COMMUNICATIONS TO .THE EDITOR
4577
Table I : Relative Yields of FIE-Labeled Products from
Reactions with Cyclanes
FIE
Parent molecule trans-
Cyclopropane
c-CsHs C-CIHE (CHa)zC4He 02 CF4 Total
5.0
...
..' 0.6 7.6
13.2
c-C~H~F'~ 100 c-C~H~F'S ... CHs=CHF" 44f3 CH2=CHCHzFla 58f3 c~s-CHF'~=CHCH~ 1 2 f l ~RZ~-CHF'B=CHCH~ 12f1 CHz=CF"CHa 3*1
.
I
I
100
...
39f2 47322 10f1 9 f l 2 f l
...
15.0
38.6
...
*..
...
10 75 157
(12 1 (20) liq
0.7 6.1 12.4
2.0
4.3
15.0 32.0
36.5
100
...
Product Yields 100
35f3 44f3 llfl 9 f l 4 f l
...
26f2 31f2 7 f l 6 f l 33tl
A complementary pressure dependence is found for reactions with cyclobutane between the directsubstitution product, fluorocyclobutane, and its decomposition product, vinyl fluoride. In the corresponding reaction with trans-l,3-dimethylcyclobutane, appreciable yields of the 3-, 1-, and 2-fluoropropenes are found, corresponding to decomposition of the direct substitution products formed by reaction of energetic F1*with the primary, secondary, and tertiary hydrogen positions, respectively of the parent molecule. The vinyl fluoride from this latter system presumably arises from secondary decomposition of the excited product obtained by substitution of F for CH3 in the parent molecule. The energetic considerations for F for H substitution have a strong similarity to the behavior found for the reactions of energetic tritium atoms from nuclear recoil with cyclopropane,l2 cy~lobutane,'~ and other molecules.*4 The current experiments do not actually furnish any information about the threshold energy for the F for H substitution reaction, and it may possibly proceed down to rather low fluorine atom energies. The alkane fluorination experiments carried out with photolytic fluorine atoms from Fz are unable to distinguish reaction 1 from reaction 2, since the succeeding reaction with Fzof the atom or radical from eq 1 or 2 will form that product, H F or RF, not formed in the initial step.6-* While the abstraction of halogen is the only reaction found with alkanes for thermal bromine and chlorine atom^,^^^ the corresponding substitution reactions are 15-40 kcal/mole more endot.hennic and would not be experimentally observable at these reaction temperatures. Both the substitution and abstraction F18
...
5.6
... ...
.
3.7 47.5 79.5
...
... ...
.
.
Cyclobutan--
Gas Pressure, cm 72 (24)
28.3
1,3-Dimsthyl cyclobutane
...
...
79.4
...
...
100 217 f 22 0
0 0 0
100 214 f 11 0
0 0 0
100 121 f 10
0 0 0 0
...
19.2 4.0 19.8 43.0
... ... 210 f 18 100 59 f 6 52 f 5 46 f 5
reactions are usually thermoneutral or exothermic for fluorine atoms, and contributions from eq 1 might be detectable for thermal F atoms under some appropriate conditions. (12) J. K.Lee, B. Musgrave, and F. 9. Rowland, Can. J. Chem., 38, 1756 (1960). (13) E. K. C. Lee and F. S. Rowland, J. Am. Chem. Soc., 85, 897 (1963). (14) See, for example, Y.-N. Tang, E. K. C. Lee, and F. S. Rowland, ibid., 86, 1280 (1964). (15) This research was supported by AEC Contract No. AT(11-1)-34,Agreement No. 126, with the University of California, Imine, Calif.
