1240
EIJIIKADA
Dielectric Properties of Some Diols by Eiji Ikadal Institute for Chemical Research, Kyoto University, Uji,Kyoto-Fu, 611, Japan
(Received July 91, 1970)
Publication costs borne completely by The Journal of Physical Chemistry
The dielectric properties of the four diols, 2-methyl-2,4-pentanediolj dipropylene glycol, 2-ethyl-1,3-hexanediol, and thiodiglycol, were studied to correlate the dielectric properties with the molecular structures. The measurements of the dielectric constant and loss were carried out over the audio- and radiofrequency range at temperatures from -70 to 60’. All of these diols except thiodiglycol showed the Davidson-Cole-type dispersions. No significant differenceconcerning the molecular structure in the shape of the dielectric relaxations was observed for these rather complicated diols. The dielectric behavior of diols was discussed in contrast with those of polyamino compounds.
Introduction
the more the shape of the complex loci differs from that of the Davidson-Cole-type dispersion. The shape of Owing to the dipole-dipole association, the static the complex locus in aminoethylethanolamine, howdielectric constants of hydrogen-bonding molecules are ever, more closely resembles the shape of the Davidsonlarger than those of the normal polar liquids, and the Cole-type dispersion than those of ethylenediamine strong interaction between the molecules leads to large oligomers do. values of relaxation time in breaking and reforming of Moriamez, et al., also analyzed the dielectric disperhydrogen bond accompanying reorientation of the disions of diol molecules such as 2-methyl-2,4-pentanepoles.2 The dielectric relaxation of the monohydroxyl diol8 and 2-ethyl-1,3-hexanediolg in terms of the supercompounds generally shows the Debye-type dispersion position of the Debye-type dispersions. In view of involving a single relaxation time and the relaxation these situations, it is definite that the relaxation mechamechanism is reasonably explained in terms of breaking nism is different with the liquid involving the different and reforming of OH---0 hydrogen bond.3 For the type of the hydrogen bond. dielectric behavior of the diols and triolsj4however, the On the other hand, DennylO studied the dielectric situation seems to be much more complicated in comproperties of the three isoalkyl halides and found that parison with that of the monohydroxyl compounds. the dielectric dispersion of these compounds having no The liquid structure of the polyhydroxyl molecules has hydrogen bonds showed also the Davidson-Cole-type not yet been clarified and remained unsolved, although dispersions. In these compounds the hydrogen bond it is no doubt that the hydrogen bond takes part in the does not exist. This fact, therefore, shows that the cluster formation of liquid diols.5 hydrogen bond is not a necessary condition for the The dielectric dispersions of the polyhydroxyl comDavidson-Cole-t ype dispersion. pounds do not exhibit the Debye type, but the DavidThe purpose of the present study was to investigate son-Cole-type dispersion. the dielectric relaxation of the complicated diols and to RIeanwhile, the present author has studied the dielectric behavior of the polyamino molecules such as ethylenediamine oligomers H~I\‘CBH((HNCZH~)._~P\IH~, (1) Correspondence should be addressed to Faculty of Engineering, (n = 1,2,3, and 4),6monoethanolamine, diethanolamine, Kobe University, Kobe, Japan. It mas found that the and amin~ethylethanolamine.~ (2) G. C. Pimentel and A. B. McClellan, “The Hydrogen Bond,” W. H. Freeman and Co., San Francisco, Calif., 1960,p 15. dielectric behavior of these amines was considerably (3) See, e.g., C. P. Smyth, “Dielectric Behavior and Structure,” different from that of the hydroxyl cotnpounds such as McGraw-Hill, New York, N. Y.,1955,p 105. alcohols and diols. I n contrast with the Davidson(4) D. W. Davidson and R. H. Cole, J . Chem. Phys., 19, 1484 Cole-type dispersion of the polyhydroxyl compounds, (1951). neither ethylenediamine oligomers nor aminoethyl(5) G.E.McDuffie, Jr., and T. A, Litovitz, ibid., 37, 1699 (1962). ethanolamine showed this type of dispersion in spite of (6) E. Ikada, Bull. Inst. Chem. Res., Kyoto Univ., 45, 352 (1967). (7) E. Ikada, Y.Hida, H. Okamoto, Z, Hagino, and N. Koizumi, the hydrogen-bonding molecules, but showed the exis&id., 46, 239 (1968). tence of the two large dispersion regions which were (8) C1. Moriamez, M. Moriamez, and R. Arnoult, “Spectroscopy and analyzed as the superposition of the relaxations of the Relaxation at Radio Frequency,” North-Holland Publishing Co., Amsterdam, 1962, p 47. Debye or the Cole-Cole and the Davidson-Cole type. (9) C1. Moriamez and M. D. Allab. “Magnetic and Electric ResoThe shape of the complex loci in the dielectric relaxation nance and Relaxation,” North-Holland Piblishing Co., Amsterdam, of ethylenediamine oligomers differs with each oligomer. 1963, p 338. The larger the molecule of ethylenediamine oligomers, (10) D. J. Denny, J . Chem. Phys., 27,259 (1957) The Journal of Physical Chemistry, Vol. 76, N o . 9, 1971
1241
DIELECTRIC PROPERTIES OF SOME DIOLS compare these results with those of the polyamino compounds.
