Transport Parameter Dependence on Intermolecular Forces - ACS

Chapter 6

Transport Parameter Dependence on Intermolecular Forces Marvin Charton

Downloaded by COLUMBIA UNIV on June 26, 2012 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0606.ch006

Chemistry Department, Pratt Institute, DeKalb Avenue and Hall Street, Brooklyn, NY 11205

The intermolecular force (IMF) model provides a much better quantitative description of transport parameters for substituted benzenes and alkanes when the dipole moment μ is included as a parameter and the steric effect is modeled by the multiparametric segmental method. Use of μ in place of μ gave poorer results. Attempts at improving the parameterization for hydrogen bonding and for charged substituents were unsuccessful. In parameterizing the hydrogen bonding it is necessary to take into account the levelling effect in aqueous phases which results in the formation of the greatest possible number of hydrogen bonds between water and substrate. The general form of the IMF equation may now be written as: 2

Q =Lσ +Dσ +Rσ +Mµ +Aα +H n +H n +Ii +B n +B n +SΨ +B ° X

lX

dX

eX

X

X

1

HX

2

nX

X

DX

DX

AX

AX

X

Sets of log Ρ values for XG where the hybridization of the C atom of the XC bond is the same throughout may be combined into a superset by using a parameter n which accounts for the number of C atoms in G. Sets of log k' values determined under varying conditions of mobile phase or column packing may be combined by the ζ method. The IMF model provides an explanation for the success of the Hansch - Fujita model in the quantitative description of bioactivities. It also shows that bioactivities may be directly correlated with the IMF equation. CG

Our overall objective in this series of papers has been to determine the basis of the Hansch - Fujita model for the quantitative description of bioactivity. As the keystone of this model is the use of transport parameters such as the logarithms of the partition coefficient Ρ and the high pressure liquid chromatography capacity factor k' it is therefore necessary to determine their nature. These and other related transport parameters are a measure of the difference in intermolecular forces between substrate initial phase and those between substrate - final phase. Thus: 0097-6156/95/0606-0075$12.25/0 © 1995 American Chemical Society In Classical and Three-Dimensional QSAR in Agrochemistry; Hansch, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

76

CLASSICAL AND THREE-DIMENSIONAL QSAR IN AGROCHEMISTRY


τ = A G . = G,. , - G.. ,

(1)

where G is the Gibbs free energy, i denotes the initial and f the final phase, and imf indicates intermolecular forces. These intermolecular forces are listed in Table 1 together with the quantities on which they depend. The data sets studied in this work are of the form X G where: 1. X is a variable substituent. 2. The skeletal group G to which X is bonded is usually constant. In order to parameterize the intermolecular forces (imf) between X G and its surroundings it is necessary to consider: 1. The imf between X and its surroundings. These are modelled by parameters that describe the hydrogen bonding, bond moment, polarizability, and ionizability of X. 2. The effect of X on the imf between G and its surroundings. When G is sp hybridized in whole or in part X may exert an effect on: a. Hydrogen bonding to G which may act as a hydrogen acceptor. b. Charge transfer involving G which may act as either an electron acceptor or an electron donor. c. Steric effects on the solvation of G. When G is wholly sp hybridized X may exert an effect on H atoms bound to the same C atom which affects the extent to which they form weak hydrogen bonds. The effects of X on the imf between G and its surroundings are modelled by the electrical effect parameters. The steric effect of X on the solvation of G is accounted for by a steric parameterization. 2

3

Table 1. Intermolecular Forces and the Quantities Upon Which They Depend. Intermolecular Force

Quantity

Molecule - molecule Hydrogen bonding (hb)

E

Dipole - dipole (dd) Dipole - induced dipole (di) Induced dipole - induced dipole (ii) Charge transfer (ct) affinity

dipole moment dipole moment, polarizability polarizability ionization potential, electron

h b

Ion - molecule ion - dipole (Id) ion - induced dipole (Ii)

ionic charge, dipole moment ionic charge, polarizability

In earlier work we have shown that transport parameters including log Ρ, π, and chromatographic properties such as log k', R , and retention indices are quantitatively modelled by the intermolecular force (IMF) equation. " The IMF equation has been written in its most general form in the past as: M

1

5

In Classical and Three-Dimensional QSAR in Agrochemistry; Hansch, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

6. CHARTON Q =L o^Do^R X

77

Transport Parameter Dependence on IMF ο +Α ^H n ^H n^Ii^B n ^B^n^S^^B Λ

x

H

2

DX

°

D

(2)

where: Q is the quantity to be correlated. σ is the localized electrical effect parameter. It is identical to the o and o κ

o o

d X

e X

x

F

constants.

is the intrinsic delocalized electrical effect parameter. is the electronic demand sensitivity electrical effect parameter.

