Indian Journal of Chemistry Vol. 38A, March 1999, pp. 237-243

Excess molar volumes and excess partial molar volumes of diethylene glycol monoethyl ether - n-alcohol mixtures at 298.15 K

Arnalendu Pal' & Gurcharan Dass Department of Chemistry, Kurukshetra University,

Kurukshetra 136 119, India

Received 15 June 1998; revised 7 December 1998

Excess molar volumes V E have been measured for binary mixtures of diethylene glycol monoethyl ether with methanol, ethanol, 1-propanol, I-pentanol and I-hexanol as a function of composition using a continuous-dilution dilatometer at 298.15 K. The excess molar volumes V E are negative over the entire range of composition for the systems diethylene glycol monoethyl ether + methanol, + ethanol , and + I-p;~panol and positive for the remaining systems, diethylene glycol monoethyl ether + I-pentanol, and + I-hexanol. The measured V E values increase towards positive direction with increase in chain length of the n-alcohol. The V E results have been used to estimate the excess partial molar volumes V E . of the components and have also been analysed using the Prigogine - Flory - Patterson (PFP) theory. An analysis of each of the three ·~o'ntributions viz. interactional, free volume and internal pressure to V.,E shows that the free volume effect and internal pressure contribution are negative for all the mixtures, whereas the interactional contribution is negative

for methanol and positive for remaining systems. The behaviour of V./' , V.,E ,i ' and XJ2 (Flory's interaction parameter) with composition and the number of carbon atoms in the alcohol molecule is discussed.

In continuation of our program of research on the physico-chemical properties of binary mixtures contain­ing the oxygen (-0-) and hydroxyl (-OH) functional groupsl .4, we report here a new experimental data of ex­cess molar volumes V E of binary solvent mixtures con-

m

taining diethylene glycol monoethyl ether with metha-nol, ethanol, I-propanol, I-pentanol or I-hexanol over the whole mole fraction range at 298.15 K and at atmos­pheric pressure. The aim of this work is to provide a set of values for the characterization of the molecular inter­action between alkoxyethanol and n-alcohols and also to assess the effect of the chain length of alcohols on excess volumes . The experimental V E results have been

m

analysed here in the light of Prigogine-Flory-Patterson theory). An attempt is also made to rationalize the re­sults by collecting the data from literatures on alkoxyethanols + n-alcohol mixtures.

Materials and Methods

Diethylene glycol monoethyl ether (Fluka , purum , GC > 98%) was used without further purification. Metha­nol (SRL, Bombay, GC min. 99.8%), ethanol (Riedel­de Haen, Germany, GC min. 99.8%), I-propanol (SRL, GC min. 99.5%), I-pentanol (Acros, USA, 99%), and 1-hexanol (SRL, Bombay, GC min. 99%) were dried and fractionally distilled as described elsewhereo. All liquids

were stored in dark bottles to prevent contamination from air and dried over 4"\ molecular sieves to reduce the water content. Prior to measurements, all liquids were partially degassed under vacuum. The purities of the liquid were checked by measuring and comparing the densities at 298.15 K and atmospheric pressure with their corre­sponding literature values6.~. The densities were meas­ured with a bicapillary pycnometer that gave an accu­racy of 5 parts in 105

• The pycnometer was calibrated at 298.15 K with doubly distilled water.

Excess molar volumes, which are accurate to ± 0.003 cm3 mol·l, were measured using a continuous- dilution dilatometer in similar fashion to that described by Dickinson et al lO

• Details of its calibration, experimen­tal set up, and operational procedure have been described previously I . !!. The composition of each mixture was ob­tained with an accuracy of ±.I x 10.4 from the measured apparent masses of the components. All masses were corrected for buoyancy. The measurements over the full mole fraction range were completed by two runs, i.e: one for the alcohol rich regions starting from pure alco­hol and the other from the alkoxyethanol rich regions starting from diethylene glycol monoethyl ether up to the composition of about 50 wt%. A thermostatically controlled, well-stirred water bath whose temperature was controlled to ± 0.01 K was used for all the measure­ments.

