NOTES
3205
H
1.61
"i
CHL N(CH,), CCHS
) .
TI, mon TI, mic 2.1 sec. 0.75 sac.
2 . 3 ~ ~ . 24 sec. 1.4 sec.
/I
I .2
c-cmc (rnoles/liter) Figure 2. Plots of C/TIvs. ( c c.m.c.) snd derived values of and T1,miofor DCsAO.
-
and slopes of l,/Tl,mic. Plots of this type are shown in Figure 2 and to a good approximation straight lines are produced for all of the proton moieties. The values of T1,,,, and Tl,mioextracted from the plots are tabulated in Figure 2. The order of the 1'2 values remain the same in both the micellar and monomeric forms. The micellar values are about 1 sec. less than the monomeric values. The decrease in the relaxation times with micelle formation may reflect the restraint placed upon the molecules when incorporated into micelles. It is expected that internal chain motions (both translational and rotational) would be hindered in the micellar species relative to the corresponding motions in the monomeric form. Another factor which may be important is the change in environment which a molecule undergoes during micelle formation. The intermolecular interactions would be mainly between protons and deuterons for the monomer, but the same interactions would be mainly protonproton interactions in the micelles-this would lead to a relative decrease in relaxation for the micellar form. The relaxation time of the HOD in the solvent was also determined at several different concentrations of surfactant. The observed value decreases from 4.3 sec. in the pure solvent to about 3.9 see. for a 1M solution of DCAO. No indications of a maximum were found near the c.m.c. of the surfactant as shown by the DCAO relaxation times. The value of 4.3 sec. observed for the pure solvent is less than previously re-
ported values of TIfor HOD6 and probably represents the upper limit of Tlwhich can be measured under the experimental conditions used in this investigation. The decrease in the TI(increase in the relaxation rate) of the HOD with increasing concentration of surfactant probably reaults from the increase in the amount of solvent tied up in ordered layers about the micelles as the number (and perhaps the size) of the micelles increases. Water, or HOD, molecules in hydration shells have increased reorientation times and thus increased relaxation rates as compared to pure water. The correlation times of water of hydration have been found to be anywhere from two7to ten* times as long as those in the pure liquid state. The change in the observed Tldepends upon both the amount of water in the hydration layers and the degree of binding. It appears that 2'1 measurements may offer another method of determining critical micelle concentrations; however, the relatively low sensitivity of the n.m.r. experiment offers a serious limitation to the method. Determination of the relaxation times of the species present in a micellar solution, which can be obtained from data collected entirely above the c.m.c., appears to offer a method of obtaining information about the species not readily obtainable by other methods. (0) W. A. Anderson and J. T.Arnold, Phu8. Rep., 101, 611 (1950).
(7) H.G. Hertz and M. D. Zeidler, Ber. Bunsenges. phys2k. Chem.,68, 821 (1964). (8) 8. S. Danyluk and E. S. Gore, Nature, 203, 748 (1964).
Mercury-PhotoBensitized Isomerization
of Perfluorobutene-2l
by Dennis Saunders and Julian Heicklen Aeroapocs Cmporation, El Segundo,CdifmniO (Received May 18, 1066)
The study of excited states has been reviewed recently by Hammond and Turr~.~* Wyman's review of cistrans isomerization2bprovides a background to the subject. In recent years, a number of papers have appeared on the photosensitized isomerization of butene-2. a-7 Each has discussed the role of excited states (1) Thie work WBB supported by the U.8.Air Force under Contract No. AF 04(696)-469. (2) (a) G. 8. Hsmmond and N. J. Turro, ScisncS, 142, 1641 (1903); (b) G.M. Wyman, Chem. Rep., 55,026 (1966). (3) R. B. Cundall and T.F. Palmer, Tram. Faraday SOC.,56, 1211 (1900).
