NOTES
1597
ion is about the same in the four nitrates, e.g., 2.55 k 0.14 in NaN03, 2.45 0.10 in KN03, 2.38 f 0.08 in RbN03, and 2.38 f 0.06 in &NO3 (units 10-4cm.2/v. sec.). The ratio of the ionic mobility 'OL and the diffusion coefficient D, ( R T / P ) ( u / D ) ,has also been calculated in these sixteen different cases.2 It has been found that this ratio is always less than unity (usually about 2/3), contrary to the Nernst-Einstein equation which predicts ( R T / F ) ( u / D )= 1.
is given in Fig. 1. The resonances of the phenyl and H-C=S protons are shifted to lower fields and are omitted from the figure. Line positions are referred to tetramethysilane and are given in C.P.S. at 60 Iclc. With increasing temperature, the following changes in the spectra are observed.
--I
-cn,
Acknowledgment. The present investigations have been carried out under the auspices of the Netherlands Foundation for Chemical Research (S.O.N.) and with financial aid from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.) ~~~
~~
~
~
eauation has been discussed bv several authors; for example: 1,. Yang, J . Chem. Phys., 27, 60i (1957); R. W. Laity, ibid., 30, 682 (1959). 12) The Nernst-Einstein ~~,
DMTF (purr)
~
ibo
The Activatison Energy to Hindered Internal Rotation in Some Thionamides
by A. Loewenatein, A.. Melera, P. Rigny, and W. Walter V a r i a n AG Research Laboratovy, Z u r i c h 8, Switzerland (Received December 12, 1963)
The energy barrier, E , to hindered rotation of thie C-N bond in several amides has been measured by thle nuclear magncbtic resonance (n.m.r.) technique. The temperature dependence of the internal rotation ia conveniently described by the Arrhenius equation, k = k , exp( - E / R T ) , and the measured E values range from 6 to 18 kcal./mole.l It is of interest to compare these values to the corresponding ones in the thionamides2 and this communication reports some results obtained for the latter with the n.m.1.. technique. The compounds measured were : N,X'-diniethylthionform-. amide (DMTF') and r\',N'-diisopropylthionforinaniide (DITF). In another compound, X-methyl-"-phenylmethylthionformamide (AIPTF), the enthalpy difference, A H , between the cis and trans forms. was obtained from the temperature dependence of the equilibrium constant. The n.ni.r. spectra of DAlTF and RIPTF have previously been given by Walter and Maerten.3 A schematic description of the methyl, methylene, and methine proton resonances a t low temperatures
'
cls.
Figure 1. Schematic representation of the spectra of N-methyl-N'-phenylmethylthionformamide( MPTF), S,N'-diisopropylthionformamide (DITF), and N,N'-dimethylthionformamide (DMTF). The abscissa indicates the separation to lower magnetic field, in c.P.s., from tetramethylsilane. The relative intensities of the resonances in different groups are not drawn to scale.
(1) The intensities of the two CH, and two CHZ resonances in MP'TF change and tend to equalize. The logarithm of the intensity ratio of the CHZresonances was plotted as a function of the reciprocal absolute temperature and from the slope AH between the cis and trans forms was found to be 2.4 f 0.5 kcal./mole (temperature range 25-90'). ( 2 ) I n D I T F the two doublets and two septets broaden and eventually collapse to give a single doublet and a single septet folowing the well-established pattern of exchange modified n.m.r. multiplets. The coalescence temperature of the doublet is approximately 173'. The mean lifetimes, T = l / k , of the rotamers were obtained from the changes in the line shapes of the two doublets using the calculated curves for an exchange broadened doub1et.l From the slope of a plot of In 1 / r us. 1/X, E was obtained. It should be noted that a complication arises from the fact that the chemical shift between the two spin-spin doublets (1) A. Loewenstein and T. RI. Connor, Be?. Bunsenges. P h y s i k . Chem., 67, 280 (1963). (2) Nomenclature follows R. N. Hurd and G. DeLaMater, Chem. Rev., 61, 45 (1961). (3) W. Walter and G. Maerten, Ann., 669, 66 (1963).
