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Excess enthalpies of binary mixtures containing unsaturated hydrocarbons
M-1622 J. Chem.
Thermodynamics
1984, 16,219-224
Excess enthalpies of binary mixtures containing unsaturated hydrocarbons W. W6YCICKI Institute Warsaw,
(Received
of Physical Poland
II
August
Chemistry,
Polish
Academy
of Sciences,
1983)
The excess molar enthalpies Hz over the whole composition range of I-n-hexene + trans-2hexene, + tram-3-hexene, + 1,5-hexadiene, + trans-1,3-hexadiene, + trans-ZChexadiene, and + cis,trans-1,3,5-hexatriene, of trans-2-hexene + mans-3-hexene, + 1,5-hexadiene, and + tmns1,3-hexadiene, of tmns-3-hexene + 1,5-hexadiene and + trans-1,3-hexadiene, and of 1,5-hexadiene + tram-1,3-hexadiene and + c&tram-1,3,Shexatriene were measured in a McGlashan-type calorimeter at 298.15 K. The influence of the unsaturated-bond position in the alkenes and dienes examined on the apparent magnitude of X-X interactions is discussed.
1. Introduction In preceding papers (rm3) it has been pointed out that rc-TCin interactions occurring between the molecules of an unsaturated hydrocarbon may considerably differ from analogous interactions occurring in another unsaturated hydrocarbon with an identical number of carbon atoms. The reasons underlying these diverse interactions may include the position, the number, and the relative ratio (separation or conjugation) of unsaturated bonds in the molecules involved, and their steric configurations (cis-trans isomerism; open or closed chains). Generally, this diversification of interactions is explicable in terms of different basicities of the molecules considered,‘4’ varying accessibilities to the rc-bond, and different degrees of aromaticity. Thus, in mixtures of unsaturated hydrocarbons the aforementioned differences may well be expected to result in distinct molecular interactions leading to different values for the excess molar enthalpy. Earlier fragmentary studies’” were concerned with the effect of cis-tram isomerism on n--x interactions. For (trans-2-hexene + trans-3-hexene), those early measurements are now supplemented to cover a broader range of compositions and results. The total programme involved 13 mixtures grouped in four series. Series 1 and 2 involved the polar molecules: I-n-heptene and trans-Zhexene; and series 3 and 4 involved the non-polar molecules: truns-3-hexene and 1,5-hexadiene (separated double bonds) as fixed components. The second components in the mixtures studied were unsaturated hydrocarbons whose basicity increased as the double bond was shifted toward the centre of gravity of the molecule, the number of double bonds was raised, and separation or conjugation of bonds was altered. 0021~9614/84/030219+06
%02.00/O
0
1984 Academic
Press Inc. (London)
Limited
220
W. WOYCICKI TABLE
x
H:
Wf,
J.mol-’
J.mol-’
1. Excess enthalpies
x
x(1-n-C,H,,)+(l 0.1033 0.2047 0.3033
3.5 5.5 7.6
0.2 -0.4 -0.2
0.4041 0.4961 0.5890
0.1047 0.2289 0.3147
4.5 7.3 9.3
0.1 -0.5 -0.9
0.1059 0.1929 0.2902
25.0 40.1 58.0
0.6 -1.7 0.9
0.1231 0.2302 0.3126
24.8 47.4 59.9
-1.9 1.1 1.9
0.1089 0.1830 0.2960
25.6 45.1 58.4
- 1.2 2.5 -2.3
0.0920 0.1960 0.2842
62.0 113.4 133.1
0.4 -8.5 -8.6
0.0871 0.2373 0.2989
-0.9 - 1.4 -2.3
-0.2 0.4 -0.2
0.1034 0.1992 0.3133
110.7 160.0 177.8
4.8 -2.1 2.8
