SHORT COMMUNICATION

Substituent Parameters v. Lanthanide-Induced Shifts in the Interpretation of the '"C Nuclear Magnetic Resonance Spectrum of 5,5-Dimethyl=2-norbornanone

Peter Yates* and Dong Dao Cong Lash Miller Chemical Laboratories, University of Toronto, Toronto, Ontario, Canada M5S 1 A l

Earlier assignments of "C NMR signals to C-6 and C-7 in 5,5-dimethyl-2-norbornanone (1) based on lanthanide-induced shifts are interchanged on the basis of studies of deuterium-labeled derivatives of 1. The revised assignments are in accord with predictions based on substituent parameters.

The application of I3CNMR spectroscopy to the de- termination of the structures of organic compounds rests heavily on the use of additive substituent parameters for the prediction of chemical shifts. Al- though largely empirical, this approach has served organic chemists well. It is therefore perturbing to encounter a case where the application of another methodology suggests chemical shift assignments that are different from those based on substituent parame- ters.

It has recently been reported' that lanthanide- induced shift studies lead to the tentative assignments of signals at 6 37.27 and 41.21 ppm in the I3CNMR spectrum of S,5-dimethyl-2- norbornanone (p-fencho- camphorone; 1) in CCl, to C-6 and C-7, respectively.

1 X , = X , = X 3 = H 2 X , = X , = D , X , = H 7 X , = D , X ,=X3=H

3 X = H 4 X = D

5 X = H 6 X = D

* Author to whom correspondence should be addressed.

ccc-0030-492

These are the reverse of the assignments predicted from consideration of substituent parameters. This is particularly surprising in view of the wealth of I3C NMR spectroscopic data recorded for substituted 2-n0rbornanones.~.~ In order to pursue this matter further we have examined the I3C NMR spectrum of S,S-dimethyl-2-norbornanone-1,3,4,7,7-dS (2).

The deuteriated compounds 2 and 4 were prepared from cyclopentadiene-d,, via 6 by the route shown in Scheme 1, which is analogous to the route previously employed for the preparation of the unlabeled com- pounds 1, 3 and 5;' compounds 2 and 4 were sepa- rated by the use of Girard T reagent. Both 'HNMR spectroscopy and mass spectrometry indicated that 2 was obtained with CQ. 70 atom-% D incorporation.

Comparison of the peak height^^,^ of the signals in the proton-noise decoupled I3C NMR spectrum of this product and of 1 in CDCI,, together with the single frequency off-resonance spectrum of the latter, lead to the assignments shown in Table 1. (The chemical shifts in the spectrum of 1 in CDCI, are very similar to those reported previously for 1 in CCl,;' none differ by more than 0.2ppm, with the exception of that of the carbonyl carbon.) These were corroborated by com- parison with the spectra of 5,5-dimethyl-2-norborn- anone-1,4,7,7-d4 (7), obtained by treatment of 2 with sodium hydroxide in methanol-water, and of 5,s- dimethyl-2-norbornanone-3-d, (8), obtained by treat- ment of 1 with sodium deuteroxide in CH30D-D,0.7 Thus the time-honored application of substituent effects is vindicated.

We have also taken the opportunity to examine the I3C NMR spectra of 6,6-dimethyl-2-norbornanone- 1,3,4,7,7-d5 (4), which is in accord with the assign- ments for 3 previously made by Stothers et ~ l . , ~ and of S,5-dimethyl-2-norbornene-1,2,3,4,7,7-d6 (6), which is in accord with the following assignments for 5; 6 28.2 (endo-Me), 30.7 (em-Me), 37.6 (C-S), 41.5 (C-6), 43.7 (C-l), 48.3 (C-7),53.2 (C-4), 135.7 and 136.0 (C-2 and C-3) ppm.

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0 Wiley Heyden Ltd, 1982 ORGANIC MAGNETIC RESONANCE, VOL. 20, NO. 3, 1982 199

P. YATES AND D. D. CONG

Scheme 1.

5,5-Dimethyl-2-norbomenene-l,2,3,4,7,7-d, (6) Table 1. I3C NMR chemical shifts of 1 and 2n*b

c- 1 c-2 c-3 c-4 c-5 C-6 c-7 C-8 c-9

1 2

s 52.28 (73)

217.90 (16) 41.54 (100) 46.55 (68) 36.17 (29) 41.29 (92) 37.39 (87) 31.16 (96) 26.64 (81)

6

52.24 (7) 218.10 (7) 41.47 (14) 46.44 (7) 36.03 (14) 41.1 5 (46) 37.20 (10) 31.13 (61) 26.61 (80)

a In CDCI,; the single frequency off-resonance spectrum of 1 is in accord with the assignments.

Peak heights are given in parentheses.

EXPERIMENTAL

The 13C NMR spectra were obtained at 20 MHz with a Varian CFT-20 spectrometer in the Fourier trans- form mode. The 'H NMR spectra were obtained at 60 MHz with a Varian T-60 spectrometer by the CW method. Both types of spectra were recorded in CDCI, solution (5-10%) with tetramethylsilane as in- ternal reference. Mass spectra were recorded at 70 eV with a Bell and Howell CEC 21-490 single focusing spectrometer.

Cyclopentadiene-d, was prepared by the method of McLean et ~ l . , ~ except that NaOD was prepared by reaction of Na, rather than Na202, with D20. After one exchange process the product was used to prepare compound 6 by the method previously described for the preparation of its unlabeled analogue 5;4*8 the deuterium content of 6 was ca. 70 atom-% D: 6.0 (m, 0.6H; H-2 and 3), 2.74 (m, 0.3H; H-l) , 2.23 (m, 0.3H; H-4), 0.7-1.7 (m, 2.6H; H-6 and 7), 1.17 (s, 3H; em-CH,), 0.83 (s, 3H; endo-CH,).

5,5-Dimethyl-2-norbomanone-1,3,4,7,7-d5 (2) and 6,6-dimethyl-2-norbornanone-1,3,4,7,7-d5 (4)

Compound 6 was converted to a mixture of com- pounds 2 and 4 by the method used previously for the preparation of the unlabeled analogues 1 and 3539 and the mixture was separated by the use of Girard T

The deuterium content of each compound was ca. 70 atom-% D: 2; H6 2.5 (m, 0.3H; H-l), 1.13 (s, 3H) and 1.05 (s, 3H) (exo- and endo-CH,); m/e (relative abundance) 138 ( O S ) , 139 (2.5), 140 (7), 141 (17), 142(22), 143(11.5); 4; 2.6 (m, 0.3H; H-4), 1.11 (s, 3H) and 1.02 (s, 3H) (exo- and endo- CH,); m/e 138 ( O S ) , 139 ( l ) , 140 (9, 141 (15), 142 (22), 143 (15).

Acknowledgments

We thank Professor Stewart McLean for advice concerning the deuteriation of cyclopentadiene and the Natural Sciences and En- gineering Research Council of Canada for support of this work.

REFERENCES

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Received 23 February 1982; accepted (revised) 31 May 1982

200 ORGANIC MAGNETIC RESONANCE, VOL. 20, NO. 3, 1982