NOTES
liquids, because viscous flow in these is determined in rate not by the availability of holes, but by the breaking of bonds in the associated structure.6 Equation 3 would not be expected to be exact because it involves the approximation AHJ* = 0. In accordance with this, it is seen from Figure 1 that the experimental values tend to be a little higher than the prediction of eq. 3. Recent work7 in this laboratory on the heat of activation for self-diffusion in molten salts at constant volume (Le., AHJ*) has shown that this is about ‘ / 6 of that at constant pressure in the case of molten sodium nitrate. The agreement recorded here between the predicted and observed heats of activation for viscous flow strongly supports the hole model. Indeed, it became difficult t o escape from this model for ionic liquids after the confrontation of the disparity between the volume change on melting and the free volume’ and after reliable knowledge became available8-11 that the internuclear distance decreases upon fusion while the corresponding volume change is (e.g., for the alkali halides) large and positive. The model rested here produces successful predictions of both equilibrium1J1J2and transport properties in ionic liquids.*JJ2Ja The latter are the only calculations in the field hitherto published which do not use adjustable parameters. It is pertinent to note that the work of Reiss, et aZ.,14which gives rise to successful calculations of surface tension,I6 cornpressibility,l6 and interionic distance,17also involves a consideration of the work of hole formation.
Acknowledgment. The authors are grateful to the Atomic Energy Commission for support of this work under Contract No. AT30-1-1769. (6) J. O’M. Bockris and D. C. Lowe, Proc. Roy. SOC.(London), A226, 423 (1954). (7) M. I(.Nagarajan, L. Nanis, and J. O’M. Bockris, J . Phys. Chem., 68, 2726 (1964). (8) V. I. Danilov and S. Ya. Krasnitskii, Dokl. A h d . Nauk SSSR, 101, 661 (1955). (9) J. Zarzycki, Compt. rend., 244, 758 (1957); J. phys. radium, 18, 65A (1957); 19, 13A (1958). (10) H. A. Levy, P. A. Agron, M. A. Bredig, and M. D. Danford, Ann. N . Y . Acad. Sci., 79, 762 (1960). (11) J. O’M. Bockris, A. A. Pilla, and J. L. Barton, Rm. Chim., 7,59 (1962). (12) H. Bloom and J. O’M. Bockris, “Fused Salts,” B. R. Sundheim, Ed., McGraw-Hill Book Go., Inc., New York, N. Y., 1964, Chapter 1. (13) J. O’M. Bockris, S. Yosbikawa, and 9. R. Richards, J. Phys. Chem., 68, 1838 (1964). (14) H. Reiss, H. L. Frisch, E. Helfand, and J. L. Lebowitz, J. Chem. Phys., 32, 119 (1960). (15) H. Reiss and S. W. Mayer, ibid., 34, 2001 (1961). (16) S. W. Mayer, J. Phys. Chem., 67, 2160 (1963). (17) F. H. Stillinper, J . C h m . Phys., 35, 1581 (1961).
673
The Proton Nuclear Magnetic Resonance Spectrum of 2,2’-Bipyridine
by F. Axtell Kramer, Jr., and Robert West Department of Chemistry, University of Wisconsin, Madison 6, Wisconsin (Received August 69,1964)
The proton n.m.r. spectrum of the important ligand 2,2‘-bipyridine (a,cY’-dipyridyl, I) has been described previously only in general terrns.l This paper reports a detailed interpretation of the spectrum of this compound in dichloromethane solution (Figure l), determined on a Varian A-60 n.m.r. spectrometer. This compound provides an unusual example of a very complicated spectrum which is nevertheless fully analyzable as repeated AX patterns by simple first-order spin-spin splitting theory. Four nonequivalent protons, numbered as shown for I, are present on each ring of the 2,2‘-bipyridine molecule. The n.m.r. spectrum at low resolution consists of two triplets, centered at 433 and 464 c.P.s., respectively, d o d e l d from tetramethylsilane (T 2.78 and 2-27),and two doublets at 502 and 514 C.P.S. d o d e l d ( T 1.64 and 1.44). Under high resolution, these multiplets show further splitting and a total of 30 lines are observed. Coupling by protons on adjacent carbon atoms is expected to be much larger than for more remote protons. On this basis, the principal splitting should
5 4 3 4 9 6
N.
