10110
J. Phys. Chem. 1995, 99, 10110-10113
The Influence of Chlorine- Carbon Dipolar and Indirect Spin-Spin Interactions on High-Resolution Carbon-13 NMR Spectra of Chloroketosulfones in the Solid State Klaus Eichele,' Roderick E. Wasylishen,*$+J. Stuart Grossert,+ and Alejandro C. Olivierit Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 453, and Departamento de Quimica Analitica, Facultad de Ciencias Bioquimicas y Farmaciuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Republica Argentina Received: March I , 199.5@
Carbon-13 C P M A S NMR spectra of two closely related solid chloroketosulfones have been examined. Peaks arising from carbon nuclei which are spatially proximate to chlorine nuclei exhibit extensive broadening and in some cases fine structure, particularly at the lower applied magnetic fields. Residual 35/37C1-'3C spinspin interactions are responsible for the broadening and fine structure. By consideration of the appropriate Zeeman-quadrupolar Hamiltonian, the observed I3C C P M A S NMR spectra can be reproduced by exact numerical computer calculations. The excellent agreement between the observed and calculated spectra allows one to determine both the sign and magnitude of the 35137C1 nuclear quadrupolar coupling constant, and the 35137C1-13Cindirect spin-spin coupling constant, 'J(35'37C1,13C).The values determined for the 35C1-'3C spin pair are ~ ( ~ ~=c-73 l ) f 2 MHz and 1J(35C1,'3C)= -20 f 5 Hz. This is the first direct measurement I3C);the magnitude and negative sign of this coupling constant are consistent with known periodic of 1J(35'37C1, trends.
x,
Introduction In the solid state, quadrupolar nuclei generally have nuclear relaxation times which are several orders of magnitude longer than those in solution. One important consequence of the longer relaxation times is that one can sometimes determine indirect spin-spin coupling constants, J, involving quadrupolar nuclei. Typically, one carries out high-resolution cross-polarization magic-angle spinning (CPMAS) NMR experiments on spinnuclei that are coupled to the quadrupolar nucleus.' A second important consequence of long quadrupolar relaxation times in solids is the fact that direct dipolar interactions involving quadrupolar nuclei are not completely averaged by MAS. MAS is ineffective in averaging the dipolar interaction because the magnetic moments of the quadrupolar nuclei are quantized not only by the applied magnetic field, Bo, but also by the interaction with the electric field gradient (EFG) tensor. As a result, the dependence of the nuclear spin-spin interactions on the orientation of the internuclear vector in Bo is not solely described by the familiar (3 cos2 8 - 1); Le., the magic angle is no longer "magic," and the MAS NMR spectra of spin-'/* nuclei which are strongly dipolar coupled to quadrupolar nuclei exhibit splittings even in the absence of indirect coupling. In the past 15 years, many examples of splittings arising from residual I4NI3C dipolar interactions have been observed in I3C CPMAS NMR spectra of organic compounds.la In one such system, it was possible to determine 'J(I4N,l3C)even though the magnitude of such couplings is very small, typically less than 20 Hz, compared to corresponding one-bond direct dipolar coupling constants, R(I4N,l3C).* By contrast, few examples of 35137C1I3C dipolar splittings in the I3C CP/MAS NMR spectra of solids have been r e p ~ r t e dand , ~ to date splittings due to indirect spinspin couplings involving carbon and chlorine have not been reported. Both chlorine isotopes are ~pin-~/2 nuclei with
* Author to whom correspondence should be addressed. E-Mail: RODW @ AC.DAL.CA. ' Dalhousie University. ' Universidad Nacional de Rosario. Abstract published in Advance ACS Abstracts, June 1, 1995.
