E. F. WESTRUM,JR.,W.-K. WONG,AND E. MORAWETZ
2542
Thermodynamics of Globular Molecules. XVIII. Heat Capacities and Transitional Behavior of l-Azabicyclo[2.2.2]octane and 3-0xabicyclo[3.2.2 Inonane.
Sublimation Behavior of Five Globular Molecules'
by Edgar F. Westrum, Jr.,2 Wen-Kuei Wong3 Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48104
and Ernst Morawetz Thermochemistry, Chemical Center, University of L u n d , L u n d , Sweden
(Received December 16, 1969)
The thermal properties of two globular molecules, 1-azabicyclo [2.2.2]octane (quinuclidine) and 3-oxabicyclo[3.2.2]nonane, have been determined from 5OK t o well within their liquid regions (438 and 480°K, respectively). Azabicyclooctane undergoes a solid-solid phase transition at 196.00"K and melts a t 430OK. The entropy increments corresponding to these first-order transformations are 6.34 and 3.2 cal/(mol O K ) . The oxabicyclononane undergoes a broad solid-solid transition with maximum heat capacity a t 208.50°K and melts a t 448.43"K with associated entropy increments of 8.22 and 3.61 cal/(mol O K ) . The Crystal I phases of both substances are plastic (or embefic) crystals. Mechanisms are developed to account for the magnitudes of the entropy increments. The standard molal thermodynamic functions, heat capacities, entropies, Gibbs energy functions, and Gibbs energies of formation for crystalline azabicyclooctane and the oxabjcyclononane are: 40.48, 44.23; 49.47, 56.47; -23.83, -27.04 cal/(mol OK); and 42.23, -7.04 kcal/mol a t 298.15'K. Sublimation pressures and enthalpies of sublimation of the Crystal I phases of the above compounds plus that of bicyclo [2.2.2]octane and octene, and 3-azabicyclo [3.2.2]nonaneJ were determined directly. The gas phase thermodynamic functions are presented.
Introduction As a continuation of the study of the thermodynamic characteristics of globular molecules4 in the bicyclooctane family, measurements were obtained for l-azabicyclo [2.2.2]octane, (quinuclidine, hereafter 1) and for 3-oxabicyclo [3.2.2]nonane (hereafter 2). 1 possesses a symmetry differing from that of bicyclooctane in its loss of the possible mirror plane perpendicular to the threefold axis and is similarly related to 1,4-diazabicyclo [2.2.2]octane (DABCO), the subject of a previous papera5 2 is closely related to 3-azabicyclo [3.2.2]nonane, which has been the subject of two previous calorimetric determinations of thermal properties.6 Experimental Section
A commercial sample of 1 was subjected to fractional sublimation, gradient sublimation, and zone melting refining. Anal. Calcd for 1 : C , 75.62; H, 11.79; K, 12.59. Found: C, 75.80; H, 11.81; N, 12.34. A sample (25.3588 g (vacuum mass)) of this material was sublimed into calorimeter W-37 for the cryogenic thermal measurements. Calorimeter W-22 with a 35.9492 g (vacuum mass) loading was used over the intermediate temperature range that included the fusion point of the material. Compound 2 was obtained from Eastman Chemical Products, Inc. and was subjected to the same purificaT h e Journal of Physical Chemistry, "01. 74, N o . 18, 1970
tion process. Anal. Calcd for 2: C , 76.14; H, 11.18; 0, 12.68. Found: C, 76.15; H, 11.14; 0, 12.80. The same calorimeters were used; W-37 was charged with 24.2942 g (vacuum mass) for the cryogenic region and W-22 with 28.4942 g (vacuum mass) for the intermediate region which included fusion. The Mark HI7 and Mark IVB thermostats for the cryogenic and intermediate-temperature region have been described previously as have the methods of adiabatic shield control and computational conversion of data to molal thermodynamic properties. Automatic adiabatic shield control was used above 50°K (1) This work was supported in part by the Division of Research, United States Atomic Energy Commission. (2) To whom correspondence concerning this paper should be addressed. (3) Abstracted in part from a dissertation submitted in partial fulfillment of the requirements for the Ph.D. degree from the Horace H. Rackham School of Graduate Studies at the University of Michigan, Diss. Abstr., B28(3),874 (1967). (4) W.-K. Wong and E. F. Westrum, Jr., J . P h y s . Chem., 74, 1303 (1970). (5) J. C. Trowbridge and E. F. Westrum, Jr., ibid., 67, 2381 (1963). (6) C. A. Wulff and E. F. Westrum, Jr., ibid., 68, 430 (1964); C. M. Barber and E. F. Westrum, Jr., ibid., 67, 2373 (1963). (7) E. F. Westrum, Jr., G. T. Furukawa, and J . P. McCullough, in "Experimental Thermodynamics," J. P. McCullough and D. W. Scott, Ed., Butterworth and Co., Ltd., London, 1968. (8) E. D. West and E. F. Westrum, Jr., in "Experimental Thermodynamics," J. P. McCullough and D. W. Scott, Ed., Butterworth and Co., Ltd., London, 1968.