I
give doublets for protons 3 and 6 and triplets (or quartets) for protons 4 and 5. Much work has been done on the n.m.r. spectra of pyridine2J and substiwhich establishes that protons in tuted the 3- and 5-positions to the nitrogen are the more shielded and quite generally appear at higher field. Moreover, in 2-substituted pyridines, the position of the 3-proton is dependent on the substituent at the 2-position, and electronegative 2-substituents are ex(1) M. Freymann and R. Freymann,Areha Sci. (Geneva), 13, 506 (1960); M. Freymam, R. Freymann, and D. Libermann, Compt. rend., 250, 2185 (1960). (2) E. B. Baker, J . Chem. Phys., 2 3 , 1981 (1955). (3) H. J. Bernstein and W. G. Sohneider, ibid., 24, 469 (1956); H. J. Bernstein, J. A. Pople, and W. G. Schneider, Can. J. Chem., 35, 65 (1957); W. G. Schneider, H. J. Bernstein, and J. A. Pople, ibid., 35, 1487 (1957). (4) W. Bagel, 2.Elektrochem., 66, 159 (1962).
Volume 69,Number 8 February 1966
674
NOTES
p y PROTON 3
Js=I
PROTON 5
Pcpt
:8.3c
p
I
502cp
PROTON 6
Jm = 4 9 c w
4ucpr PROTON 4
v J34:8 3cpr
H,
H3
H4
H6
Figure 1. Proton n.m.r. spectrum of 2,2‘-bipyridine, 15y0w./w. in dichloromethane, determined on a Varian A-60 spectrometer, 250-cycle sweep width. Units are c.p.3. downfield from tetramethylsilane.
pected to deshield the 3-proton. Therefore, the triplet a t 433 C.P.S.is assigned to proton 5. This assignment is consistent with the spectrum observed for 4,4’,6,6’tetramethyL2,2’-bipyridine, which we find has ring proton resonances at 407 and 483 c.P.s., attributed to the 5- and 3-protons, respectively. Assignments for the other protons follow logically and uniquely once the triplet at 433 C.P.S. has been assigned to proton 5. The other triplet at 464 C.P.S. can be assigned to the 4-proton. Because the principal J splitting for the triplet at 464 C.P.S. is equal to that of the doublet at 502 c.P.s., the latter is assigned to the 3-proton. Only the doublet at 514 C.P.S. remains, which must be assigned to proton 6. The consistency of these assignments is verified by the equivalence of the principal splitting for the peaks assigned to protons 5 and 6. Our assignment agrees with that made earlier for 11; it is also consistent with studies of substituted pyridines, which show that the 6-proton usually appears at lowest field.2-4 Splitting constants between nearest neighbor protons can now be evaluated: from the doublet for proton 3, J 3 4 = 8.3 c.P.s.; from the doublet for proton 6, Js6 = 4.9 c.P.s.; and from the triplet for proton 4, J d 5 = 8.0 C.P.S. The multiplet splittings for proton 5 are consistent with these values. Coupling between protons on nonadjacent carbon atoms is a h observed, giving further first-order splitting. Thus the resonance for proton 4 appears as a triplet of doublets. The doubling is due to coupling with proton 6, and from this splitting, J r 6 = 2.1 C.P.S. Similar reasoning allows evaluation of J35as 1.4 C.P.S. and Jae as 1.2 C.P.S. The Journal of Ph’hysical Chemistry
1 SI4CPt
I
464 cps
Figure 2. Diagrams of splitting patterns and spinspin coupling constants for protons in 2,2’-bipyridine,
The complete assignment is indicated in Figure 2. For a system of four widely separated nonequivalent protons, each coupling to one another unequally, firstorder theory predicts an eight-line pattern for each proton, or a total of 32 lines. The spectrum of I is simplified, and the analysis is aided by the nearequality of J34 and J45, and of J35 and JBB(Figure 2). At 250 C.P.S. sweep width, 28 lines are observed (Figure 1): a doublet of quartets for proton 6, a pair of separated triplets for proton 3, a quartet of doublets for proton 5, and two overlapping triplets for proton 4. At 50 C.P.S. sweep width, the resonance for proton 4 is further resolvable; the central two peaks each acquire a shoulder, giving an eight-line pattern as predicted. No further fine structure could be found. All other lines in the spectrum were unusually sharp and well-separated. Acknowledgment. The authors thank the Atomic Energy Commission for support of this research under Contract No. AT (11-1)-1164. Dielectric Relaxation of Mixtures of Dipolar Liquidsla by Surendra K. Garglb and Prasad K. Kadaba Department of Electrical Ewimmiw, university of Kentucky, Lexington, Kentucky (Received September 6,1964)
The present investigation relates mostly to the relaxation mechanism of systems composed of two polar liquids of known structure in the microwave region,