0.4163 0.5134 0.5250
0.0548 0.0770 0.2269
76.2 97.8 189.6
0.7 -1.3 2.4
x(trans-2-C&H,,) 0.3171 0.4169 0.5078
0.0899 0.2016 0.3181
18.4 39.6 58.5
0.4 -0.4 -0.5
x(1-n-C,H,,)f(l 0.4053 0.4916 0.5892
at 298.15
Hfj,
@ffl,
J.mol-’
J.mol-’
K
x
HE
SHE
J.mol-’
J.mol-’
-x)(frans-2-C,H,,) 8.6 9.5 8.7
-0.3 0.2 -0.1
0.6962 0.7733 0.8711
7.8 6.3 3.4
0.3 0.3 -0.2
-x)(trans-3-&H,,) 10.0 11.4 10.7
-0.2 0.8 0.4
0.7057 0.7868 0.5102
8.7 6.7 4.1
-0.3 -0.8 0.2
x(1-n-C,H,,)+(l-x)(1,5-C,H,,) 0.403 1 68.7 0.5035 72.3 0.5936 69.1
0.2 0.3 -0.4
0.6844 0.7892 0.8982
62.8 45.4 26.0
0.8 -1.5 0.9
-0.8 - 1.2 - 1.0
0.6763 0.7720 0.9002
65.1 52.8 25.3
1.1 1.0 -1.1
0.6862 0.7953 0.8896
58.4 42.6 21.6
0.0 1.5 -1.1
0.6919 0.7809 0.8780
131.4 108.6 66.5
-4.4 1.0 -0.1
-0.1 -0.1 -0.1
0.5916 0.7007 0.8110 0.8998
-2.4 -2.3 -1.8 -0.8
0.1 0.0 -0.2 0.1
-1.1 0.9 -3.0
0.6120 0.6977 0.8011 0.8952
145.0 123.2 98.2 42.4
-3.8 1.7 7.4 - 12.3
0.6141 0.7002 0.8017 0.8981
173.7 145.5 95.4 49.6
1.8 2.8 - 3.0 0.6
0.6843 0.7693 0.8795
59.7 43.1 27.6
0.7 -3.3 2.6
x(1-n-C,H,,)+(l-x)(trans-1,3-&H,,) 0.4150 0.4907 0.6004 x(1-n-C,H,,)+(l 0.3930 0.4690 0.5972 x(1-n-C,H,,)+(l 0.3633 0.4651 0.5643
66.8 69.7 68.5
-x)(frans-2,4-&H,,) 70.9 73.7 66.8
$x)(cis,frans-1,3,5-&H,) 163.9 166.8 163.1
x(frans-2-C,H,,)+(l 0.4042 0.4973 0.5005
0.8 1.0 -1.3
6.1 1.2 2.8
-x)(frans-3-C,H,,) -2.6 -2.7 -2.7
x(frans-ZC,Hl,)+(l-x)(1,5-C,H,,)
x(frans-3-C,H,,)+(l 0.4008 0.4939 0.5955
177.9 174.6 171.5
+ (1 -x)(frans-1,3-C,H,,) 202.7 -1.1 204.7 -1.3 193.3 -2.3
68.1 72.0 68.8
-x)(1,5-C,H,,) 0.6 0.6 -0.6
Hf, OF
UNSATURATED TABLE
x
H:
6H:
J.mol-’
J.mol-’
l-continued Hii
x
J.mol-’
0.1063 0.1907 0.3003
34.1 58.9 81.6
-3.0 -0.5 2.0
x(trans-3-C,H,,)+(l 0.4009 0.5222 0.5998
0.1082 0.2124 0.2988
12.1 17.8 21.7
0.7 -0.4 0.0
0.1021 0.1961 0.3118
16.4 30.3 38.8
-2.1 1.0 -1.5
221
HYDROCARBONS
GHfi,
x
J.mol-’
H:
J.mol-’
6%
J,mol-’
-x)(trans-1,3-C,H,,) 92.3 2.2 93.0 -0.2 87.5 -1.8
0.6874 0.8047 0.8959
78.5 57.4 39.6
-1.1 - 1.5 4.4
x(1,5-C,H,,)+(l 0.4128 0.4951 0.5998
-x)(trans-1,3-C,H,,) 23.8 -0.4 25.1 0.6 23.8 0.1
0.6956 0.7962 0.8923
21.2 17.3 10.9
-1.1 0.0 0.0
x(1,5-C,H,,)+(l 0.3858 0.5089 0.6219
-x)(cis,trans-1,3,5-C,H,) 45.0 0.7 45.5 0.1 40.6 -1.1
0.6737 0.7714 0.8805
37.0 27.2 14.5
- 1.8 -4.1 -4.6
2. Experimental A McGlashan-type calorimeter,‘5’ modified as described elsewhere,@) was used for the measurements of excess enthalpies. Provenance, purification, and stabilization of the unsaturated hydrocarbons were as reported before.“v3’
3. Results Excess molar enthalpies HE at 298.15 K are listed in table 1 together with values of 6Hi where(*)
GH2(J.mol-‘)
= H$‘(J.mol-‘)-x(1
-x)
i 4,(2x- 1)“. (1) n=O The coefficients A,,, found by the method of least squares, the standard deviations s(HE), and values of 100s(H~)/0.25Ao are listed in table 2. The number of terms in equations (1) was chosen as that for which s(HE) shows a minimum. The observed and calculated HE (from equations 1) are plotted against x in figure 1 for all the mixtures except for (1-n-hexene + trans-1,3-hexadiene) and (I-n-hexene + tram-2,4hexadiene) whose Hz(x) is nearly identical with that for (1-n-hexene + 1,5-hexadiene); for (1-n-hexene + trans-3-hexene) also identical with that for (1-n-hexene + trans-2-hexene); and for (trans-2-hexene + trans-3-hexene) whose HE(x) is very small.