~-AZABICYCLO [2.2.2]OCTANEAND 3-OXABICYCLO[3.2.2jNONANE and all measurements were referred to calibrations and standardizations by the National Bureau of Standards. The heat capacity of the sample in the cryostat ranges from 85% of the total at 10°K to a minimum of 55% a t 105°K; above this temperature (except in the transition regions) it steadily increases to 70% in the solid and drops to 65% for the liquid phase. All calorimetric measurements on the condensed phases were made a t the University of Michigan. Directly measured enthalpies of sublimation for five globular molecules were obtained at the University of Lund on the same samples used to obtain the thermal data. The measurement techniques employed for these measurements have been described elsewhere. Sublimation pressures can be calculated from the flow rates obtained from the measuremeiita of the enthalpies of sublimation. Since, however, the vapor flow from the calorimeter (Knudsen cell) is adiabatic and not molecular (ie,, the flow Knudsen number Kn c 1))A is the orifice area in om2, 2 is flow time in seconds, K is the ratio of the heat capacity at constant pressure to the heat capacity a t constant volume. I n fact, the expression is the well known Knudsen formula except for the factor c and the term in square brackets which corrects for compressibility effects. It was found that the magnitude of the square root of this term is rather insensitive to small variations of K. For octane through hexadecane (1.046 < K < 1.020) the average value was calculated to be 1.51 f 0.005 (maximum d e v i a t i ~ n ) . ~ From flow rate measurements on octane ( P , = 14.3 Torr), 3,4-xylenol (Pa = 0.01 Torr) and water (Ps= 22.3 Torr) an approximate value of Kc = 0.90 f 0.08 (maximum deviation) was obtained for a number of orifices. Using this value, sublimation pressures were calculated from flow rate measurements. Results The experimental heat capacities are listed in Table I and shown in Figures 1 and 2. The entries in Table I include the mean temperatures from which temperature increments within a series may be estimated. It is believed that probable errors in these data decrease from 5% a t 5°K to 1% a t 10°K and fall below 0.1%
Temperature , O K
Figure 2. The heat capacity of 3-oxabicyclo [3.2.2] nonane.
above 25°K. The data are stated in terms of the thermochemical calorie defined as 4.1840 J and an ice point of 273.15OK. Molal thermodynamic functions are presented, a t selected temperatures, in Table 11. Increments over regions devoid of thermal anomalies were obtained by suitable integrations of polynomials fitted to the heat capacity by high-speed computer. For regions of transition and fusion, the numerical investigations were obtained from large-scale plots of the data. It is believed that the probable errors in the derived functions are comparable to those of the heat capacities themselves. Evidence for this supposition is obtained by comparison (9) (a) E. Morawetz and S. Sunner, Acta Chem. Scand., 17, 473 (1963) ; (b) E. Morawetz, “Thermodynamik Symposium,” Klaus Schafer, Ed., Heidelberg, 1967, and Acta Chem. Scand., 22, 1509 (1968). (10) C. W. Nutt, G. W. Penmore, and H. J. Biddlestone, Trans. Faraday SOC.,55, 1516 (1959). The Journal of Physical Chemistry, Vol. 74, N o . 1.9, 1970
