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Rotational barriers and thermodynamic functions for CF3CH2X molecules
Rotational
Barriers
and Thermodynamic CF,CH,X
Functions
for
Molecules
CIHARLOTTE It. WARD
c'. H. Waltu
Pot,ent.ial barriers to internal rotation were determined from observed Raman t,orsional frequencies for the CF&HsS (S = I?,Cl, Br, and I) series of molecules. The variation of rotational barrier as a function of the S substituent is established and discussed. The results for these CFB top molecules have also been compared to published results for the corresponding CHI top molecules. Thermodynamic functions, including t~~rsional contributions, for each molecule were calculated at 100” intervals from 298.15 to 1ooO”K for the ideal gas state at one atmosphere. 1. I?;TRODIJCTIOh’
Determination of the potential barrier to internal rotation of molecules is of importance in evaluating thermodynamic properties of molecules and is of COIIniderable interest in connection with chemical bonding theory. Although a quantitative theory of barrier heights has not been formulated, certain qualitative aspects are apparent ( Z-3). The methods for experimental evaluation of barrier heights have recently been reviewed by Wilson (2). Results from microwave studies have been collected by J,in and Swalen (4). The infrared and Raman method, which involves experimental observation of the torsional frequency, is perhaps the simplest and most direct method. The usefulness of this method is greatly limited in that 6he torsional frequencies of many molecules are inactive in the infrared and/or Raman, i.e., forbidden by selection rules. lrntil recent years, use of this method was further hampered by the unavailability of proper prism materials for infrared and excessive background radiation from conventional mercury arcs used for Raman sources since the torsional modes are found at low wave numbers.
WARD
Although the barrier heights for a considerable number of isolated molecules have been reported, it is difficult to make valid comparisons and correlations because of the diversity of methods employed and the absence of results for series of molecules having a common rotating top. CH, top molecules have been most extensively studied (2-d). CF, top molecules have been subjected to very limited study (8, 5). This paper reports the results for the complete CFS-CH2X (where X = F, Cl, Br, or I) series obtained from Raman spectral studies. This is believed to be the first series for which complete data are available. II. BARRIERS
TO INTERNAL
ROTATION
The structure of CFG+ZH,X molecules is shown in Fig. 1. These molecules belong to the Cr, point group, i.e., the only symmetry element is a symmetry plane bisecting the X, Cl , Cz and F, atoms of the molecule. Complete vibrational assignments, from infrared and Raman data, for the CF&JHtF, CF3CH2Br, and W&H21 molecules were reported in an earlier paper (6). Nielsen and co-workers have reported on the CF&H&l molecule (7) and have also studied the CF&H2Br molecule (8). For all molecules, the torsional frequency was observed in the Raman spectrum of liquid samples. The torsional frequency of CF&HzF has also been observed in the infrared spectrum of a gaseous sample by Danti and Wood (9). The r, y, z axes of Fig. 1 are molecular axes, with the II:axis parallel to the C-C bond and the plane of symmetry corresponding to the 52 plane. The origin
lies at the center of gravity of the molecule. The S, Y, Z axes are the principal axes of the molecule; the principal moments of inertia lie along these axes. The angle between the x and X axis, the angle 0 of Fig. 1, determines the orientation of the x, !/, x axes with respect to the X, Y, Z axes. Bond distances used in the calculations were taken from Sutton (IO) : (1-C = l..NA, C-H = l.OYA, C-1; = 137A, C-Cl = 1.77A, C--Br = 1.94‘4, and C-I = 2.11A. The chemical scale of atomic weights was employed. The principal moments of inertia were calculated by standard procedures; a det#ailed summary of these procedures is given by Godnev (Ii ). The equations t>mplo.vedwere as follows: I,, = c I,,, = I;,
=
c
/l/,,(,/$ + Z,?),
,,Li(XLY + ii’;),
c
/1/,(Xi2+ yi.?, (1)
111,is the mass of the ith atom and .r, , y;, x, are the coordinates of the ith atom. I I, Iv I, = I* I, I,* =
I
-I rl’l
4:; --x
-L
- I,, -Iuz
(2)
Iz: 1.