comparable quadrupole moments, Q(35Cl)= -8.17 x m2 and Q(37Cl)= -6.44 x m2: and magnetogyric ratios, ~ ( ~ ~=c2.6240 l ) x IO7 rad s - l T-l and = 2.1842 x lo7 rad s-l T-'.5 The natural abundances of 35C1and 37C1are 75.53% and 24.47%, respectively. The objective of the present investigation is to demonstrate that moderate- or low-field I3C CPMAS NMR studies (Bo 5 4.7 T) allow one to derive the maximum information from solidstate NMR studies of the 35137C1-'3Cspin pair. Specifically, we show that the sign of the chlorine quadrupolar coupling constant can be deduced. As well, we present the first example of a system from which it is possible to deduce both sign and magnitude of the indirect spin-spin coupling involving 35137Cl and I3C. All previous measurements of J(35'37C1,"C) have been obtained indirectly from I3C NMR relaxation measurements,6 which do not provide sign information.
Theory Consider two isolated nuclear spins I and S, where I is the resonant spin-'/* nucleus and S is a nearby quadrupolar nucleus. The appropriate Hamiltonian operator is
F=5Tf+ F:+3-;+
3-iS + 57-7
(1)
where 5Tf and 9"; account for the interaction of spins I and S, respectively, with the applied magnetic field, 9Tz is the direct dipolar interaction, Tisis the indirect spin-spin coupling interaction, while T?is the quadrupolar interaction. For the 35C1-13C or the 37C1-'3C spin pairs
IFflx
I % q x I F T I >> IC$'I v c s I
(2)
Since the general theory necessary to permit the calculation of I-spin MAS line shapes of the I,S spin pair has been discussed in detail el~ewhere,~ we only highlight a few points here. Because the quadrupolar S nucleus is not solely quantized along the applied magnetic field, eigenstates of the quadrupolar nucleus are generally expressed as a linear combination of
0022-3654/95/2099-10110$09.00/0 0 1995 American Chemical Society
I3C NMR Spectra of Chloroketosulfones
J. Phys. Chem., Vol. 99, No. 25, 1995 10111
Zeeman states, i e . ,
where I+I> = 1312>, IVz>= I1h),lVs>= l-'h>,and IV4) = For cases where 01/4S(2S - 1)vs) > 1, firstorder perturbation theory can also be used to calculate an approximate NMR ~pectrum.~ In the present study we have investigated 13CCPMAS NMR spectra of the 35,37C1-13Cspin pairs in two closely related chloroketosulfones. 0 I1
1,
2.
9P
R=Et R=Me
Even at the highest of the magnetic fields employed in this study, BO = 9.40 T, the value of @/12vs) is approximately 0.15 for values of typical of organochloro compounds,s making the first-order approach of limited utility. At lower applied fields, the perturbation approach is definitely not valid. In such cases, the Zeeman-quadrupolar eigenvalues have to be calculated numerically. This problem has been discussed previously in the literature7 and will not be repeated here. However, it is necessary to emphasize that, while R,ff and x are correlated linearly in the regime valid for the first-order perturbation treatment (eq 4), this is not the case in the intermediate regime, where both vs and x are of comparable magnitude. Under these conditions it is possible to determine Reffand x independently. An illustrative example has been presented by Gan and Grant.lo
x
Experimental Section The preparation of the two chloroketosulfones investigated here, 2-chloro-2-(phenylsuIfonyl)-l-phenylbutanone, 1,' and 2-chloro-2-(phenylsulfonyl)-l-phenylpropanone, 2," and the crystal structure of 1 have been described previously."
i I
200
I50
100
50
0
[PP~I Figure 1. I3CCPMAS NMR spectrum of 1 obtained at 9.40 T. Spinning sidebands (S.S.) are indicated. Spinning rate, 7.3 kHz;5000 scans.