Experimental Section Materials. Commercial reagents of thiodiglycol, 2-methyl-2,4-pentanediol, dipropylene glycol, and 2ethyl-1,3-hexanediol mere repeatedly distilled in a 70 X 2-cm glass bead-packed column operated at a high reflux ratio under reduced pressure. Refractive indices were measured by a Piilfrich refractometer, and densities were measured by the Lypkin-type pycnometer. Physical constants of these diols are collected in Table I.
Table I : Physical Constants of Diols Sample
MP,
2-Methyl-2,4-pentanediol
Refractive Indices Temp,
89.5 (9 mm) 113.7 (8mm) 124.5 (7 mm) 115.5 (9 mm)
OC
60 50 40 30 20 10
0
- 10 - 20 -30 -40 - 50 - 60 - 70
2-Methyl2,Cpentanediol
2-Ethyl-1,3hexanediol
Diprop ylene glycol
20.10 21.50 22.91 24.36 25.86 27.67 29.44 31.38 33.42 35.71 38.05 40.78 43 96 47.80 I
15.66 16.73 17.88 19.02 20.38 21.83 23.38 25.08 26.88 28.85 30.86 33.08 34.50
15.24 16.08 17.00 17.91 18 73 19.75 20.88 21 84 22.88 23.90 25 * 00
22.74 24 09 25.49 26.98 28.61 30.56 32.37 34.46 36.52
... ...
...
I
I
I
...
Thiodiglyool
...
value at lower temperature. expressed by
The observed values are
nD
OC
2-Methyl-2,4pentanediol
Dipropylene glycol
2-Ethyl-1,3hexanediol
Thiodiglycol
20 30 40 50
1.4276 1.42415 1.42065 1.41735
1.44092 1 43770 1.43459 1.43067
1.46076 1.44734 1.44353 1.44012
1,521084 1.51770 1.51464
Temp, O C
2-Methyl-2,4pentanediol
Dipropylene glycol
2-Ethyl-1,3hexanediol
Thiodiglycol
20 30 40 50
0.92109 0.91390 0.91390 0.89965
1.02147 1.01389 1.01389 0.99856
0.93971 0.93253 0,93253 0.91771
1.18723 1,17425 1.17425 1.15989
I
Temp,
BP, "C
O C
Glassy Glassy Glassy -10.2
Dipropylene glycol Z-Ethyl-l,3-hexandiol Thiodigly col
Table 11: Static Dielectric Constants of Diols
...
Densities (g/ml)
Dielectric Measurements. Dielectric constant and dielectric loss were measured by a transformer ratioarm bridge (Ando Electric Co. TR-1A) over the frequency range from 7 . 5 Hz to 5 MHz. Dielectric measurements at higher frequencies up to 250 MHz were made by the use of a Boonton 250 A RX meter. The dielectric cell was a platinum concentric cell of which vacuum capacitance was determined by the standard liquids. l1 The measurement of cell temperature was made by the calibrated thermometer and an Au-Co vs. Cu thermocouple.
Results Static Dielectric Constants. The observed static dielectric constants of the diols are listed in Table 11. The variation of dielectric constants was experimentally represented by the straight lines with respect to the reciprocal of absolute temperature except that of 2ethyl-1,3-hexanediol which increased more slowly with decreasing temperature, tending to approach a limiting
where eo is the static dielectric constants, a and b are the empirical constants, and T is the absolute temperature. Numerical values of a and b are listed in Table I11 in comparison with those of other hydrogen-bonding liquids.