Diagonalization of the matrix of Eq. (2) yields 8 (the angle between the J and X axis 1 and values of Is , I y , and lZ (the principal moments of inertia). Numerical results for the CF$H& molecules are given in Table 1. The moment of inertia of the CF, top about the rotational axis, Ir(CFaj, is given by
where the summation extends only over the CE’a top. The reduced moment of inertia, 1, , is then given by the equation
1, = IZ(CF3) il - LtC~,,[oxII.%-) + (,XY”JY)+ (A,‘/&)]},
(‘4)
where XX is the direction cosine, i.e., cosine of the angle between the x and X axis. Xy and X, are the corresponding quantities for the Q and Y axis and z and % axis, respectively. l$uation (1) was first derived by Clrawford ( 12) and is discussed by Godne\ ( 13) and by I’itzer and Brewer ( I,$ ).
WARD
292
The barrier to internal rotation, V, , is then calculated from the observed torsional frequency, vtors, the calculated value of I, as given by Eq. (4)) and the internal symmetry number, n, of the CF, top according to the equation (13) : Vtors= (nl27r)-\/(V,/ar,,
(f,)
or V, = 113.508 X lO”“J,&,, cal mole-‘.
(6)
Calculated values for the CF,CH2X series are given in Table I.
TABLE:I. MOLECULAR PARAMETERSOF CF3CH2XMOLECULE.5
CF3CH2F
CF3CH2C1
CF3CH2Br
CF3CH21
123.518
167.455
235.325
304.101
In (amuA2)
186.294
283.279
436.372
567.428
I,, (mu A2)
161.068
214.116
299.339
361.619
I,, (mu A2)
-39.137
-88.817
-165.296
-232.120
95.101
95.101
95.101
95.101
164.173
164.289
164.307
164.307
IB - Iz(g clti2f104')308.308
469*2I.I_
723,365
940.951
Ic - Iy(g cm2flO40)
309.292
470.311
724,482
942.067
IAIBICx l&
15.6551
36.2545’
86Jo75
W.6481
32alf
3703@
39031’
bo28'
(1 X)2
0.71626
0.62703
0.s9505
0.5640
(i y)2
0
0
0
0
(mu A21
&
Ix(CF3)(arnu A2) IA = IX(g a2fld+')
0
(x z)2 L, (8 cm2flo40)
0.28374
0.37297
0.40495
0.43860
26.223
42.954
53.669
61.105
v tars (a-1)
124
log
101
V, (kcal.moleal)
4s77
5.793
6.214
94 6.129
TABLE II. BARRIER HEIOHTS FOR CF3 ANTICH3 TOP MOLECULES IN CALORIES PER MOLE.
CH34H2H
CF3-CH2H
CF3-CF2H
2075 l
3b80 6
?
CH3-CH2F
CF3-CH2F
CF3-CF2F
3306 2
L580 7
4350 8 CF,cF,Cl
CF3-CH,Cl
CH3-CH2C1
5670 9
5790 7
3685 3
CF3-CF2Br
CF3-CH2Br
CH3-CH2Br
3567 Ir
6210 7
6400 9
CH3-CH21
CF3-CH21
CF3-CF21
32205
6130 7
7090 9
CH3-CH3
CH3-CH2F
CH3-CHF2
CH3-CF3
CH2F-CF 3
CHF2-CF 3
CF3-CF3
2875 1
3306 2
3180 2
3lr806
h580 7
?
Jl3508
' K. S. Pitzer, DiscussionsFaraday Sot. 10, 66 (1951). J 6. Phvs. 2J"358-(1956). --; i*. i* a&"; . D . JaTabs, J. Chem. Phys. 6, 12h5 (1962). . ~~~$~I% 4 D. R. Lide, Jr., J. Cbem. Phys. 30, 37 (1959). 5 Ph -. sot. J; apan 15; 1273 (1960). 6 T. T. Kasuya, 2.and ---?. P.D ailcy, -Ninden Phys. Rev. 82, 338 (1951 L). 7 H. Present work. 9 8 E. L. Pace, J.Rx Chem. -. l&, 7h (19b8). 0. Risgin an?! Taylor, Spectrochim.--9 Acta 15 1036 (1959).
Barriers to internal rotation for the present series and for related C’F:: and (21, top molecules are listed in Table II. Several qualitative conclusions are apparent from these data. C’Fzjtop molecules have larger barriers than the corresponding C’H3 top molecules. This effect is probably partially due to increased elcctr&atic forces rather than steric forces alone since the van der Waal radius of an J; atom is not markedly greater than that of an H atom. Although both the Raman and infrared vibrational spectra of CF8CFzH have been investigated, the torsional mode was not observed i 26). A reinvestigation of this molecule in t,hr t,orsional range is planned.