Carbon-13 CPMAS NMR spectra were obtained at 9.40, 4.70, and 2.35 T, using Bruker AMX-400, MSL-200, and MSL100 NMR spectrometers, respectively. All spectra were acquired using standard high-resolution CP/MAS techniques. Typical 90" pulse widths were 4.0 ps, contact times were 5 ms, and recycle delays were 10 s. Carbon-I3 MAS NMR line shapes were calculated by diagonalization of the appropriate Hamiltonian (eq 1) using a program written in C.7i The efficiency of the calculation was enhanced by using the POWDER routine.I3 With parameters typically employed in such calculations (e.g., 2049 crystallite orientations, 36 steps per rotation period), the calculations require 2 min per spin pair using a 80486 microprocessor. The calculations assume an axially symmetric electric field gradient at the quadrupolar nucleus, which we believe is an excellent assumption for the compounds studied here.s The calculations are general in that they allow one to vary the relative orientations of the quadrupolar EFG (S-spin) and direct dipolar (I-S) tensors. The angle between the largest component of the EFG tensor, eq,,, and rls will be denoted by ,8. Our implementation has been tested extensively against other reported calculations and has been found to be in good agreement, except for the calculations presented by Zumbulyadis et al.,7d which do not show the expected field dependence (cf. their Figure 2). However, the authors themselves questioned the applicability of the adiabatic approach to the 35,37C1-13C
Results and Discussion The I3C CPMAS NMR spectrum of 1 obtained at 9.40 T is shown in Figure 1. Several features are worth mentioning. First, the I3C directly attached to chlorine exhibits a doublet at 6 = 95.2 ppm with a splitting of 467 Hz. This is in qualitative agreement with the first-order perturbation theory (vide supra). Second, the peak at 33.6 ppm arising from the methylene group is noticeably broadened (fwhh = 3 16 Hz). As well, the carbonyl carbon (193.1 ppm) and methyl carbon (12.1 ppm) peaks are broader (fwhh = 108-148 Hz) than what one expects for a crystalline organic solid such as compound 1. In order to investigate the 35/37C-13Cinteractions further, we obtained I3C CP/MAS NMR spectra of 1 at 4.70 and 2.35 T. Observed and calculated I3C CPMAS NMR spectra arising from the carbon directly bonded to chlorine are illustrated in
10112 J. Phys. Chem., Vol. 99, No. 25, 1995
!A
Bo
n ,
2.35 T
I""I""1""I""I""l""I
1
0
Eichele et al.
l ' ' ' ' l " ' ~ ' " l ~ " ' l ' ' " l ' " ~
-1
1
0
-1
Wzl [kHz1 Figure 2. Observed and calculated I3C C P M A S NMR spectra of 1 obtained at 9.40, 4.70, and 2.35 T. Only peaks arising from the directly attached to 3s137C1 are shown. Peaks at approximately 1 kHz in the 4.70 and 2.35 T spectra correspond to a spinning sideband of the carbonyl carbon or to the aromatic carbons, respectively. The calculated spectra were obtained using the following parameters: R(3'C1,'3C) = 510 Hz, = -73 MHz, J(35C1,13C)= -20 Hz, and p = 0". Values of R(37C1,'3C),~ ( ~ ~ cand l ) ,J(37C1,'3C) were obtained by appropriate scaling of the above values.
