2494
In the calculation the usual assumption was made that the linear terms are -0.1 of the corresponding 3 ? quadratic terms. Bond lengths are not available for these ions, and so distances RCC= 1.39 A, yccl = 1.79 A, and rCBr = 1.90 A were assumed. Force constants and for UBFF were refined by iterative calculation using a Consoli3 dated Data Corp. 1604 electronic digital computer. 2 VUBFF = 2 VSVFF 2C Kcc'RAR, In the SVFF calculation, the observed frequencies r=l 3 3 3 were all equally weighted except for the band at 200 2CKcx'rAr, 2 C H c c x ' r 3 W CFcx[(Aqctx,+J2 cm-', which was given a weighting one-half as large as z=1 ;=l i=l the others. The agreement of the calculated and ob3 served frequencies were within i 0 . 4 x except for the (A4C,X,-J21 2 c F c x ' [ 4 c x ( ~ ~ c ,1 x , +Aqc,x,-JI r=l 200-cm-' band, which showed a deviation of - 5.1 %, 3 3 Cxx(Aqx,x,+J2 2 c c x x ' ( ~ x x ~ 4 x , xJ, + Acknowledgments. We thank the National Science ,=l r=l Foundation for partial support of this work, and the where K and H have their usual meanings of stretching National Institutes of Health for a predoctoral fellowand bending force constants, respectively, X denoting ship to S. W. T. We are indebted to the Argonne halogen. FCX and Cxx are geminal and cis repulsion National Laboratory for making Raman equipment terms, respectively, between nonbonded atoms; q available to us, to Mr. Joseph Wheeler for constructing is the distance between nonbonded atoms. The linear the special Raman tubes, and to Mr. Paul Kwitowski terms are indicated with a prime. for the preparation of C3Cl4.GaCI3.
+
+
+ + c
+
+
+
+
+
Thermally Induced Skeletal Rearrangements of Tropilidenes' Jerome A. Berson and M. Robert Willcott, 1112 Contributionfrom the Department of Chemistry, University of Wisconsin, Madison, Wisconsin. Received February 4, 1966 Abstract: 3,7,7-Trimethyltropilideneheated at 300" in the gas phase gives a mixture containing recovered starting and m- and p material, 2,7,7-and 1,7,7-trimethyltropiidenes,3- and 6-isopropenyl-l-methyl-l,4-cyclohexadienes, cymenes. The nonaromatizing rearrangements are reversible. Under the same conditions, 1,5-dideuterio-3,7,7-trimethyltropilidene gives the corresponding dideuterated products, in each of which the alternating pattern (D, H, lone methyl, H, D) of substitution characteristic of the starting material is preserved. The rearrangement is therefore one in which the carbons 1-6 of the starting material remain in the same sequence, while C-7 and its geminal methyls are allowed to wander and reattach between any adjacent pair.
T
ropilidene (1) is perhaps the most intensively studied member of the class of odd-numbered cyclic polyenes CH2(CH=CH), ( n = 1, 2,. . . . .). Its response to thermal energies over the temperature range from -150 to above 400" has been examined by a variety of techniques. The most facile change is the conformational ring inversion (e.g., l a $ l b ) of two nonplanar isomers revealed by the low-temperature nmr spectrum of the parent compound (E, = 5.7-6.3 kcal/ and the 2-t-butyl-3,7,7-trimethylderivative.4 At a perhaps slightly higher level of activation energy
la
Ib
(1) (a) We are indebted to the Camille and Henry Dreyfus Fund and to the Army Research Office (Durham) for support of this work. (b) For preliminary reports, see J. A. Berson and M. R. Willcott, 111, J. Am. Chem. SOC.,87, 2751,2752(1965). (2) National Institutes of Health Postdoctoral Fellow, 1964-1965. (3) (a) F. A. L. Anet, J. Am. Chem. SOC.,86, 458 (1964); (b) F. R. Jensen and L. A. Smith, ibid., 86, 956 (1964). (4) I
