August, 1.962
HYDROGEN BOND
FORMATION I N
CHLOROFORM-BENZENE-CYCLOHEXANE SYSTEM 1469
indicates that when HzO adsorbs a t 180' it completely dissociates on the iron surface. In summary, it appears for the compounds investigated that oxygen, except where it can form multiple bonds with carbon, t>ends to dissociate from its compounds to presumably form oxide ions on the metal surface. Water dissociates so as to leave no OH groups on the surface. Oxygen adsorbs to form an oxide lattice a t 180". COZ dis-
sociates on a clean surface at 20' to form chemisorbed CO and presumably an oxide ion. CO shows no tendency to dissociate, even a t 180' where chemisorbed and gas phase CO are in dynamic equilibrium. On the basis of several bands appearing for chemisorbed CO, the surface is presumed to have a heterogeneity consisting of several regions which are reasonably homogeneous within themselves.
THER160DYNAMIC CONSTANTS FOR HYDROGES BOND FORMATION IN T.HE CHLOROFORM-BENZENE-CYCLOHEXANE SYSTEM BY CLIFFORD J. CRESWELL AND A. L. ALLRED Department of Chemistry, Northwestern University, EvarLston, f l l z n o ~ s Receaved March 6, 1961
The association of chloroform and benzene has been investigated in the temperature range 25-75' by nuclear rriagnetic rcmnance spectroscopy. The equilibrium constant at 25' is 1.06 i.0.30 (m.f.)-l and the enthalpy and entropy of association are - 1.97 i0.35 lrcal. mole-' arid -6.5 i.0.5 cal. mole-' deg.-l, respectively A system involving thc solvent cyelohexane and a low, iixcd concentration of chloroform was chosen to minimize contributions from solvent effects t o chemical shifts. The vhemical shift (8bonzeno...r.hlorofonn - 8ohlorofunn) due to hydrogen bond formation is 1.91 =k 0.40 p.p.m. From a comparablc' investigation of the association of chloroform and triethylamine, values of the equilibrium constant a t 25", enthalpy, cntropy, and (6t,,otirylo,nlnaahloroforin Bol,loroform) a t 25" are 4.2 =k 0.2 (in.f.)-l, -4.15 i.0.20 Ircal. mule-', - 11.0 cal. deg.-I, and - 1.48 p.p.m., respectively.
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Introduction This paper reports the irivest'igatioii of t,he extent of h;ydrogen bond formation bet'weeiz chloroform and benzene. The association of chloroform with various bases has been demonstrated by vapor prcssure measurements,1 dielectric polarization, s ~ l u b i l i t i e s ,heats ~ ~ ~ of mixing,6 ultrasonic absorption,6 infrared s p e c t r o s ~ o p y , ~change -~ of volume upon mixing, lo nuclear magnetic resonance (n.m.r.),11-13freezing point diagrams,12 and E'VT behavior. I 4 For additional references and discussion concerning hydrogen bonding by chloroform, see refercnoe 15. Evidence for t,he specific interact'ion of chloroform with benzene includes heat's of mixing, l6 enhancement of the intensity of infrared absorpt'ion due to the C-D stretch of chloro(1) E. Beckman and 0. Faust, Z. phusik. Chem., 89, 247 (1914). ( 2 ) D. P. E h r p and 8. Glasstono, J. Chenz. SOC..1709 (1935). ( 3 ) M. J. Oopley, G. F. Zellhoefer, and C. S.Marvel, J. Am. Chem. Soc.. 60, 1337 (1038). (4) J. H. Eldebrand and R. L. Scott, "Solubilities of Non-eleotrolytes," Reinhold Publ. Corp., New York, N. Y., 1950. ( 5 ) W. Gordy and S.C. Stanford, J . Chem. Phys.. 9, 204 (1941). ( 6 ) R. Parshad, Indian J. Phys., 18, I , 307 (1942). (7) G. M. Barrow and E. A. Yerger, J . Am. Chem. Soc., 76, 5247 (1954). ( 8 ) C. BI. 'Huggins and G. C. Pimentel, J. Chem. Phys., 23, 896 (1955). (9) R. C. LNord, B. N o h , and H. D. Sticlham, J . Am. Chem. Xoc., 77, 1365 (1956). (10) L. A. K. Staveley. W. I. Tugman, and K. R. Hart, Trans. Paraday SOC.,51, 323 (1955). (11) C. M. Huggins, G. C. Pimentel, and J. N, Shoolery, J. Chem. Phys., 23, 1244 (1955). (12) L. W. Reeves and W. G. Schneider, Can. J . Chem., 85, 251 (1957). (13) G. J. Iiorinek and W. G. Schneider, ibid., 86, 1157 (1957). (14) J. D. Lambert, J. S. Clarke, J. F. Duke, C. L. Hioks, S. D. Lawrence, D. M. Morris, and M. G. T. Shone, Proc. Roy. Soc. (London), 249A, 414 (1959). (15) G. C. I'imentel and A. L. 3loClellan, "The Hydrogen Bond," l h e m a n , San Francisco, 1960, p. 197. (16) M. Tamres, J . An. Chem. Sue., 74, 3375 (1952).
form-d,8and the n.m.r. chemical shift of chloroform dissolved in benzene.12917Hydrogen bonding involving electron-donating n-orbitals is discussed elsewhere. The general low-field shift in proton magnetic resonance spectra due to hydrogen bonding has been recognized for over a decade,19s20and theoretical interpret>ationsof t,he hydrogen bond shift have been. given However, when compounds, including chloroform, having a propensity for hydrogen bond formation are dissolved in aromatic solvents, a high-field shiit of the resonance of the donor proton is observed,1z3178z2-z4 This high-field shift, which is opposite to the chemical shift of protons known to be involved in hydrogen bond formatmionin other types of systems, can be attributed t30the magnetic anisotropy of benzene and other aromatic compounds. The anisotropy arises from the induced circulation of n electroizs26.26and produces a secondary field which opposes the applied field in the vicinity of the symmetry axis of benzene and augments the field near the edge of the ring. The relat'ive contributioiis to the high-field shift by specific hydrogen bonds, by "stat'istical" positioning of the solute between aromatic planes, and by (17) A. A. Bothner-By and R. E. Glick, J . Chem. Phys., 26, 1651 (1957). (18) (a) Ref. 15, p. 202; (b) M. L. Josien and G. Soorisseau, "Hydrogen Bonding," ed. by D. Hadai, Pergamon Press, New York, N. Y.,1959, pp. 129-137. (19) U. Liddel and N. F. Ramsey, J . Chem. Phys., 19, 1608 (1951). (20) J. T. Arnold and M. G. Packard, ibid., 19, 1608 (1951). (21) W. G. Schneider, H. J. Bernstein, and J. A. Pople, ibid., 28, 601 (1958). (22) A. D. Cohen and C. Reid, ibid., 25, 790 (1956). (23) T. Schaefer and W. G. Schneider, ibid., 32, 1218 (19130). (24) J. C. Davis, Jr., and I