x(w)
Figure 2. The value of the chlorine-carbon bond length, rC1-c = 1.776(4) A," permits the calculation of the direct dipolar coupling constant, R(35C1,13C)= 510 Hz. Assuming the internuclear vector and the direction of the unique component of the EFG tensor to be coincident @ = OO), the following parameters were used for the 35C1-13C spin pair to simulate the experimental spectra: ~ ( ~ ~=c-73 l ) f 2 MHz and J(35Cl, I3C) = -20 f 5 Hz. The parameters for the 37C1-'3C spin pair were taken to be related by the ratios of the corresponding nuclear constants. While the 9.40 T spectrum does not provide information regarding the sign of the chlorine nuclear quadrupolar coupling constant, it was impossible to obtain a fit of the 4.70 and 2.35 T spectra without using a negative value for (35Cl). Furthermore, it was impossible to obtain satisfactory agreement between observed and calculated spectra at 4.70 T unless J(35C1,'3C)is set equal to -20 f 5 Hz. Negative values of x(35,37C1)for chloroalkanes have been deduced from previous high-resolution microwave spectroscopy experiments.8a As well, negative values for x(35.37C1)have been inferred from other recent I3C CPMAS NMR Interestingly, the sign of nuclear quadrupolar coupling constants is generally unavailable from standard nuclear quadrupole resonance (NQR) experiments.8b The value of the indirect chlorine-carbon coupling observed here is the first direct measurement of 5(35,37C1,13C).The influence of J(35.37C1,'3C)on calculated I3C CPMAS NMR spectra at 4.70 T is illustrated in Figure 3. In this case, the experimental spectrum is that of compound 2, although for all practical purposes the peaks arising from the carbon directly bonded to chlorine are indistinguishable in the two compounds. From Figure 3 it is clear that the high-frequency portion of the I3C NMR spectrum is most sensitive to the sign and magnitude of J(35'37C1,13C).This is precisely what one would expect on the basis of the first-order approach, since the high-frequency
x-
1
0
-1
IkH4
Figure 3. Observed and calculated I'C CP/MAS NMR spectra of 2 obtained at 4.70 T. Only peaks arising from the 13C directly attached to 35137C1 are shown. The arrow indicates the spectral feature which provides the sign of J in both compounds 1 and 2. The 13C multiplet is centered at r3 = 83.0 ppm. All other parameters are given in Figure 2.
portion of the spectrum, v(I3C) > 0.1 kHz, is associated with mcl = i 3 / 2 . Particularly noteworthy of these spectra is the feature indicated by the arrow in Figure 3. The origin of this feature is apparent from the calculated spectra illustrated in Figure 4. Focusing on the subspectrum arising from the 35ClI3C spin pair, it is clear that the "peak' indicated by the arrow in Figure 3 arises from the low-frequency shoulder of the "Pakelike" doublet corresponding to mcl = f 3 / 2 . With J(35C1,13C) = 0, the "Pake-like" doublets corresponding to mcl = +3/2 and mcl = -3/2 overlap considerably. As J(35C1,i3C) becomes more negative, the two powder patterns separate. Extensive line shape simulations are only compatible with J(35C1,13C) = -20 i 5 Hz. That is, the reduced spin-spin coupling constant, K(Cl,C), is negative." A negative value for the reduced coupling, 'K(Cl,C), is entirely consistent with known periodic trends.I5 For example, it is well-known that 'K(F,C) values are negative,I5 thus it is reasonable to assume that 'K(C1,C) should be negative as observed. Furthermore, it has been demonstrated recently that 'K(Br,C) is also n e g a t i ~ e . ~ 'Finally, .~ the magnitude of 'K(C1,C) obtained for 1 and 2 is in excellent agreement with the magnitude of 'K(C1,C) deduced from I3C NMR relaxation measurements in solution on related compounds.6 Finally, the observed and calculated I3C CPMAS NMR line shapes for the carbonyl resonance of 1 obtained at 2.35 and 4.70 T are shown in Figure 5; the parameters used to obtain the calculated spectra are indicated in the figure caption. Again, the value of R was calculated using the k n o ~ n ~ ~ ' ~ ~ C l - ' ~ C separation from X-ray diffraction." The value of p was obtained using the X-ray diffraction data and by assuming that the unique component of the chlorine EFG tensor is coincident with the Cl-C bond axis, where C is directly bonded to chlorine. The excellent agreement between the observed and calculated spectra supports the value determined for x(35'37C1)from analysis of the peak of the quaternary carbon directly bonded to chlorine. In fact, the spectra are quite sensitive to the 35'37C1-13C
I3C NMR Spectra of Chloroketosulfones
J. Phys. Chem., Vol. 99, No. 25, 1995 10113 In summary, this study demonstrates that in favorable cases a wealth of information is available from high-resolution CP/ MAS NMR spectra of spin-'/* nuclei which are spin-spin coupled to quadrupolar nuclei. Particularly intriguing is the fact that from a single spectrum one can obtain information on coupling interactions which differ by 6 orders of magnitude (ie., and J)!