4. Discussion The resulting curves Hi(x) are almost symmetrical and positive except for (trans-2-hexene + trans-3-hexene) in keeping with the fragmentary results reported
222 TABLE
W. WOYCICKI 2. Values
at 298.15
A, for equation lOOs(H~/O.25A,
K of coefficients
(I), standard
deviations
A,
A* x(1-n-C,H,,) +(1 -x)(trans-2-C,H,,) +( 1 -x)(trans-3-C,H,,) +(I -x)(1,5-GH,,) +(1-x)(trans-1,3-C,H,,) +(1 -x)(trans-2,4-C,H,,) +(l -x)(cis,trans-1,3,5-C,H,)
36.9 42.2 281.8 284.4 290.5 660.5
x(trans-2-C,H,,) +(1-x)(trans-3-&H,,) +(I -x)(1,5-C,H,,) +(l -x)(trans-1,3-C&,,)
- 10.6 696.6 785.3
x(trans-3-C&,,) +(I -4(WC,H,,) +(l -x)(trans-1,3-C,H,,) x(1,5-C,&) +(1 -x)(trans-1,3-C,&,,) +(l -x)(cis,trans-1,3,5-C,H,)
TABLE
3. Contributions
A
- 1.9 -1.0 10.2 30.5 -28.9 -71.9
El ___ J.mol-’
and values of
lOOs(H:)
W:) _____
0.25A,
J.mol-’
-5.5 7.5 - 34.9 -23.3 60.0 27.1
0.3 0.6 1.1 1.6 1.8 6.0
3.2 5.7 1.5 2.2 2.5 3.6
-0.9 - 349.6 - 302.3
1.4 319.0 231.7
0.2 6.2 2.3
7.5 3.7 1.2
285.8 372.9
4.4 -8.2
-92.8 17.6
1.8 2.7
2.5 2.9
97.9 182.2
-2.6 - 29.2
29.0 -38.0
0.6 2.5
1.2 5.5
- 309.6
-
to Hz(x = 0.5) of HE(0.5 A+0.5 C,H,,), Hi(0.5 calculated according to equation (2); n, the number
B
s(Hk),
H30.5 A+0.5 J.mol-’
C,H,,)
B+0.5 C,H,,), of n-bonds
H30.5 Bf0.5 J.mol-’
C&I,,)
and
n-
HE(int.)
Hk(int.)/n J.mol-’
0.5(1-n-C&,,) + O.S(trans-2-C&,,) +0.5(trans-3-&H,,) +0.5(1.5-C,H,,) +0.5(trans-1,3-C,H,,) +O.S(trans-2,4-C,H,,) +O.S(cis,trans-1,3,5-&H,)
9 10 70 70 13 165
61 a 61’ 61 a 61” 61” 61”
54” 63” 247 b 250 b 251’ 487 JJ
1 1 2 2 2 3
- 106 -114 -119 -120 -120 -127
0.5(trans-2-C,H,,) +O.S(trans-3-C&,,) +0.5(1$C,H,,) fO.S(trans-1,3-C,H,,)
-3 174 195
54” 54” 54”
63” 247 * 250 b
1 2 2
-120 -64 -55
O.S(trans-3-C,H,,) +0.5(1,5-C&,) +O.S(trans-1,3-C&,,)
72 92
63” 63”
247 b 250 b
2 2
-119 -111
0.5(1,5-C&,,) +0.5(trans-1,3-C,H,,) +0.5(cis,trans-1,3,5-C,H,)
25 46
247 b 247 b
250 b 487 b
4 6
-118 -115
a Reference
1;
* reference
3;
’ single new result.