E. F. WESTRUM,JR.,W.-E(. WONG,AND E. MORAWETZ
,2544
Table I: Experimental Heat Capacity Determinations on l-Aeabicyolo[2.2.2]octaneand 3-0xabicyclo[3.2.2] lionanen -
Ca
Data Taken in Mark I11 Calorimetric Cryostat
Data Taken in Mark 111 Calorimetric Cryostat
Series I1 AH Run (I)
28.24
AHt Run A
32.56 33.51 34.53 35.57 36.63 37.68 38.75 39.74 40.80 41.92 43.02 44.11 45.29
Series I11 86.71
-T
3-Oxabicyclo [ 3.2.21 nonane
148.76 19.93 157.73 21.51 166.85 22.70 176.66 24.69 186.29 28.75 193.61 63.87 197.22 233.9 199.71 106.6 206.01 31.96 215.09 31.49 224.05 32.40
226.73 236.48 245.99 255.40 264.88 274.32 283.67 292.92 302.15 311.72 321.56 331.37 341.11
CB
1-Azabicyclo[ 2.2.21 octane Series I
185.54
-T
ea
T
14.01
95.38 14.77 104.30 15.54 113.39 16.40 122.51 17.28 131.48 18.19 140.65 19.18 150.03 20.28 AH Run (11) 186.98 29.45 AHt Run B Series IV 5.89 7.26 8.26 9.33 10.39 11.56 12.82 14.14 15.60 17.26 19.14 21.26 23.59 26.12 28.94 32.08 35.66 40.06 44.67 49.25 54.71 60.66 66.65
0.0603 0.1346 0.1835 0.3119 0.4416 0.5989 0.8230 1.098 1.455 1.887 2.425 3.055 3,772 4.537 5.348 6.211 7.112 8.075 8.945 9.713 10.50 11.28 11.97
73.23 80.45 88.07
12.62 13.36 14.12
Series V 176.31 180.06 184.37 188.20 191.37 193.91 195.40 195.96 196.17 196.39 196.77 197.30 198.09 199.58 203.13 208.55
24,59 25,65 27.21 29.73 35.88 57.28 155.2 691.4 752.1 599.6 279.9 264.0 132.0 121.2 35.82 30.86
Series VI 151.68 160.71 169.33 AHt Run
20.54 21.77 23.20 C
Series VI1 168.56 23.06 AHt Run D
Series I 5.70 6.73 7.94 8.74 9.72 10.74 11.90 13.23 14.61 16.12 17.76 19.37 21.14 23.45 26.61 30.02 33.18 36.50 40.06 44.13 48.94 54.36 60.59 67.18
0.0916 0.1510 0.2617 0.3762 0.5566 0.7532 0.9798 1.329 1.729 2.202 2.751 3.283 3.881 4.678 5.648 6 622 7.441 8.209 8.934 9.651 10.42 11.18 12.01 12.81 I
Series I1 54.08 62.39 70.54 77.89 84.66 91.61
11.15 12.24 13.18 14.04 14.87 15.66
99.41 16.52 107.73 17.48 116.49 18.54 125.73 19.70 135.23 20.93 144.68 22.21 153.93 23.63 163.19 25.33 172.54 28.47 181.75 35.92 189.75 52.91 196.06 78.13 200.79 108.93 204.46 142.66 207.96 127.28 212.51 70.65 219.78 38.84 228.75 36.47 237.56 37.26 246.43 37.65 255.73 39.13 264.44 39.79 273.70 41.63 283.13 42.45 292.63 43.56 302.23 44.75 311.89 46.01 321.58 47.25 331.28 48.50 340.86 49.72 Series I11 AH Run (I)
168.14 26.58 173.40 28.69 AHt Run A Series IV AH Run (11)
168.28 AHt Run
26.72
B
Series V 171.65 176.92 181.77 186.14 190.09 193.49 196.33 198.77 200.92 202.93 204 86 206.67 208.31 209.89 211.71 214.05 216.88 220.13 224.06 228.40 232.73 236.99
26.29 29.09 34.19 40.10 46.26 59.19 73.32 86.35 98.64 102.1 109.1 117.1 137.8 126.9 99.03 70.36 59.88 50.81 36.91 37.17 36.74 38.75
Data Taken in Mark IV Calorimetric Thermostat Data Taken in Mark IV Calorimetric Thermostat Series VI11 299.48 309.49 319.29 328.91 338.43 347.98 357.61
40.80 41.97 43.11 44.21 45.41 46.59 47.78
367.28 377.02 386.69 396.26
49.05 50.29 51.72 53.48
Series I X 404.84 408.72
55.93 57.01
412.51 416.18 419.66 422.87 425.68 428.02 429.94 431.43 432.49 433.34
Series VI 59.20 62.27 68.08 78.33 96.66 128.3 173.3 267.7 364.5 428.5
298.15 309.86 316.05 325.69 335.43 345.22 335.03 364.67 374.18 383.72 393.38 403.02 412.65
44.07 45.18 46.66 48.06 49.23 50.44 51.87 53.41 54.67 55.92 57.32 58.64 60.21
Series VI1 397.40 a
Units: ca1, mol,
OK.
