branched fluorinated allyl radicals

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  • BRANCHED FLUORINATED ALLYL RADICALS

    B. L. Tumanskii, L. L. Gervits, S. P. Solodovnikov, K. N. Makarov, L. T. Lantseva, and N. N. Bubnov

    UDC 543.422.27:541.515: 547.384'161

    Kochi et al. [i] have carried out an EPR spectral study of perfluoroalkyl and ~-alkoxy- fluoroalkyl radicals formed upon the photolysis of perfluoroketones in solution. In the present work, we studied the photochemical transformations of branched fluorinated vinyl ketones.

    The photolysis of vinyl ketone (I) in the presence of 2-propanol leads to the formation of allyl radical (II), whose EPR spectrum has the following constants for coupling of the unpaired electron with fluorine nuclei: a F = 13.02 (CF3), 19.16 2(CF3) a, 26.0 (IF), 0.76 Oe 2(CF3) b (Fig. la):

    O OH II h_~> ~-PrOH CL~

    (CF3hC=C--C--CF~ -- [(I)]* (CF3hac I I %? \ CF(CF3)= C CFs

    I b (I) CF(CF3)~ (11)

    The EPR spectrum simulated with these constants is in complete accord with the experi- mental spectrum.

    An allyl radical similar in structure to (II) is formed upon the reaction of silicon- centered radicals with (I).

    (CH~)3COOC(CH3)3 ~ 2(CH8)8C0" (CH3)sCO" + HSiEt~ ~ $iEta + (CH3)3COH

    OSiEt~ I

    (I) + $iEt3 --* (CF~)~ac 1 C~

    %C ' / \CF3 I CFCCF3)2 b

    The rep lacement of the hydrogen atom by the S iE t 3 group on ly s l ight ly enhances the den- s i ty o f the unpa i red e lec t ron on C2:a F = 15.6 (CF3), 18.4 2(CF3) a, 21,6 (1F) , 0 .80e 2(CF3) b.

    Analysis of the coupling constants showed that the large splitting due to the b-fluorine atom and small splitting due to the x-fluorine atoms of the CF(CF3) 2 group indicate that the C-F bond of this group is located in the same plane as the axis of the 2pz orbital of the unpaired electron, while the C-CF 3 bonds are located near a nodal plane. This implies the lack of free rotation of the CF(CF3) = group. The rotation of this group is also inhibited on the NMR time scale [2].

    In this regard, it was of interest to compare our data with the coupling constants with the 8- and y-fluorine atoms in the stable triperfluoroisopropylmethyl radical, which features a different arrangement of the perfluoroisopropyl group and different coupling con- stants [3]. Free rotation of the perfluoroisopropyl group in (II) and (III) should have led to a decrease in the coupling constants for the ~-fluorine atom by at least a factor of 2.

    Thus, radicals (II) and (III) have an unpaired electron density distribution similar to that characteristic for the allyl radical: the unpaired electron density on the terminal carbon atoms is +2/3, while the density on the central atom is -1/3 [4].

    r

    A. N. Nesmeyanov Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1397- 1399, June, 1989. Original article submitted May 19, 1988.

    1278 0568-5230/89/3806-1278512.50 9 1989 Plenum Publishing Corporation

  • ,_ a~IztS)

    _ ~!

    Fig. i.

    b

    O

    EPR spectrum of radical(II) at 20~ (a) and its outer components (b).

    The photolysis of (I) in the absence of hydrogen donors also leads to the formation of a similar allyl radical [i].

    CF(CF3)~ h~; I .

    (I) -o [(CF3)2C=C--C iF3] -~ (CF3)2C=C + CF3 + CO i l O CF(CF3)2

    (A)

    OR F

    (I) -~ R F ~ (CFs)2aC I C ~ k.../

    C \CFa 1 b CF(CF3)2 (iv)

    R F=~Fa or (A).