Hz OF UNSATURATED
HYDROCARBONS
223
J I
I
I
0.2
0.4
0.6
I
0.8
1
x FIGURE 1. Values of Hfl,at 298.15 K plotted against x for x(1-n-C,H,,)+: b, (1 -x)(1,5-C&H,,); c, (1 -x)(cis,trans-1,3,5-C,H,); x(1,5-C,H,,)+: d, (1 -x)(trans-1,3-C,H,,); e, (1 -x)(cis,trans-1,3,5-&H,); x(trans-2-C,H,,)+: f, (1 -x)(1,5-C,H,,); g, (1 -x)(trans-1,3-C,H,,); and x(trans-3-C,H,,)+: h, (1 -x)(1,5-C,H,,); i, (1 -x)(trans-1,3-C,H,,).
a, (1 -x)(trww2-C,H,,);
earlier.‘” Large differences between the HE(x) values in (trans-2-hexene + a diene) and (trans-3-hexene + a diene) are rather surprising and difficult to explain. To evaluate HE(int.) as a contribution to the excess molar enthalpy due to that approximate part responsible for R-Z interactions between the components involved, the calculation scheme described elsewhere”’ was applied: Hz = HE{xA+(l--x)C6H,,}+Hi{xB+(1-x)C,H,,)+Hi(int.),
i-3
In this scheme the thermal contributions due to dilution of components A and B were assumed to be identical with the corresponding excess molar enthalpies in n-hexane as the homomorphous solvent and thus HE(int.) could be referred to the number of molecules responsible for x--7~ interactions. Values for x = 0.5 and auxiliary data are listed in table 3. As may be seen, division of Hz(int.) by n = 1, 2, or 3 according to the number of unsaturated bonds occurring in a given component B (alkene, diene, or triene) yields closely related values in most cases. Interestingly, almost identical Hz(int.)/n values are also obtained for (diene + diene) and (diene + triene) with n = 4 and 6, respectively. This suggests in the first case that two molecules of one diene interact
224
W. WOYCICKI
with two molecules of another diene, and in the second case that three molecules of diene interact with two triene molecules. The close values of HE,(int.)/n, especially those found for (1-n-hexene + a diene), suggest that neither separation nor conjugation of unsaturated bonds is of major consequence. This situation differs considerably from that observed for (tetrachloromethane + a diene)“’ and (trichloromethane + a diene). cg) On the other hand, in 1-n-hexene + trans-2-hexene or + trans-3-hexene, as the unsaturated bond is progressively shifted toward the centre of gravity of the molecule (and the basicity difference between the components is increased), Hi(int.)/n does increase though sparingly. And similarly, when the number of unsaturated bonds in component B is increased HE(int.)/n also increases though only slightly. Generally, taking HE(int.) as the consequence of n--n: interactions, the interactions between the unsaturated molecules are seen to be less intense than those in the corresponding mixtures involving tetrachloromethane @c-n interactions)“’ and much smaller than those in the mixtures involving trichloromethane (n-N interactions).‘g’ This work was carried out under the Research Project 03.10. REFERENCES 1. Wbycicki, W. J. Chem. Thermodynamics 1975, I, II. 2. Wbycicki, W.; Rhensius, P. J. Chem. Thermodynamics 1979, 11, 150. 3. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 165. 4. Becker, H. Einfghrung in die Elektronentheorie organ&h-chemischer Verlag der Wissenschaften: Berlin. 1961. 5. Larkin, J. A.; McGlashan, M. L. J. Chem. Sot. 1961, 3423. 6. Wbycicki, W. J. Chem. Thermodynamics 1974,6, 141. I. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 161. 8. Scatchard, G.; Ticknor, L. B. J. Am. Chem. Sot. 1952, 74, 3725. 9. Wbycicki, W. J. Chem. Thermodynamics 1979, 11, 727. 10. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 761.
