2838
j. R. LACHER, J. W. POLLOCK, W. E. JOHNSON
AND
J. D. PARK
VOl. 73
ICONTRXBUTION PROM THE UNIVERSITY OF COLoRADO]
The Magnetic Susceptibilities of Some Methyl Derivatives of Methane and Ethylene' BY J. R. LACHER, J. W. POLLOCK, W, E.
JOHNSON AND
J. D. PARK
The diamagnetic susceptibilities of several compounds have been measured : propane, isobutane, neopentane, propylene, The Quincke method was used. The experimental molar susceptibilities deviate from a simple additivity rule. The standard heats of formation of the methyl derivatives of methane and of ethylene show the same types of deviation from this rule as do the corresponding molar susceptibilities. The experimental data for the methyl derivatives of methane may be satisfactorily interpreted when tetrahedral interactions are assumed. In case of the methyl derivatives of ethylene, the deviations may be simply related to the geometry of the ethylenic rectangle.
cis- and trans-butene-2, isobutene and tetramethylethylene.
The molar diamagnetic susceptibilities of the hal- loan from API Research Project 45 through the courtesy ogen derivatives of methane deviate considerably of Professor Boord, Department of Chemistry, Ohio State Its purity was greater than 99% and the comfrom a simple additivity rule. We showed recently2 University. pound was free of peroxides. The experimental results are that these susceptibilities may be interpreted suc- summarized in Table I. The second column in this table cessfully as being equal to the sum of atomic incre- gives the measured molar susceptibility and the fourth the calculated susceptibility. The method used ments plus six interaction terms corresponding to column to make these calculations will be described later. The the edges of a tetrahedron. The electron clouds of thud and last columns give the change in susceptibility the halogen atoms are sufficiently large so that a which result when a hydrogen atom is replaced by a methyl mutual crushing takes place. This will reduce the group. It is believed that our experimental data are rcmolar susceptibility of the molecule since atomic liable to 1%. Bitter's' values for methane, ethane and ethylene are also included in the table. Their critical susceptibilities are, to a first approximation, pro- temperatures are such that they could not be studied in our portional to the square of the radii of the electron present apparatus. The value of 12.0 for ethylene seems orbits. This is supported by the facts that the to us t o be much too low. Bitter has also reported 40.5 magnitude of the halogen-halogen interaction in- and 56.3 for the molar susceptibility for propane and isobutane, respectively. Pascal8 reported the molar suscepticreases with increasing size of the halogen atom and bility for trimethylethylene. that hydrogen-halogen interactions are small except TABLE I for fluorine. MOLAR I ~ A M A G N E T I C SUSCEPTIBILITIES Mutual crushing of the electron clouds should -xexpt. - xcnled. give rise to repulsive potentials, These potentials Conrpound x 10' A X lot' A should manifest themselves in the standard heats of A . Methyl derivatives of methane formation of the compounds involved, Unfortu12.27 13.4 nately, reliable thermochemical data for the halogen 15.1 13.4 27.37 26.8 derivatives of methane and ethylene are not yet 12.3 12.8 39.6 39.6 available. The standard heats of formation of the 12.1 12.1 5 1 . 7 51.7 methyl derivatives are known from the work of 11.4 11.4 63.1 63.1 Rossini and co-worker~.~The molar susceptibilities of some of these compounds have been measured Methyl derivative< CJf ethylene and are reported in this paper. CHa=CHz' 12 0 1~ 2o 11 4 CHFCHCH~ 31.5 31 8 Experimental 11.4 The magnetic susceptibilities of these compounds have been measured : propane, isobutane, neopentane, propylene, cis- and trans-butene-2, isobutene and tetramethylethylene. AI1 measurements were made by means of the Quincke method,' using an apparatus previously described.6 Carefully purified benzene (% = -0.702 X 10-6) was employed as a standard for the measurements. Since all but one of the hydrocarbons are vapors at room temperatures, a high pressure Quincke tube was used. All of the hydrocarbons except trans-butene-2 and tetramethylethylene were pure grade as supplied by the Phillips Petroleum Company and were used without further purification. The trans-butene was obtained by distillation of a mixture of the cis- and truns-isomers in a Hyper-Cal Podbielniak column. The infrared spectra of the transcompound so obtained showed no absorption due to the czs-isomer.' The tetramethylethylene was obtained on (1) Presented before the Division of Inorganic and Physical Chemistry, 118th Meeting of the American Chemical Society, Chicago, Sept. 3-8, 1950. This work was supported by Contract N6-our-231, Task Order 6, with the Office of Naval Research, United States Navy. (2) J. R. Lacher, R . E. Scruby and J. D. Park, TEISJOURNAL, 72, 333 (1950). (3) American Petroleum Institute Research Project 44 a t the National Bureau of Standards, Selected Values of Chemical Thcrmodynamic Properties Series 111, Vol. I (4) G. Quincke, Ann. Physik, 24, 247 (1885); 84, 401 (1888). (5) J. R. LRcher, R . 13. Scruby and J. D. Park, T H r s J O U R N A L , 71, 1797 (194Y). ( 6 ) D I I ('simpion, P'h 1) T h e s i s , 1!l14, l ' t i i v e r 4 t y of
