J. Am. Chem. SOC.1981, 103, 3539-3543 the products and obtain their material balances which are listed in the last two columns of Table V, where they are expressed as percentages of the initial amounts. The very small differences indicate reasonable analytical precision and no loss of material
3539
in the course of the thermal disproportionation. The differences are nevertheless sufficiently large to preclude quantitative analysis for the much less extensive concentration changes specifically due to the 0 atom reactions in the experiments listed in Table IVC.
13C-lH Coupling Constants in Carbocations. 3.’ Variation of AJ with Electron Demand in Aryldialkyl Carbocations David P. Kelly,* Graeme J. Farquharson, Joseph J. Giansiracusa, Wendy A. Jensen, Helmut M. Hugel, Anne P. Porter, Ian J. Rainbow, and Pamela H. Timewell Contribution from the Department of Organic Chemistry, University of Melbourne, Parkville, Victoria 3052, Australia. Received August 4, 1980
Abstract: One-bond ‘T-H coupling constants for groups adjacent to the cationic center have been measured for 3-arylnortricyclyl (l), l-aryl-l-cycIopropylethyl(2),2-arylnorbrnyl(3), 1-aryl-1-methylethyl(4), and 1-arylcyclopentyl (5) carbocations. The differences AJ between ‘JCHin the cations and those in neutral, model ketones are linearly dependent upon electron demand at the cationic carbon as measured by cr’ constants. Combination of this relationship and the original AJ equation gives a new equation for aryldialkyl carbocations which relates AJ to both the dihedral angle between the C-H orbital and the vacant p orbital and the electron demand at the cationic carbon, AJ = (1 + 0.6a+)(10.9 - 14.3 cosz 0).
We have previously examined the applicability of one-bond 13C-lH coupling constants (lJCH) as a criterion for structure determination in a range of alkyl carbocations.l In static, classical, tertiary, alkyl cations we have shown that JcH of groups adjacent to the cationic carbons differ from those in appropriate, neutral model compounds (ketones) by an amount depending upon the dihedral angle 6 between the C-H bond and the unoccupied p 0rbital.l This dependency is given by AJ = A - E cos2
e
9, m
p
R
1
Results and Discussion The use of aryl substituents to vary the charge density at an attached cationic carbon in a controlled fashion is well documented both for solvolytic studies3and for N M R studies in superacidse (1) Part 11: Kelly, D. P.; Underwood, G. R.; Barron, P. F. J . Am. Chem. SOC.1976, 98, 3106-311 1. (2) Pachler, K. G. R., Pachter, R. Org. Magn. Reson. 1979, 12, 183-184. AJ = a. + a2 cosz 0 + a4 cos‘ 0 , a = 5.51 Hz, a2 = 18.4 Hz, a4 = 7.08 Hz; the hyperconjugative constant is thus -1 1.32 Hz.
0002-7863/81/lS03-3539$01.25/0
2
%
3
3
(1)
where W is the JcH value in the cation less that in a model ketone, A is the maximum inductive enhancement of JCH(22.5 Hz), and B is the maximum hyperconjugative diminution of JCH (33.1 Hz). Thus a maximum enhancement of JCH occurs for ions where 6 = 90’ (+22.5 Hz) and an actual diminution of JCHwhere 0 = 0’ (I-1OHz). For ions where 0 = 30°, for example, C2-H of 1-methylcyclopentyl and C3-H of 2-methylnorbornyl cations, no difference is observed from the values of cyclopentanone and 2-norbornanone, respectively.’ Recent INDO-FPT calculations of Pachler and Pachter confirm the validity of the general form of our equation, although the calculated values of the constants are somewhat less than our experimental ones.* Equation 1 was derived from data for static, tertiary methyl carbocations in which a “full” positive charge was considered to reside on the cationic carbon and the A term was therefore considered to be a measure of the inductive effect of a “full” charge. The obvious extension of our systematic investigation was thus to measure JCH as a function of charge density at the adjacent cationic carbon. We now report the results of this investigation for cations 1-5 where the aryl group provides a controlled variation in the electron demand at the cationic center which can be quantified by the appropriate Hammett substituent constant.