WARD
294
Successive substitution of larger halogen atoms for one atom of the CH2X frame attached to CH, top molecules leads to a maximum barrier height for the chloride, while the corresponding Cl’, top molecules exhibit a maximum for the bromide. CFs top molecules having a CP,X frame do not exhibit a maximum, but the barrier continues to rise as the halogen substituent becomes larger. These trends indicate that steric effects, either alone or in combination with polarizability differences, cannot completely account for barrier height changes in the three series. It is anticipated that the results of a planned study of the
TABLE III. THERMODYNAMICPROPERTIESOF CF3CH2F T
CO P
(OK)
SO
Ho-Ho -e
(Cal deg'l) (Cal deg'1) (cal deg'1) (Cal deg'l) t+r+v tors total
1;.;@&
7;.;:;
6y.g;
20:817
75:*49
621168
t+r+v tors total
18.733 2.172 20.905
400
t+r+v tors total
222%i~ 25:232
500
t*r+v tors total
26.309 2.316 28.625
600
t+r+v tors total
8;‘;;; 94:072
70.973 2.886 73 .*59
700
t+r+v tors total
93.879 5.147 99.026
7?::: 77: 106
19.959 1.961 21.920
800
t+r+v tors total
32.489 2.046 34.535
103:542
76.684 3.449 80.133
21.430 1.979 23.409
t+r+v tors total
3:% 35:694
102.016 5.662 107.678
7?6”:24
82:966
22.732 1.980 24.712
t+r+v tors total
‘“:% 111: 4**
81.740
2:.;22
3?::71 36:62*
*::8$
25:*55
298.15
300
900
1000
12.128 1.553 13.681
62:252
12.168 1.558 13.726
7%: 821607
64.382 2.146 66.528
14.352 1.727 16.079
*44’;:6’ 8*:617
67.810 2.542 70.352
6y.i;;
9;.,‘;j
corresponding CH3CF.A’, CCl&H&‘, CCI&C&Y, and CH,CCI,X series will be of value in accounting for barrier height changes due to successive atom substitution. The barrier heights for molecules formed by successive substitution of E’ fol H in CH,-CH, are also given in Table II. These data suggest that the CI”zH frame is uuique in that the barrier for CH3CF2H is less than either CH3CE’Hr or CH&F, . Data for the CF:$l:,H molecule, when available, should clearly substantiate or negate this suggested effect. Further data will be furnished by bhe study of corresponding molecules formed by Cl successive substitutjion.
TABLE IV. THERMODYNAMIC PROPERTIES OF CF3CH2Cl T
CO P
(cal deg-l) (cal deg")
(OK) 298.15
300
400
500
600
so
t +r+v tors total t+r+v tors total
74.678 3.414 78.092 19.281 2.10& 21.389
62.121 6:: %
6f.9’~ 74*2E 78:224
64: 043
t+r+v tors total
23.324 2.222 25.546
80.915 4.053 84.96g
66.126
t+r+v tors total
26.566 2.301
86.483 4.560 91.043
69.649 2.720 72.369
91.558 4.980 96.538
7y3;$
28.867
t+r+v tors total
2.329 31.407
700
t+r+v tors total
31.032 2.302 33.334
800
t+r+v tors total
29.078
12.557 1.580 14.137
2.321 68.447
14.789 1.732 16.521
751946 20.306 Il.977 22.283
100.442 5.642 106.084
2w 23:760
900
t+r+v tors total
33.828 2.153 35.981
104.354 5.902 110.256
23.022 2.030 25.052
1000
t+r+v tors total
3';*% 36:916
107.973 6.124 114.097
24.156 2.041 26.197
296
WARD TABLE V. T
Fe-Hz Ho-Ho 0 T T -( 1 (Cal deg-l)(cal deg-')(cal deg' 1 (cal deg")
t+r+v tors total
w
t+r+v tors total
400
t+r+v tors total
2;.@;
t+r+v tors total
2;.;;6'
600
700
800
900
1000
6f.s”;; 71’F3 66:174 go:593
21:668
300
500
so
c;
(OK) 298.15
THERMODYNAMIC PROPERTIES OF CF3CH2Br
12.852 1.611 14.463 83.385 4.184 67.569
15.075 1.746 16.821
29:177
89.031 4.687 93.716
17.132 1.846 18.978
t+r+v tors total
2zS 31:681
9%9' 99:270
t+r+v tors total
31.265 2.326 33.591
9?% 104:300
25:892
t+r+v tors total t+r+v tors total
332.w:
t+r+v tors total
34.993 2.127 37.120
36:206
20.597 1.979 22.576
103.113 5.773 108.886
";.;;t 84:836
22.029 2.021 24.050
107.046 6.038 113.084
83.753 3.991 87.744
23.293 2.047 25.340
11y;
86.266 4.209 90.475
24.415 2.059 26.474
116:949
III.THERMODYNAMIC
PROPERTIES
The thermodynamic properties of CF&HIF, CP&H&l, CF3CH2Br, and CF3CH,I are given in Tables III, IV, V, and VI, respectively. The translational, rotational, and vibrational contributions were calculated by means of standard equations of statistical thermodynamics (11) using the molecular parameters given in Table I and the reported vibrational frequencies (6, 7). Computation was by machine using a tested polyatomic gas program. The torsional contributions were obtained from the tables of Pitzer and Gwinn
TABLE VI.