238

x

0.0150 0.0290 0.0453 0.0635 0.0825 0.0968 0.1162 0.1328 0.1 565 0.1883 0.2230 0.2545 0.2732

0.0131 0.0393 0.0666 0.0959 0.1265 0.1448 0.1701 0.2089 0.2336 0.2582 0.3157 0.3309

0.0080 0.0243 0.0449 0.0613 0.0733 0.0873 0.1 053 0.1244 0.1422 0.1637 0.1932 0.2244 0.2494 0.26 19 0.2835

INDIAN J CHEM, SEC. A, MARCH 1999

Table 1- Excess molar volumes V.,E and partial molar volumes V m, 1 and V m,2 for x CZHj (OCZH4

))OH +

(I-x) C"Hz,,+ ,OH mixtures at 298.15 K

v.; x v;, Vm,1 Vm,2 Vm, 1 Vm.2

cm'mor l cm'mor l cm'mor l cm'mor l

cm'mor l cm'mor l

X CZHj {O(CH z)z IPH + (I-x) CHpH

-0.058 132.465 40.709 0.2963 -0.559 135.496 40.039 -0.110 132.741 40.675 0.32 15 -0.563 135.60 1 40.000 -0.170 133.038 40.634 0.3418 -0.567 135.674 39.964 -0.230 133.342 40.586 0.3746 -0.569 135.775 39.920 -0.282 133.634 40.536 0.4139 -0.549 135.872 39.876 -0.320 133.834 40.499 0.5000 -0.513 136.019 39.815 -0.360 134.085 40.448 0.5678 -0.465 136.096 39.794 -0.400 134.28 1 40.405 0.6335 -0.419 136.155 39.789 -0.430 134.532 40.345 0.7119 -0.350 136.21 7 39.782 -0.478 134.822 40.267 0.7839 -0.282 136.270 39.751 -0.514 135.806 40.186 0.8744 -0.176 136.329 39.625 -0.539 135.284 40.11 9 0.9418 -0.086 136.360 39.422 -0.550 135.386 40.082

x CZHj {O(CHz)lIPH + (I-x) CzHpH

-0.019 134.536 58.613 0.3654 -0.286 136.008 58.195 -0.066 134.753 58.548 0.3770 -0.287 136.026 58.192 -0.110 135 .015 58.488 0.4002 -0.290 136.060 58.186 -0.149 135. 113 58.433 0.4535 -0.277 136. 128 58.177 -0.182 135.299 58.384 0.5030 -0.267 136.180 58.173 -0.201 135.387 58.358 0.5612 -0.246 136.232 58.174 -0.2 19 135.496 58.326 0.6218 -0.222 136.275 58.180 -0.249 135.64 1 58.286 0.6971 -0.182 136.3 18 58.191 -0.260 135.716 58.265 0.7619 -0.148 136.344 58.201 -0.269 135.785 58.241 0.8662 -0.077 136.367 58.204 -0.278 135 .918 58.215 0.9726 -0.014 136.371 58.161 -0.284 135.947 58.207

x CZHj {O(CHz))PH + ( I-x) C)HpH

-0.005 133.947 75.178 0.3099 -0.084 136.229 75.033 -0.010 135.957 75.178 0.3203 -0.084 136.238 75.029 -0.02 1 135.969 75.175 0.3427 -0.085 136.255 75.022 -0.027 135.982 75 .17 1 0.3540 -0.085 136.264 75.019 -0.031 135.991 75.166 0.3976 -0.084 136.294 75.012 -0.036 136.003 75.160 0.4346 -0.081 136.3 14 75 .012 -0.039 136.020 75 .151 0.4863 -0.074 136.336 75 .018 -0.046 136.039 75.140 0.5371 -0.067 136.350 75.030 -0.052 136.058 75.129 0.5743 -0.062 136.356 75.041 -0.057 136.081 75.115 0.6359 -0.056 136.362 75 .061 -0.064 136. 113 75.096 0.6943 -0.046 136.364 75 .077 -0.072 136. 146 75.076 0.7542 -0.037 136.364 75.085 -0.076 136.172 75.061 0.8040 -0.029 136.364 75.083 -0.080 136.184 75.054 0.8833 -0.0 17 136.366 75.059 -0.082 136.205 75.044 0.9445 -0.010 136.369 75.020

Contd ...