R
3%
R
4
5
The choice of substituent constant to quantify this variation in charge density is critical, as has recently been demonstrated for 13Cshift correlations of cations in superacids.’ For the groups adjacent to the cationic center in ions 1 - 5 , y e have used both Brown’s gC8 and a substituent constant uaC , derived from the methyl carbon shifts of a range of meta- and para-substituted 1-methyl-1-phenylethyl cations (4) generated in HSO3F/SbFS/ SOtClF.’ (3) For example, H. C. Brown’s “Tool of Increasing Electron Demand”: Brown, H. C. “The Nonclassical Ion Problem”; Plenum Press: New York, 1977; Chapter IO. This technique has been applied to the systems under consideration here. 3-Nortricyclyl (1): Brown, H. C.; Peters, E. N. J . Am. Chem. SOC.1975, 97, 1927-1929. 1-Cyclopropylethyl ( 2 ) : Brown, H. C.; Peters, E. N.; Ravindranathan, M. Ibid. 1977, 99, 505-509. 2-Norbornyl (3): Brown, H. C.; Ravindranathan, M.; Takeuchi, K.; Peters, E. N. Ibid. 1977, 99, 2684-2690. 1-Cyclopentyl (5): Brown, H. C.; Peters, E. N. Ibid. 1975, 97, 7454-7457. (4) (a) Farnum, D. G.;Wolf, H. D. J . Am. Chem. SOC.1974, 96, 5166-5175. (b) Farnum, D. G.; Botto, R. E.; Chambers, W. I.; Lam, B. J . Am. Chem. SOC.1978, 100, 3847-3855. (5) Olah, G. A,; Prakash, G. K. S.; Liang, G. J . A m . Chem. SOC.1977, 99, 5683-5687. ( 6 ) Kelly, D. P.; Spear, R. J. Aust. J . Chem. 1977, 30, 1993-2004. (7) Kelly, D. P.; Spear, R. J. Aust. J . Chem. 1978, 31, 1209-1221. (8) The values of upt are M e 0 -0.78, Me -0.31, F -0.07, CI 0.1 1, and CF3 0.61; umt CF30.52: Stock, L. M.; Brown, H. C. A d a Phys. Org. Chem. 1963, I , 35. (9) The values of updc+ are M e 0 -1.29, Me -0.49, F -0.24, CI -0.07, Br -0.1, and CF3 0.70; umd+ CF3 0.51, derived frop the least-squares analysis of meta and para cations 4 (A6(CH3) = 4 . 1 2 4 r 0.990, SD 0.22). Brown, H. C.; Kelly, D. P.; Periasamy, M. J . Org. Chem., in press.