THERFlODYNAMICPROPERTIES OF CF3CH21
T
CO P (cal deg”)
(OK)
SO (cal deg'1)
298.15
t+r+v tors total
%07~ ‘Es 82:3i% 21:777
300
t+r+v tors total
19.758 2.104 21.862
400
t+r+v tors total
500
78.743 3.710 82.453
12.912 1.638 14.550 6:oo7:; 671858
l~*z! 14:595
23.822 2.209 26.031
69.823 2.560 72.383
15.181 1.770 16.951
t+r+v tors total
27.021 2.293 29.314
732.g 76:402
17.243 1.866 19.109
600
t+r+v tors total
29.472 2.331 31.803
95.832 5.254 101.086
76.746 3.313 80.059
19.086 1.941 21.027
700
t+r+v tors total
31.365 2.322 33.687
100.523 5.612 106.135
79.813 3.616 83.L29
20.710 1.996 22.706
800
t+r+v tors total
32.860 2.272 35.132
104.813 5.920 110.733
R3".@2
22.139 2.034 24.173
900
t+r+v tors total
34.065 2.200 36.265
108.755 6.1e3 114.938
1000
t+r+v tors total
35.052 %.116 37.16%
"E 118L!O?
86:560
23.399 2.057 25.456 87.880 4.344 92.224
(l.$, Ifi), usingthe parametersT',,:/R7 and l/‘Qf I,r, where 0, T,, =
( 1/‘rt,) (&“I
/.7’:p)*/’ T’ /
RECEIVED: .June 20, 1968
I. I,. PAC:IJNG, “The Xnture of t,he Cheruic:tl Bond,” Ithaca, New York, 1960. 2. E. R. WILSON, “Advances in Chemic:tl Physics,” Intersrirncc, rl’ew York, 1959.
’ ed., p. 130. Come11 ITniv. Press, 3rd Vol. II,
p. 367. (I. Prigogine.
ed.).
298
WARD
3. V. MAGNASCO, A’uozja cimento 24, 425 (1962). LIN AND J. D. SWALEN, Revs. Modern Phys. 31, 841 (1959). 5. 0. RISGIN AND R. C. TAYLOR, Spectrochim. Acta 15, 1036 (1959). 6. W. F. EDGELL, T. R. RIETHOF, AND C. R. WARU, J. Mol. Spectroscopy (to be published). 7. J. R. NIELSEN, C. Y. LIANG, AND D. C. SMITH, J. C’hem. Phys. 21,106O (1953). 8. J. R. NIELSEN AND R. THEIMER, J. Chern. Phys. 27, 891 (1957). 9. A. DAN’~I AND J. L. WOOD; J. (‘hem. Phys. 30, 582 (1959). 10. “Tables of Interatomic Distances and Configuration in Molecules and Ions,” (L. E. Sutton, ed.). The Chemical Society, London, 1958. 11. I. N. GODNEV, “Calculation of Thermodynamic Functions from Molecular Data,” Chapter VIII, U. S. Atomic Energy Commission Report AEC-tr-3855, 1959. lb. B. L. CRAWFORD, JR., J. Chenl. Phys. 3, 273 (1940). 13. I. N. GODNEV, “Calculation of Thermodynamic Functions from Molecular Data,” Chapter S, U. S. Atomic Energy Commission Report AEC-tr-3855, 1959. 14. G. N. LEWIS AND M. RANDALL, “Thermodynamics,” 2nd ed., rev. by K. S. Pitser and L. Brewer, Chapter 27. McGraw-Hill, New York, 1961. 15. J. R. NIELSEN, H. H. CLAASSEN, AND N. B. MORAN, J. (‘hem. Phys. 23, 329 (1955). 16. K. S. PITZER AND W. D. GWINN, J. Chew Phys. 10, 428 (1942).