x
Acknowledgment. We thank NSERC of Canada and CONICET of Argentina for financial support in the form of research and equipment grants. We are grateful to Mr. Brian G. Sayer, McMaster University, for obtaining the spectra at 2.35 T. Also, we wish to thank Dr. Michael S. McKinnon for obtaining some preliminary I3C CPMAS NMR spectra of these compounds and Dr. H. R. W. Dharmaratne for their preparation. References and Notes
r
~
1
~
'
'
I
'
~
"
0
/
'
'
"
J
'
"
'
J
"
~
-1
[kHz1 Figure 4. Calculated I3C CP/MAS NMR spectrum of 2 (Bo = 4.70 T). The middle and lower spectra correspond to the 35C1-13C and 37C1-13C spin pairs, respectively. The upper spectrum is the sum of the two lower spectra, convoluted by 60 Hz. The relative intensities of the two spectra are appropriately weighted according to the natural abundances of 35Cl and 37Cl. The pattern arising from each spin pair consists of four "Pake-like" powder pattems associated with each of the Zeeman states of the s p h 3 / 2 nucleus (from high to low frequency, the +3/2. -3/2, -l/2, and spin states). The parameters used to calculate the spectra correspond to those given for Figure 2.
0.5
-0.5
Figure 5. Observed and calculated I3C CP/MAS NMR spectra of 2 obtained at 2.35 and 4.70 T. Only peaks arising from the carbonyl 13C are shown. The parameters used to calculate the spectra are R(35C1,'3C) = 13.5 Hz, ~ ( ~ ' c 1=) -73 MHz, p = 35".
separation and the angle p. For organic compounds containing chlorine one could, in principle, use variable-field highresolution I3C CPMAS NMR measurements to test the reliability of a proposed structure or conformation if a crystal structure determination were not possible.
(1) (a) Harris, R. K.; Olivieri, A. C. Progr. NMR Spectrosc. 1992,24, 435-456. Newer references not included in this review: (b) Collins, M. J.; Ripmeester, J. A,; Sawyer, J. F. J . Am. Chem. SOC. 1987, 109, 41134115. (c) Eichele, K.; Wasylishen, R. E. Angew. Chem., Znt. Ed. Engl. 1992, 31, 1222-1224. (d) Baker, L.-J.; Bowmaker, G. A,; Healy, P. C.; Skelton, B. W.; White, A. H. J . Chem. Soc.. Dalton Trans. 1992, 989997. (e) Moran, K. L.; Gier, T. E.; Harrison, W. T. A,; Stucky, G. D.; Eckert, H.; Eichele, K.; Wasylishen, R. E. J . Am. Chem. SOC. 1993, 115, 10553-10558. (f) Eichele, K.; Wasylishen, R. E.; Comgan, J. F.; Doherty, S.; Sun, Y.; Carty, A. J. Inorg. Chem. 1993,32, 121-123. (8) Wasylishen, R. E.; Wright, K. C.; Eichele, K.; Cameron, T. S. Inorg. Chem. 1994, 33, 407-408. (h) Eichele, K.; Wasylishen, R. E. Inorg. Chem. 1994,33,27662773. (2) Eichele, K.; Wasylishen, R. E. Solid State Nucl. Magn. Reson. 1992, 1, 159-163. (3) (a) Fleming, W. W.; Fyfe, C. A,; Lyerla, J. R.; Vanni, H.; Yannoni, C . S. Macromolecules 1980,13,460-462. (b) Mooibroek, S.; Wasylishen, R. E. Can. J . Chem. 1987, 65, 357-362. (c) Cravero, R. M.; GonziilezSierra, M.; Femiindez, C.; Olivieri, A. C. J . Chem. Soc., Chem. Commun. 