NOTES
Figure 2 shows that now at the highest sucrose concentration the experimental light scattering turbidity is nearer to Stigter’s thermodynamic value. In addition, the experimental turbidities for the two wave lengths are closer together now, especially at the higher concentrations where pu ,m measurements become more accurate. In general, the effect discussed will not be very important in turbidity measurements. As shown by Table I and Figure 3, however, attention should be paid tto it if one is concerned with the interpretation of the depolarization itself.
691
i
w
i
d
d
i
d
d
8 m
c?
N
d
Acknowledgment. We gratefully acknowledge valuable discussions with Dr. D. Coumou of this laboratory.
Electric Moment of Isonicotinamide in Benzene and Dioxane Solutions1 . .
by William P. Purcell and Judith A. Singer
.
N N
*
N
N
Department of Pharmaceutical and Medicinal Chemistry, College of Pharmacy, University of Tennessee, Memphis, Tennessee (Received August 3,196.4)
We recently reported the dipole moments of some selected N-alkyl-substituted nicotinamides2 measured in benzene solution, and the calculated values for the corresponding amide group moments. Nicotinamide and the monosubstituted derivatives were so insoluble in benzene that we were forced to measure very dilutelsolutions. The compounds are soluble in dioxane, but the increase in problems of association between solvent and solute molecules makes this an unattractive ~ o l v e n t . ~As a result, we have applied the mixed benzene-dioxane solvent technique, described by Estok, et al.,3-6 to isonicotinamide, a molecule which fits into our series2and one which has low solubility in benzene.
i
. .
N N
d
d
.
N
d
.
N
Experimental Reagent. Isonicotinamide (research grade, Aldrich (1) This investigation is being supported by the National Science Foundation (GB-2381/B-15989),U. 8. Public Health Service Grant MH-04379 and by a grant from the Geschickter Fund for Medical Research, Inc. Computer facilities were provided through U. S. Public Health Grant FR-1. (2) W.P. Purcell, J . Phys. Chem., 68, 2666 (1964). (3) G. K.Estok and C. H. Stembridge, J. Am. Chem. SOC.,76,4316 (1954). (4) G. K.Estok and S. P. Sood, J . Phys. Chem., 61, 1445 (1957). (5) G. K. Estok, S. P. Sood, and C. H. Stembridge, ibid., 62, 1464 (1958). (6) G. K.Estok and S. P. Sood, ibid., 66, 1372 (1962).
2
0 0 0 0 0 0 0 0 0 0 0 0 0 0
x 8888888
I O 0 0 0 0 0 0
Volume 69, Number 2 Febiuary 1966
692
NOTES
~
~~
~
Table I1 : Slopes, Orientation Polarizations a t Infinite Dilution, Observed Moments, and Amide Group Moments of Isonicotinamide a t 25'
a
Pz,,, cc./mole
Solvent
Technique
a
Y
Benzene Benzene Dioxane Dioxane Dioxane
Pure solvent Mixed benzene-dioxane solvent Pure solvent Pure solvent Mixed benzene-dioxane solvent
8.952 12.232 16.784
0.8937 0.1736 0.4322
17.120
0.3943
184.6 276.7 328.1 311.3" 334.8
P, D.
ma,D.