0 1981 American Chemical Society
3540 J . Am. Chem. SOC.,Vol. 103, No. 12, I981
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J. Am. Chem. SOC.,Vol. 103, No. 12, 1981 3541
l3C-'H Coupling Constants in Carbocations
I
-
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Consideration of eq 1 applied to the aryl cations 1-5 provides us with the following expectations. First, substitution at the cationic carbon by aryl groups (rather than methyl') should result in lower values of A and B due to delocalizationof charge. Second, for a series of ions with the same stereochemistry, the greatest variation of A J with electron demand should occur for those with 0 = 90'. From the data collected in Table I, we obtain values of AJ for ions where the dihedral angles are expected to be 90' (1, C2-H; 2, C,-H), 80' (3, C1-H), 45' (2, 4, C-H3), and 30' (3, C3-H; 5, C2-H). 8 N 90". 3-Arylnortricyclyl (l),l-Aryl-l-cyclopropylethyl(2), and 2-Arylnorbomyl(3). The C2 doublets of 1 in some cases were obscured by other multiplets in the normal coupled spectrum, but selective excitation of C2 allowed accurate measurement of JC H (see Experimental Section). In these rigid ions the dihedral angle of C2-H is unambiguous (19 = 90') and gives rise to large values of A J (based on the JCH value of nortricyclnanone, 186 Hz') which vary from 5 Hz for p-OCH3 to 16 Hz for 3,5-(CF3)2. Satisfactory linear correlations are obtained with both u+ and c f C + ( r 0.997, 0.994, respectively.). Since uaC* has been shown to yield more accurate correlations than 'u with cy-carbon chemical shifts9 it is surprising that such little difference is observed in the correlations with JCH. This may be due to the fact that we cannot measure JC,H with the same relative accuracy as we can measure chemical shifts in these cations. In the flexible 1-cyclopropylethyl cations (2) there is the possibility of distortion of 0 from the most favorable bisected arrangement. AJ values for the apical methine carbon (C2-H) based on the value for cyclopropyl phenyl ketone (6, 167 Hz) increase from 7 Hz for p-OCH3 to 18 Hz for 3,5-(CF3), with an excellent linear correlation (u' r 0.997) and an identical gradient to that for 1.l0 The latter indicates that there has been no deviation in the dihedral angle from that in 1. This is confirmed by consideration of the change in chemical shifts of cyclopropyl carbons in 1 and 2. In 1 the cyclopropyl group is locked into the favored bisected arrangement with the cationic center. a-II delocalization of positive charge into the cyclopropyl ring is most favored in this orientation," as evidenced by the substantial change in 6C2 and 6c1,6from R = p-OCH3 to R = 3,5-(CF3),; C2 33.6 61.1 (27.5 ppm) and Cl.6 43.1 80.4 (37.3 ppm) (Table I). For the nonrigid cyclopropyl cations 2 the values are 21.7 ppm (C,) and 25.8 ppm (C3,J, somewhat less than for 1 but still much greater than for C, and C, carbons in other cations, for example, 3, C1 1 1.8 and c 6 7.5 ppm.I2 In addition the para carbon shift (R = p-H), which is the most reliable criterion for charge density at the cationic carbon,' is slightly less for 2 (145.9) than for 1 (148.9). Significant deviation of the dihedral angle from 90' would result in higher charge at C1 and a greater para shift. We are now left with one anomaly. The AJ values for 2 are consistently 2 Hz greater than those for 1 and 3 (Figure 1A). Initially this suggests a higher positive charge at the cationic carbon, brought about either by rotation of the aryl substituent
w
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5 ;w c w
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9
w
F'
r-
03
2
2
2 I/
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-
(10) The AJ values would be significantly higher (4 Hz) if cyclopropyl methyl ketone (163 Hz) had been used as the neutral model compound. (1 1) Brown, H. C. "The Nonclassical Ion Problem"; Plenum Press: New York, 1977; Chapter 5 . (12) The greater chemical shift range (A8C ppm) of c,5over C, observed for 1 and 2 requires some comment. In some aryl cations such as l-aryl-lcyclopentyl,l 1-aryl-1-cyclohepty1,band 3-aryl-3-pentylc 6Cg varies very little and is close to zero (AX, N 8-12, A8C,5 N 0.1-3), in others such as 2aryl-2-adamantylc and 3, A6CBis significant (7-9) but still less than A8C, (12-14), while in 1 and 2 it is large and greater than A K , . This is probably due in part to the ability of C, to delocalize the charge and may be dependent upon c,-c,5 hyperconjugation. Changes in the hybridization of C, are not indicated in 1 as Jc, 6H is constant. In 2, Jc varies a small amount (4 Hz) which may indicate'some change in hybridization or structure. However, excellent linear correlations of A8C, or A K , with &+ constants for both 1 and 2ddo not support such changes. The factors influencing both J and 8 are complex and cannot be elaborated further at this stage. (a) Brown, H. C.; Kelly, D. P.; Periasamy, M. Proc. Nail. Acad. Sci. U.S.A. 1980, 77, 6956-6960. (b) Brown, H. C.; Periasamy, M. J . Org. Chem., in press. (c) Kelly, D. P.; Jenkins, M. J.; Mantello, R. A. J . Org. Chem., in press. (d) Brown, H. C.; Giansiracusa, J. J.; Kelly, D. P.; Periasamy, M., unpublished results.