Table I11 : Numerical Constants of a and b of the ( b / T ) with the Values of the Equation E O = a
+
Other Hydrogen-Bonding Liquids Molecules
a
2-Methyl-2,4-pentanediola
-22.38 -18.94 -21.23 -28.75 -7.20 -7.36
Dipropylene glycola Thiodiglycola Ethylene glycolb Diethanolaminec Diethylenetriamined
b
1.415 1.155 1.463 2.070 9.658 5.874
X 104 x 104 X 104 X lo4 X 10s X lo3
a The difference between the observed and the calculated dielectric constants is within &2%. b N. Koizumi and T. Hanai, J.Phys. Chem., 60,1496 (1956). Reference 7. Reference 6.
Dielectric Dispersion. These diols exhibited the dielectric dispersions in the glassy state over the measuring frequency range. Thiodiglycol solidified at the melting point and the dielectric constants reduced to the small values of the order of the magnitude of induced polarization. The primary dispersions of the three diols were observed at the lower frequency region. The complex loci of the dielectric dispersion of 2(11) A. A. Maryott and E . R . Smith, Natl. Bur. Stand. Circ.,514, 1 (1951). The Journal of Physical Chemistry, Vol. 76, No. 0,1071
1242
EIJIIKADA
'1
2-Methyl-2.4-pentanediol
Ik
6'
Figure 1. Complex dielectric constant loci for 2-methyl-2,4-pentanediol.Data points are: 0, 5". The numbers beside data points denote frequency in kHz.
C),
-60';
i),
-50';
0, -40';
8,-30';
E'
Figure 2. 0, -200;
Complex dielectric constant loci for 2-ethyl-l,3-hexanediol.
e
-100;
Data points are: 0, -40";
S, -30';
e , 5'.
me thyl-2,4-pentanediol and 2-e thyl- 1)3-hexanediol are shown in Figures 1 and 2, respectively. Further at the high frequency region, the small residual dispersions were observed for 2-methyl-2,4-pentanediol and 2ethyl-lj3-hexanediol. These principal dispersions are expressed by the Davidson-Cole skewed arc equation4
where e * is the complex dielectric constant, eo is the static dielectric constant, and e, is the limiting high frequency dielectric constant, TO is the relaxation time, The Journal of Physical Chemistry, Vol. 76,N o . 0 , 1971
and ,8 is the distribution parameter of relaxation times. The real and imaginary parts of complex dielectric constants are given by E'
e''
em
= (eo
= (eo
- €,)(COS + ) B
- e,)(cos
cos
+)@ sin ,8+
where tan (b = W T ~ . Putting 0 = tan-1 [ e f f / ( e f e,)], then tan 0 = tan ,8+, or w0= tan (e/@). For the Davidson-Cole-type dispersion, plots of log tan (e/p) against log frequency should give a straight line with the slope of unity. The values of the distribution parameter ,8 and the limiting high frequency dielec-
1243
DIELECTRIC PROPERTIES OF SOME DIOLS Table IV : Relaxation Times and Distribution Parameters p of Diols 7--Dipropylene
~Z-hlethyl-Z,4-pentanediol-TO B
20 10 5 - 10 - 20 - 30 - 40 50 - 60 - 65 - 70
0.68 4.42
0.85
x
...
2.56 x 1.58 X 1.32 X 2.26 x 9.64 x 1.11 x
0.85 0.74 0.73 0.71 0.69 0.67
-
TO
...
...
---Z-Ethyl-l,3-hexanediol-0 TO
glycol---
B
4.58
... x 10-9
10-9
1.16
0.71 0.70 0.64 0.57
5 - 0 4 x 10-7 3.04 x 3.14 X 5.34 x 10-4
0.67 0.62 0.59 0.55 0.53
10-7
10-4 10-4 10-2
...
1.86 x 10-7 1.08 X 10-6 8.90 X 1.16 x 10-4 3.70 x 10-3
.,.
.
...
I
.
...
... ...
* .
..,
x
0.71 0.72
... ...
...
... ...
