J . Am. Chem. SOC.1983, 105, 4185-4190
4185
Experimental and Theoretical Studies of 3C-13C Coupling Constants. 1. Conformational and Substituent Dependencies of Long Range Coupling Constants 4J(13C-13C) Steven R. Walter,ln James L. Marshall,*lb,CCat0 R. McDaniel, Jr.,lb Edward D. Canada, Jr.,lb and Michael Barfield*ln Contribution from the Departments of Chemistry, University of Arizona, Tucson, Arizona 85721, and North Texas State University, Denton, Texas 76203. Received October 25, 1982
Abstract: The series of I3C-labeled 1- and 2-substituted adamantanes and 2-substituted bornanes were synthesized, and their I3C N M R parameters were accurately measured. Of particular interest in this study are the long range intercarbon coupling constants over four saturated bonds 4J('3C-C-C-C-13C) as these have not previously been investigated. Depending on conformational and substituent factors, these coupling constants have magnitudes ranging from 0.1 to 0.73 Hz in the compounds investigated. Because of their relatively small values, the J-resolved technique of two-dimensional Fourier transform N M R was important for many of the measurements. In contrast to interproton coupling constants over four saturated bonds, 4JHH$ the maximum values of 4Jcc.are obtained in those conformations in which the coupled atoms are in closest proximity, rather than in the all-trans arrangements for which the 4Jcc. are 0.3-0.6 Hz. Calculated results for the Fermi contact contributions to 4Jccl, which were based on the INDO-FFT molecular orbital method, are in exceedingly good agreement with the experimental values. As a consequence, it appears that the computational methods improve as the coupled atoms are further separated, and that the long range coupling constants will be useful for spectral assignments.
Because of their relatively small magnitudes (usually less than
0.6 Hz), there are only a few examples in the literature24 of long range 13C-'3Ccoupling constants between carbon atoms separated by four or more aliphatic bonds. T h e use of the J-resolved techniques of two-dimensional Fourier transform NMR permits the accurate measurement of small coupling constants.5v6 Furthermore, a major limitation associated with the requirements of I3C labeling appears to have been removed by the introduction of double q u a n t u m coherence technique^,^,^ which permit the measurement of small coupling constants in natural abundance samples. However, because of the abundance of information in the resulting spectra, some additional criteria m a y be required to assign the coupling constants correctly (e.g., in ref 7 it was incorrectly assumed that 14Jcc,l < 1 2Jcc,l). As a consequence, it will be of interest for such assignments to have information about the conformational a n d substituent factors for vicinal, geminal, a n d long range I3C-l3C coupling constants. Vicinal I3C-I3C coupling constants 3Jcc, have been the subject of a large number of studies from these and other laboratories,24i"8 and a r e often ( I ) (a) University of Arizona. (b) North Texas State University. (c) Present address: Motorola Inc., Fort Worth, Texas 76137; adjunct professor.lb
(2) Barfield, M.; Brown, S. E.; Canada, E. D., Jr.; Ledford, N. D.; Marshall, J. L.; Walter, s. R.; Yakali, E. J . Am. Chem. SOC.1980, 102, 3355. (3) Della, E. W.; Pigou, P. E. J . Am. Chem. SOC.1982, 104, 862. (4) For reviews of directly bonded, geminal, and vicinal 13C-13Ccoupling constants, see: Hansen, P. E. Org. Magn. Reson. 1978, 11, 215. Wray, V. Prog. N M R Spectrosc. 1979, 13, 177. (5) Bodenhausen, G.; Freeman, R.; Niedermeyer, R.; Turner, D. L. J . Magn. Reson. 1977, 26, 133. (6) Niedermeyer, R.; Freeman, R. J. Magn. Reson. 1978, 30, 617. (7) Bax, A.; Freeman, R.; Kempsell, S. P. J. Am. Chem. SOC.1980,102, 4849. Bax, A.; Freeman, R.; Kempsell, S. P. J . Magn. Reson. 1980, 41, 349. (8) Bax, A,; Freeman, R. J . Magn. Reson. 1980, 41, 507. (9) Marshall, J. L.; Miiller, D. E. J . Am. Chem. SOC.1973, 95, 8305. (10) Barfield, M.; Burfitt, I.; Doddrell, D. J. Am. Chem. SOC.1975, 97, 263 1. ( 1 1) Marshall, J. L.; Miiller, D. E.; Conn, S. A,; Seiwell, R.; Ihrig, A. M. Arc. Chem. Res. 1974, 7 , 333. (12) Barfield, M.; Conn, S. A.; Marshall, J. L.; Miiller, D. E. J . Am. Chem. Soc. 1976, 98, 6253. (13) Walker, T. E.; London, R. E.; Whaley, T. W.; Barker, R.; Matwiyoff, N. A. J . Am. Chem. SOC.1976, 98, 5807. (14) Marshall, J. L.; Conn, S. A,; Barfield, M. Org. Magn. Reson. 1977, 9, 404. ( I 5 ) Berger, S. J . Org. Chem. 1978, 43, 209. (16) Marshall, J. L.; Canada, E. D., Jr. J . Org. Chem. 1980, 45, 3123. (17) Marshall, J. L.; McDaniel, C. R., Jr.; Walter, S. R., unpublished work. 1981.
