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JAKO198213464447949.Pdf 66 Bulletin of Korean Chemical Society, Vol. 3, No. 2t 1982 J니 ng—Hyu Shin (17) K. Shinoda, T. Hayashi, T. Yoshida, K. Sakai A. Nakajima, Biopolymers. 17, 805 (1978). Polym. J.r 8, 202 (1976). (26) H. Fukuda Y. Kiku아 li. Bull. Chem. Soc. Jpn. 51, 1142 (18) K. P. Schodt and J. Blackwell, Biopolymers, 15, 469 (1978). (1976). (27) K. Abe, H. Ohno A. Nii and E. Tsuchida, MakromoL Chem., (19) M. Hosono, S. Sugii, 0. Kusudo and W. Tsuji, Kobunshi 179, 2043 (1973). Ronbunshu. 33/ 509 (1976). (28) T. Kdmoto, Y. Kojima and T. Kawai, MacromoL Chem., (20) Y. Kiku아 li, Y. Onishi, M. Kodama, J. Appl. Polym. Sci.. 179, 1861 (1978). 20, 3205 (1976). (29) A. Nakajima and S. Tanaka, Polym. Prepr. Japan, 17, (21) K. Abe. M. Koide and E. Tsuchida, Polym. J., 9, 73 (1977). 473 (1968). (22) K. Abe and E. Tsuchida, Polym. J., 9, 79 (1977). (30) K. Itoh, B. M. Foxman and G. D. Fasman, Biopolymers, (23) H. Fukuda and Y. Kik니아 li, MakromoL Chem.t 178, 2895 15, 419 (1976). (1977). (31) N. Greenfield and G. D. FasnMn, Biochemistry, 8, 4108 (24) S. Sugii, M. Hosono and R. Kitamaru, Kobunshi Ron- (1969). bunshu, 35, 441 (1978). (32) C. W. Bunn, Nature, 161> 929 (1948). (25) S. Hirano, C. Mizutani, R. Yamaguchi and O. Miura, Direct Observation of an Antihomoaromatic Bicyclooctadienyl Cation Jung-Hyu Shin Department of Chemistry, Seoul National University, Seoul 151, Korea (Received February 2, 1982) The question of the bicyclohomoaromatic stabilization and destabilization is examined. The chemistry of bicyclo (3. 2. 1.) octa-3, 6-dienide anion has been studied on order to test these concepts. The bicyclooctadienide anion is shown to be stable delocalized ion which undergoes a facile proton-deuterium exchange reaction. The solvolysis of bicyclo (3.2.1) octa-3,6 -dienyl p-nitrobenzoate is much slower than the monoene analog. We have made direct observation of the bicycloocata- dienyl and octenyl cations by 19F-nmr spectroscopy, and were able to demonstrate that the bicyclooctadienyl cation was bishomoantiaromatic. about the long-range stabilization of ionic centers by remote Introduction carbons. One of the most fascinating concepts to develop The stabilization of carbonium ions and carbanions by from this interest was the theory of homoaromaticity5. means of cyclic charge delocalization or aromaticity is well Goldstein6 used MO symmetry arguments to extend the documented and universally accepted. concept of the homoaromatic ions to bicycloaromatic The cyclopropyl cation I1 and the cyclopentadienyl anion species. 22 are just two examples of a large number of the welJknown Bicyclo(3.2.1)octa-3,6~diene(5), previously reported by carbonium ions and carbanions whose unusual stability is Brown and Occolowitz7, is more reactive compared with the thought to be due to this effect. monoene analog 6 in allylic proton-deuterium exchange in DMSO-jBuOK. Molecular orbital symmetry arguments have suggested that anion 4 should also have enhanced stability. The iH—nmr spectrum of the bicyclohomopenta- 5 dienide anion 4 has been reported by Winstein8, and all of the features are in accordance with the delocalized six- ^-electron bishomaromatic species with appreciable ring currents. The rates of the solvolysis of the p-nitrobenzoates of bycyclo〔321〕octa—3,6—dienyl(7) and bicy이 。〔321〕 octenyl (8) in aqueous acetone have been studied by Diaz 3 4 6 and his coworkers9. Recently many evidences have been presented in support of Here, 나 le 6,7-double bond in 7 makes the intermediate a new stabilization mechanism for carbonium ions and cation a four-7r-electron antiaromatic species and, therefore, carbanions, generally known as homoaromaticity3. retards the reaction in contrast with monoene analog 8. The 7-norbornenyl cation 3 and the bicyclooctadienyl anion It occured to us that a study of the 19F-ninr and 13C-nmr 4 are considered to be homologs of 1 and 2, respectively, and spectra of the /j-fluorophenyl bicyclooctadienyl cation 9 their unusual stability has been attributed to homoaromaticity. and especially comparison of these spectra with those of Since the early work on the solvolysis of the cholestryl the /y-fluorophenyl bicyclooctenyl cation 10 would be chloride4, Winstein and his coworkers have been concerned ideally suited in providing the information about long- Direct Observation of an Antih이 Tioa「omatic Cation Bulletin of Korean Chemical Society, Vol. 3, No. 2, 1982 67 Results and Discussion The carbinols were prepared from the Grignard reagent and the corresponding ketones in dry ether. Preparation