Voluma 60,Number 0 Sephnber 1986
NOTES
3206
in isomerization. The results of Heicklen, Knight, and Greenes-ll have indicated that triplet states are L produced by the mercury-sensitized photolysis of CzF4, CsF6, and C~FS-2. It was our purpose, then, to prove the existence of this excited species by studying the cis-trans isomerization of perfluorobutene-2. Matheson Company perfluorobutene-2 was separated 0.530 mrn cis C4F8 into its components chromatographically, by use of 0.4 the column described by Greene and Wachi.12 The r 0 . 4 9 1 rnrn trans c4F8 infrared spectra of each isomer identically matched those reported by Heicklen, Wachi, and Knight.l3 0.2 1.46 rnrn trans C4F8 Analyses were accomplished by calibration of all of the infrared bands against a Consolidated Vacuum 0 Corp. McLeod gauge. The optical assembly and the 0 400 800 1200 gas-handling techniques have been described preTIME, min vi0us1y.l~ I , was calculated by photolyzing mixtures Figure 1. Froction of c.iS-CSs us. time. of 10 mm. of CZH4 and 500 mm. of NzO and measuring the noncondensables formed. The procedure was simply to introduce a sample of one isomer and to scan the infrared spectrum frequently during photolysis. With the scan rate of the instrument known, 1.46 rnm trans C4 F8 0.8 the time rate of change of both reactant and products .could be followed. 0.6 Initially, 0.6 mm. of the unseparated mixture was 0.491 rnrn trans C4F8 photolyzed for 36 hr. The final equilibrium mixture e contained 40% cis, corresponding to a slight gain in a' 0.4 the cis concentration. All other runs were made with pure isomers but not quite run to equilibrium. In all 1.47 mm cis C4 Fa 0.2 cases, no products were found other than cis- and transC4Fs-2. Figure 1 is a plot of the pressure of the cis compound P,,, divided by the initial pressure P i n i t i a l as a function of time in four runs. Two of the runs TIME, rnin were started with 100% cis, the others with 100% Figure 2. Fraction of trans-CZs us. time. trans. Figure 2 is a complementary set of curves for the pressure of the trans compound P,,,,, in the same fluorine substituents is further attenuated, no dissociafour runs. tion has been observed, even at 37Oo.l1 Thus, the exIt is not clear whether the above-mentioned curves come to a common asymptote. The initial linear (4) R. B. Cundall and D. G. Milne, J . Am. Chem. SOC.,83, 3902 regions of che reactions were plotted and the quantum (1961). yields calculated. The results are compiled in Table (5) R. B. Cundall, F. J. Fletcher, and D. G. Milne, J . Chem. Phys., 39, 3536 (1963). I. The @,,,(formation) is fairly constant at about (6) 8. Sato, K. Kikuchi, and M. Tanaka, ibid., 39, 239 (1963). 0.045, while the @trans (formation) varies considerably, (7) R. J. CvetanoviE, H. E. Gunning, and E. W. R. Steacie, ibid., but is about 0.12. No pressure dependence is in31, 573 (1959). dicated. The sum of the average quantum yields is (8) J. Heicklen, V. Knight, and S. A. Greene, ibid., 42, 221 (1965). about 0.16. (9) J. Heicklen and V. Knight, Aerospace Corp. Rept. TDR-469(525040)-5, Feb. 15, 1965; J . Phys. Chem., in press. Excited with 2537-A. radiation, mercury possesses (10) J. Heicklen and V. Knight, Aerospace Corp. Rept. TDR112.7 kcal.,/mole of triplet energy over its ground state. 469(5250-40)-7, Feb. 15, 1965; J . Phys. Chem., in press. When this energy is transferred to CzF4, dissociation (11) V. Knight, unpublished results of this laboratory. occurs through a vibrationally excited molecule.a (12) 8. A. Greene and F. M. Wachi, Anal. Chem., 35, 928 (1963). In C3F6, however, where the bond energy is 114.9 (13) J. Heicklen, F. Wachi, and V. Knight, Aerospace Corp. Rept. TDR-269(4240-20)-5, July 24, 1964; also J . Phys. Chem., 69, 693 kcal./mole, dissociation does not occur significantly (1965). unless additional thermal energy is ~ u p p l i e dlo. ~ ~ (14) D. Saunders and J. Heicklen, J. Am. C h m . SOC.,87, 2088 Finally, in C4Fs-2, where the inductive effect of the (1965). 0
e
>
~~
The J O U Tof ~Physical chemistry
NOTES
3207