YI-NOO TANQ F. S. ROWLAND
DEPARTMENT OF CHEMISTRY~~ UNIVERSITY OF CALIFORNIA IRVINE, CALIFORNIA92650 RECEIVED SEPTEMBER 11,1967
Electron Spin Resonance of Hexafluoroacetone Ketyl
Sir: In a continuation of electron spin resonance studies of trifluoromethyl-substituted free radicals,' we have made hexafluoroacetone ketyl by the electrolytic reduction of hexafluoroacetone in acetonitrile. This radical has been suggested
0
II CFa-C-CFa
0e
l
+CFa-C-CFs
I Volume 71. Number 15 December lQS7
COMMUNICATIONS TO THE EDITOR
4578
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Figure 1. The esr spectrum of hexafluoroacetone ketyl in CHaCN at room temperature. The positions and intensities of the lines in the “stick diagram” are the second-order lines as predicted for six equivalent nuclei ( I =
as an intermediate in certain reactions of bis(trimethy1sily1)mercury and hexafluoroacetone2 and probably is formed in the l i t h i ~ m odium,^^^ ,~ or magnesium5 reduction of hexafluoroacetone to give salts of perfluoropinacol.O The electrolytic reduction a t room temperature of dilute solutions of hexafluoroacetone in dry oxygenfree acetonitrile, containing tetraethylammonium perchlorate as carrier electrolyte, gives a spectrum of seven groups of lines separated by -35 gauss. No signal could be obtained from saturated solutions.’ The halfwave potential* in acetonitrile is -0.8 v vs. saturated aqueous calomel electrode. The intensities and spacing of the lines within each multiplet are well accounted for by second-order effects9 (Figure 1). The positions of the lines as calculated in gauss from the center line, i.e., the first high-field line of the center multiplet, are: -106.1, -71.3, -70.3, -36.9, -35.7, -35.1, -2.2, -1.1, -0.4, 0, 33.3, 34.3, 34.8, 68.7, 69.8, and 106.4. AF = 34.7 0.3 gauss. The g value is 2.00397.’0 Hexafluoroacetone ketyl is stable in acetonitrile for 2-5 min after electrolysis is stopped. I n tetrahydrofuran only a weak single line has been obtained with potassium. Presumably dimerization to the alkali metal perfluoropinacolate is predominant in nonpolar solvents. It is of interest to note the similarity in the magnitude of the [%fluorine coupling in I as compared to the following two neutral radicals
OH
I/*).
(4) A partially resolved esr signal has been previously obtained by the reaction of hexafluoroacetone with potassium in tetrahydrofuran: A. F. Janzen, personal communication. ( 5 ) W. J. Middleton and R. V. Lindsey, Jr., J . Am. Chem. SOC.,86, 4948 (1964). (6) For a review of hexafluoroacetone chemistry see C. G . Krespan and W. J. Middleton, Fluorine Chem. Reus., 1 , 145 (1967). (7) The reason for this observation is not known a t this time. (8) A commercial three-electrode polarograph (Heath EUA-19-2) was used. We are grateful to W. B. Harriaon for assistance in these
determinations. (9) R. W. Fessenden, J. Chem. Phys., 37, 747 (1962); 39, 2147 (1963); 43, 2704 (1965); R. Livingston and H. Zeldes, ibid., 44, 1245 (1966). (10) Spectra were obtained as described in ref 1. Field measurements for the line positions in Figure 1 were made by calibrating the spectrum with a Magnion G502 nmr gaussmeter. The @ value
was obtained by simultaneously measuring field and frequency using a Hewlett-Packard 5245L frequency counter with 5253B frequency converter and 540B transfer oscillator. (11) P. Smith, J. T. Pearson, and R. V. Tsins, J. Can. Chem., 44, 753 (1966) ; no second-order splitting was reported. (12) S. Siege1 and H. Hedgpeth, J. Chem. Phys., 46, 3904 (1967) and references therein. (13) National Defense Act Trainee, 1964-1967.
DEPARTMENT OF CHEMISTRY THEUNIVERSITY OF GEORGIA ATHENS, GEORGIA 30601
EDWARD G. JANZEN JOHNL. GERL0CKla
RECEIVED SEPTEMBER 22, 1967
Comments on ‘‘Dispersion Energies and Surface Tensions of Noble Metals”
F
Sir: I n a recent note, Thelen’ has attempted to correlate the cohesive energy density with the dispersion CFI-C-H mv CFZ-C-CF2 contribution to the surface tension of selected noble I1 I11 metals by employing wettability data in conjunction I n 11, AF = 31.8 f 0.6,” and in HI,& = 3 4 g a u ~ s . l ~ with the Fowkes-Young equation. We shall attempt to demonstrate using the results of the scaled particle theory of liquids2 that the approach of Thelen implies (1) E. G. Janzen and J. L. Gerlock, J . Am, Chem. Soc., 89, 4902 (1967). that the ratio ydLv/yLv for this group of metals is (2) A. F. Janzen, P. F. Rodesiler, and C . J. Willis, Chem. Commum., essentially constant. We shall show further that metals 672 (1966). I
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(3) R. A . Braun, J . Am. Chem. SOC.,87, 5516 (1965); C . L. Frye, R. hl. Salinger, and T. J. Patin, ibid., 88, 2343 (1966).
The J O U Tof ~Physical Chemistry
(1) E. Thelen, J . Phys. Chem., 71, 1946 (1967).
