June, 1943
THEVIBRATIONAL
FREQUENCIES OF
ALIPHATIC RING SYSTEMS
[CONTRIBUTION FROM T H E SCHOOL OF CHEMISTRY AND PHYSICS OF
1135
THEPENNSYLVANIA STATE COLLEGE]
The Heat Capacity and Entropy, Heats of Transition, Fusion and Vaporization and the Vapor Pressures of Cyclohexane. .The Vibrational Frequencies of Alicyclic Ring Systems' B Y J. G. ASTON,GEORGEJ. SZASz AND HERMAN L.FINK
The present paper presents measurements of complete thermal data from 10 to 294°K. and of heats of vaporization a t 298.16"K. for cyclohexane from which the entropy of the ideal gas has been calculated a t 298.16OK. The entropy thus obtained has been found to agree with the value calculated from the spectroscopic and molecular data using values for the y frequencies (vibrations perpendicular to the ring) of y1 = y2 = 210 cm.-', 7 3 = 377 cm.-l. Inasmuch as similar y frequencies were assumed for cyclopentane2*4 in an earlier paper pointing to a non-planar structure, this result can be taken as substantiating the results of that paper. Preparation and Purification of Cyclohexane.A purified sample of cyclohexane was furnished us through the kindness of Professor M. R. Fenske of the Petroleum Refining Laboratory of this College. The cyclohexane (from Rohm and Haas) was purified by Dr. W. R. Scott by acid extraction and fractionation through a glass column. After being dried over phosphorus pentoxide and freed from the last traces of air by repeated freezings and evacuations to mm. of mercury, about 43 cc. of the material was condensed into a weighed glass sample bulb and then introduced into the calorimeter in the manner previously described.3 The method used to distill the sample into the calorimeter without its coming into contact with anything but glass, was described recently.' The Heat Capacity Measurements.-The apparatus, method, and temperature scale were as already described.a Calorimeter B was used for all measurements with resistance thermometers R-200 (platinum-rhodium) and R-102 (constantan). The indications of these thermometers were compared a t ten-degree intervals with the standard thermocouple S-9 which was soldered to the ~alorimeter.~The maximum deviation noted was (1) The results of this paper have already been cited by J. G. Aston and R. M. Kennedy, Symposium on Low Temperature Phenomena, 104th meeting of the American Chemical Society, Buffalo, N. Y.,Sept., 1942 (paper presented by S. C. Schumann). (2) Aston, Schumann, Fink and Doty, THIS JOUXNAL, 68, 2029 (1941). (3) Aston and Eidinoff, ibid., 61, 1533 (1939). (4) Aston, Fink and Schumann, ibid., 66, 341. (1943).
the in0.05'. For reasons previously di~cussed,~ dications of R-200 and R-102 were considered more reliable than those of S-9. A pressure of one third of an atmosphere of helium wm introduced into the calorimeter while cooling for and during the heat capacity measurements on the solid but not on the liquid as this would have rendered corrections for vaporization into the filling line ambiguous. When the helium was present no effort was made to keep the inner block wanner as no appreciable quantity of solid could have collected in the time of the heat TABLE I THEMOLALHEATCAPACITY OF CYCLOHEXANE Mol. wt. 84.156; 0.39651 mole in calorimeter; 0°C. = 273.16'K. Temp.. OK.
CP
cal./deg.)mole
iT, T",mp., K.
Series I11
Solid 12-73 15.24 17-45 19.31 21.36 24.18 27.93 31.55 35.28 39.04 43.19 48.00 53.18 58.40 63.87
0.56
9.53 10.19
2.4 2.3 2.2 2.0 2.7 3.0 3.8 3.7 3.9 3.9 4.5 5.2 5.3 5.3 5.8
58.91 63.87 68.38 72.90 77.74 82.87 88.17 93.45 98.40 103.13 107.61 112.20 121.86 126.43
Series I1 9.60 10.24 10.77 11.25 11.79 12.30 12.88 13.37 13.87 14.23 14.71 15.14 16.04 16.55
5.2 4.7 4.3 4.7 5.0 5.3 5.5 5.2 4.9 4.7 4.5 4.8 4.9 4.7
1.06 1.56 1.99 2.42 3.20 4.20 4.84 5.63 6.48 7.33 8.08
8.83
CP,
K.
cal./deg./mole
131.16 136.16 146.47 151.49 161.30 166.37 171.32 176.04 180.83 191.30 196.24 201.46 206.60 211.98 217.77 223.41 228.75 234.21 239.53 249.73 254.79 259.83 265.40 271.13
$T, K
16.90 17.40 18.30 18.87 20.03 20.70 21.28 22.00 22.58
5.0 4.7 5.2 5.0 5.3 5.1 5.0 4.7 5.2
Transition 25.80 26.02 26.14 26.44 26.65 26.95 27.35 27.62 28.04 28.56 29.33 29.54 30.02 30.62 30.92
5.5 5.3 5.3 5.2 5.9 5.8 5.7 5.6 5.5 5.2 5.1 5.0 5.6 5.5 6.1
Series I Liquid 36.11 36.48 36.88 37.12
2.8 3.7 4.0 3.3
281.63 284.89 288.79 292.46
capacity measurements, as demonstrated experimentally. One defined calorie was taken equal tcs 4.1833 international joules. Corrections to the heat capacities for vaporization into the filling line were made using the values for the density given by Eg1off.j The molal heat capacities are listed in 'Table I and plotted in Fig. 1, where are also plotted the measurements of Parks, Huffman and Table I1 contains a comparison of heat capacity values a t rounded temperatures as obtained in this research and by Parks, Huffman and ThomasG
lemp.. OK.
12 (soIid I) 15 50 25 30 40 50 60 70 80 90 100 110
OF
CYCLOHEXANE
180
130 140 150 160 170 180 190 (solid 11) 200 210 220 230 240 250 260 270 280 (liquid) 290 295
Cp, cai./deg./mole This Research P., H. and .'i
0.54 1.02 2.17 3.37 4.50 6.72 8.38 9.74 10.93 12.02 13.04 14 01 14.95 15.88 16.80 17.73 18.73 19.87 21.15 22.50 25.77 26. lti
26.61 27.13 27.75 28.48 39.29 30.18 31.08 35.89 36.9?
37.25
2.12 21.10 40.08
AT
13.02 14.04 14.99 15.97 16.88 17.79 18.73 19.78 21.00 22.48 25.93 26.40 26.73 37.21 27.76 28.40 29.14 29.98 30.88 35.32 36.11 36.70
Dev , Qlo
-0 15 t0.21 f O 27 +0 60 +O 48 +O 32 000 +o 46 -0 71 -0 09 +O 62 +O 92 +0.45 +o 29 +0 04 -0 28 -0 51 -0.66 -0 64 -1.58 -2 33 -1 48
The Transition and Melting Points.-The procedure was the same as that described prev i o ~ s l y . ~The equilibrium temperatures during transition and fusion are listed in Tables I11 ( 5 ) Egloff, "Physical Constants of Hydrocarbons," Vol. XI, Reinhold Publishfng Compaoy, New York, N. Y., 1940. (ti) Parks, Huffman and Thomas, THls JOURNAL, 6S, 1081 (1930). 17) Aatlan and Messcrly, ibid., 58. 2354 (19.36).
TABLE I11 TEMPERATURES OF TRANSITION OF CYCLOHEXANE (DATE 4/9/42)
Tutti! lime, miii.
I',O K . T , OK. ThPrmoeouple Res. T h s !! R-2Ol)
(io 19