Reaktionen.
VEB, Deutsche
Thermodynamics
1984, 16,219-224
Excess enthalpies of binary mixtures containing unsaturated hydrocarbons W. W6YCICKI Institute Warsaw,
(Received
of Physical Poland
II
August
Chemistry,
Polish
Academy
of Sciences,
1983)
The excess molar enthalpies Hz over the whole composition range of I-n-hexene + trans-2hexene, + tram-3-hexene, + 1,5-hexadiene, + trans-1,3-hexadiene, + trans-ZChexadiene, and + cis,trans-1,3,5-hexatriene, of trans-2-hexene + mans-3-hexene, + 1,5-hexadiene, and + tmns1,3-hexadiene, of tmns-3-hexene + 1,5-hexadiene and + trans-1,3-hexadiene, and of 1,5-hexadiene + tram-1,3-hexadiene and + c&tram-1,3,Shexatriene were measured in a McGlashan-type calorimeter at 298.15 K. The influence of the unsaturated-bond position in the alkenes and dienes examined on the apparent magnitude of X-X interactions is discussed.
1. Introduction In preceding papers (rm3) it has been pointed out that rc-TCin interactions occurring between the molecules of an unsaturated hydrocarbon may considerably differ from analogous interactions occurring in another unsaturated hydrocarbon with an identical number of carbon atoms. The reasons underlying these diverse interactions may include the position, the number, and the relative ratio (separation or conjugation) of unsaturated bonds in the molecules involved, and their steric configurations (cis-trans isomerism; open or closed chains). Generally, this diversification of interactions is explicable in terms of different basicities of the molecules considered,‘4’ varying accessibilities to the rc-bond, and different degrees of aromaticity. Thus, in mixtures of unsaturated hydrocarbons the aforementioned differences may well be expected to result in distinct molecular interactions leading to different values for the excess molar enthalpy. Earlier fragmentary studies’” were concerned with the effect of cis-tram isomerism on n--x interactions. For (trans-2-hexene + trans-3-hexene), those early measurements are now supplemented to cover a broader range of compositions and results. The total programme involved 13 mixtures grouped in four series. Series 1 and 2 involved the polar molecules: I-n-heptene and trans-Zhexene; and series 3 and 4 involved the non-polar molecules: truns-3-hexene and 1,5-hexadiene (separated double bonds) as fixed components. The second components in the mixtures studied were unsaturated hydrocarbons whose basicity increased as the double bond was shifted toward the centre of gravity of the molecule, the number of double bonds was raised, and separation or conjugation of bonds was altered. 0021~9614/84/030219+06
%02.00/O
0
1984 Academic
Press Inc. (London)
Limited
220
W. WOYCICKI TABLE
x
H:
Wf,
J.mol-’
J.mol-’
1. Excess enthalpies
x
x(1-n-C,H,,)+(l 0.1033 0.2047 0.3033
3.5 5.5 7.6
0.2 -0.4 -0.2
0.4041 0.4961 0.5890
0.1047 0.2289 0.3147
4.5 7.3 9.3
0.1 -0.5 -0.9
0.1059 0.1929 0.2902
25.0 40.1 58.0
0.6 -1.7 0.9
0.1231 0.2302 0.3126
24.8 47.4 59.9
-1.9 1.1 1.9
0.1089 0.1830 0.2960
25.6 45.1 58.4
- 1.2 2.5 -2.3
0.0920 0.1960 0.2842
62.0 113.4 133.1
0.4 -8.5 -8.6
0.0871 0.2373 0.2989
-0.9 - 1.4 -2.3
-0.2 0.4 -0.2
0.1034 0.1992 0.3133
110.7 160.0 177.8
4.8 -2.1 2.8
0.4163 0.5134 0.5250
0.0548 0.0770 0.2269
76.2 97.8 189.6