PAL e/ al.: EXCESS MOLAR VOLUMES OF ETHER -n-ALCOHOL MIXTURES 239

Table 1- Excess molar volumes V,,/; and partial molar volumes V m, I and V m,2 fo r x C2H; (OC2H4\OH +

(I-x) CnH1n+IOH mixtures at 298. 15 K (Contd ... )

x ~ v;,

Vm,1 V m,2 X

Vm,1 Vm,2

cm' mor l cm'mor l cm'mor l cm3mor l

cm3mor ' cm'mor l

xC 2H; {O(CH2)JPH + (I-x) C;H"OH

0.0219 0.010 136.840 108.689 0.4511 0.143 136.586 108.83 8 0.0432 0.016 136.834 108.699 0.4722 0.145 136.571 108.847 0.0629 0.029 136.830 108.707 0.4858 0.146 136.562 108.853 0.0886 0.042 136.82 1 108.717 0.5084 0.145 136.546 108.864 0.1202 0.052 136.807 108.728 0.5463 0.144 136.520 108.882 0.1482 0.067 136.793 108.736 0.5747 0. 14 1 136.502 108.897 0. 1702 0.077 136.781 108.743 0.60 16 0.136 136.486 108.9 11 0.2041 0.079 136.761 108.753 0.6373 0.131 136.465 108.930 0.2358 0.100 136.741 108.763 0.6795 0.126 136.444 108.954 0.2684 0. 11 1 136.719 108.772 0.7 188 0.114 136.426 108.977 0.3086 0. 121 136.691 108.785 0.7511 0.101 136.4 13 108.997 0.3398 0.126 136.668 108.796 0.7960 0.088 136.398 109.024 0.3676 0.130 136.648 108.805 0.8527 0.063 136.384 109.058 0.4053 0.136 136.620 108.820 0.9389 0.027 136.373 109. 107 0.4382 0.144 136.596 108.833 0.9728 0.015 136.37 1 109. 122

x C2H; {O(CH2\ lPH + ( I-x ) CfiH 11 0H

0.0367 0.030 137.117 125.340 0.5000 0.219 136.640 125.603 0.0626 0.049 137.099 125 .352 0.5474 0.220 136.594 125 .638 0.1273 0.095 137.041 125 .383 0.5920 0.210 136.554 125 .673 0. 1895 0.127 136.978 125.4 14 0.6195 0.205 136.531 125 .675 0.2324 0.150 136.93 1 125.437 0.6566 0.1 90 136.502 125.727 0.2790 0.168 136.879 125.463 0.709 1 0. 173 136.466 125.794 0.3420 0.200 136.809 125.499 0.7649 0.148 136.433 125.806 0.3913 0.205 136.754 125.530 0.8030 0.130 136.414 125.868 0.3961 0.208 136.748 125 .533 0.8671 0.095 136.39 1 125 .93 1 0.4 168 0.215 136.726 125.546 0.9176 0.060 136.378 125.986 0.4312 0.218 136.711 125.553 0.9710 0.D25 136.372 126.043 0.4553 0.219 136.685 125.572

Results and Discussion The experimental values of excess molar volumes V E

11/

where Ai is the polynomial coefficients, k is the polyno­mial degree and x is the mole fraction of alkoxyethanol , respect ively. The values of the coefficients A were evalu-for the systems of diethylene glycol monoethy l ether with

five alcohols are presented as a function of mole frac­tion in Table I and are graphica ll y represented in Fig. I . The va lues of V E for all systems were fitted to an em-

11/

pirical equation of the form:

n

V /: =x( l -x) L A ( 1-2x)i //I 1=0 J

.. . ( I )

J ated by the method of leas t squares with all points weighted equally and are listed in Tab le 2 along with standard deviations s (V E):

11/

... (2)

where N is the number of experimental data. For all mix­tures s(V 1:: ) < 0.003, in accord with the good accuracy

111 -

attainable with the d il atometer used here .