Barriers
and Thermodynamic CF,CH,X
Functions
for
Molecules
CIHARLOTTE It. WARD
c'. H. Waltu
Pot,ent.ial barriers to internal rotation were determined from observed Raman t,orsional frequencies for the CF&HsS (S = I?,Cl, Br, and I) series of molecules. The variation of rotational barrier as a function of the S substituent is established and discussed. The results for these CFB top molecules have also been compared to published results for the corresponding CHI top molecules. Thermodynamic functions, including t~~rsional contributions, for each molecule were calculated at 100” intervals from 298.15 to 1ooO”K for the ideal gas state at one atmosphere. 1. I?;TRODIJCTIOh’
Determination of the potential barrier to internal rotation of molecules is of importance in evaluating thermodynamic properties of molecules and is of COIIniderable interest in connection with chemical bonding theory. Although a quantitative theory of barrier heights has not been formulated, certain qualitative aspects are apparent ( Z-3). The methods for experimental evaluation of barrier heights have recently been reviewed by Wilson (2). Results from microwave studies have been collected by J,in and Swalen (4). The infrared and Raman method, which involves experimental observation of the torsional frequency, is perhaps the simplest and most direct method. The usefulness of this method is greatly limited in that 6he torsional frequencies of many molecules are inactive in the infrared and/or Raman, i.e., forbidden by selection rules. lrntil recent years, use of this method was further hampered by the unavailability of proper prism materials for infrared and excessive background radiation from conventional mercury arcs used for Raman sources since the torsional modes are found at low wave numbers.
WARD
Although the barrier heights for a considerable number of isolated molecules have been reported, it is difficult to make valid comparisons and correlations because of the diversity of methods employed and the absence of results for series of molecules having a common rotating top. CH, top molecules have been most extensively studied (2-d). CF, top molecules have been subjected to very limited study (8, 5). This paper reports the results for the complete CFS-CH2X (where X = F, Cl, Br, or I) series obtained from Raman spectral studies. This is believed to be the first series for which complete data are available. II. BARRIERS
TO INTERNAL
ROTATION
The structure of CFG+ZH,X molecules is shown in Fig. 1. These molecules belong to the Cr, point group, i.e., the only symmetry element is a symmetry plane bisecting the X, Cl , Cz and F, atoms of the molecule. Complete vibrational assignments, from infrared and Raman data, for the CF&JHtF, CF3CH2Br, and W&H21 molecules were reported in an earlier paper (6). Nielsen and co-workers have reported on the CF&H&l molecule (7) and have also studied the CF&H2Br molecule (8). For all molecules, the torsional frequency was observed in the Raman spectrum of liquid samples. The torsional frequency of CF&HzF has also been observed in the infrared spectrum of a gaseous sample by Danti and Wood (9). The r, y, z axes of Fig. 1 are molecular axes, with the II:axis parallel to the C-C bond and the plane of symmetry corresponding to the 52 plane. The origin
lies at the center of gravity of the molecule. The S, Y, Z axes are the principal axes of the molecule; the principal moments of inertia lie along these axes. The angle between the x and X axis, the angle 0 of Fig. 1, determines the orientation of the x, !/, x axes with respect to the X, Y, Z axes. Bond distances used in the calculations were taken from Sutton (IO) : (1-C = l..NA, C-H = l.OYA, C-1; = 137A, C-Cl = 1.77A, C--Br = 1.94‘4, and C-I = 2.11A. The chemical scale of atomic weights was employed. The principal moments of inertia were calculated by standard procedures; a det#ailed summary of these procedures is given by Godnev (Ii ). The equations t>mplo.vedwere as follows: I,, = c I,,, = I;,
=
c
/l/,,(,/$ + Z,?),
,,Li(XLY + ii’;),
c
/1/,(Xi2+ yi.?, (1)
111,is the mass of the ith atom and .r, , y;, x, are the coordinates of the ith atom. I I, Iv I, = I* I, I,* =
I
-I rl’l
4:; --x
-L
- I,, -Iuz
(2)
Iz: 1.
Diagonalization of the matrix of Eq. (2) yields 8 (the angle between the J and X axis 1 and values of Is , I y , and lZ (the principal moments of inertia). Numerical results for the CF$H& molecules are given in Table 1. The moment of inertia of the CF, top about the rotational axis, Ir(CFaj, is given by
where the summation extends only over the CE’a top. The reduced moment of inertia, 1, , is then given by the equation
1, = IZ(CF3) il - LtC~,,[oxII.%-) + (,XY”JY)+ (A,‘/&)]},
(‘4)
where XX is the direction cosine, i.e., cosine of the angle between the x and X axis. Xy and X, are the corresponding quantities for the Q and Y axis and z and % axis, respectively. l$uation (1) was first derived by Clrawford ( 12) and is discussed by Godne\ ( 13) and by I’itzer and Brewer ( I,$ ).