α is a polarizability parameter. It is defined by the equation: α = (MR - MRJI100 = (MR ~ 0.0103)/100 X

(3)

where M R and M R are the group molar refractivities of X and Η respectively. n and n are hydrogen bonding parameters. n is equal to the number of OH or N H bonds in X while n„ is equal to the number of lone pairs on Ο or Ν atoms in X . i is a parameter which accounts for the effects of the charge on ionic groups. It takes the value 1 when the side chain is ionized and 0 when it is not. n and n are charge transfer parameters. n is 1 when X acts as an electron donor and 0 when it cannot. n is 1 when X can function as an electron acceptor and 0 when it cannot. ψ is an appropriate steric effect parameterization, ψ may be monoparametric, using the υ steric parameters; multiparametric, using a branching model such as the simple branching equation, where: X


X

H

n

D

A

H

H

D

A

M

£ψ = Β η χ

χ

+Bn 2

+ B^

2

+ ... =

(4)

or the segmental model, where: £ψ = S v x

%

+ S x> 2

2 +

£ υ 3

3

+

... = Σ £ . υ , ( 5 ) i-l

or a composite model using a combination of the υ parameter and the branching model. In this work we consider several problems involving the improvement of the parameterization in the IMF equation. 1. Examination of the residuals in the correlation of log Ρ or π for PhX with the IMF equation shows that the model is incomplete. This does not seem to be the case for A k X (Ak = alkyl) or for aromatic data sets in which a constant substituent results in a sufficiently large permanent dipole moment. 2. We have considered the possibility of improving the parameterization of hydrogen bonding by the use of the parameters proposed by Abraham and coworkers. 3. We have also considered the possibility of improving the parameterization for ionic groups by means of a parameter which reflects acid and/or base strength. 4. We have reexamined the steric effect parameterization to determine whether it can be improved by use of the segmental method. We have also considered the possibility that the first segment may exert a steric effect only when it is larger than the half thickness of a benzene ring. 7



78 Method

We have correlated suitable test sets of transport parameters with appropriate variants of the IMF equation by means of multiple linear regression analysis. The substituent constants required for the correlations were taken when possible from our compilations. If values were unavailable they were estimated by methods described therein. ' " The dipole moments were taken from the compilations of McClellan. 6 8

10


1112

Test Set Requirements. The requirements for a suitable test set include: 1. A sufficient number of data points to permit a test of the IMF model. Our experience suggests that the minimum number is such that there will be at least three degrees of freedom per independent variable for chemical property data sets. 2. A wide range of substituent types in order to encompass a sufficient range of each of the variables and to minimize clustering. 3. Reliable determination of the transport parameters in the data set, preferably in the same laboratory in order to maximize the cancellation of experimental error. The test sets chosen are reported in Table 3. Composition of the Substituent Effect. We find it convenient in discussing our results to make use of the per cent contribution, Q of each independent variable in the regression equation. This quantity is given by the expression: ς

= 100|β |/Ϊ|β | Λ

(6)

Λ

where aj is the regression coefficient of the i-th independent variable and Xj is its value for some reference group. In this work we have defined a hypothetical reference group for which: σ

ι

=

°d

=

M

=

n

H

=

"η

=

υ

i^ ι

= Υ

2

=

Υ

3

=

n

D

=

n

A

=

U ^ = 0.1, α = 0.2, ζ = 0.3. c

Results PhX Transport Parameters. Our original parameterization of dipole-dipole and dipoleinduced dipole interactions made use of electrical effect parameters to account for the dipole moment. We find that this is fully justified when: 1. The substituent is incapable of exerting a delocalized electrical effect. 2. The substrates have a large innate dipole moment. In the case of PhX transport parameters neither of these requirements is met. It is therefore necessary to use as a parameter. The problem occurs because the dipole dipole and dipole - induced dipole reactions depend on the magnitude of the moment and not its direction. The electrical effect constants will not represent the dipole moment unless the sign of the charge is taken into account if delocalized electrical effects can occur. Thus, correlation of dipole moments for PhX with the L D R equation: (7)


6. CHARTON

79

Transport Parameter Dependence on IMF

gives the regression equation 8 when the moments of groups (other than halogens) with negative o values are assigned negative values and only symmetric groups are included in the data set. d

Vphx

=

5.47(±0.359)σ^ + 4.30(±0.44φσ^ + 6.94(±1.91)o^ + 0.420(±0.172)

2

(8)

2

100R , 96.23; F, 110.7; S , 0.342; S°, 0.222; Adj. 100R , 95.69; P , 44.0 ± 5.25; η , 1.61 ± 0.411; n = 17. C 52.3; C , 41.1; C , 6.63. Mt