240 INDIAN J CHEM, SEC. A, MARCH 1999

XXXX JC X X x 0.2

x · x 000000000<>0000 0 x o x

0 ·' x 0 0 00 x 00 0

• 00 • . .0'0 '00 .

0 o • lP, o 0 .. D

0 D

06 ODD D D D D

DaooDctO o D .. 0 .. -0·' o ..

E .. .. M~

. 0 <- .. 0

-0.2 .. .. .. ..... o · .. .. WE .... .. .. > 0 A t.66 .. 0

-0 .3 0

0 o·

-0.4 0 0

0

0 0

-0 .5 0 o · 0

00000

0

-0·6

0 0.2 0.4 0 .6 0.8 ,.0 x

Fig. 1- Excess molar volumes V"., for [x C2 Hj {O(CH2 ) 2 ) 2 OH + (I-X)C

nH

2n+IOH]: O,methanol, t:. ,ethanol ; 0, I-pro­

panol;e,l-butanol (ref 14) ; 0, I-pentanol; x,l­hexanol.

We have also calculated excess partial molar vol-

urnes E * V m, I = (V m.1 - V m.l) and

V;'2 = (Vm.2- V:.2)from VmE whereV~. 1 andV~.2 represent the molar volume of the components. The par­

tial molar volumes Vm.1 and Vm.2 are given in

Table I, while Fig. 2 shows the excess partial molar vol­

umes, Vm.1 and V!.2 plotted against x . The partial mo­

lar volumes V m.1 and Vm.2 in these mixtures were

evaluated ' 2. 13 over the whole composition range by us­

ing Eqs (3) and (4) :

Vm.1 = v./' +V~.I-(I-X)(OV}/o (I-X») P. T ... (3)

Vm.2 = V .. E V* + m,2 ... (4)

The derivatives in Eqs (3) and (4) were obtained by differentiation of Eq. (l).

Excess volume against composition plots in Fig. I show that VmE are negative over the entire range of com­position for methanol, ethanol, and I-propanol and positive in the case of I-butanol (reported by Cobos et al. '4 from density values obtained using vibrating-tube densitometer are also plotted in Fig. 1) , I-pentanol and I-hexanol at 298.15 K. For the same value of x, the ex­cess V E increases with increase in the chain length of

m

alcohol. The location of the V E minimum shifts from x m

= 0.37 for methanol to x = 0.35 for I-propanol whereas the V E maximum shifts from x = 0.64 for I-butanol to x

m

= 0.55 for I-hexanol. It is well-known that alkoxyethanols exist as associ­

ated structures like the alcohols '5. '7 in the liquid state; the association may be due to the intramolecular hydro­gen bond formation between the ether oxygen atom and the -OH group, as in the case of alcohols, this associa­tion may be through the H-bonding of their -OH groups . The magnitude of V £ is the result of contributions from

m

different effects which can be divided into physical, chemical and structural contributions. The physical in­teractions involve mainly disruption of liquid order on mixing; unfavourable interactions between the same unlike molecules produce positive V E values. The chemi-

m

calor specific interactions result in a volume decrease and these include possible depolymerisation of self-as­sociated alkoxyethanols by the alcohols and self associ­ated alcohols by the alkoxyethanols and/or formation of new hydrogen bonds between alkoxyalkanols and

Table 2- Parameters Aj and standard deviations O'(V} ) for least-squares representations by equation(l ) of V f: for studied mixtures at 298.15 K

'" Diethylene glycol monoethyl ether All AI A2 A

J O'(V",E)

(cm1mol·l )

