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J. Phys. Chem. 1984, 88, 3570-3574
reasonably accurate. The validity of the first assumption was verified by adding a small amount of perdeuterioethanol to a sample containing the mixture of labeled ethanols. The resulting 2H N M R spectra showed essentially the same spectral splittings except for some line broadening due to 2H-2H direct coupling in the perdeuterioethanol, If this assumption were not valid, additional spectral lines would have appeared since the quadrupolar splittings are dependent upon the orientation of the solute molecules. The second assumption is justified by the spectra themselves which showed the characteristic septet for a CD3 group,2 indicating that all three deuterons of the methyl group are experimentally indistinghishable, probably because of the rapid reorientation of the methyl group. As in previous s t u d i e ~ , ~the J I ~QD’s ~ ~ determined in phase IV are lower than the corresponding values obtained in ZLI-1167. Previous investigations of Diehl et al.2’ indicated ZLI-1167 to be the most inert nematic solvent because it gave the “best” ra structure of benzene. Hydrogen-bonding interactions or electronic interactions of the solute with the nematic solvent are less likely for ZLI-1167 because its single polar group (a nitrile group) is much less active than the alkoxy groups and/or aromatic rings in phase IV and other nematic solvents. The effect of substitution on QD of a highly polar group is readily apparent from Table V. The electron-withdrawing effects of a hydroxyl group tend to lower the Q D of the group to which it is bound. This is in agreement with the results of Rinne and DepireuxZ2on a variety of substituted molecules. Whether or not
substitution on the methylene carbon has any effect on the Q D of the methyl group cannot be discerned. Further studies employing different electron-donating and -withdrawing substituents are needed to provide such information. These values for the quadrupole coupling constants of the methyl and methylene groups can be combined with the measured ZHrelaxation times4 to estimate the internal rotation rate of the methyl group. This is calculated to be 0.68 X 10” s-l by using the QDvalue measured in the more inert nematic solvent, ZLI1167. This is in excellent agreement with Levine et al.,23 who estimated an average internal rotation rate of 0.5 X 10” s-I for terminal methyl groups on short hydrocarbon chains (less than 10 carbon atoms) from 13C relaxation times. Since the estimate of the methyl group internal rotation rate for ethanol from 2H relaxation studies4 was not possible until the more accurate quadrupole coupling constants reported herein became available, it serves to illustrate how important accurate quadrupole coupling constants are to the development of 2H N M R for molecular motion studies.
Acknowledgment. Support for this work was provided by the donors of the Petroleum Research Fund, administered by the America1 Chemical Society (Grant PRF- 13066-AC6). We greatly appreciate the assistance of Dr. H. K. McDowell with the ab initio calculations. Registry No. I3CD3CH20H,1759-87-1; CH313CD,0H,1859-09-2; ZLI-1167, 67009-49-8; Phase IV, 11 106-54-0. (22) M. Rime and J. Depireux, Adu. Nucl. Quadrupole Reson., 1, 357
(1974).
(23) Y.K. Levine, N. J. M. Birdsall, A. G. Lee, J. C. Metcalfe, P. Partington, and G. C. K. Roberts, J . Chem. Phys., 60, 2890 (1974).
Two Crystal Modifications of 4-Hydroxybiphenyl: The Biphenyl Structure without an Inversion Center and a Fully Ordered Structure Containing Nearly Planar Molecules’ Carolyn Pratt Brock* and Kurt L. Haller Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (Received: November 7, 1983; In Final Form: April 2, 1984)
The structures of two polymorphs of 4-hydroxybiphenyl have been determined. Crystals grown by sublimationunder reduced pressure are essentially isostructural with biphenyl but belong to the space group C$,-P2,/a [ a = 8.067 (2), b = 5.449 (l), c = 20.022 (5) A, p = 95.14 (2)O at 295 K] and have a full molecule, rather than a half-molecule, in the asymmetric unit. Even in the absence of any symmetry restriction, the atomic distribution corresponds to a nearly planar molecule [$, the conformation angle about the phenyl-phenyl bond, = 1.6 (2)OI. As in the case of biphenyl, the structure seems to be complicated by subtle static and/or dynamic disorder. Satellite reflections have been observed at room temperature that may correspond to a structure modulation involving rotation about the long molecular axis. The structure has been refined both in the usual way (570 observations, 118 variables, final R index on Fo of 0.042) and by using a rigid-group least-squares procedure that incorporates the TLS description of rigid-body motion (38 variables, final R index on Fo of 0.071). The latter refinement indicates that the motion about the long molecular axis is significantly different for the two phenyl groups; the libration components in this direction are 62 (6) and 95 (7) degZrespectively for the substituted and unsubstituted rings. Crystals grown from solution belong to the space group Di-P212L21[ a = 15.472 (8), b = 5.469 (7), c = 20.600 (14) 8, at 295 K] and contain two independent, nearly planar molecules [$ = 2.3 (2), 2.0 (3)OI. For this latter polymorph (1 171 observations, 235 variables, final R index on F, of 0.042) an analysis of the refined atomic U tensors in terms of the Schomaker-Trueblood rigid-body model reveals no abnormally large thermal motion that might hide disorder. The libration components associated with the long molecular axes are 78 (5) and 65 (6) deg2 for the two independent molecules and do not differ significantly for the two rings within a single molecule.
The biphenyl molecule has been extensively studied for 20 years, and its structure often cited, because of the important conformational change it undergoes during crystallization. In discussions
of “crystal packing effects”, biphenyl is the paradigm. The inter-ring torsion angle averages 42 (2)’ in the gas phase2 but is apparently compressed to 0’ in the solid state at both room
(1) This paper is dedicated to Prof. Jack D. Dunitz on the occasion of his 60th birthday.