3.00 f 0.09 3.68 4.01 3.8P 4.05
2.88 3.77 4.19 4.03 4.23
D. G. Leis and B. C. Curran, J. Am. Chem. Soc., 67,79 (1945).
Chemical Co., Inc.) was recrystallized five times from ethyl acetate; m.p. 148.9-149.4' (lit.7m.p. 155') and was dried under vacuum in an Abderhalden pistol. Solvents. The compound was measured in dilute benzene solution using Speetroquality benzene (Matheson Coleman and Bell), in dilute p-dioxane solution using Spectroquality p-dioxane (Matheson Coleman and Bell), and in dilute mixed benzene-p-dioxane solutions, using the above mentioned solvents. Apparatus. The dielectric constants, E, and refractive indices, nD, as a function of the weight fraction, w2, of the solute were measured at 25' as previously described.2 The data are given in Table I. Calculations. The dipole moments in pure benzene and in pure dioxane solution were calculated from the equations and methods described by Smith.8 The dipole moment in pure benzene was also calculated from the equations and methods described by Halverstadt and Kumlers and Guggenheim,10 and the standard error of this value was calculated from the equation used by Kumler,l1which takes into account only errors in the dielectric constant measurement. The dipole moments measured in mixed solvent were calculated from a modification of the method described by Estok, et aL3+ The value a, (slope of E vs. w2 in hypothetically pure benzene or dioxane solution) was calculated exactly as described by these authors; a corresponding value, ym (slope of T L D ~vs. w2 in hypothetically pure benzene or dioxane solution) was calculated in an analogous manner. These values were then used to calculate the dipole moment by the Smith method.8 Least-squares analyses were applied to determine all slopes and intercepts used in the calculations.
Results and Discussion Table I1 gives the slopes of the dielectric constant and square of the refractive index with concentration, the orientation polarization calculated from Smith's modification8 of the Guggenheim method, lo the dipole moments in Debye units, and the amide group moThe Journal of Ph,ysical Chemistry
ments, m2. The amide group moments were calculated from eq. 1 which is a special case of Eyring's equation12 p2 = m12
+ mZ2- 2m1m2cos 8 cos qi
(1)
assuming free rotation or symmetrical rotational energy barrier^.'^ We used 1721 = 2.28 (the observed value for pyridine measured in benzene solution2) for the benzene values, ml = 2.22 (the observed value for pyridine measured in dioxane solution14J5) for the dioxane values, 8 = B O ' , and d, = 110' (from Bates and Hobbs16). There is no literature value for the moment of isonicotinamide measured in benzene, but the dioxane value, 3.88, reported by Leis and C ~ r r a n can ' ~ be compared with our value, 4.01. The benzene value, 3.00, measured in the pure solvent is 0.68 D. lower than that measured by the mixed solvent technique. The latter moment, 3.68, agrees exactly with the moment, 3.68, of isonicotinamide calculated from eq. 1 reported earlier.2 The agreement between the mixed solvent, 4.05, and the pure solvent, 4.01, for the dioxane values is very good. The large difference between the two moments for isonicotinamide in benzene can be interpreted in terms of the formation of dimers of zero moment6 with pure benzene as the solvent, thus lowering the observed moment in this medium. The excellent agreement be(7) K. W. Merz and H. Stolte, Arch. Pharm., 293,92 (1960). (8) J. W.Smith, Trans. Faraday SOC.,46, 394 (1950). (9) I. F. Halverstadt and W. D. Eumler, J. Am. Chem. SOC.,64, 2988 (1942). (10) E.A. Guggenheim, Trans. Faraday SOC.,45, 714 (1949). (11) W.D.Kumler, A. Lewis, and J. Meinwald, J. Am. Chem. SOC., 83,4591 (1961). (12) H.Eyring, Phys. Rm., 39, 746 (1932). (13) H.B. Thompson, J . Phys. Chem., 64, 280 (1960). (14) D.G. Leis and B. C. Curran, J. Am. Chem. SOC.,67, 79 (1945). (15) J. Barassin and H. Lumbroso, Bull. SOC. chim. France, 492 (1961). (16) W.W. Bates and M. E. Hobbs, J . Am. Chem. SOC.,73, 2151 (1951).