The Journal of Physical Chemistry, Vol. 74, No. 18, 1070
57.89
406.41 415.93 425.65 432.91 437.67 441.98 444.81 446.16 447.15 447.96 450.16 454.48
59.13 60.56 62.02 63.31 64.28 83.61 214.1 364.0 412.5 425.6 77.26 69.02
Series VI11 435.84 63.51 440.36 73.22 443.73 184.8
445.46 446.24 446.88 447.44 448.29
311.2 409.6 462.8 565.9 301.1
Series I X A H m Run A
Series X AHrn Run 455.71 461.09 466.43 471.72 476.99
B 69.37 69.88 71.20 71.88 72.55
2545
~-AZABICYCLO [2.2.2]OCTANEAND 3-OXABICYCLO[3.2.2]NONANE oct,aneand 3-0xabicyclo[3.2.2]nonane" Table 11: ThermodynamicProperties of l-Azabicyclo[2.2.2] -(UO
F
CS
S O
H o - H'o
-
l-Asabicyclo[2.2.2] octane
Crystal I1 Phase 5 10 15 20 25 30 35 40 45
0.029 0.380 1.303 2.677 4,199 5.648 6.938 8 053 9,011 9.836 11.19 12.31 13.32 14.28 15.20 16.11 17.03 18.01 19IO9 20,30 21.67 23.29 25.50
50
60 70 80
90 100 110 120 130 140 150 160 170 180
0.020 0.121 0,430 0.986 1.746 2.642 3,612 4.613 5.618 6.612 8.530 10.34 12.05 13.68 15.23 16.72 18.16 19.56 20,94 22.29 23.65 25.01 26.40
0.076 0.899 4,862 14.68 31.87 56.54 88.09 125.6 168.4 215.5 320.9 438.6 566.8 704.8 852.2 1009 1174 13.50 1535 1732 1942 2166 2410
0.005 0.031 0.106 0.252 0.472 0.757 1.095 1,472 1.877 2.301 3.181 4.076 4.967 5.845 6.706 7.549 8.374 9.181 9.971 10.75 11.51 12.27 13.01
27.90 30.19 35.19
2688 3133 4119
13.75 14.21 14.60
37,12 38.58 40.02 41.44 42.85 44.24 45.62 46,06 47,OO 48,36 49.47 49.72 51.08 52.42 53.77 55.10 56.44 57.77 59.11 60.44
4512 4827 5151 5485 5829 6184 6551 6669 6929 7318 7645 7720 8132 8556 8992 9441 9901 10376 10862 11363
15.63 16.64 17.63 18.59 19.53 20.45 21.36 21.64 22.25 23.13 23.83 23.99 24,84 25,69 26.52 27.34 28.15 28,95 29.75 30.54
Transition Region 190 196.00 200
(32) (955) (83)
Crystal I Phase 210 220 230 240 250 260 270 273,15 280 290 298.15 300 310 320 330 340 350 360 370 380
31,Ol 31,96 32.90 33.89 34I94 36.06 37.22 37.58 38,38 39.54 40.48 40.69 41.84 43,Ol 44.20 45.43 46.71 48.04 49 41 50.76
3-Oxabicycloj2.2.21nonane
5
T
30 35 40 45 50
60 70 80 90 100 110 120 130 140 150
CS
S O
6.603 7.865 8.929 9.826 10.60 11.92 13.12 14.31 15.48 16.62 17.76 18.95 20.22 21.58 23.02
Ho
- HOo
-(Qo
-
Hoo)/T
3.420 4.535 5.657 6.762 7.838 9,890 11.82 13.65 15.40 17.09 18.73 20.32 21.89 23,44 24.98
71.61 107.9 149.9 196.9 248.0 360.7 485.9 623.06 772.0 932.5 1104 1288 1484 1693 1916
1.033 1.453 1.909 2.387 2.878 3.878 4.876 5.859 6.822 7.765 8.687 9.591 10.48 11.35 12.20
26.51 28.08 29.79 31,91 35.23 40.05 41.03 44.38
21531 2412 2711 3106 3753 4740 4945 5661
13.05 13.89 14.72
Transition Region 160 170 180 190 200 208.50 210 220
24.6 27.3 33.6 46.6 89.4 (147) 127.3 41.5
15.57 16.46 17.32 17.48 18.6j
Crystal I 230 240 250 260 270 273.15 280 290 298.15 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 448 82*
36 60 37.27 38.20 39.50 40 8: 41.26 42.10 43.27 44.23 44.45 45.71 47 05 48.43 49.81 51.18 52.57 54.00 55 46 56.89 58.27 59.65 61.19 62.86 64.40 (63.70)
46.06 47.63 49.19 50.78 52,38 52,84 53.88 55.41 56.47 56.81 58.16 59,69 61,16 62.72 64.16 66.69 67.16 68.56 70,03 71,44 72.81 74.25 75.91 77.37 78.47