WARD
292
The barrier to internal rotation, V, , is then calculated from the observed torsional frequency, vtors, the calculated value of I, as given by Eq. (4)) and the internal symmetry number, n, of the CF, top according to the equation (13) : Vtors= (nl27r)-\/(V,/ar,,
(f,)
or V, = 113.508 X lO”“J,&,, cal mole-‘.
(6)
Calculated values for the CF,CH2X series are given in Table I.
TABLE:I. MOLECULAR PARAMETERSOF CF3CH2XMOLECULE.5
CF3CH2F
CF3CH2C1
CF3CH2Br
CF3CH21
123.518
167.455
235.325
304.101
In (amuA2)
186.294
283.279
436.372
567.428
I,, (mu A2)
161.068
214.116
299.339
361.619
I,, (mu A2)
-39.137
-88.817
-165.296
-232.120
95.101
95.101
95.101
95.101
164.173
164.289
164.307
164.307
IB - Iz(g clti2f104')308.308
469*2I.I_
723,365
940.951
Ic - Iy(g cm2flO40)
309.292
470.311
724,482
942.067
IAIBICx l&
15.6551
36.2545’
86Jo75
W.6481
32alf
3703@
39031’
bo28'
(1 X)2
0.71626
0.62703
0.s9505
0.5640
(i y)2
0
0
0
0
(mu A21
&
Ix(CF3)(arnu A2) IA = IX(g a2fld+')
0
(x z)2 L, (8 cm2flo40)
0.28374
0.37297
0.40495
0.43860
26.223
42.954
53.669
61.105
v tars (a-1)
124
log
101
V, (kcal.moleal)
4s77
5.793
6.214
94 6.129
TABLE II. BARRIER HEIOHTS FOR CF3 ANTICH3 TOP MOLECULES IN CALORIES PER MOLE.
CH34H2H
CF3-CH2H
CF3-CF2H
2075 l
3b80 6
?
CH3-CH2F
CF3-CH2F
CF3-CF2F
3306 2
L580 7
4350 8 CF,cF,Cl
CF3-CH,Cl
CH3-CH2C1
5670 9
5790 7
3685 3
CF3-CF2Br
CF3-CH2Br
CH3-CH2Br
3567 Ir
6210 7
6400 9
CH3-CH21
CF3-CH21
CF3-CF21
32205
6130 7
7090 9
CH3-CH3
CH3-CH2F
CH3-CHF2
CH3-CF3
CH2F-CF 3
CHF2-CF 3
CF3-CF3
2875 1
3306 2
3180 2
3lr806
h580 7
?
Jl3508
' K. S. Pitzer, DiscussionsFaraday Sot. 10, 66 (1951). J 6. Phvs. 2J"358-(1956). --; i*. i* a&"; . D . JaTabs, J. Chem. Phys. 6, 12h5 (1962). . ~~~$~I% 4 D. R. Lide, Jr., J. Cbem. Phys. 30, 37 (1959). 5 Ph -. sot. J; apan 15; 1273 (1960). 6 T. T. Kasuya, 2.and ---?. P.D ailcy, -Ninden Phys. Rev. 82, 338 (1951 L). 7 H. Present work. 9 8 E. L. Pace, J.Rx Chem. -. l&, 7h (19b8). 0. Risgin an?! Taylor, Spectrochim.--9 Acta 15 1036 (1959).
Barriers to internal rotation for the present series and for related C’F:: and (21, top molecules are listed in Table II. Several qualitative conclusions are apparent from these data. C’Fzjtop molecules have larger barriers than the corresponding C’H3 top molecules. This effect is probably partially due to increased elcctr&atic forces rather than steric forces alone since the van der Waal radius of an J; atom is not markedly greater than that of an H atom. Although both the Raman and infrared vibrational spectra of CF8CFzH have been investigated, the torsional mode was not observed i 26). A reinvestigation of this molecule in t,hr t,orsional range is planned.