3542 J. Am. Chem. SOC.,Vol. 103, No. 12, 1981 20
Kelly et al.
T
t
C
(-B cos2 e) exactly cancels the inductive enhancement ( A ) by the positive charge so that no change occurs for JcH of the group between that of the neutral ketone and that of the carbocation. Thus for C3-H of 3 and C2H of 5, AJ is expected to be constant (zero), independent of electron demand of the cationic center. This is indeed the case as is shown in Figure 1C. The AJ values for 3 were based on Jca for 2-norbornanone ( 9 ) measured at 67 MHz (previously measured at 18 MHz') to reduce the experimental error. The C3 multiplets of 3 could all be measured at 25 M H z without recourse to selective excitation techniques, as at least two adjacent lines of the triplet were always visible. This is not the case for C6and C7 where substantial overlap of the multiplets occurs. Selective excitation of each multiplet in turn provided the data in Table I. General Conclusions Within the experimental error, AJ is linearly dependent upon electron demand at the adjacent cationic carbon for all the aryl cations 1-5. From the data for the parent phenyl cations (1-5, R = p-H) we obtain an equation
ELECTRON
DEMAND
+
Figure 1. Correlations of AJc,
with electron demand in 1-aryldialkyl c a r h a t i o n s where the dihedral angles are A, 90'; B, 45O; and C, 30'. Error bars are 1 Hz.
out of orthogonality with the vacant p orbital (which would have to be the same in all the aryl substituents since the plot is linear and of the same gradient as for 1) or by decreased ability of the alicyclic moiety in 2 to stabilize the charge.I3 From the above discussion of chemical shifts this does not appear to be the case and we can only conclude that there are factors other than dihedral angle and charge density affecting AJ still to be delineated. In the case of 2-arylnorbornyl cations 3, the CI-H bond makes an angle of approximately 80" with the adjacent p orbital,' from which we may expect a reduction in the AJ values and/or the slope of the correlation line. However, the values are almost coincidental with those for 1 (a+ r 0.997) which is in fact reasonable, since a change of 10" results in an insignificant change in AJ (C0.5 Hz) as determined by eq 2 derived from data for the 1-phenyl cations 1-5, R = p-H (see below). Application of the para carbon shift criterion to 3 (1 52.5, R = p-H) indicates that there may be greater positive charge at C2than at the cationic carbons in 1 and 2, the effect of which would be to offset any decrease in AJ due to changes in 0. For clarity of presentation the AJ values for 1, 2, and 3 are plotted together against u+ in Figure l A , the overall linear correlation with u+ being inferior to that of each individual series 1, 2, and 3 (u', uoC+r 0.966, 0.962). 8 = 45". 1-Aryl-1-cyclopropylethyl(2)and 2-Aryl-Zpropy1(4). In freely rotating methyl groups, the dihedral angle between the C-H orbital and the adjacent p orbital is effectively 45", that is (cos2 e) = 0.5.14 Thus the AJ values of the methyl groups of 2 and 4 are expected to be lower than those of groups where 0 = 90". This is observed, as seen in Figure 1B. The small positive slope (0.78) shows the much reduced dependence of AJ on electron demand as 0 decreases and as a consequence the correlation coefficient of the line decreases. In order to show that the variation in AJ is a result of variation in Jc.H of the cation and not the model compound, we have measured Jc,H of the methyl groups of p-methoxy (7)and p (trifluoromethy1)acetophenones (8) where the methyl quartets are sharp (absence of long-range coupling) and the couplings can be measured to C f l Hz. The values are identical (128 Hz, Table 1)* 0 = 30". 2-Aryl-2-norbornyl (3) and 1-Arylcyclopentyl (5). From eq 1, when 0 = 30" the hyperconjugative diminution of AJ (13) Stabilities of alicyclic carbocations in the gas phase are determined in part by the number of carbon atoms in the skeleton: Solomon, J. J.; Field, F. H. J . Am. Chem. SOC.1976, 98, 1567-1569. Staley, R. H.; Wieting, R. D.; Beauchamp, J. L. J. Am. Chem. SOC.1977, 99, 5964-5972. Saluja, P. P. S.;Kebarle, P. Ibid. 1979, 101, 1084-1087. (14) Heller, C.; McConnell, H. C. J. Chem. Phys. 1960, 32, 153551539,