...
where eo is the static dielectric constant, e, is the high frequency dielectric constant, p o is the dipole moment in vacuo, N o is the number of molecules per cubic centimeter, and g is Kirkwood’s correlation factor. It is necessary to know the value of the dipole moment in vacuo in order to evaluate g factor. The values of the dipole moment of the diols are considerably dependent on the solvent. The dipole moment of 2methyl-2,4-pentanediol was observed as 2.9 D in benzene solution and as 2.2 D in dioxane ~ o l u t i o n ; ’it~ is rather difficult to estimate experimentally the Kirkwood’s correlation factor of polyhydroxyl compounds. Lin and Dannhauser15 introduced a reduced dielectric constant (e& by rearranging eq 3 I
I
Figure 3.
I0’
(EO)R
I0 ‘
Hz 1
Frequency (
I
I
I
Id
Frequency plot to determine relaxation time
Discussion Static Dielectric Constant. Trouton’s constantst2 were calculated as 45.5 for dipropylene glycol, 41.5 for 2-methyl-2,4-pentanediolj and 29.0 for 2-ethyl-1,3hexanediol which can be regarded as a measure of molecular association’ These larger than those of ethylenediamine oligomers showing that hydrogen bonds play a important role in the liquid structure of diols. F~~ the hydrogen-bonding liquids, regularity and strength of the short-range order has been discussed in terms.of E(irkwood’s correlation factor in the folloLving . E,
+ (
-/- 2
___
2EO “
em
3
)
4TNo/.402 ___ 3kT
+
6,)
M P
TO.
tric constant e m were selected to satisfy this condition as is shown in Figure 3. The relaxation time was determined from the frequency where the logarithm of tan (O/p) corresponds to unity on this straight line. The values of p and T~ are listed in Table IV.
Eo=Em+---
+
4nNpo2 (eo - tm)(2eo = 9kT %(em 2)2
= -g
(3)
where N is Avogadro’s number, M is the molecular weight, and p is the density. The values of T X (& of diols were plotted against temperature and compared with that of diethylenetriamine in Figure 4. This plot shows that the molecular association of diols due to the hydrogen bond changes more markedly with temperature than that of diethylenetriamine in this temperature range. The coefficient b in eq 1 of the amino compounds and polyhydroxyl molecules are compared in Table 111. As is seen in Table 111, these (12) Trouton’s constant was calculated by dividing the heat of vaporization by the boiling point. The values of heat of vaporize tion and the boiling point at atmospheric pressure were adopted from the following references. The heat of vaporization of dipropylene glycol and 2-ethyl-1,3-hexanediol: K. Dolittle, “Technology of Solvents and Plasticizers,” Wiley, New York, N. Y., 1954, .pp 678-680. The heat of vaporization of Z-methyl-2,4-pentanediol: c. Marsden, “Solvents Manual,” Cleaver Hume, London, 1954, p 224. The boiling points: G. 0. Curme and F. Johnston, “Glycols,” Reinhold, New York, N.Y., 1952. (13) G. Oster and J. G. Kirkwood, J . Chem. Phys., 11, 175 (1943). (14) L. G. Wesson, “Tables of Electric Dipole Moments,” The Technology Press (MIT), Cambridge, Mass., 1948, p 32. (15) R. Lin and W. Dannhauser, J . Phys. Chem., 67, 1805 (1963). The Journal of Physical Chemistry, Vol. 75, No. 9 , 1971
1244
EIJIIJLADA
1.2
-
Y
-
0.7
Temp., (“C)
Figure 6. Static dielectric constants of diols plotted against the reciprocal of absolute temperature.
Figure 4. Plots of T(eo)~. against temperature.
3.0
3.5
io3
40
T
Figure 5 . Comparison of the static dielectric constants of various HOC2HaXC2H40Hmolecules.