WARD
294
Successive substitution of larger halogen atoms for one atom of the CH2X frame attached to CH, top molecules leads to a maximum barrier height for the chloride, while the corresponding Cl’, top molecules exhibit a maximum for the bromide. CFs top molecules having a CP,X frame do not exhibit a maximum, but the barrier continues to rise as the halogen substituent becomes larger. These trends indicate that steric effects, either alone or in combination with polarizability differences, cannot completely account for barrier height changes in the three series. It is anticipated that the results of a planned study of the
TABLE III. THERMODYNAMICPROPERTIESOF CF3CH2F T
CO P
(OK)
SO
Ho-Ho -e
(Cal deg'l) (Cal deg'1) (cal deg'1) (Cal deg'l) t+r+v tors total
1;.;@&
7;.;:;
6y.g;
20:817
75:*49
621168
t+r+v tors total
18.733 2.172 20.905
400
t+r+v tors total
222%i~ 25:232
500
t*r+v tors total
26.309 2.316 28.625
600
t+r+v tors total
8;‘;;; 94:072
70.973 2.886 73 .*59
700
t+r+v tors total
93.879 5.147 99.026
7?::: 77: 106
19.959 1.961 21.920
800
t+r+v tors total
32.489 2.046 34.535
103:542
76.684 3.449 80.133
21.430 1.979 23.409
t+r+v tors total
3:% 35:694
102.016 5.662 107.678
7?6”:24
82:966
22.732 1.980 24.712
t+r+v tors total
‘“:% 111: 4**
81.740
2:.;22
3?::71 36:62*
*::8$
25:*55
298.15
300
900
1000
12.128 1.553 13.681
62:252
12.168 1.558 13.726
7%: 821607
64.382 2.146 66.528
14.352 1.727 16.079
*44’;:6’ 8*:617
67.810 2.542 70.352
6y.i;;
9;.,‘;j
corresponding CH3CF.A’, CCl&H&‘, CCI&C&Y, and CH,CCI,X series will be of value in accounting for barrier height changes due to successive atom substitution. The barrier heights for molecules formed by successive substitution of E’ fol H in CH,-CH, are also given in Table II. These data suggest that the CI”zH frame is uuique in that the barrier for CH3CF2H is less than either CH3CE’Hr or CH&F, . Data for the CF:$l:,H molecule, when available, should clearly substantiate or negate this suggested effect. Further data will be furnished by bhe study of corresponding molecules formed by Cl successive substitutjion.
TABLE IV. THERMODYNAMIC PROPERTIES OF CF3CH2Cl T
CO P
(cal deg-l) (cal deg")
(OK) 298.15
300
400
500
600
so
t +r+v tors total t+r+v tors total
74.678 3.414 78.092 19.281 2.10& 21.389
62.121 6:: %
6f.9’~ 74*2E 78:224
64: 043
t+r+v tors total
23.324 2.222 25.546
80.915 4.053 84.96g
66.126
t+r+v tors total
26.566 2.301
86.483 4.560 91.043
69.649 2.720 72.369
91.558 4.980 96.538
7y3;$
28.867
t+r+v tors total
2.329 31.407
700
t+r+v tors total
31.032 2.302 33.334
800
t+r+v tors total
29.078
12.557 1.580 14.137
2.321 68.447
14.789 1.732 16.521
751946 20.306 Il.977 22.283
100.442 5.642 106.084
2w 23:760
900
t+r+v tors total
33.828 2.153 35.981
104.354 5.902 110.256
23.022 2.030 25.052
1000
t+r+v tors total
3';*% 36:916
107.973 6.124 114.097
24.156 2.041 26.197
296
WARD TABLE V. T
Fe-Hz Ho-Ho 0 T T -( 1 (Cal deg-l)(cal deg-')(cal deg' 1 (cal deg")
t+r+v tors total
w
t+r+v tors total
400
t+r+v tors total
2;.@;
t+r+v tors total
2;.;;6'
600
700
800
900
1000
6f.s”;; 71’F3 66:174 go:593
21:668
300
500
so
c;
(OK) 298.15
THERMODYNAMIC PROPERTIES OF CF3CH2Br
12.852 1.611 14.463 83.385 4.184 67.569
15.075 1.746 16.821
29:177
89.031 4.687 93.716
17.132 1.846 18.978
t+r+v tors total
2zS 31:681
9%9' 99:270
t+r+v tors total
31.265 2.326 33.591
9?% 104:300
25:892
t+r+v tors total t+r+v tors total
332.w:
t+r+v tors total
34.993 2.127 37.120
36:206
20.597 1.979 22.576
103.113 5.773 108.886
";.;;t 84:836
22.029 2.021 24.050
107.046 6.038 113.084
83.753 3.991 87.744
23.293 2.047 25.340
11y;
86.266 4.209 90.475
24.415 2.059 26.474
116:949
III.THERMODYNAMIC
PROPERTIES
The thermodynamic properties of CF&HIF, CP&H&l, CF3CH2Br, and CF3CH,I are given in Tables III, IV, V, and VI, respectively. The translational, rotational, and vibrational contributions were calculated by means of standard equations of statistical thermodynamics (11) using the molecular parameters given in Table I and the reported vibrational frequencies (6, 7). Computation was by machine using a tested polyatomic gas program. The torsional contributions were obtained from the tables of Pitzer and Gwinn
TABLE VI.
