771
Communications to the Editor characteristic benzene bands of weak, medium, and high intensity are all clearly present. Vibrational structure in the longest wavelength band is not very pronounced and exhibits a slight shift toward shorter wavelength and lower intensity when compared with higher homologues. The IR spectrum of 3 (CHC13) shows bands at 2940,2870,1615, 1470,1384,1270, and 1 100 cm-'. Unlike 6-radialene, tricyclobutabenzene appears to be a quite stable molecule. It can be remelted with decomposition, will survive VPC temperatures of 250 "C, and remains unchanged after room temperature storage for several days. W e are continuing to investigate the chemistry of this intriguing molecule.
Acknowledgment. Financial support from the Robert A. Welch Foundation and the donors of the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged. We also thank Dr. Janice L. Greene of the SOH10 Corporation for a generous gift of 1,2-cyclobutanedicarboxylic acid. References and Notes (a) A. J. Barkovich, E. S.Strauss, and K. P. C. Vollhardt, J. Am. Chem. Soc., 99, 8321 (1977); (b) P. Schiess and M. Heitzmann, Helv. Chim. Acta, 61, 844 (1978); (c) L. G. Haruff, M. Brown, and V. Boekelheide, J. Am. Chem. Soc., 100, 2893 (1978). A . J. Barkovich and K. P. C. Vollhardt, J. Am. Chem. Soc., 98, 2667 (1976). (a) R. L. Soulen, S. K. Choi, and J. D. Park, J. Nuorine Chem., 3 , 141 (1973174); (b) R. P. Thummel, J. D. Korp, I. Bernal, R. L. Harlow, and R . L. Soulen, J. Am. Chem. Soc., 99, 6916 (1977); (c) R. E. Cobbledick and F. W. B. Einstein, Acta Crystallogr., Sect. B, 32, 1908 (1976). R. P. Thummel, J. Chem. Soc., Chem. Commun., 899 (1974). (a) R. P. Thummel, J. Am. Chem. Soc., 98, 628 (1976); (b) R. P. Thummel and W. Nutakul, J. Org. Chem., 42, 300 (1977); (c) R. P. Thummel, J. D. Korp, and I. Bernal, Tetrahedron, 33, 3069 (1977). (a) R. P. Thummel, W. E. Cravey, and W. Nutakul, J. Org. Chem., 43, 2473 (1978): (b) R. P. Thummel and W. Nutakul, J. Am. Chem. SOC., 100, 6171 (1978). F. Heinrich. PhD. Thesis, University of Gottingen, 1972. H. Normant and P. Maitte, Bull. SOC. Chim. Fr., 1424 (1960). R. N. McDonald and R. R. Reitz, J. Org. Chem., 37, 2418 (1972). TheVPCcolumnwas5ftX 1.5% OV-101 onChromsorbG 100/120 mesh at 180 OC and 30 mL/min. D. BelluS, H.-C. Mez, and G. Rihs, J. Chem. SOC.,Perkin Trans. 2, 884 (1974). It was found that this yield could be increased to 3.6% (10.8 mg) when only 1 equiv of lead tetraacetate was employed. After chromatography, the material thus obtained appeared to be mostly 9 by NMR but could be smoothly converted to 3 by treatment with DDQ. The fate of the remaining organic material in this decarboxylation is a question which is now receiving our serious attention in an effort to further increase the yield of this reaction. Although nonequivalent, these cyclobutyl protons show a coincidental singlet. The preparation and properties of this molecule will be described in a full paper regarding this work. R . P. Thummei and W. Nutakul, J. Org. Chem., 43, 3170 (1978). The VPC column was 6 ft X in. 3 % SP-2100 on Supelcoport 100/120 mesh at 120 O C (programmed at 4'/min) and 30 mL/min.
Wutichai Nutakul, Randolph P. Thummel* Austin D. Taggart Department of Chemistry, Uniuersily of Houston Houston, Texas 77004 Receified September 27, 1978
Intramolecular Excimer-Forming Probes of Aqueous Micelles Sir: We describe here the use of intramolecular excimer-forming compounds of type I as microviscometric probes of the interior of aqueous micelles. Since the conformation of I required for excimer formation would be sparsely populated in the ground state, a conformational transition is required during the lifetime of the excited For a given Ar and X, the rate constant for excimer formation ( k , ) is inversely dependent on the viscosity of the medium.l,2 At sufficiently low temperatures 0002-7863/79/1501-0771SO1 .OO/O
I
CTAC
oi
k b Ib
Id 16
;I
;I
;O
i2
P---J 40 42
44
7) (CP)
Figure 1. Im/Id vs. viscosity for probe Ia at 20 O C : (1) ethanol; (2) l-butanol; (3) triethylcarbinol; (4) 19:lO (v/v) ethanol-glycerol; ( 5 ) tributyrin; (6) 40:60 (v/v) ethanol-glycerol, EG (viscosity of 19.9 cP) exhibited an I m / I d ratio of >15. Dotted line represents extrapolation of the experimentally determined plot. Arrows indicate im/i,j ratios of Ia solubilized in micellar solutions and their corresponding microviscosities in centipoises.
22 ka
'
(".\ Ar..
Ia: X=O; Ar-4-biphenyl
Ib: X = N I I Z + C l - ;
Ar=l-napnthyl
.. .Ar
I
where the dissociation of the excimer ( k d ) may be neglected, the ratio of the intensities of excimer and normal fluoresence ( I d / I m ) is characteristic of kL,.'s4 Since compounds of type I are solubilized in solutions of aqueous micelles, miceller microviscosities may be estimated from a comparison of the Id/l,,1 ratios of the solubilized probes with appropriate references. This method has a distinct advantage over the intermolecular excimer fluorescence techniques because multiply occupied micelles are not required. la6 was chosen for our initial investigations because of its high quantum yield of emission and because the temperature a t which k d becomes significant is well above room temperature. Conditions were maintained so that >94% of the occupied micelles were singly occupied ([la] < IO-4 M; [surfactant] = 0.05-0.06 M).7 Thus, the contribution from intermolecular excimer emission is negligible. The micelles were labeled either by warming the aqueous micellar solutions containing the probe to 90 "C for 50 min and then cooling rapidly or by injecting an ethanol solution of the probe into the micellar solution (ETOH concentration
