693
stants calculated by the method of nonlinear least squares' and presented in Table I1 have standard deviations of 6 %. Product analysis by glpc-proportionalflow counting showed that I11 was the only peak to contain radioactivity.
Acidity of Hydrocarbons. XXIV. Proton Exchange of 9-Substituted Fluorenes with Methanolic Sodium Methoxide. Stabilization of 9-Trifluoromethylfluorenyl Anion by Inductive Effects
Sir: Interaction mechanisms of fluorine substituents are of particular interest. In the accompanying paper we Table 11. Kinetic Data for Tritium Incorporation Rates into have presented evidence that hyperconjugation effects 1 H-Undecafluorobicyclo[2.2.llheptane in Sodium Methoxideare not important in stabilizing fluoroalkyl anions. Methanol Solution In the present paper we demonstrate that normal in[NaOMe] Temp,* 10k2, M-' ductive field effects suffice to rationalize the relative Run no. X lo2, Ma "C secstability of 9-trifluoromethylfluorenyl anion. Pro-23.0 d 149 0.10 todetritiation kinetics were run in methanolic sodium -44.7 5.1 167 0.24 methoxide of several 9-substituted 9-tritiated fluorenes -44.9 9.1 180 0.25 including that from 9-trifluoromethylfluorene (I). This -52.9 2.89 228 1.1 0.80 222 5.3 -63.5 compound is reported in the literature as the product 0.93 190 5.2 -63.5 in 7.5% yield from the treatment of diphenyltrifluoro0.124 218 5.3 -74.1 methylcarbinol with sulfuric acid at room temperature,2 Substrate concentration 0.003 to 0.021 M. b &0.2". c f6z; but this product was characterized only by a melting corrected for the variation of the density of methanol with tempoint, 170.5-171 '. We find the cyclodehydration to be perature. d Complete isotopic equilibration in less than 3.3 min. more satisfactory in polyphosphoric acid at 120-1 30" for 1.5 hr, but the product recrystallized in quantitative yield from petroleum ether has mp 95.5-96.5°.3 The nmr spectrum (CCL) shows a complex multiplet The extreme reactivity of compound I11 is shown by in the aromatic region, 7 2.25-3.00 (8 H), and a wellcomplete isotopic exchange in less than 4 min at -23" defined quartet at 7 5.66 with JHF= 9 cps (1 H). This with 0.001 N base. Least-squares activation paramevidence together with the molecular weight (calcd, 234; eters calculated to be AH* = 12.4 f 0.2 kcal/mole found (osmometry), 222) confirms the structure of I ; and AS* = -3.7 f 1.1 eu allow comparison with the the compound isolated by Kaluszyner and Cohen2 is exchange rates determined by A n d r e a d e ~ . ~From the something else. Tritium was incorporated into the results summarized in Table I it is to be noted that 9 position to give I-t by treatment with pyridine concompound I11 is some five times more reactive than taining tritium-enriched water. The product of a tris(trifluoromethyl)methane,* This comparison prosimilar reaction with DzO showed the aromatic mulvides important evidence that carbon-fluorine notiplet of the nmr unchanged but the methine quartet was bond resonance does not provide significant stabilizaabsent. tion in tris(trifluoromethy1)methyl anion and, conThe exchange reaction of I-t with methanolic sodium sequently, that such hyperconjugation is probably methoxide was self-quenching ; from the reaction mixwithout significance in the other systems to which the ture there was isolated 9-trimethoxymethylfluorene, concept has been applied. The relative stability of colorless needles, mp 130.0-131.5°,3 but only if the these fluorinated carbanions undoubtedly derives largely reaction mixture was rigorously anhydrous. With from an inductive field e f f e ~ t . ~This comparison also traces of water the reaction product was methyl 9suggests that tris(trifluoromethy1)methyl anion has a fluorenecarboxylate. Protodetritiation kinetics were pyramidal rather than a planar structure; it is noteworthy that tris(trifluoromethy1)amine has a pyramidal obtained by using excess base (pseudo zero order in structure about the nitrogen. lo sodium methoxide) at low temperature with the experimental conditions of the preceding paper. The Acknowledgment. The authors wish to express gratifollowing reaction mechanism is indicated, but only tude to Professor J. C. Tatlow for his gift of a generous the rate of the first step is important in the present amount of compound 111. This research was supported context. The results summarized in Table I lead to in part by Grant No. GM-12855 from the National the activation parameters, AH* = 12.3 f 0.2 kcal/mole Institutes of Health, U. S. Public Health Service. and AS* = -15.6 f 0.9 eu. Protodetritiation kinetics of the other 9-substituted (7) We are indebted to Professor D. F. DeTar, Florida State Unifluorenes were normal and were followed by convenversity, for making available to us a copy of his LSKINI computer protional liquid scintillation counting methods. The gram. (8) Tritium was used in the present study. Andreades employed relative rates are summarized in Table 11. deuterium. Isotope effects do not alter the significance of the arguThe logarithms of the relative rates for the 9-subments presented. (9) A. Streitwieser, Jr., A. P. Marchand, and A. H. Pudjaatmaka, stituted fluorenes are plotted against the pK's of the J. Am. Chem. SOC.,89, 693 (1967). corresponding acetic acids in Figure 1. An equivalent (10) R. L. Livingston and G. Vaughan, ibid., 78, 4866 (1956). plot can be constructed us. uI of the substituents with (1 1) Woodrow Wilson Fellow, 1964-1965; National Science Foundation Predoctoral Cooperative Fellow, 1965-1967; Eastman Kodak the same results. Only the compounds with tertiary Science Award, 1966. hydrogens are plotted; fluorene itself, in which the exchangeable hydrogens are secondary, is omitted but ~~~~
0
A. Streitwieser, Jr., David Holtzll
Department of Chemistry, University of California Berkeley, California 94720 Received September 24, 1966
(1) A. Streitwieser, Jr., and D. Holtz, J. Am. Chem. Soc., 89, 692 (1967). (2) A. Kaluszyner and S. Cohen, Tetrahedron, 11, 252 (1960). (3) All new compounds in this paper have satisfactory analyses.