6040 6409 6786 7175 7576 7706 7991 8418 8775 8857 9307 9771 10249 10740 11245 11763 12296 12844 13405 13981 14571 15175 15795 16431 16919
19.80 20.92 22.04 23.19 24.31 24.63 25.34 26.38 27.04 27.29 28.13 29.15 30.10 31.13 32,03 33.01 33,92 34.76 35.66 36.48 37.27 38.12 39.17 40.03 40.78
(67.96) 68.35 70.01 71.58 72.91
82.08 82.46 83.98 85,50 87.02
18533 18703 19394 20103 20825
40.78 40.90 41.82 42.73 43,64
Liquid
Crystal I1 10 15 20 25
-
HOo)/T
0.065 0.591 1.849 3.499 5.137
0.021 0.180 0.637 1.391 2.351
0.080
1.372 7.220 20.52 42.18
0.005 0.043 0.156 0.365 0.664
448.8Zb 450 460 470 480
Units: cal, mol, "K. Assuming melting to be truly isothermal. The Journal
of
Phusical Chemistry, Vol. 74, N o . 12, 1970
2546
E. F. WESTRUM, JR., W.-K. WONG,AND E. MORAWETZ
of long enthalpy-t'ype runs wit'h integrated heat capacities over the same temperature region (cf. Table 111).
insoluble in organic solvents and liquid ammonia was found in the silver calorimeter with an elementary analysis. Anal. Calcd for 1: C, 72.12; H, 11.24; N, 11.14, and 5.50% residue. The single result indicated that fusion occurred a t 430°K with an enthalpy increment of 1.4 kcal/mol corresponding to ASm = 3.2 cal/(mol OK). The melting temperature is higher than a literature value of 156O." While the uncertainty to be assigned to the entropy of fusion is certainly larger than normally obtainable by this method, it is still believed to be less than 0.3 cal/(mol OK). No purity determination by fractional fusion was obtained from the calorimetric sample. Table 111 also contains the data for the transition and melting regions of 2. For the broad solid-solid transition, spanning the region 165-230°K four series of measurements, listed in Table 111, average a ASt = 8.22 cal/(mol OK). Fusion data contained in Tables 111 and IV indicate an amount of liquid-soluble, solid-insoluble impurity in the sample of 0.34 mol % and a
Table 111: Enthalpy Increments of Transition for l-Azabicyclo [2.2.2]octane and of Transition and Fusion for 3-Oxabicyclo[3.2.2] nonane'
1-Azabicyclo[ 2.2.21octane Transition" Source of data
Series I Series I1 Series I11 Series VI Series VI1
No. of runs
6 1 1 1 1
Ti
Ta
H T ~HTI
190.87 188.11 191.82 173.54 172.76
219.63 221.81 214.02 224.87 221.09
2154 2240 1882 2724 2359
HZ16
-
Him
2004 2002 2007 2008 2005 Av 2005 i 1 Graphical integ 2007 Lattice contrib 736 AHt 1249
3-Oxabicyclo [ 3.2.21nonane Transitiond Hpso
-
H I 6 6
Series I1 Series I11 Series IV Series V
12 3 2 20
149.33 165.74 164.09 168.93
233.32 246.71 244.96 230.56
4255 4356 4332 3652
4O1lb 4010 4010 4O0gb Av 4 0 1 0 ~ k1 Graphical integ 4009 Lattice contrib 2333 AHt 1677
3-Oxabicyclo [3.2.2]nonane Meltinge Haffi
-
H480
Series VI11 Series I X Series X
8 1 3
430.53 432.82 435.68
456.73 451.49 463.79
3949* 3947 3954 3950& 2 Graphical integ 3951 Lattice contrib 2336 2828 3509 Av
a Units: cal, mol, OK. * A correction has been made for quasi-adiabatic conditions, E ASt = 6.34 cal mol OK; T t = ASt = 8.22 cal/(mol OK); TI = 208.50'K. e A H m = 196'K. 1614 & 2; ASm = 3.61 cal/(mol "K); T m = 448.43"K.