glycol, X = -NH- to diethanolamine,’ and X = -CH2to 1,5-pentanediol.17 Of these substituents, ether oxygen of diethylene glycol and imino group of diethanolamine are capable of hydrogen bonding. It seems that the electronegativity’s of X group has no direct correlation with the values of the static dielectric constants of these diols. I n other words, the X group of these diols does not contribute much to the value of the static dielectric constant. The steric hindrance in the diol molecule is a more important factor for the effective cluster formation which is characteristic of the polyhydroxy1 compound as pointed out by IllcDuffie, et ala5 As is seen in Figures 5 and 6, the static dielectric constants of diethylene glycol are larger than those of dipropylene glycol since two methyl groups on each end carbon of the latter molecule give the steric hindrance for the intermolecular hydrogen bond. The same effect is recognized in the dielectric constants of 2-ethyl-1,3-hexanediol which has the large ethyl group on the carbon chain. The deviation of the static dielectric constant from the linear relationship would be related with this steric hindrance as seen in Figure 6. On the other hand, according to Davidson’s data of the isomeric pentanediol, the static dielectric constants of the vicinal diols (1,2- and 2,3-pentanediol17) increase more rapidly at lower temperature. This result is contrasted with the temperature dependence of 2ethyl- 1,3-hexanediol. Dielectric Dispersion. I n the glassy state, ethylenediamine oligomers6 and aminoethylethanolamine’
coefficients increase in the order of ethylenediamine oligomers, ethanolamines, and diols. It is supposed that this order results from the difference in the relative contribution of the hydrogen bond in cluster formation of these compounds. The (16) N. Koizumi and T. Hanai, J . Phys. Chem., 60, 1496 (1956). static dielectric constants of various HOC~H~XCZH~OH (17) D. W. Davidson, Can. J . Chern., 39, 2139 (1961). molecules are compared in Figure 5, where X = -0(18) L. Pauling, “Nature of the Chemical Bond,” Cornel1 University corresponds to diethylene glycol,16 X = -S- to thiodiPress, Ithaca, N. Y . , 1940, Chapter 2. The Journal of Physical Chemistry, Vol. 76,No. 0,2072
1245
DIELECTRIC PROPERTIES OF SOME DIOLS showed considerably complicated dielectric dispersions. The shapes of the complex loci of these dispersions apparently resembled the shape of the Davidson-Coletype dispersion. The detailed analysis, however, clarified that the dispersion of the above amino molecules could not be represented by the Davidson-Coletype dispersion. Unfortunately, the dielectric dispersion of diethanolamine, which is also a kind of diol and amino compound, could not be observed over the measuring frequency range, because this molecule solidified at the melting point. It has been known that the dielectric dispersions of the polyhydroxyl compounds in the liquid or supercooled state are generally of the Davidson-Coletype dispersion with an exception of 1,5-pentanediol.l7 These structurally complicated diols such as 2-ethyll,&hexanediol and dipropylene glycol also showed the Davidson-Cole-type dispersion. The structural difference in the diols seems to produce no significant difference in the relaxation mechanism of diols. Further, it seems that the principal dielectric dispersions of all the diols studied are better represented by the Davidson-Cole-type dispersion than by the superposition of the Debye-type dispersion as reported by ILIoriamee, et al.8t9 This point is an important difference between the dispersions of polyhydroxyl and polyamino compounds. Iloieumi and HanaiI6 reported that the large glycol such as tetraethylene glycol shows the Davidson-Cole-type dispersion. On the other hand, the dispersion of tetraethylenepentamine was not of the Davidson-Cole-type but was analyzed by the superposition of two different types of dispersion. The relaxation times of diols increase more rapidly with decreasing temperature. The Arrhenius plots of relaxation time did not show straight lines, but were adequately represented by the following equation4 as is shown in Figure 7 log
70
=
A
B
+ T___ - T,
where T , is the characteristic temperature and A and B are the empirical constants. The values of A , B, and T , are given in Table V together with those of pentanediols. One can recognize the good coincidence of the characteristic temperature T , for the relaxatiobs of the polyhydroxyl compounds with the different molecular structures as is seen in Table V. It can be supposed that this characteristic temperature which is considered as the freezing temperature of dipolar reorientation is related to the relaxation mechanism of the polyhydroxyl compounds. Davidson and Cole4 and Berberian and Coleig studied the dielectric properties of the hydrogen-bonded compounds and isoamyl bromide, respectively, and found that there was good agreement between the empirical constants T , calculated from the temperature dependence of the relaxation times and T , calculated from the tempera-
//
0 Dipropylenoglycol 8 2-Ethyl-I,3-hexanediol 2-Methyl-2,4-pentanediol
@
I 08
I 14
I 12
I
10
I 16
IO*/(T-Tml
Figure 7. Relaxation times as a function of the reciprocal of ( T - T-).