Communications to the Editor
694 Table 1. Protodetritiation of 9-Trifluoromethylfluorene-9-r [I-%
N
[NaOMe], N
0.00421 0.00421 0.00427 0,00427
0.143 0.262 0.145 0.266
104kl, sec-l
103k2,a 1. mole-’ sec-1
20.9 i 0 . 3 44.2 f 0 . 6 4.55 0.02 9.02 i 0.10
14.6 f 0 . 2 . 16.9 i 0 . 2 3.13 f 0.11 3.39 f 0 . 3 7 9700b
Temp, ‘C -31.5 f 0 . 3 -31.0 + 0 . 1 -45.3 & 0 . 4 -45.0 f 0 . 1 45
*
a At the reaction temperature; that is, kz is corrected for solvent contraction from room temperature. temperatures.
its inclusion would not alter the conclusions. A line drawn through the hydrocarbon substituents passes rather close to the point for the trifluoromethyl substituent. Because of the reactivity differences long
* Extrapolated from data at lower
Table 11. Protodetritiation of 9-Substituted Fluorenes in Methanolic Sodium Methoxide at 45’ 9-Substituent, Y
kreia
pKb YCOOH
H CH3 CHaCH, CH*Ce,Hj CH20CH3 CF3
1 .oo 0.26 0.18 0.72 12.9 2 x 104
... 4.76 4.88 4.31 3.57c -0.26, 0.23
-OCH,
+
k2 for fluorene-9-t is (43.2 i 1.5) X 1. mole-’ sec-I. We are indebted to R. A. MacQuarrie, R. I. Sadayasu, J. S . Wright, and Dr. T. L. Kruger for individual kinetic runs. J. F. King in “Technique of Organic Chemistry,” Vol. XI, Part 1, K. W. Bentley, Ed., Interscience Publishers, Inc., New York, N. Y . , 1963, p 317. c E. J. King, J. Am. Chetn. SOC., 82, 3575 (1960).
CH,OH.
extrapolations are required. The methoxymethyl group deviates significantly from the line, but this value is the result of a single kinetic run. The present conclusion does not change significantly if we draw the
precisely with additional compounds and measurements. Nevertheless, the present data suffice to establish that the trifluoromethyl group does not produce reactivity significantly in excess of that expected from inductive effects alone. In particular, there is no room in these results for any significant contribution from C-F anionic hyperconjugation. This study and that of the preceding paper’ are independent and involve different assumptions and logic, but lead to the same conclusion; taken together they provide compelling evidence for tlle absence of fluorine hyperconjugation as a significant stabilizing phenomenon in fluoroalkyl anions. Acknowledgment. This research was supported in part by a Petroleum Research Fund grant and by Grant No. GM-12855 of the National Institutes of Health, U. S. Public Health Service. (4) National Institutes of Health Postdoctoral Fellou, 1965-1966.
A. Streitwieser, Jr., Alan P. M a r ~ h a n dA. , ~ H. Pudjaatmaka Department of Chemistry, Utiicersity of Califortiin Berkeley, Califortiin 94720 Receiced September 14, 1966
Photochemical Rearrangement of o-Divinylbenzene
pK
YCOOH
Figure 1 . Comparison of kinetic acidities of 9-substituted fluorenes with the acidities of the corresponding substituted acetic acids.
best line to include the methoxymethyl group. Because of the importance of the correlation line in defining the magnitude of inductive effects in the exchange reactions of 9-substituted fluorenes, we expect to define it more Journal of the American Chemical Society
1 89:3
Sir : As a result of our interest in CloHlocompounds containing an aromatic ring fused to a system containing a small ring’ we decided to examine a possible route to one or more of these by a photochemical rearrangement of o-divinylbenzene (I). When a solution of I, pre-
ELm I
II
(1) M. Pomerantz, J . Am. Chem. SOC.,88, 5349 (1966).
February I , 1967