0.7 -1.3 2.4
x(trans-2-C&H,,) 0.3171 0.4169 0.5078
0.0899 0.2016 0.3181
18.4 39.6 58.5
0.4 -0.4 -0.5
x(1-n-C,H,,)f(l 0.4053 0.4916 0.5892
at 298.15
Hfj,
@ffl,
J.mol-’
J.mol-’
K
x
HE
SHE
J.mol-’
J.mol-’
-x)(frans-2-C,H,,) 8.6 9.5 8.7
-0.3 0.2 -0.1
0.6962 0.7733 0.8711
7.8 6.3 3.4
0.3 0.3 -0.2
-x)(trans-3-&H,,) 10.0 11.4 10.7
-0.2 0.8 0.4
0.7057 0.7868 0.5102
8.7 6.7 4.1
-0.3 -0.8 0.2
x(1-n-C,H,,)+(l-x)(1,5-C,H,,) 0.403 1 68.7 0.5035 72.3 0.5936 69.1
0.2 0.3 -0.4
0.6844 0.7892 0.8982
62.8 45.4 26.0
0.8 -1.5 0.9
-0.8 - 1.2 - 1.0
0.6763 0.7720 0.9002
65.1 52.8 25.3
1.1 1.0 -1.1
0.6862 0.7953 0.8896
58.4 42.6 21.6
0.0 1.5 -1.1
0.6919 0.7809 0.8780
131.4 108.6 66.5
-4.4 1.0 -0.1
-0.1 -0.1 -0.1
0.5916 0.7007 0.8110 0.8998
-2.4 -2.3 -1.8 -0.8
0.1 0.0 -0.2 0.1
-1.1 0.9 -3.0
0.6120 0.6977 0.8011 0.8952
145.0 123.2 98.2 42.4
-3.8 1.7 7.4 - 12.3
0.6141 0.7002 0.8017 0.8981
173.7 145.5 95.4 49.6
1.8 2.8 - 3.0 0.6
0.6843 0.7693 0.8795
59.7 43.1 27.6
0.7 -3.3 2.6
x(1-n-C,H,,)+(l-x)(trans-1,3-&H,,) 0.4150 0.4907 0.6004 x(1-n-C,H,,)+(l 0.3930 0.4690 0.5972 x(1-n-C,H,,)+(l 0.3633 0.4651 0.5643
66.8 69.7 68.5
-x)(frans-2,4-&H,,) 70.9 73.7 66.8
$x)(cis,frans-1,3,5-&H,) 163.9 166.8 163.1
x(frans-2-C,H,,)+(l 0.4042 0.4973 0.5005
0.8 1.0 -1.3
6.1 1.2 2.8
-x)(frans-3-C,H,,) -2.6 -2.7 -2.7
x(frans-ZC,Hl,)+(l-x)(1,5-C,H,,)
x(frans-3-C,H,,)+(l 0.4008 0.4939 0.5955
177.9 174.6 171.5
+ (1 -x)(frans-1,3-C,H,,) 202.7 -1.1 204.7 -1.3 193.3 -2.3
68.1 72.0 68.8
-x)(1,5-C,H,,) 0.6 0.6 -0.6
Hf, OF
UNSATURATED TABLE
x
H:
6H:
J.mol-’
J.mol-’
l-continued Hii
x
J.mol-’
0.1063 0.1907 0.3003
34.1 58.9 81.6
-3.0 -0.5 2.0
x(trans-3-C,H,,)+(l 0.4009 0.5222 0.5998
0.1082 0.2124 0.2988
12.1 17.8 21.7
0.7 -0.4 0.0
0.1021 0.1961 0.3118
16.4 30.3 38.8
-2.1 1.0 -1.5
221
HYDROCARBONS
GHfi,
x
J.mol-’
H:
J.mol-’
6%
J,mol-’
-x)(trans-1,3-C,H,,) 92.3 2.2 93.0 -0.2 87.5 -1.8
0.6874 0.8047 0.8959
78.5 57.4 39.6
-1.1 - 1.5 4.4
x(1,5-C,H,,)+(l 0.4128 0.4951 0.5998
-x)(trans-1,3-C,H,,) 23.8 -0.4 25.1 0.6 23.8 0.1
0.6956 0.7962 0.8923
21.2 17.3 10.9
-1.1 0.0 0.0
x(1,5-C,H,,)+(l 0.3858 0.5089 0.6219
-x)(cis,trans-1,3,5-C,H,) 45.0 0.7 45.5 0.1 40.6 -1.1
0.6737 0.7714 0.8805
37.0 27.2 14.5
- 1.8 -4.1 -4.6
2. Experimental A McGlashan-type calorimeter,‘5’ modified as described elsewhere,@) was used for the measurements of excess enthalpies. Provenance, purification, and stabilization of the unsaturated hydrocarbons were as reported before.“v3’
3. Results Excess molar enthalpies HE at 298.15 K are listed in table 1 together with values of 6Hi where(*)
GH2(J.mol-‘)
= H$‘(J.mol-‘)-x(1
-x)
i 4,(2x- 1)“. (1) n=O The coefficients A,,, found by the method of least squares, the standard deviations s(HE), and values of 100s(H~)/0.25Ao are listed in table 2. The number of terms in equations (1) was chosen as that for which s(HE) shows a minimum. The observed and calculated HE (from equations 1) are plotted against x in figure 1 for all the mixtures except for (1-n-hexene + trans-1,3-hexadiene) and (I-n-hexene + tram-2,4hexadiene) whose Hz(x) is nearly identical with that for (1-n-hexene + 1,5-hexadiene); for (1-n-hexene + trans-3-hexene) also identical with that for (1-n-hexene + trans-2-hexene); and for (trans-2-hexene + trans-3-hexene) whose HE(x) is very small.