(2) Almenningen, A.; Bastiansen, 0.Kgl.Nor. Vidensk. Selsk. Skr. 1958, 4, 1-16.
0022-3654/84/2088-3570$01.50/0
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0 1984 American Chemical Society
Two Crystal Modifications of 4-Hydroxybiphenyl temperature3 and 110 KS4 But there have been doubts about this structure because the crystallographic agreement factors and thermal parameters are quite high. The location of the molecule on a crystallographic inversion center is problematic: it guarantees coplanarity of the phenyl rings, but may do so by obscuring subtle effects such as short-range ordering of slightly twisted molecules. Recently, both incommensurateSand “orderedw6phases have been discovered below 100 K in which the inversion symmetry is broken and is nonzero but small, ca. loo. This behavior has been explored with semiempirical lattice-energy calculation^.^ In the room-temperature phase the phenyl rings are thought to librate about the central C-C bond under the influence of a symmetric double-well potential having a relatively small central maximum at = 0.5*7The overall form of the potential results from the competition between dominant intermolecular interactions that favor a planar, centrosymmetric, molecule and relatively weaker intramolecular forces, especially the ortho-hydrogen repulsions, that would prefer a twisted conformation. At room temperature, biphenyl and its 4,4’-dihydroxy derivative* are isostructural, crystallizing in PZl/a with Z = 2. The structures of p-terphenyl and p-quaterphenyl are closely related and have the same ~ y m m e t r y .We ~ thought that the same basic organization might be preserved in crystals of the monosubstituted 4hydroxybiphenyl, while the molecular inversion center would of necessity be absent. That is indeed the case. A second polymorph was also found. Herein we report the structures of two crystal modifications of 4-hydroxybiphenyl which have crystal packing arrangements and molecular conformations that mimic those of the aforementioned compounds, but in which the molecules are not required to conform to inversion symmetry.
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Experimental Section Crystal Growth. Initially, the only suitable crystals of 4hydroxybiphenyl (Eastman) we could obtain were grown by slow sublimation under reduced pressure; after about 1 week a few of the very long needles had cross sections of about 0.05 X 0.25 mm. Numerous attempts were made to grow crystals from various solvents including methanol, ethanol, acetone, dichloromethane, methyl ethyl ketone, and acetic acid. Later, knowing the structure of the crystal (see below), we also tried adding small amounts of 4-methoxybiphenyl to the solutions with the idea that it might be selectively adsorbed on the (010)faces and retard growth along the needle a x k g None of these attempts was successful, but large, elongated crystals did grow in the bottom of a filter flask containing acetone, ethanol, some acetic acid, and a small amount of 4-methoxybiphenyl in unknown proportions. Although these latter crystals appeared to have the same morphology as those grown by sublimation, they proved to be a different, but closely related, polymorph. Crystal Structure Determinations. Crystals were mounted in air and showed no signs of sublimation over the course of the experiment. Data collection, structure solution (direct methods using MULTAN77), and refinement utilized programs and procedures described previously;’0 details are summarized in Table I. Comments about the individual determinations follow. Orthorhombic Polymorph. The crystals grown from solution belong to the orthorhombic system. They have very large mosaic (3) (a) Trotter, J. Acta Crystallogr. 1961, 14, 1135-40. (b) Robertson, G. B. Nature (London) 1961, 593-4. (c) Hargreaves, A.; Rini, S. H. Acta Crystallogr. 1962,15,365-73. (d) Charbonneau, G.-P.; Delugeard, Y . Acta Crystallogr., Sect. B 1977, 33, 1586-8. (4) Charbonneau, G.-P.; Delugeard, Y . Acta Crystallogr., Sect. B 1976, 32, 1420-3. (5) Cailleau, H.; Baudour, J. L.; Meinnel, J.; Dworkin, A.; Moussa, F.; Zeyen, C. M. E. Faraday Discuss. Chem. SOC.1980, 7-18. (6) Cailleau, H.; Baudour, J. L.; Zeyen, C. M. E. Acta Crystallogr., Sect. B 1979, 35, 426-32. (7) Busing, W. R. Acta Crystallogr., Sect. A 1983, 39, 340-7. (8) Akhmed, N. A.; Farag, M. S.; Amin, A. Zh. Strukt. Khim. 1971.12, 738-9. (9) (a) Van Mil, J.; Gati, E.; Addadi, L.; Lahav, M. J . Am. Chem. SOC. 1981, 103, 1248-9. (b) Addadi, L.; Gati, E.; Lahav, M. Ibid. 1981, 103, 1251-2. (10) Brock, C. P.; Attig, T. G. J . Am. Chem. SOC.1980, 102, 1319-26
The Journal of Physical Chemistry, Vol. 88, No. 16, 1984 3571 TABLE I: Summary of Crystal Data and Details of Intensity Collection and Refinement formula formula wt, amu space group a, 8,
b, A c,
A
ClZHlOO 170.21 p 2 I2121 15.472 (8) 5.469 (7) 20.600 (14)
P, deg temp, K
Z g c131-3 prominent faces
PCSlcd9
crystal dimensions, mm radiation scan angle, deg,” and type decomposition, % linear absorption coeff, cm-I transmission factors max 2 4 deg unique data unique data with F,z > 3.(F,z) final number of variables R, R, on F (>30) error in observation of unit weight, elargest features in final difference Fourier map, e- .k3
295 (1) 8 1.297 (2) {001l, (100L{1011, { l o l l 0.62 X 0.62 X 0.14 Mo Ka,graphite monochromator 0.75 ( w )
P21la 8.067 (2) 5.449 (1) 20.022 (5) 95.14 (2) 295 (1) 4 1.290 (1) {ooi),( l o r ) 0.38 X 0.25 X 0.05 0.80 (8-20)