(I-x) methanol -2.052 1.157 -0.864 0.147 0.003 (I-x) ethanol -1.071 0.565 -0.163 0.153 0.003 (I-x) propanol -0.297 0.250 -0.019 -0.141 0.002 ( I-x) pentanol 0.579 -0.001 -0.115 -0.006 0.002 ( I-x) hexanol. 0.876 -0.021 -0. 115 0.012 0.003

PAL el al. : EXCESS MOLAR VOLUMES OF ETHER -Il-ALCOHOL MIXTURES 24 1

Table 3- Calcul ated values of the three contribution to the excess volume from the Prigoginc-Flory-Patterson theory fo r diethylene glycol monoethyl ether + alcohols at 298. 15 K

X12 Calculated contribution

(J cm-» Interaction Free volume p'effect

(I -x) methanol -24_ 11 22 -0.23 15 -0.084 1 -0.1963 ( I-x) eth anol. 0.4026 0.0048 -0.0563 -0.2 164 (I-x) propanol 8.6990 0. 11 66 -0.0292 -0. 16 12

( I-x) butanol 10.7600 0. 1560 -0.0 105 -0. 1099 ( I-x) pentanol 14.2 197 0.2 147 -0.0036 -0.0659 ( I-x) hexanol. 15.7058 0.2549 -0.001 0 -0.0349

Table 4 - Parameters of pure components at 298. 15 K

Component k/TPa-') V V(cm>mol-') V'(cm>mol-') T '(K) p. (J em-I)

Diethylene glycol

monoethyl ether 627.56 1.2 153 136.37

Methanol 1265.77 1.2875 40.75

Ethanol. 11 58.22 1.2663 58.65

I-Propanol 10 18.58 1.2483 75 .1 8

I-Butanol 940. 15 1.2336 9 1.96

I-Pentanol 883 .79 1.2253 108 .68

I-Hexnanol. 842.39 1.2204 125 .32

alcohols and other complex-forming interactions. Struc­tural effec ts ari sing from interstiti al accommodation due to differences in the molar vo lumes and free volumes 'x

between liquid components contribute to negati ve V}

values . The V E values increase in the sequence methanol <

11/

eth anol < I-propanol < I-butanol < I-pentanol < 1-hexanol. The interactions between die thylene g lyco l monoethyl ether and methanol are relati vely strong. In­creasing the chain length of the alcohol tends to dilute

the interaction between die thylene g lycol diethyl ether and alcohol; V E decreases and becomes pos itive for the

"' larger alcohols. It is observed that the molar vo lumes of the alcohols increase with chain length and the free vol­umes fo ll ow in verse trend (Table 3). Therefore, the struc­tural contributi ons ari sing from insterstiti al accommo­dati on due to difference in molar vo lume and free vo l­ume between the components does not play any s igni fi­cant role in the magnitude of V E. In fact, we observe

11/

s imilar characteri stics for V E as in mi xtures of diethyl-11/

ene g lyco l monomethy l ether2. , ~ or e th yle ne g lyco l monoethyl ether20 with alcohols: a marked decrease in the algebra ic value of V E here . It is suggested 1 ~ . 21 that

11/

increas in g the number of OC2H4

groups or repl ac ing methyl by e thyl groups leads to more negati ve excess

molar vo lumes .

11 2.2 1 5758 593.63

3 1.65 4752 468.74

46.32 4989 450.75

60.23 5223 457.49

74.55 5442 449.78

88.70 5579 452.30

102.69 5664 458.6 1

The excess partial molar vo lumes increase system­atically with increasing chain length of the alcoho l. T he sharp increase in V,}.I values at small x (Fig . 2) prov ides evidence for the breaking of the self-assoc iated struc­ture of diethylene g lycol monoethyl ether. The increase in V E 7 values at higher x suggests the breaking of the

III ._

alcohol structure in thi s concentration range. Thi s ob-servation leads us to suggest that there is relatively strong hydrogen bonds formati on between die thylene g lyco l monoethyl ether and methanol molecules rathe r than structure breaking effect.

