., 73, 283 (1973). R. F. Hadson, Angew. Chem., 85, 63 (1973). L. V. Gurevich, G. V. Karachevtsev, V. N. Kondrat'ev, Yu. A. Lebedev, V. A. Medvedev, and V. K. Potapov, Rupture Energy of Chemical Bonds. Ionization Potentials and Electron Affinity [in Russian], Nauka (1974). A. Dargelos and C. Sandorfy, J. Chem. Phys., 67, 3011 (1977). A. A. Buchachenko and A. M. Vasserman, Stable Radicals [in Russian], Khimiya (1973), p. 201.

CLEAVAGE OF NITRO GROUP IN 6-NITRO-2,9-DIOXA-I-AZABICYCLO-

[4.3.0]NONANE DERIVATIVES

I. E. Chlenov, I. M. Petrova, B. N. Khasapov, V. M. Shitkin, N. S. Morozova, and V. A. Tartakovskii

UDC 542.92:547.8

In 6-nitro-2,9-dioxa-l-azabicyclo[4.3.0]nonanes (I) the nitro group undergoes nucleo- philic substitution [1-3], the stere.chemistry of which indicates prior dissociation of the C--NO2 bond [i, 2]. Additional proof for such dissociation is given in the present paper and the reasons responsible for the process are discussed. The reaction of (Ia) with the K salt of nitroethane (II) in aqueous DMF leads to (V) [3]. When this reaction is run in DMF + H2*'O, the obtained (V) is devoid of *'O, and consequently the following reaction scheme was postulated in [3]:

o

(Ia) (lid (IV) (V)

The d i s s o c i a t i o n of the C--NO, bond in ( Ia ) g ives ( I I I ) , which a t t a c k s the ambident n i t r a t e an ion a t t he 0 t o g ive n i t r i t e ( IV) , t he r e a c t i o n of which wi th ( I I ) g i v e s (V). The fixation of (IV) would be a strong argument for the dissociation of the C--N02 bond, since the intramolecular isomerization of C-nitro compounds to the corresponding nitrates fails to take place in the ground state of nitro compounds. Proof for this scheme is given below.

In the PMR spectrum of (la) in DMF-dT, containing -10% of H20, together with the signal of the X proton of (la) (~ 5.71 ppm, JAX = 9.1, JBX = 5.8 Hz), is observed the appearance of the signal of an X proton (~ 5.46 ppm, JAX = 8.9, JBX = 7.5 Hz), which we assign to (IV). The transition (la) + (IV) takes place initially, without decomposition of the compounds, but after ~0.5-1.5 h, when the solution contains both (la) and (IV), the decomposition of (IV) begins, which cannot be isolated due to its instability. The ~SC NMR spectral data show that the skeleton of the (IV) bicycle is retained. The presence of the nitrite group in (IV) was established via the IR spectrum in DMSO. Previously it was shown via the PMR spectra that replacing DMF by DMSO has no effect on the transition of (la) =o (IV); the stability of (IV) is somewhat higher in DMSO. The IR spectrum was taken at the stage where only (la) and (IV) were present in the solution (PMR spectrum). Together with the absorption band of the nitro group of (la) (v 1550 cm -~) is observed an absorption band with ~ 1630 cm -I, which is char-

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. ii, pp. 2613-2615, November, 1979. Original article submitted March 22, 1979.

�9 1980 Plenum Publishing Corporation 2427 0568-5230/79/2811- 2427507.50