Table V : Numerical Values for the Equation 70 = A [B/(T- T m ) ]
+
log
A
Molecule
2-Methyl-2,4-pentanediola Dipropylene glycola 2-Ethyl-1,3-hexanediol" 2,4-Pent anediolb 2,3-Pentanediolb
- 13.24 -14.07 -13.64 -15.33 -15.28
633 793 738 985 985
145 145 160 143 145
5 The difference between the observed and the calculated values of log r0 is within 3 ~ 3 % . Reference 17.
ture dependence of viscosity and between B and B, in the equation
It is supposed from these situations that the mechanism of dielectric relaxation in the polyhydroxyl compounds and isoalkyl halides is closely associated with that of the viscous flow because both dipolar relaxation and viscous flow are governed by the rotational diffusion process. Davidson16reported that the dielectric properties of the isomeric pentanediols depend on the regularity of the hydrogen bonding. It seems that irregularity of the liquid structure with the random intermolecular hydrogen bonding is an important factor for the Davidson-Cole-type dispersion in the polyhydroxyl compounds. The same type of dispersions for isoalkyl halides may be related with the structural irregularity of the supercooled liquids. These irregularly hydrogenbonded clusters characteristic of the polyhydroxyl compounds may not be formed in the weakly hydrogenbonded ethylenediamine oligomers. Thus the relaxa(19) J. 0.Berberian and
R. H. Cole, J. Amer. Chem. Soc., 90, 3100
(1968).
The Journal of Physical Chemistry, Vol. 75, N o . 9 , 1971
1246
SILVERMAN, SOLTZBERG, YANNONI, AND KRUKONIS
tion of the weakly hydrogen-bonded molecules such as ethylenediamine oligomers are different from that of the strongly hydrogen-bonded polyhydroxyl compounds. The dielectric relaxation of aminoethylethanolamine is an intermediate case between those of ethylenediamine oligomers and the polyhydroxyl molecules. The
dielectric dispersions of the polyhydroxyl compounds depend on the liquid structure rather than the molecular structure.
Acknowledgment. The author wishes to thank Professor N. Koizumi for many helpful discussions.
Perchlorodiphenylmethyl Stable Free Radical. X-Ray Analysis of a Disordered Mixed Crystalla by J. Silverman,* L. J. Soltzberg,lbN. F. Yannoni, and A. P. Krukonis A i r Force Cambridge Research Laboratories, Bedford, Massachusetts 01730
(Received August 28, 1970)
Publication costs assisted by A i r Force Cambridge Research Laboratories
A single crystal originally believed to be pure perchlorodiphgnylmethyl free radical, (C&I&CCl, is monoclinic, space group P21/c, with a = 9.71, b = 13.29, c = 14.67 A, fl = 97.1". The X-ray structure determination was supplemented by the analytical techniques of elemental microanalysis, esr spectroscopy, mass spectrometry, and neutron activation analysis in order to characterize a crystalline disorder present in the specimen. While about 37% of the molecules in the crystal are the expected free radical, the crystal also contains about 36% of a related molecule with bromine, probably (CeCl&CBrCl, and also a third species, possibly (CeCl&CHCl. Although the elements of disorder in the structure limit the accuracy of the determination, the main features of the free-radical structure as well as the deformations in the similarly overcrowded molecules are revealed. The "composite molecule" obtained in the X-ray analysis has approximately twofold symmetry with the phenyl rings rotated by 47 and 43' with respect to the trigonal plane of the central carbon atom. The five chlorine atoms of each phenyl ring deviate from planarity in zigzag fashion.
Introduction Ballester and coworkers2 have succeeded in synthesizing a novel series of alkaromatic chlorocarbons, perchlorotoluene being the first example. Many of these CI
I CI-c-CI
CI cl@::
ci compounds have very severe intramolecular steric strain and for this reason act readily as the synthetic precursors for the formation of stable free-radical species in the solid. One of these radicals is analogous to the well known hydrocarbon free radical, diphenylmethyl, namely perchlorodiphenylmethyl (PDAI ; shown below with the unpaired electron indicated by a dot). PDRT was synthesized3 in 1964, and an esr study4 has been reported on the molecule in solution. T h e Journal of Physical Ch,emistry, Vol. '76,N o . 9 , 1971
c'QclCI
CI
PDM (1) (a) Presented before the American Crystallographic Association, Ottawa, Canada, Aug 1970; (b) National Research Council Postdoctoral Research Associate, Jan-Sept 1969. (2) M. Ballester, Pure A p p l . Chem., 15, 123 (1967); Bull. SOC. Chem. Fr., 7 (1966), and references therein. (3) M. Ballester and J. Riera, J. Amer. Chem. Soe., 86,4505 (1964). (4) H.R. Falle, G. R. Luckhurst, A. Horsfield, and M. Ballester, J . Chem. Phys., 50, 258 (1969).