NOTES
693
tween the observed mixed solvent moment and calculated moment, and between the value of m2, 3.77;and the moment of benzamide, 3.774 (the group moment values, m2 (Table II), represent the -CONH2 group attached to the aromatic ring and, therefore, might be compared with the benzamide moment) in benzene using mixed solvent techniques indicates that this technique apparently circumvents the problems of association to a large extent.6 The mixed solvent moment for benzamide in dioxane is 3.88,4which should be compared with our m2 value, 4.23; the agreement here is not so good as that of the benzene values from mixed solvent techniques. The larger moment found in dioxane as compared with benzene is in keeping with other experimental measurements and has been discussed in detail elsewhere.l7 For example, associated molecules, when diluted with dioxane, break into single molecules (via the formation of hydrogen bonds to the dioxane oxygen atoms), whereas nonpolar solvents lack the ability to disrupt these associations.l8 I n addition, Woodbrey and Rogerslg found that the energy barriers restricting internal rotation about the central C-N bond in N,Ndisubstituted amides increased with increasing polarity of the solvent in which the amide was measured. This would indicate greater contribution of the resonance form -'>C=h< in the more polar solvents, a corresponding increase in m2,and, therefore, an increase in the observed moment; this explains qualitatively the increase in moment measured in dioxane over that measured in benzene (the moment of dioxane is 0.4,20 whereas the moment of benzene is OZo). Assuming that the mixed solvent moment in benzene, 3.68, is virtually free of association problems,6 the number of dimers in pure benzene solution was calculated from eq. 2,21where pobsd is the observed moment, P'obed
= Cunassociated P'unassoaiated
f
c d i m e r P'dimer
(2)
3.00, in pure benzene, Cunassociated is the fraction of unassociated molecules with moment (Punassooiated), 3.68, and Cdimcr is the fraction of the isonicotinamide molecules in the dimer configuration having zero (Pdimer) moment. The values obtained are 66% unassociated, 34% in the dimer form. (17) C. P. Smyth, "Dielectric Behavior and Structure," McGrawHill Book Co., Inc., New York, N. Y., 1955, p. 329. (18) P. A. Geary and J. G. Miller, J. Electrochem. SOC.,97, 54 (1950). (19) J. C. Woodbrey and M. T. Rogers, J . Am. Chem. SOC.,84, 13 (1962).
(20) A. L. McClellan, "Tables of Experimental Dipole Moments," W. H. Freeman and Co., San Francisco, Calif., 1963. (21) C. P. Smyth, ref. 17, p. 293.
The Infrared Spectra of Perfluorocyclopropane and cis- and trans-Perfluorobutene-2l
by Julian Heicklen, Francis Wachi, and Vester Knight Aeroapaes Corporatwn, El Segundo, California (Received August 4 , 2064)
We wish to report the infrared spectra in the NaCl region of three simple fluorocarbons. The preparation and purification procedure of the compounds cycloCaF6,cis-C4F8-2,and trans-CrF8-2 is described by Greene and Wachi.2 For the cis and trans compounds, it was necessary that we perform the purification procedure twice for complete separation. The spectra were obtained on a Perkin-Elmer 21 infrared spectrometer and the bands and their relative intensities are listed in Table I. The infrared spectrum of cydO-c&'~ has not been previously reported. The molecular symmetry is D 3 h , and the only allowed infrared fundamental vibrations are the two Az" and the four E' bands. The two intense bands at 1368 and 1272 cm.-l must consist mainly of C-F stretching motions. Thus, one of these is an Az" band and the other an Ef band; it is not clear which is which. However, there are some indications to suggest that the 1368-cm.-l band has A2" symmetry and the 1272-cm.-l band has E' symmetry. The A2lf band involves the asymmetric stretching motion of the CF2 group, whereas the E f band involves the symmetric stretching motion. Usually, the asymmetric mode has higher frequency, which corresponds to the assignments of cyclo-C&. Furthermore, if the 2532-cm.-l band is the overtone of the 1272-cm.-1 band, then the latter band must be of E' symmetry as the overtones of A,'' bands are symmetry forbidden. The disturbing feature is that asymmetric bands are usually more intense, but our assignment requires the reverse. The strong band at 859 cm.-l undoubtedly corresponds to the CF2 deformation of E' symmetry. The two bending frequencies associated with the motion of the CF2groups relative to the carbon skeleton lie below 650 cm.-l and are not observed. The Ef ring-deformation frequency of cyclopropyl compounds usually lies within 25 cm.-l of 1025 cm.-la4 No such band ap(1) This work was supported by the U. S.Air Force under Contract M(695)-269. (2) 6. A. Greene and F. M. Wachi, Anal. Chem., 35, 928 (1963). (3) (a) H. H. Giinthard, R. C. Lord, and T. K. McCubbin, Jr., J . Chem. Phy6., 2 5 , 768 (1956); (b) H. E. Duckworth, Can. J. Phys., 34, 1448 (1956).
NO.AF
Volume 69,Number 2 Peebruary 1366