Compound 1 was obscrved to undergo transition at 196.OO0K. Five series of thermal measurements through the region centered on this temperature are listed in Table 111. Heat capacities approaching 900 cal/(mol O K ) were observed and are indicative that the solid-solid transition is first order. The intermediaterange calorimetric data covering the fusion region are tentative. Partial reaction of the sample with the silver calorimeter a t elevated temperatures (noted by abnormal, progressively increasing positive drifts as the melting point was approached) prohibited more than a single evaluation of the thermodynamics of the fusion process. A white powdery residue (0.200 g) The Journal of Physical Chemistry, Vol. 7.4, N o . 12, 1970
Table IV: Fractional Melting Data for 3-Oxabicyclo[3.2.2]nonaneaIb T
CS
AT
ZAH
Tfinal
1/F
445.46 446.24 446.88 447.44
311 410 463 900
0.872 0.680 0.608 0.304
527 757 1096 1346
445.90 446.58 447.19 447.46
3.063 2.132 1.473 1.199
a Units: ca1, mol, OK. Data from Melting Runs Series VIII. Triple point of sample, 447.59; triple point of pure compound, 448.43; mole fraction impurity, 0.0034.
triple-point temperature of 448.43'1~for the pure substance. The relatively low purity may be a contributing factor in the breadth of the solid-solid transition region. Recent enthalpy of combustion datal2 have been used together with tabulated values for the entropies of the elementsla to evaluate the standard enthalpies and Gibbs energies of formation of 1 and 2 as AHjo (1) = -13.17 f 0.14, AHfo (2) = -65.89 f 0.10 kcal/mol and AGfo (1) = 42.23 f 0.18, AGf" (2) = -7.04 k 0.14 kcal/mol for the Crystal I phases a t 298.15OK. The sublimation pressures and enthalpy of sublimation results are presented in Table V together with the pertinent standard deviations. Using these data, the thermal functions for (ideal) gaseous phase, i.e., the (11) S. Wawzonek, M. F. Nelson, Jr., and P. J. Thelen, J . Amer. Chem. SOC., 73, 2806 (1951). (12) S.-w. Wong, Ph.D. Thesis, University of Michigan, 1966. Diss. Abstr., B28(6), 2383 (1967). (13) D. D. Wagman, W.H. Evans, I. Halow, V. B. Parker, S. M. Bailey, and R . H. Schumm, U. S. National Bureau of Standards Technical Note 270-1,U. S. Government Printing Office, Washington, D. C., 1965.
~-AZABICYCLO [ 2-2.2]OCTANE ~~
AND
3-OXABICYCLO[3.2.21NONANE
2547
~
Table V : Enthalpy of Vaporization (Sublimation) and Vapor Pressure of Globular Molecules a t 298.15% ,..------
Substance
Series
A H v , kcal/mol-Exptla
Cor
Mean A Z , ~ kcal/mol
P.atrC
Torr
Bicyclo [2.2.2]octane
I I1
11.4502=00.014 11.485 f 0.023
11.464 11.499
11.48 f 0.05
2 . 7 f 0.6
Bicyclo [2.2.2]octene
I I1
10.468 (f0.016)d 10.474 f 0.017
10.482 10.488
10.48 f 0 . 0 3
6.6 f 1.4
l-Azabicyclo[2.2.2] octane
I I1 I
11.918i.0.016 12.137(f0.024)d 13.791 f 0.012 1 3 . 5 9 8 2 0.005 12.745 f 0.016
12.132 12.151 13.805 13.812
12.14f0.04
0.93 f 0.19
13.81&0.03
0.27 f 0.06
3-Azabicyclo[3.2.2] nonane
I1 3-0xabicyclo[3.2.2] nonane
I
*
0.45 f 0 . 0 9
a Precision indices are standard deviations. Precision indices are "absolute" errors. Precision indices are average deviations, three determinations per series. deviations.