AJ = 10.9 - 14.3 COS^
e
(2)
where the magnitudes of the constants reflect the decrease in charge density at the cationic center from that in the corresponding methyl cations. For each series of ions 1-5 with the same substituent, similar equations are obtained but with different values of the constants. From the ratios of each constant AR+H/AR=H and BR+H/BR=Hwe derive an empirical relationship relating AJ to both dihedral angle and the electron demand at the cationic center
AJ = (1
+ 0.6~+)(10.9
14.3 COS^
e)
(3) where the electron demand (charge density) is measured by u+. The excellent linear correlations of AJ with electron demand as given by both the solvolytic constant u+ and the superacidic constant&* indicate that AJ is a reliable probe for charge density at adjacent cationic carbon. Use of this equation constitutes the first quantitative experimental method for determining stereochemistry of carbocations in superacids. -
Experimental Section NMR Spectra. "C spectra of the model compounds in CDC13 were recorded at probe temperature on either a Bruker HX-270 ( 9 ) or a JEOL FX-100 instrument ( 6 8 ) . Spectra of the ions were recorded at various temperatures between -25 and -70 'C (see below) on either or both a hybrid Varian HA-60/Digilab/PDP-l5 spectrometer operating at 15.08 M H z in the F T mode or a JEOL FX-100 spectrometer operating at 25.00 MHz. Field stabilization was provided by a concentric capillary (3 mm 0.d.) of acetone-d6 containing Me4% Chemical shifts are f 0.1 ppm from external Me4Si. The proton-coupled spectra were obtained by the normal gated decoupling technique with a minimum 50% duty cycle, using spectral widths of 3128 H z and 8K data points (HA-60) or 5000 H z and 16K data points (FX-100). Coupling constants were measured by hand from multiplets plotted over 500 Hz chart width and are accurate to f l Hz. In some cases, e.g., 1 and 3 R = p-H, p-F, 3,5-(CF3)? selective excitation of a single "C multiplet was employed to obtain accurate values of JCH. This excitation was achieved by using a DANTE sequence of 50 pulses of 2 ps duration with a repetition period calculated for the first sideband.15 The decoupler was gated off during acquisition only. Assignments of the carbon resonances were straightforward, based on (a) previous assignments for 1-methyldialkyl', 3-nortricyclyl, 2-norb ~ r n y l-cyclopropyl,16 l~~ and 1-methylethyl' carbocations, (b) C-H and C-F coupling constants, and (c) known substituent effects in disubstituted phenyl cations.17 Least-squaresanalyses were performed on AJ for each series of cations with both u+ and uact. For A J = uu + b ( u type, a, standard deviation (SD), b, S D correlation coefficient (r)): 1, u', 6.17, 0.22, 9.83, 0.13, 0.997; 1, 4.37,0.26, 10.53, 0.20, 0.994; 2, u', 6.14,0.25. 11.81,0.15,
&,
(15) Morris, G. A.; Freeman, R. J . Magn. Reson. 1978, 29, 433-462. Bodenhausen, G.; Freeman, R.; Morris, G. A. Ibid. 1976, 23, 171-175. (16) Olah, G. A,; Westerman, P. W.; Nishimura, J. J. Am. Chem. SOC. 1974, 96, 3547-3559. (17) Hiigel, H. M.; Kelly, D. P.; Spear, R. J.; Bromilow, J.; Brownlee, R. T. C.; Craik, D. Aust. J . Chem. 1979, 32, 1511-1519.