and ezg(dzu,dsey2) orbitals is less certain. The purpose of this communication is to show that fairly definite conclusions may now be arrived at concerning the Is, 10-11 -Initial pressure, m m . 7 quanta/ -Initial orbital order in the d6 complexes, C r ( b ~ ) ~and + FeCi8 tram 00. sea. *tram (CP>2+. 5.1 0.037 000 0.491 The question of the relative stabilities of the ezg 5.1 0.045 000 1.46 and alg orbitals in Cr(bz)2+ and F e ( ~ p ) ~was + dis5.1 0.067 000 1.73 cussed by Levy and Orge12 in 1961. They used a 000 5.02 5.1 0.031 ligand field model and on the basis of the experimental 0.075 0.530 000 6.0 absorption spectrum concluded that in F e ( ~ p ) ~ + 0.086 0.653 000 5.4 the ezg level lay about 0.7 e.v. below the alp level. 0.032 1.47 000 6.0 They also concluded that the ezg level in C r ( b ~ ) ~lay + 0.158 1.49 000 5.4 0.229 5.26 000 5.4 about 2.9 e.v. below the alg level. However, these 0.148 5.29 000 6.0 authors pointed out that their use of the free-ion Slater-Condon parameters, F2 and F4, was incorrect and would cause an overestimation of the energy separacited molecule proposed is deactivated to the ground tion between the ezg and alg orbitals. state. In the present study, the excited-state interLet us consider the ferricenium cation. We agree mediate has been confirmed. As seen in Table I, with Levy and Orgel that the ground state of this comactsis 0.045 and +T7,,s is 0.12; the sum is clearly not plex is 2Ezg[(alg)2(ezg)a]on the basis of its magnetic unity. susceptibility. The excitation energy to the lowSome runs were conducted in the presence of 02, lying 2A1, [(alg)1(ezg)4] state, neglecting any configuraand it was found that @(CFaCFO)= 0.16. At elevated tion interaction, is given by temperatures, Knight1’ has found an additional product which is also produced in CaFrO2photoly~is.~JO 2Ezg+2A1g The small yield of CFaCFO in the presence of oxygen, T. E. = hE(e2g - alg) 20B(complex) in the absence as well as the small sum of acts where B(comp1ex) is the Racah parameter for the of oxygen, suggests that both the CFaCFO production complex. Since p(nephe1auxetic parameter) = B(comand the isomerization occur from the same electronic plex)/B(free ion), this excitation energy may be restate and that t’hisstate is produced with an efficiency written as less than one. Alternatively, the excited molecule might be produced with unit efficiency, but a barrier 2E2g +2A1, to internal rotation or oxidation of about 1 kcal./mole inhibits reaction. T. E. = hE(e2, - alg) 20@B(freeion)
-
Table I: Photolysis of Perfluorobutene-2
+
+
+
Acknowledgment. The authors wish to thank Mrs. Barbara Peer for assistance with the manuscript.
The Ground State Electronic Configurations of Ferricenium and Dibenzenechromous Cations18
Taking B(Fe3+,free ion)a = 1090 cm.-’ and assigning the experimental absorption band at 16.21 kKS4as the 2E2g-t 2A1gtransition, we may readily show that the aIg level lies below the ezg level for all values of p less than 0.74. Since the value for ,6 in ferrocene has been determined to be 0.4,6it is reasonable to expect that p in F e ( ~ p ) ~is+ less than 0.74. Using an estimated @-value of 0.5, we estimate that the alg orbital lies 5300 cm.-I below the ezg level in F e ( ~ p ) ~ + .
by Donald R. Scottlb and Ralph S. Becker Depart& of Chemistry, Univeredty of H&m, (Received M a y 14, 1966)
Houeton, Team
The question of the relative ordering of the d orbitals in the sandwich complexes has been a matter of great interest since the discovery of these compounds. It is now generally accepted that the els(dz,dVz)orbital is least stable, but the relative stabilities of the als(de2)
(1) (a) Supported in part by the Robert A. Welch Foundation, Houston, Texas; (b) Abstracted from the Ph.D. Dieaertation of D. R.Scott, University of Houston, Houston, Texas, Jan. 1966; National Science Foundation Cooperative Predoctoral Fellow, 1962-1963. (2) D. A. Levy and L. E. Orgel, Mol. Phys., 4,93 (1961). (3) C. E. J@rgensen,“Absorption Spectra and Chemical Bonding in Complexes,” Pergamon Press, Ltd., Oxford, 1962, p. 109. (4) D. R. Scott, Ph.D. Disaertation, Univereity of Houston, Jan. 1966; ferricenium tetrafluoroborate in water or dibenzenechromium iodide in water. (6) D. R. Scott and R. S. Becker, J . Organonzetal. Chsm., in press.
vohnte 69, Number 9 September 1966