Precision indices are estimated standard
and bicyclooctene would be similar. The 8.22 value for 2 is indeed comparable to the 8.54 cal/(mol OK) sum for the two transitions of bicyclooctene. The differAHf" (1) = -1.03 f 0.18; ence is well within the range of values that have been AHf" (2) = -53.19 f 0.14 associated with increased librational e n t r ~ p y . ' ~The transitional entropy increment for 2 differs considerAGf" (1) = 46.20 f 0.22; AGf" (2) -- -2.63 f 0.18 ably, however, from that observed for the corresponding Discussion amine, 3-asabicyclo [2.2.2]0ctane.~ The possibility of The existence of solid-solid phase transitions with a disordered state for 2 persisting to 0°K cannot be entropy increments considerably larger than those for excluded at this point, nor can the existence of a unique the subsequent fusions are evidence that both 1 and 2 transition mechanism for the azabicyclononane. Such are embefic crystals. Guthrie and ~ I c C ~ l l o u ghave h ~ ~ a mechanism may be necessary to account for the larger suggested a model (based on a superposition of molecular envelope needed to include the hydrogen molecular symmetry elements with subgroups of the bonded to nitrogen and/or the possibility of hydrogenlattice site symmetry) to account for transitional enbonded clusters in the azabicyclononane Crystal 11. tropy increments in these systems. Crystal-structural The assumed number of quasiisoenergetic configuradata have not been obtained for 1 but it is reasonable to tions available to the systems in the Crystal I phases assume that the molecules occupy O h lattice sites as they are consistent with the melting theories of Amsel and do for other globular molecular crystals. Only the Becka." The latter authors also discuss the implicaCSvsubgroup provides a natural set of symmetry eletions contained in the ideas of Darmon and Brot18 as ments for the 1 cage. Using the four threefold lattice they can be applied to these cage-like systems. axes and the head-for-tail distinguishability of 1, sixteen possible orientations are apparent for the disAcknowledgment. The authors appreciate the enordered Crystal I phase. If one assumes that Crystal abling financial support of the Division of Research of I1 is ordered (to be considered in detail subsequently)15 the U. S. Atomic Energy Commission and the experithe model predicts an entropy increment of R In 16 = mental assistance of W. G. Lyon and Carolyn Barber. 5.54 cal/(mol"K) ; the observed value, 6.34 cal/(mol"K) We thank Mr. Craig Garren of the Eastman Chemical is attributable to increased libration of the molecule Products, Inc. for their kind provision of the sample of above the transition temperature. The difference beoxabicyclononane. tween the transitional entropies for bicyclooctane and l, 6.66 - 6.34 = 0.32 cal/(mol"K) is in accord with the models adopted for bicyclo [2.2.2]0ctane~~ and 1 which (14) G. B. Guthrie and J. Y . McCullough, J . Phys. Chem. Solids, 18, 53 (1961). predict R In (20/16) = 0.44 cal/(mol OK). (15) C. A. Wulff and E. F. Westrum, Jr., J . Chem. Therm., in press. Compound 2 (Figure 2 ) differs in symmetry from bi(16) 0. Ermer and J. D. Dunitz, Chem. Commun., 10, 567 (1968). cyclooctane in the same way as does bicyc300ctene.16 (17) L. M . Amzel and L. N. Becka, J . Phys. Chem. Solids, 30, 521 One would therefore expect that the same model would (1969). be applicable and that, the entropies of transition of 2 (18) I. Darmon and C. Brot, Mol. Crystallogr., 2, 301 (1967). standard enthalpies and Gibbs energies of formation (in kcal/mol) a t 298.15"K, are
The Journal of Physical Chemistry, Vol. 74, No. l?A 1970