J . Am. Chem. SOC.1981, 103, 3543-3550 0.997; 2 &+, 4.71,0.25, 12.56, 0.19, 0.994; 3, u+, 6.14,0.25, 9.81,0.15, 0.997; 3, e+, 4.71, 0.25, 10.56, 0.19, 0.994. For the coybined series of ions: 1-3, u+, 6.17, 0.41, 10.48, 0.25, 0.966; 1-3, & , 4.73, 0.33 11.22,0.26,0.962; 2 , 4 (45O), u+, 0.78,0.20,4.17,0.12,0.777;2,4, e+:
3543
-65 "C, (R = p-F) 0.35, HS03F/SbF5, -65 OC, (R = p-CF,) 0.60, HSO,F/SbF, -40 OC, (R = 3,5-(CF,)2) 0.33, HSO3F/SbF5,-65 OC; 2 (R = P-OCH,) 0.77, HSO3F, -60 OC, (R = p C H J 0.89, HSO,F, 4 0 OC,(R = p-H) 0.85, HSOIF, 4 0 OC, (R = pC1) 0.75, HSOoF, -60 OC, (R : p-CF3) 0.54, HSO,F/SbF, -70 OC, (R 3,5-(CF,)2) 0.45, HSOsF/SbF5, -70 OC; 3 (R = pOCH3) 0.46, HSO3F, -25 OC, (R p-CH,) 0.56, HSOSF, -25 OC, (R = p-H) 0.64, HSO3F, -25 OC, (R = P-CI) 0.54, HSO,F, -25 "C, (R = p-CFJ 0.47, HSO,F, -30 OC, (R = 3,5-(CF&) 0.38, HS03F,-30 OC; 4 (all HS03F/SbF5,-40 O C ) ' (R = p-OCH3) 0.44, (R = p C H J 0.48, (R = p-H) 0.51, (R = p-F) 0.51, (R = P-CF,) 0.38, (R = 3,5-(CFj)2 0.33; 5 (R = pOCH,) 0.77, HSO3F, -60 "C, (R = p-CH3) 0.84, HSO,F, -60 "C, (R = p-H) 0.91, HS03F, -60 OC, (R = P-CI) 0.75, HSO,F, -60 "C, (R = p-CF3) 0.53, HSO,F/SbFS, -60 OC, (R = 3,5-(CF3)2) 0.35, HSO,F/SbF5, -60 "C.
0.58,0.16,4.27,0.12,0.752;3,5(300),u~,0.19,0.24,-0.36,0.15,0.244; 3, 5, 0.15,0.19,-0.33,0.14,0.252.
e',
Ion hecursors. The tertiary alcohol precursors for 1-3 and 5 were
all prepared by standard Grignard procedures from the corresponding alkanones or were available from a previous s t ~ d y Physical .~ constants of these materials are available in the literature (H. C. Brown et a1.j) and we have measured their "C spectra. Preparation of Ions. The ions were prepared in known concentration from the tertiary alcohols either by direct addition to the precooled (-78 "C) acid solution or by addition of a solution (-10 to -70 "C) of the alcohol to the precooled acid solution. Ion, concentration, superacid, temperature of I3Cmeasurement: 1 (R = pOCH3)0.46 M, HSO,F, -25 OC, (R = p-CH3) 0.78, HSOjF, -70 OC, (R = p-H) 0.34, HSO,F/SbFj,
Acknowledgment. This work was supported by the Australian Research Grants Committee.