1993, 1253-1254. (d) Harris, R. K.; Siinnet@oglu, M. M.; Cameron, S. S.; Riddell, F. G. Magn. Reson. Chem. 1993, 31, 963-965. (e) Olivieri, A. C.; Elguero, J.; Sobrados, I.; Cabildo, P.; Claramunt, R. M. J . Phys. Chem. 1994,98,5207-5211. (f) Aliev, A. E.; Hams, K. D. M.; Barrie, P. J.; Camus, S. J . Chem. Soc., Faraday Trans. 1994, 90, 3729-3730. (g) Alarcbn, S. H.; Olivieri, A. C.; Carss, S. A,; Harris, R. K. Angew. Chem., Int. Ed. Engl. 1994, 33, 1624-1625. (h) Nagasaka, B.; Takeda, S.; Nakamura, N. Chem. Phys. Lett. 1994, 222, 486-492. (4) (a) Pyykko, P. Z. Nuturforsch. 1992,47u, 189-196. (b) Sundholm, D.; Olsen, J. J . Chem. Phys. 1993, 98, 7152-71.58. ( 5 ) Mulrinuclear NMR; Mason, J., Ed.; Plenum Press: New York, 1987; p 625. (6) (a) Mlyn6rik, V. Progr. Nucl. Magn. Reson. 1986, 18, 277-305. (b) Mlynfik, V. Org. Magn. Reson. 1984, 22, 164-165. (7) (a) VanderHart, D. L.; Gutowsky, H. S.; Farrar, T. C. J . Am. Chem. SOC.1967,89,5056-5057. (b) Spiess, H. W.; Haeberlen, U.; Zimmermann, H. J . Magn. Reson. 1977, 25, 55-66. (c) Maricq, M. M.; Waugh, J. S. J . Chem. Phys. 1979, 70,3300-3316. (d) Zumbulyadis, N.; Henrichs, P. M.; Young, R. H. J . Chem. Phys. 1981, 75, 1603-1611. (e) Menger, E. M.; Veeman, W. S. J . Magn. Reson. 1982, 46, 257-268. (f) Hexem, J. G.; Frey, M. H.; Opella, S. J. J . Chem. Phys. 1982, 77,3847-3856. (g) Bohm, J.; Fenzke, D.; Pfeifer, H. J . Magn. Reson. 1983, 55, 197-204. (h) Sastry, D. L.; Naito, A.; McDowell, C. A. Chem. Phys. Lett. 1988,146,422-427. (i) Alarcbn, S. H.; Olivieri, A. C.; Harris, R. K. Solid Stute Nucl. Magn. Reson. 1993, 2, 325-334. (8) (a) Gordy, W.; Cook, R. L. Microwave Molecular Spectra; John Wiley & Sons: New York, 1984; p 766. (b) Lucken, E. A. C. Nuclear Quadrupolar Coupling Constants; Academic Press: London, 1969; pp 167190. (c) Allen, H. C., Jr. J . Am. Chem. SOC.1952, 74, 6074-6076. (d) Ege, 0.; Hamai, S.; Negita, H. Z. Naturforsch. 1992, 47a, 401-408. (9) Olivieri, A. C. J . Magn. Reson., Ser. A 1993, 101, 313-316. (10) Gan, Z.; Grant, D. M. J . Magn. Reson. 1990, 90, 522-534. (1 1) Grossert, J. S.; Dharmaratne, H. R. W.; Cameron, T. S.; Vincent, B. R. Can. J . Chem. 1988, 66, 2860-2869. (12) Grossert, J. S.; Sotheeswaran, S.; Dharmaratne, H. R. W.; Cameron, T. S. Can. J . Chem. 1988, 66, 2870-2879. (13) Alderman, D. W.; Solum, M. S.; Grant, D. M. J . Chem. Phys. 1986, 84, 3717-3725. (14) K(C1,C) = J(35C1,'3C)/4n2hy~.13y~,.3~; note, the reduced spin-spin coupling constant is independent of the magnetogyric ratios of the two coupled nuclei (cf. ref 15). (15) Jameson, C. J. In loc. cit. ref 5 , pp 89-131. JP950627H