4. Discussion The resulting curves Hi(x) are almost symmetrical and positive except for (trans-2-hexene + trans-3-hexene) in keeping with the fragmentary results reported
222 TABLE
W. WOYCICKI 2. Values
at 298.15
A, for equation lOOs(H~/O.25A,
K of coefficients
(I), standard
deviations
A,
A* x(1-n-C,H,,) +(1 -x)(trans-2-C,H,,) +( 1 -x)(trans-3-C,H,,) +(I -x)(1,5-GH,,) +(1-x)(trans-1,3-C,H,,) +(1 -x)(trans-2,4-C,H,,) +(l -x)(cis,trans-1,3,5-C,H,)
36.9 42.2 281.8 284.4 290.5 660.5
x(trans-2-C,H,,) +(1-x)(trans-3-&H,,) +(I -x)(1,5-C,H,,) +(l -x)(trans-1,3-C&,,)
- 10.6 696.6 785.3
x(trans-3-C&,,) +(I -4(WC,H,,) +(l -x)(trans-1,3-C,H,,) x(1,5-C,&) +(1 -x)(trans-1,3-C,&,,) +(l -x)(cis,trans-1,3,5-C,H,)
TABLE
3. Contributions
A
- 1.9 -1.0 10.2 30.5 -28.9 -71.9
El ___ J.mol-’
and values of
lOOs(H:)
W:) _____
0.25A,
J.mol-’
-5.5 7.5 - 34.9 -23.3 60.0 27.1
0.3 0.6 1.1 1.6 1.8 6.0
3.2 5.7 1.5 2.2 2.5 3.6
-0.9 - 349.6 - 302.3
1.4 319.0 231.7
0.2 6.2 2.3
7.5 3.7 1.2
285.8 372.9
4.4 -8.2
-92.8 17.6
1.8 2.7
2.5 2.9
97.9 182.2
-2.6 - 29.2
29.0 -38.0
0.6 2.5
1.2 5.5
- 309.6
-
to Hz(x = 0.5) of HE(0.5 A+0.5 C,H,,), Hi(0.5 calculated according to equation (2); n, the number
B
s(Hk),
H30.5 A+0.5 J.mol-’
C,H,,)
B+0.5 C,H,,), of n-bonds
H30.5 Bf0.5 J.mol-’
C&I,,)
and
n-
HE(int.)
Hk(int.)/n J.mol-’
0.5(1-n-C&,,) + O.S(trans-2-C&,,) +0.5(trans-3-&H,,) +0.5(1.5-C,H,,) +0.5(trans-1,3-C,H,,) +O.S(trans-2,4-C,H,,) +O.S(cis,trans-1,3,5-&H,)
9 10 70 70 13 165
61 a 61’ 61 a 61” 61” 61”
54” 63” 247 b 250 b 251’ 487 JJ
1 1 2 2 2 3
- 106 -114 -119 -120 -120 -127
0.5(trans-2-C,H,,) +O.S(trans-3-C&,,) +0.5(1$C,H,,) fO.S(trans-1,3-C,H,,)
-3 174 195
54” 54” 54”
63” 247 * 250 b
1 2 2
-120 -64 -55
O.S(trans-3-C,H,,) +0.5(1,5-C&,) +O.S(trans-1,3-C&,,)
72 92
63” 63”
247 b 250 b
2 2
-119 -111
0.5(1,5-C&,,) +0.5(trans-1,3-C,H,,) +0.5(cis,trans-1,3,5-C,H,)
25 46
247 b 247 b
250 b 487 b
4 6
-118 -115
a Reference
1;
* reference
3;
’ single new result.