V o l u m e 68, Number 6
J u n e , 1964
KOTES
1598
Table I Solvent
Compound
DMTF DMTF DITF DITF
Pure 407, V in o-CaH4C1,
Pure 407, V in o-CsH4C12
E , kcal./mole
ka, a e c . 7
27.9 f 1 . 1 36.2 i 1 . 7 31.8 i2 . 8 24.2 i5 . 6
(4.4 0 . 5 ) x 1013 ( 1 . 2 f 0 . 3 ) x 10*9 (8.9 f 2 . 8 ) X lOI4 ( 5 . 8 i 4 . 2 ) X 10l2
is small; and thus, they partially overlap. Since only the cheiiiical shift is averaged by fast rotation and the J splitting remains uiiaff ected, the collapse occurs between neighboring pairs of lines. (3) I n DRlTF the two closely spaced doublets of the methyl resonances collapse a t high temperature to a single doublet. The rates of rotation were obtained by the approxiiiiate procedure used4 in the similar case of dimethylforniamide. A Loreiitzian “envelope” was drawn on each of the closely separated doublets and the resulting, slightly broadened “doublet” was treated in the usual I n pure DMTF, only “ratios” were used since the collapse temperature could not be attained, whereas in solution three nieasurements were obtained from the collapsed “doublet,” using the fast exchange approximation.1 The results are summarized in Table I. All errors are probable errors calculated by least-squares fits of the lines. The number of measurements and the teniperature ranges are also given. The results show that the activation energies to hindered rotation in thionamides are much higher than the corresponding values in amides. Whereas in D I T F sonle steric hindrance due t o the bulky isopropyl groups iiiight be effective. this can be ruled out for DMTF, the corresponding E value in S,S’-diThe contrimethylformainide being 10 k~al.,/niole.~ bution of the polar form -X-C=S+, where X is oxygen or sulfur, probably determines the ralue of E . It must thus be concluded that this contribution is higher in thioiianiides than in amides. This is so in spite of the higher electronegativity of oxygen relative to sulfur. The same conclusion was reached in other studies of the carbon-sulfur double bond by means of infrared, ultraviolet, and dipole moment measurement s. It should be noted that there is a marked solvent effect for E (‘Table I) and for the chemical shifts (Fig. 1). The solvent effect has opposite direction for DITF and DJITF. This suggests that the solvent molecules are strongly associated with the thionaniides and are also involved i n the traiisition state. Similar effects were noticed for E measurements in amides and for T h e Journal of Physical Chemistry
Number of measurements Temp. range, “ C .
4 7 8 6
176-1 93 141-179 162- 186 147-175
ring The nature of the association seems to be different in the two thionamides studied and thus far is not understood. All measurements were performed on a Varian A-60 n.m.r. spectrometer equipped with a V-6040 variable temperature attachment. Compounds were prepared by a method given by Walter and ;14aerten.3 Acknowledgment. A. L. and P. R. wish to thank Varian AG Research Laboratory for the kind hospitality during their summer visit. (4) G . Fraenkel and C . Franconi, J . Am. Chem. Soc., 8 2 , 4478 (1960). (5) (a) L . J. Bellamy, “Organic Sulfur Compounds,” N . Kharasch, Ed., Pergamon Press, London, 1961, p. 52; (b) C. 31. Lee and W. D. Kumler, J . O r g . Chem., 27, 2082 (1962); (c) S. C. Abrahams, Quart. Res. (London), 10, 407 (1956); (d) M .J. Janssen, Rec. traz;. chim., 8 2 , 931 (1963).
Relation between Steady-Flow and Dynamic Viscosity for Polyethylene Melts’
by Shigeharu Onogi. Tsuguo Fujii, Hideo Kato, and Sadahide Ogihara Department of Polymer Chemistry, Kyoto L’nicersity, Kyoto, J a p a n (Received December $3, 1968)
The relation between steady-flow and dynamic viscosities is an important problem which has been studied theoretically and experimentally by many investigators cited below. Enfort unately, however, the conclusions of these investigations are diverse, and we cannot know the nature of. apparent viscosity at present. In the previous paper,2 rheological properties of polyethylene melts at various temperatures were nieas(1) Paper presented a t the 12th Annual Symposium on Rheology, Tokyo. Japan, September, 1963. ( 2 ) M .Horio, T. Fujii. and S. Onogi, paper presented a t the 145th National Meeting of the American Chemical Society, Xew York, K . Y . , September, 1963 (to be published).
