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April, 1963 saturated hydrocarbons which have molecular weights of 176 and 226, respectively. These values along with the gas chromatographic analyses indicate very strongly that the highest molecular weight products, a t least in the earlier stages of radiolysis, are those of C16 carbon content. Unsaturation.-In addition to the identification of the two unsaturates that can be formed by loss of hydrogen from the parent hydrocarbon (Table 11) and gas chromatographic evidence for triisobutylene and tetraisobutylene as radiolytic products, evidence for unsaturation in the CS-cl6 radiolysis products has been found by catalytic hydrogenation and infrared measurements. G-values for carbon-carbon double bond formation, respectively, for total doses of 1.5 X loz2 e.v. and 8 X 1 0 2 2 e.v. were: (1) irradiated 2,2,4-trimethylpentane after removal of radiolysis products of less than Cs content, 1.16 and 0.86; (2) irradiated 2,2,4-trimethylpentane after removal of radiolysis products of less than Cs and greater than C12, 0.83 and 0.62; and ( 3 ) ClrCl6 products (obtained by difference), 0.33 and 0.24. A comparison of these G-values with and -2 those of Table I1 for '2,4,4-trimethylpentene-1 shows that a major portion of the unsaturation in the c S c 1 6 products is due to the CSunsaturates. Infrared spectra of the radiolytic product of the C12c16 range showed that the most likely carboncarbon double bonds present are those of the trans double bond, the RIR2C=CH2 group and the R1R2C= CHRI group. There are a t least 40 radiolysis products in the Cs-Cls range from irradiatedr 2,2,4-trimethylpentane. Since very few authentic hydrocarbons above Cl0 of the types expected from the radilolysis of 2,2,4-trimethylpentane are available, identification of most products above Cl0 cannot be made. Comparison of the total G-values for '2.4, with the total G-values for CS-ClS products, G 5.6, shows that the processes C1-C7 products, G leading to the lower molecular weight products predominate. I n addition to the identification of 2,4,4trimethylpentene-1 and -2, evidence for unsaturation in the Cs-CIGrange was obtained from Hz-uptake meas-. urements and infrared spectra. Molecular weight measurements on the higher molecular weight product showed that it is in the Clz to CIS range. These measurements along with the gas chromatographic analyses indicate that the largest molecular products are those due to dimerization of two Cs components, a t least in the earlier stages of irradiation. Acknowledgment.-This work was supported in part by the United States Atomic Energy Commission, Division of Research, Contract No. AT (40-1)-2490.
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N
RADIATION D-44MAGE 1N SOLID TETRAMETHYLAnlhSO~-IUNHALIDES. FREE RADICALS STABLE AT LOW TEMPERATURES1 BY A. J. TENCH Department of Chemistry, Broolchaven National Laboratwu, Lipton, Long Island, N e w York Receiued September 38, 196.9
The electron spin resonance (e.s.r.) spectra of irradiated tetra-n-butylamnionium iodide and bromide (1) Research performed under the auspices of the U. S. Atomic Energy Commission.
923
have been reported by BurrelL2 The spectra consist of seven lines and have been interpreted as arising from the interaction of an odd electron with six protons. Burrell assumed that the radicals remained attached to the central, positively charged nitrogen. The e.s.r. spectra of the iodide and bromide salts were found to be very similar, in contrast to the work reported below on irradiated tetramethylammonium halides. Experimental Dry, powdered samples and in some cases single crystals of the recrj&dlized tetramethylammonium halides were sealed in silica tubes under vacuum. The halides were irradiated a t 298 and 77°K. with ?-rays from a Coso source. After irradiation, one end of the silica tube was thermally annealed t o remove radiation defects and the sample transferred to the annealed end. The sample was maintained at 77°K. throughout this operation. The spectra were measxed a t either 298 or 77°K. on a Varian Model V-4501 100-kc. e.8.r. spectrometer and recorded as the first derivative. The samples were thermally annealed in a liquid bath at 148°K. for various lengths of time; the annealing processes were quenched by rapid cooling to 77°K. and the spectra then were measured at this temperature.