Hz OF UNSATURATED
HYDROCARBONS
223
J I
I
I
0.2
0.4
0.6
I
0.8
1
x FIGURE 1. Values of Hfl,at 298.15 K plotted against x for x(1-n-C,H,,)+: b, (1 -x)(1,5-C&H,,); c, (1 -x)(cis,trans-1,3,5-C,H,); x(1,5-C,H,,)+: d, (1 -x)(trans-1,3-C,H,,); e, (1 -x)(cis,trans-1,3,5-&H,); x(trans-2-C,H,,)+: f, (1 -x)(1,5-C,H,,); g, (1 -x)(trans-1,3-C,H,,); and x(trans-3-C,H,,)+: h, (1 -x)(1,5-C,H,,); i, (1 -x)(trans-1,3-C,H,,).
a, (1 -x)(trww2-C,H,,);
earlier.‘” Large differences between the HE(x) values in (trans-2-hexene + a diene) and (trans-3-hexene + a diene) are rather surprising and difficult to explain. To evaluate HE(int.) as a contribution to the excess molar enthalpy due to that approximate part responsible for R-Z interactions between the components involved, the calculation scheme described elsewhere”’ was applied: Hz = HE{xA+(l--x)C6H,,}+Hi{xB+(1-x)C,H,,)+Hi(int.),
i-3
In this scheme the thermal contributions due to dilution of components A and B were assumed to be identical with the corresponding excess molar enthalpies in n-hexane as the homomorphous solvent and thus HE(int.) could be referred to the number of molecules responsible for x--7~ interactions. Values for x = 0.5 and auxiliary data are listed in table 3. As may be seen, division of Hz(int.) by n = 1, 2, or 3 according to the number of unsaturated bonds occurring in a given component B (alkene, diene, or triene) yields closely related values in most cases. Interestingly, almost identical Hz(int.)/n values are also obtained for (diene + diene) and (diene + triene) with n = 4 and 6, respectively. This suggests in the first case that two molecules of one diene interact
224
W. WOYCICKI
with two molecules of another diene, and in the second case that three molecules of diene interact with two triene molecules. The close values of HE,(int.)/n, especially those found for (1-n-hexene + a diene), suggest that neither separation nor conjugation of unsaturated bonds is of major consequence. This situation differs considerably from that observed for (tetrachloromethane + a diene)“’ and (trichloromethane + a diene). cg) On the other hand, in 1-n-hexene + trans-2-hexene or + trans-3-hexene, as the unsaturated bond is progressively shifted toward the centre of gravity of the molecule (and the basicity difference between the components is increased), Hi(int.)/n does increase though sparingly. And similarly, when the number of unsaturated bonds in component B is increased HE(int.)/n also increases though only slightly. Generally, taking HE(int.) as the consequence of n--n: interactions, the interactions between the unsaturated molecules are seen to be less intense than those in the corresponding mixtures involving tetrachloromethane @c-n interactions)“’ and much smaller than those in the mixtures involving trichloromethane (n-N interactions).‘g’ This work was carried out under the Research Project 03.10. REFERENCES 1. Wbycicki, W. J. Chem. Thermodynamics 1975, I, II. 2. Wbycicki, W.; Rhensius, P. J. Chem. Thermodynamics 1979, 11, 150. 3. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 165. 4. Becker, H. Einfghrung in die Elektronentheorie organ&h-chemischer Verlag der Wissenschaften: Berlin. 1961. 5. Larkin, J. A.; McGlashan, M. L. J. Chem. Sot. 1961, 3423. 6. Wbycicki, W. J. Chem. Thermodynamics 1974,6, 141. I. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 161. 8. Scatchard, G.; Ticknor, L. B. J. Am. Chem. Sot. 1952, 74, 3725. 9. Wbycicki, W. J. Chem. Thermodynamics 1979, 11, 727. 10. Wbycicki, W. J. Chem. Thermodynamics 1980, 12, 761.
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