0002-7863/83/1505-4185$01.50/0
Table I. Calculated INDO-FPT MO Results for 4 J ~in ~Pentane, J 1-Pentanol, and Pentanoic Acid as a Function of the Dihedral Angles Q 1 and Q,a
4Jcc',HZ @,, deg
G2,deg
pentaneb
1-pentanol
pentanoic acid
0 0 60 60 60 180 180 180 300 300 300
60 180 0 60 180 0 60 180 0 60 180
20.82 0.46 20.82 -0.05 -0.01 0.46 -0.01 0.16 20.82 19.81 -0.01
20.83 0.46 20.39 -0.67 -0.06 0.60 -0.01 0.30 20.39 19.66 -0.06
17.71 -0.47 260.33 -0.16 -0.17 0.81 0.05 0.25 -1.14 - 1.45 -0.23
For the definition of the dihedral angles and Q2,see 1;igure In Figure 2, ' J C C ' for pentane is plotted as a function of O1 and Q2. a
1.
larger in magnitude than 2Jcctand 4Jcc,.An experimental and theoretical study of geminal I3C-I3C coupling 2Jcc. will be the subject of the second paper in this series.Ig Because the conformational and substituent dependencies of long range 'H-IH coupling constants over four bonds have been reasonably well characterized,20s21it seems reasonable to examine the similarities to I3C-l3C coupling over four bonds; the extension of the argument from 4 J ~in ~propane , to 4Jcc. in pentane suggests that the latter will depend on the dihedral angles C$l and C$2 as depicted in Figure I . T h e most conspicuous feature of 4JHH, in propanic systems is the large, positive maximum for the all-trans arrangement of the protons in which both dihedral angles are 180". For other orientations the 'H-IH coupling constants tend to be much smaller in magnitude, and the resulting signs are probably determined by a combination of conformational and substituent effects, Substituents a t the C 2 carbon of propane produce shifts (18) Barfield, M.; Marshall, J. L.; Canada, E. D., Jr. J . Am. Chem. SOC. 1980. 102. 7. (19) Barfield, M.; Walter, S. R. J. Am. Chem. Soc., following paper in this
issue. (20) Barfield, M.; Chakrabarti, B. Chem. Reu. 1969, 69, 757. (21) Barfield, M.; Dean, A. M.; Fallick, C. J.; Spear, R. J.; Sternhell, S.; Westerman, P. W. J . Am. Chem. SOC.1975, 97, 1482.
0 1983 American Chemical Society
4186
J . A m . Chem. SOC..Vol. 105, No. 13, 1983
Walter et al.
Table 11. Comparisons of Calculated and Vxperimental Results for Long Range 13C-13CCoupling Constants in the 1-Substituted Adamantanes 2, the 2-Substituted Adamantanes 4 , and the 1-Substituted 3,5-Dimethyladamantanes 3n 2-substituted adamantanes 4
1-substituted adaniantanes 2 4J(C5 .c11)C
4.J(C4,C1l i b
4J(C7,Cll)b
'J(C6,Cll)
substituent
exptl
calcd
exptl
calcd
exptl
calcd
exptl
calcd
a, R = CH, b, R = CH,OH c, R = CO,H d, R = CH,I e, R = CH,CN f, R = CO,CH,
(-)0.48 (-) 0.55 (-)0.5 1 (-)0.55 (-10.53 e
-0.44 -0.48 -0.58
(-)0.19 (-)0.13