Transport of Photoproduced Ions in Water in Oil Microemulsions: Movement of Ions from One Water Pool to Another S . S.Atik and J. K. Thomas* Contribution from the Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556. Received December 1, 1980
Abstract: Pulsed laser photolysis techniques were used to study the following reactions in reversed micelles of AOT/alkane/water:
-
+ Fe(CN)63Ru"(bpy),* + MV2+
Ru"(bpy),*
+
-
PTST FS
Ru"'(bpy),
--
Ru"'(bpy),
+ Fe(CN)64+ MV'
PTS
PTST + Cu2+
PTS
where Ru"(bpy), and MV2+represent ruthenium tris(bipyridy1) and methyl viologen, respectively, while PTST and FS represent the triplet excited state of pyrenetetrasulfonic acid and Fremy's salt, respectively. These ionic reactants are associated only with the water pools of the reversed micelle systems, a situation which introduces unusual features into the kinetics. Analysis of the kinetics shows that the reactants distribute themselves among the micelles according to a Poisson rather than a geometric distribution. Analysis of the decay kinetics under various conditions enables the measurement of the exchange rate of ions among micelles to be measured. This ion exchange occurs only on collision of water pools, and the effectiveness of exchange is 1% or less in a simple AOT system for both Cu2+and the anionic Fremy's salt. Various additives such as benzyl alcohol markedly increase the efficiency of ion exchange, while solutes such as benzene decrease it. These data are discussed in terms of the interactions of the additives with the micellar head groups.
The last few years have seen considerable activity in the area of micellar catalysis. In particular, catalysis in reversed micelles or microemulsions has received detailed attention2s3 as these systems strongly catalyze many reactions. Much is known about the structure of specific systems:" and a reasonable description of reaction sites can be put forward with some confidence. Basically, these systems consist of pools of water (radii 15-150 A) stabilized in a bulk hydrocarbon by a suitable surfactant, e.g., disodium diisooctylsulfosuccinate (AOT), or a surfactant-cosurfactant pair, e.g., potassium oleate/hexanol or cetyltrimethylammonium bromide (CTAB)/hexanol. The surfactants
are located a t the water-hydrocarbon boundary. The nature of the water has received some attention,' and it is found that many physical measurements indicate that the properties reminiscent of bulk water are only approached in larger water bubbles. Micellar systems are of general interest as suitable vehicles for promotion of photochemical studies.* The correct selection of a system can lead to large yields of photoproduced ions which are stabilized by the micelle s y ~ t e m . ~ JSome ~ work in reversed micelles or microemulsions"-'3 suggests that these systems may (7)
2391. (1)
24861.
We thank the NSF for support of this research via Grant CHE-78-
(2) Fendler, J. H. Acc. Chem. Res. 1976, 9, 1953. Menger, F. Ace. Chem. Res. 1979, 12, 111. (4) Zulauf, M.; Eicke, H. F. J . Phys. Chem. 1979, 83, 450. (5) Shinoda, K.; Friberg, S . Ado. Colloid Inferface Sci. 1975, 4, 281. (6) Bansal, V. K.; Chinnaswamy, K.; Ramachandran, C.; Shah, D. 0.J . Colloid Interface Sci. 1979, 72, 524. (3)
0002-7863/81/1503-3543$01.25/0
Wong, M.; Thomas, J. K.; Griizel, M. J . Am. Chem. SOC.1976, 98,
( 8 ) Thomas, J. K.; Almgren, M. In "Solution Chemistry of Surfactants"; Mittal, K. L., Ed.; Plenum Press: New York, 1979; p 559. (9) Razem, B.; Wong, M.; Thomas, J. K. J . Am. Chem. SOC.1978, ZOO, 1679. .. ..
(10) Kiwi, J.; Graze], M. J. Am. Chem. Soc. 1978, 100, 6314. (1 1) Matsuo, T.; Nagamura, T.; Itoh, K.; Nishijima, T. Mem. Fac. Eng., Kyushu Uniu. 1980, 40, 25. (12) Ford, W. E.; Otvos, J. W.; Calvin, M. Nature (London) 1978,274, 507.
0 1981 American Chemical Society