Results and Discussion The e.s.r. spectra of the iodide and bromide irradiated and observed a t room temperature consisted of a single line, width 30 to 40 gauss.3 A polycrystalline sample of the chloride gave a weak complex att tern.^ However when the halides were irradiated and examined at 77OK. considerable fine structure was observed. All the spectra observed were found to be centered about g = 2.003 f 0.001 by comparison with DPPH. The spectrum of the irradiated iodide (Fig. 1A) a t 77OK. is a well resolved quartet of line width 3.5 gauss and relative peak heights of 1:2.9 :2.8 : 1, superimposed on a low intensity broad line similar t o that observed for the room temperature irradiations. The relative peak heights and the coupling constant of 21.5 gauss indicate that the quartet can be identified as a methyl radical.jV6 When the irradiated iodide was thermally annealed a t 14S°K., the shape of the spectrum remained unchanged while the absorption decreased to 10% of its original value. Moreover, the spectra of an irradiated single crystal of the iodide recorded a t various orientations in the magnetic field showed no differences from the spectra of the powdered samples. The e m . spectrum of the bromide (Fig. 1B) a t 77OK. is very different. After thermal annealing a t 148OK. the spectrum reduces to a triplet (Fig. IC) of line width 16 gauss and a coupling constant of 23 gauss. Further annealing to 298OK. gives a single broad line. The complex spectrum in Fig. 1B can be synthesized by superimposing a quartet (a,b,c,d), corresponding to a methyl radical, on the triplet. The poor resolution of the triplet makes identification difficult. However, the relative peak heights indicate that the triplet probably results from the interaction of an unpaired electron with two The radical could be free CHz.+, but the thermal annealing data show that the triplet is much more stable than the quar(2) E. J. Burrell, J. Chern. Phys., 32,955 (1960). (3) All line widths quoted correspond to the distance between the points of maximum slope of the absorption curve. (4) A. J. Tench, J . Chem. Phys., in press. ( 5 ) B. Smaller and M. €3. Matheson, Ibzd., 28, 1169 (1958). (6) C. K.Jen, S. N. Foner. E. L. Cochran, and V. A. Bowers, Phys. Reu., 112, 1169 (1958). (7) I. Miyagawa a n d W. Gordy, J . Am. Chem. Soc., 83, 1036 (1961). (8) J. F. Gibson, D. J. E. Ingram, M. C. R. Symons, and M. G. Townsend, Trans. Faraday Soc., 88, 914 (1967).
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protons of CH, if this group is not rotatinglo-further broadening may be caused by an unresolved hyperfine interaction with the nitrogen atom. The chloride behaves very similarly to the bromide except that the methyl radical signal is only just observable and slowly anneals at 77°K. The spectra of the irradiated iodide and bromide did not change significantly after several weeks a t 77°K. The difference between the behavior of the iodide and that of the bromide and chloride is interesting. Since the crystal structures are the same and the dimensions of the unit cell are very similar,ll the difference may be related directly to the chemical properties of the halides. The methyl radical observed in all three irradiated salts probably is formed by decomposition of an excited tetramethylammonium species.
DPPH
C
The species tentatively identified as (CH&CCW2. could be formed as a result of hydrogen abstraction from the tetramethylammonium cation by bromine or chlorine atoms. Photochemical evidence12 shows that the iodine aton? cannot undergo such a reaction. KO e.s.r. signal was observed from halogen atoms, and it is assumed that matrix interaction broadens the peaks beyond detection.6 Acknowledgment.-'The author is indebted to Dr. N. Sutin for helpful discussion and comment. (10) E. L. Cochran, F. J. Adrian, and V. A. Bowels, zbad., 34, 1161 (1'261). (11) R. W. G. Wyckoff, Z. Krzst., 67, 91 (1928). (12) 'E. W. R. Steacie, "Atomic and Free Radical Reactions," Vol. 11, Reinhold Publ. Gorp., New York, N. Y., 1964, p. 701.
THE DENSITY OF LIQUID ARSENIC AND THE DENSITY OF ITS SATURATED VAPOR1 BY P. J. XCGONIUAL~ ASD A. V. GROSSE Research Institute of Temple Cnidersity, Philadelphia 44, P a .
Receieed September 26, 196B
60 gOUSS MAGNETIC F I E L D STRENGTH,
Fig. 1.-(A): The e.s.r. spectrum of RIe4S"I- ?-irradiated and observed a t 77°K.; ( B ) the e.5.r. spectrum of MedK+Br?-irradiated and observed a t 77°K; (C) the e m . spectrum of Me4N+Br- ?-irradiated a t 77°K. then thermally annealed a t 148°K. and the spectrum observed a t 77°K. -411 the e.s.r. spectra are first derivative curves.
tet, and this would indicate that a species such +
as (CH3) ,NCH2. is observed and not CH2.+. Spectra taken using a single crystal of the chloride did not give an increased resolution. The microwave power was reduced to the lowest possible levels but no further fine structure could be observed in the t r i ~ l e t . The ~ variation of signal intensity with microwave power showed that saturation was not occurring at the low power levels used. The lines may be broadened by an unequal coupling of the unpaired electron with the two (9) J. A. Simmons, J. Chem. P h y s , 36, 469 (1962).
The density of liquid arsenic is difficult to measure in spite of its comparatively low melting point (1090°K.) due to the fact that the vapor pressure of arsenic at its melting point is already 35.8 atm.3 I n the present m7ork the density of liquid arsenic and the density of its saturated vapor mere measured over a range extending from the m.p. to 1323°K. The density of liquid arsenic was determined by cathetometric measurement of the liquid level in calibrated, sealed Vycor tubes of known volume which contained a known mass of arsenic. The mass of the liquid was obtained by subtracting from the total the mass present as vapor. A total of 49 points was obtained from eight series of experiments. Least squares treatment of the data yielded the equation
D g . / ~ m= . ~5.80 - 5.35 X lO-*T
(OK.)
The probable error is d0.02 g . / ~ m . ~ . Vapor densities were determined by observing the temperature at which a known mass of arsenic vaporized completely in a sealed Vycor tube of known volume. Determinat,ions were made at seven different tempera(1) This work was supported in part b y the Kational Science Foundation under Grant 18829. (2) -4 report of this work will constitute a portion of a dissertation t o be submitted by P. J. McGonigal to the Graduate Board of Temple University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. (3) S.Horiba, 2. physik. Chem., 105, 295 (1922).