and properties of the carbinols are described in the Experimental Section. Assignment of resonance signals in the 1H-nmr spectra of the carbinols achieved by decoupling experiments a하 d by preparation of Eu (DPM)3 complexes, and that in the 13Cnmr spectra was confirmed by double-resonance experiments. Solution of carbonium ions 퍼 ， ere prepared as follows. To a stirred mixture of fluorosulfonic acid and sulfuryl chloride, a solution of each carbinol in CD2C12 was added dropwise range— 兀一 interactions and homoantiaromaticity in the at -120°C in a special reaction apparatus. The spectra of octadienyl cation. The paraproton nuclear magnetic resonance the carbonium ions were unchanged from -120°C to -30° C chemical shift of the tertiary phenyl carbonium ions (Ila) and hence, recorded at -50° C. At -20° C 나 le carbonium ions could serve as a measure of the ^-electron demand of the carbonium ion center10. rearranged producing unknown species. In the nmr spectra of the carbonium ions, the absorption signals usually 아 lifted downfield compared with the carbionols. The chemical Ila. R=H shift differences of 나 le bicyclooctadienyl (I), bicy이 ooctenyl(II) lib. R=F and bicycloheptadienyl (III) cation relative to those of the corresponding precursors are summarized in Table 1. Although a linear correlation of the chemical shift value The olefinic protons (H6, H7) in I appeared at )7.27 and with the log of the calculated delocalization energies was 少 6.84 as a triplets, both protons shifting downfield by 0.63 observed over a range of carbonium ion stabilities, the and 0.83 ppm relative to H 6,7 in the corresponding carbinols. iH—nmr chemical shift was too insensitive for energy di­ These shifts are appreciably more downfield in contrast with fferences to be useful (in the neighborhood of 1 ppm/100 these for H 6,7 of III. kcal). On the other band, the signal for H8 of I shifted downfield The 19F-nmr spectroscopy is advantageous in view of its by 1.1 ppm illative to H8 in the corresponding carbinol. order of magnitude greater sensitivity to electron demands This value is about two times greater than that (0.5 ppm) (1 ppm/0.75 kcal) of the cation center (lib), and comparative for H8 of II. insensitivity to magnetic anisotropies of the solvent and This may be attributed to a small ring current effect, which molecule. is also manifested by bicyclo (3.2.1) octa-3,6-dienide anion. We are now able to calculate the homoantiaromatic desta­ Upfield shifts of the H8 protons in the octadienide anion bilization energy by comparing the 19F-nmr chemical shifts relative to corresponding diene by 1.1 ppm are attributed at of the octenyl and octadienyl cations. least partly to a ring-current effects11. This can be explained in term of the appreciable long range ^-interactions between TABLE 1. 1 2 3 4 5 6 7 8 9 10 11 12 19F-nmr 0, PPm) I a. -1.8 -2.4 -2.9 一 1.45 一 0.63 一 0.83 一 1.1 -1.18 一 0.67 一 39.51 b. + 0.65 -134.9 +0.938 -55.18 -11.2 一 0.23 -3.5 一 19.7 + 11.29 一 12.2 -5.6 一 13.5 exo. endo. II a. -2.2 一 2.62 一 2.98 — -1.03 一 0.35 一 0.5 一 1.3 一 0.62 -35.13 b. +0.5 -131.7 +7.7 -5-18 -9.6 +3.8 一 4.05 -7.0 + 13.28 一 12.6 -5.46 -12.2 in a. -1.78 -2.9 -3.23 —.38 -0.26 -0.47 a. iH-nuir (3, ppm); b. 13C-nmr 0, ppm) 68 Bulletin of Korean Chemical Society. Vol. 3, No. 2, 1982 Jung-Hyu Shin the vacant p-orbital of the cationic center and the 6,7-double in a special apparatus. The chemical shifts in and 13C- bond in I, which leads to a bishomocyclopentadienyl species. nmr spectra of carbonium ions were determined from re­ Strikingly, the upfield shift (+7.7 ppm) of C3 in II is much ferenced internal €02€12(|55.4, 53.6). The 19F-chemical iH-nmr spectra in I and II are comparable. The small shifts of the carbonium ions were taken up from computer greater than that(+O.938ppm) in I, while 나 ic shifts in analyzed data. unfield shift of C3 in I is the result of the inefficient allylic 1. Synthesis of Carbinols conjugation due to the unfavorable electrostatic interaction (1) p-Fluorophenyl bicyclo(3.2. T)octa-3fi-dien-2~ol. with the adjacent positive center, while the allylic conjugation Bicyclo(3.2.0)hex-2-en-6-endo-Cai-boxaldehyde (Z). To a is well facilitated. rapidly stirred suspension of 110g (1.12 mole) of anhydrous The greater positive charge on C2 of I compared with C2 sodium carbonate in the solution of 83.7 g (0.9 mole) of of II is also seen in the downfield 아 lifts (-134.9 and -137.7 bicyclo(2.2.1) heptadiene in 730 m/ of methylene chloride was ppm) of the carbons relative to the corresponding carbinols.
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