THERFlODYNAMICPROPERTIES OF CF3CH21
T
CO P (cal deg”)
(OK)
SO (cal deg'1)
298.15
t+r+v tors total
%07~ ‘Es 82:3i% 21:777
300
t+r+v tors total
19.758 2.104 21.862
400
t+r+v tors total
500
78.743 3.710 82.453
12.912 1.638 14.550 6:oo7:; 671858
l~*z! 14:595
23.822 2.209 26.031
69.823 2.560 72.383
15.181 1.770 16.951
t+r+v tors total
27.021 2.293 29.314
732.g 76:402
17.243 1.866 19.109
600
t+r+v tors total
29.472 2.331 31.803
95.832 5.254 101.086
76.746 3.313 80.059
19.086 1.941 21.027
700
t+r+v tors total
31.365 2.322 33.687
100.523 5.612 106.135
79.813 3.616 83.L29
20.710 1.996 22.706
800
t+r+v tors total
32.860 2.272 35.132
104.813 5.920 110.733
R3".@2
22.139 2.034 24.173
900
t+r+v tors total
34.065 2.200 36.265
108.755 6.1e3 114.938
1000
t+r+v tors total
35.052 %.116 37.16%
"E 118L!O?
86:560
23.399 2.057 25.456 87.880 4.344 92.224
(l.$, Ifi), usingthe parametersT',,:/R7 and l/‘Qf I,r, where 0, T,, =
( 1/‘rt,) (&“I
/.7’:p)*/’ T’ /
RECEIVED: .June 20, 1968
I. I,. PAC:IJNG, “The Xnture of t,he Cheruic:tl Bond,” Ithaca, New York, 1960. 2. E. R. WILSON, “Advances in Chemic:tl Physics,” Intersrirncc, rl’ew York, 1959.
’ ed., p. 130. Come11 ITniv. Press, 3rd Vol. II,
p. 367. (I. Prigogine.
ed.).
298
WARD
3. V. MAGNASCO, A’uozja cimento 24, 425 (1962). LIN AND J. D. SWALEN, Revs. Modern Phys. 31, 841 (1959). 5. 0. RISGIN AND R. C. TAYLOR, Spectrochim. Acta 15, 1036 (1959). 6. W. F. EDGELL, T. R. RIETHOF, AND C. R. WARU, J. Mol. Spectroscopy (to be published). 7. J. R. NIELSEN, C. Y. LIANG, AND D. C. SMITH, J. C’hem. Phys. 21,106O (1953). 8. J. R. NIELSEN AND R. THEIMER, J. Chern. Phys. 27, 891 (1957). 9. A. DAN’~I AND J. L. WOOD; J. (‘hem. Phys. 30, 582 (1959). 10. “Tables of Interatomic Distances and Configuration in Molecules and Ions,” (L. E. Sutton, ed.). The Chemical Society, London, 1958. 11. I. N. GODNEV, “Calculation of Thermodynamic Functions from Molecular Data,” Chapter VIII, U. S. Atomic Energy Commission Report AEC-tr-3855, 1959. lb. B. L. CRAWFORD, JR., J. Chenl. Phys. 3, 273 (1940). 13. I. N. GODNEV, “Calculation of Thermodynamic Functions from Molecular Data,” Chapter S, U. S. Atomic Energy Commission Report AEC-tr-3855, 1959. 14. G. N. LEWIS AND M. RANDALL, “Thermodynamics,” 2nd ed., rev. by K. S. Pitser and L. Brewer, Chapter 27. McGraw-Hill, New York, 1961. 15. J. R. NIELSEN, H. H. CLAASSEN, AND N. B. MORAN, J. (‘hem. Phys. 23, 329 (1955). 16. K. S. PITZER AND W. D. GWINN, J. Chew Phys. 10, 428 (1942).