Prigog ine-Flory -Patterson Theory The Prigogine-F lory-Patterson (PFP) theory5.22.26 has

been commonly employed to estimate theoreticall y and analyse the excess the rmodynamic fun ctions. In thi s theory, V E is divided into an interactional contributi on,

11/

a free volume contributi on and internal pressure contri -bution. The e xpress ion for V E which separates the th ree

11/

contributions is g iven as

E VITI

* * "I + X2V2

(interactionalf

(v 1/3 - 1)\1 2/3 'l{ 82

[ ( 4/3) v- - 1/3 _ 1] P; X 12

242 INDI AN J CHEM, SEC. A, MARCH 1999

1.0

EZ

Dz

Cz 0.0

8z

-1 ·0 ' 0

Al ~ ~~. "-,...

wE' >

wE

> -2.0 -2.0

-3 .0

L---L-_.L..:.---L_ ...L..---1.-..1-----'- ....I---'--l-4.0

0 .2 0.4 0.6 0·8 1.0 x

Fig. 2- Pa rti a l molar exccss vo lum cs VEw . 1 and VI""" for

[xClI5{O(CH,), lPH(I) + ( I-x) CnH1n•1 OH (2)]: A, methanol; B, ethanol; C, I-propanol; D, I-pentanol; E, I-hexanol.

2 ( \'1':-'2 ) [( 14/9) v - I ] \jf\jf ____ --,-,-__ ....:.1--=.2 ( V curvature

[(4/3 )v- 1/3 _1]\i

... (5)

where lfI represents the contact energy fraction and is

g iven by

... (6)

The va lues of the parameters for the pure liquid com­ponents and the mixture are obtained us ing the Flory theory2l24 . The parameters for the pure liquid compo­nents derived by using Flory 's ex press ion are given in

Table 4. The contact interacti on parameter X12 required for the

calcul at ion of V E using the Flory-Patterson theory was adjusted by fittil~'~ the experimental V",E data at equimolar compositi on for each system investigated here . The ca l­cul ated equimolar va lues of the three contribut ions to­gether with the X

I2 parameter fo r each liquid mixture are

li sted in Table 3.

)0

20

c;'~ 10

" "-~ a ci

-~ - 10

-20

-)0 0 5 6

Fig. 3- Plot of interacti on energy parameter (XJ against number of carbon atoms in alcohols (n= 1-6).

Study of the data in Table 3 reveals th at both the p' contribution and free volume effects are negative for a ll the mixtures whereas the interactional contribution is positive for all mixtures except methanol which has a highly negative interactional term .

The interactional contribution, which is proportional

to Xll

' when negat ive for methanol system, suggests re la­tive ly strong intermolecular hydrogen bonding interac­tion with diethylene glycol monoethyl ether.

However, it shows pos iti ve for other systems, sug­gesting that the absence of hydrogen bonding or other specific interactions. Also, Fig.3 shows the variation of X

l l w ith the number of carbon atoms in a lcohols.

Th e free vo lume e ffec t whi c h is pro porti ona l to

2 - (VI - \12)' is a measure of geometrical o r interstiti al

accommodation . It becomes less negati ve as the differ­

ence between the reduced volume v of two compone nts

in the mixture decreases, as shown in Table 3. It sug­gests that , as the chain length of the alcoho l increases, interstitial accommodation becomes less significant, re­sulting V,,/' decreases. T he p' effect, which is propor-

2 tional to - (~ - \12) (PI * - p/ ), is negati ve for all sys-

tems. It appears that the dominant role is played by the difference in internal pressures and reduced vo lumes of the respective components. Thi s is the main parameter for deciding the sign and magnitude of excess vo lumes as the ir may be pos itive o r negative on the relative cohe­s ive energy of the ex panded and less ex panded compo­nent.

Acknowledgement Thi s work was financed by a DST(No. SP/SIIH-16/

94) and CSIR grant (No. 01 ( I 428)/96-EMR-II).

PAL el 01.: EXCESS MOLAR VOLUMES OF ETHER -II -ALCOHOL MIXTURES 243

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