    The EPR spectrum of (IV) has the following coupling constants: a F = 18.3 for 2(CF3) a, 12.2 for (CF3) , and 24 .80e for (IF). The concentration of (IV) is much less than for (II) and (III). The lifetime of radicals (II)-(IV) was found to be ~i h, which is riot in accord with the data of Mikhailov et al. [5], who assigned the structure of the allyl radical to a radical with lifetime of ~3 years.

    (C3F):L'. CFCF3

    t i CF2CF3

    (V)

    Our coup l ing constants ind icate that the unpa i red e lec t ron in rad ica l (V) shou ld in ter - ac t not only with one fluorine atom a F = 65 Oe [5] but also with the CF3 group fluorine atoms (a F = 10-20 Oe) and also the fluorine atoms of the perfluoroethyl group, which should be clearly seen in the EPR spectra. Thus, the proposed structure of the ailyl radical does not correspond to the stable radical discovered by Mikhailov et al. [5],

    1279

  • EXPERIMENTAL

    The EPR spectra were taken on a Radiopan SE/X-2544 spectrometer. The samples were placed into quartz ampuls and thoroughly degassed. The synthesis of (I) was described in our previous work [2].

    CONCLUSIONS

    EPR spectroscopy was used to establish the structure of the branched perfluoroallyl radicals obtained from perfluoro-3-isopropyl-4-methyl-3-penten-2-one.

    I.

    2.

    3. 4.

    5.

    LITERATURE CITED

    P. J. Krusic, K. S. Chen, P. Meakin, and Y. K. Kochi, J. Phys. Chem., 78, No. 20, 2036 (1974) V. F. Snegirev, L. L. Gervits, and K. N. Makarov, Izv. Akad. Nauk SSSR, Ser. Khim., No. 12, 2765 (1983). K. V. Scherer and T. Ono, Jr., J. Am. Chem. Soc., 107, No. 3, 718 (1985). J. Birch and J. Bolton, The Theory and Practical Application of EPR Spectroscopy [Rus- sian translation], Mir, Moscow (1975), p. 132, S. R. Allayarov, I. V. Sumina, I. M. Barkalov, and A. I. Mikhailo v, Izv. Akad. Nauk SSSR, Ser. Khim., No. 12, 2698 (1987).

    PMR SPECTRAL STUDY OF THE PROTONATION OF N,N-DISUBSTITUTED

    3-AMINO-2-ARYL-I-INDENONES

    L. I. Lavlinskaya, T. L. Usova, I. A. Dorofeev, V. A. Usov, and M. G. Voronkov

    UDC 543.422.25:547.665

    The effects of electronic and steric factors on the protonation of enaminoketones (EAK) holds significant interest since many chemical transformations of these compounds proceed in the presence of protic acids [1-3]. Acyclic EAK, depending on their electronic and three-dimensional structure, form O- (A) or C2-protonated forms (B). A bipolar meso- meric form makes a significant contribution to the structure of alicyclic EAK [4] and only O-protonation is found for these compounds [1-3].

    $ (A) (B) >~=c-c=c-o-

    We carried out a dynamic PMR study of the protonation of N,N-disubstituted 3-amino-2- aryl-l-indenones (1)-(VI). In contrast to aliphatic and alicyclic EAK, the p, T-system of these compounds is enriched by the presence of the phenylene and C=-aryl rings.

    ~i RI RI ! 2 / +/

    ~TI--~" -,~----~ir"~ "R'.~ ,' EL E-"~H R" "~"'LLt.L..k'" ~' "~o'_ ~r ~,~ "~y'~r ~ ~_.-~r

    (~) (.r)-(m (~) (zz)

    Ar=Ph; RI=R2=Me(I); R I, R2=(CH2)5 (II), (CH2)6 (III), (CH2h (IV), (CH2)s (Y); Ar=Naph, R~=R~----Me (u X=CI04, CCIaCO0.

    Irkutsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1399- 1402, June, 1989. Original article submitted June 3, 1988.

    1280 0568-5230/89/3806-1280512o50 9 1989 Plenum Publishing Corporation

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