D


b

d

c

Inclusion of nonsymmetric substituents in the data set gave equation 9. The fit is poorer than that obtained for the symmetric groups alone. Of the regression coefficients only R has changed significantly. As the symmetric group data set does not include groups with a predominant donor delocalized effect such as OMe, SMe, and N H it is not a completely representative set and some differences between equations 8 and 9 are therefore to be expected. 2

Vpta

=

4.98 (±0.448)

+ 4.33 (±0.310)σ^ + 1.50(±1.47)o + 0.169(±0.187) rf

2

(9)

2

100R , 91.72; F, 147.8; S , 0.537; S°, 0.302; Adj. 100R , 91.32; P , 46.5 ± 4.30; η , 0.347 ± 0.339; n = 44.C.,,52.7; C , 45.8; C , 1.59. est

D

d

e

The difference lies in the values of R and h which are not significant in equation 9. The values of L and D in equation 9 are not significantly different from those in equation 8. Correlation of dipole moments for symmetric M e X with the L D R equation gave the regression equation 10: μ

ΜβΧ

= 5.11 (±0.497)

+ 1.99(±0.541)σ

2

With groups G hybridized sp (G is phenyl, vinyl, styryl, 1- or 2- naphthyl, 4-biphenyl, anthryl, or phenanthryl) (set 12, Table 3) the best regression equation is: Ρ =1.64(±0.280)σ^+2.00(±0.692)σ ,-0.421(±0.0428)μ , + 6.64(±0.415) α - 0.397(^0.059)^- 0.186(±0.028) + 0.690(±0.157)v +0.281(±0.017)w + 0.483(±0.158) (23) ΛΓΟ

ΛΑ

Λ

χ

WnAr

ur

2

co

2

100R , 90.92; Adj. 100R , 90.32; F, 131.4; S^, 0.344; S°, 0.314; n, 114. C „ 31.9; C , 3.90; C , 25.8; C 8.19; C , 13.4; C ^ , 7.72; C 3.62; C , 5.46. E

A

P

m

U L

N C

Substitution of υ for υ gives as the best regression equation: Δ

l

logP =1.55(±0.279)o + 2.03 (±0.692) σ^-0.3 94(±0.0415) μ + 6.95(±0.405)α - 0.381^0.059)^-0.194^0.027)^ + 0.943(±0.216) υ ,+ 0.274(±0.016)n + 0.765 (±0.13 8) (24) ro

|r

χ

χ

ΔΛ

2

CQ

2

100R , 90.91; Adj. 100R , 90.31; F, 131.3; S^, 0.345; S°, 0.314; n, 114. Q , 31.9; C , 4.19; C . , 28.6; C.,, 8.11; C , 9.71; C „ H , 7.85; C , 3.99; C , 5.64. C

U A

M

N C

There is no real difference between the results obtained using υ and those obtained using υ . When G is alkyl (has only sp hybridized C atoms) (set 11, Table 3) the best regression equation is: λ

Δ

3

\ogP = 1.18(±0.270)0^ + 0.642(^.132)0^ + 4.79(±0.637)0^ - 0.5 8 8 (±0.045 0)μ^ + 7.91 (±0A56)a - 0.395(^.0521)^ - 0.276(±0.0262)« + 0.458(±0.168)υ , + 0.522(±0.0188)« + 0.804(±0.0953) (25) XQ

x

ηΛΓ


2Α

86


2

2

100R , 94.09; Adj. 100R , 93.71; F, 219.3; S^, 0.309; S°, 0.253; n, 134. Ç, 19.3; C* 10.5; C„ 7.82; C„ 25.8; C 9.61; C , 7.47; C ^ , 6.46; C.,, 4.51; C , 8.52. p

u2

nC

3

We have examined a second example in which X is bonded to sp hybridized carbon atoms in G where G is (CH ) Ph (set 21, Table 3). The correlation equation used is again eq. 22 but in this case the n ^ parameter is equal to the number of C H groups in G, the Ph group is not considered as it is constant throughout the data set. The best regression equation obtained is: 2

n

2

l o g P ^ = 1.15(±0320)o^+0726(±0.168)o^+4.34(±0.726)o^ - 0.521 (±0.054)μ

χ


+ 8.35(^.575)0^-0.310(^.06)^-0.255(^.024^ + 0.420(±0.042)H +2.46(±0.127)

(26)

co

2

2

100R , 93.61; Adj. 100R , 92.90; F, 113.5; S^, 0.272; S°, 0.271; n, 71. Q, 21.0; C , 13.2; C , 7.91; C , 30.4; C 9.49; C ^ , 5.65; C 4.64; C , 7.66. d

e

a

p

m

nC

Except for a lack of dependence on υ the resemblance between the coefficients of equation 25 and those of equation 26 is striking. 2

Combination of Data Sets Studied in Different Media. We have shown that it is possible to combine data sets studied under different conditions or having different structural features into a single data set by means of internal parameters. This technique, which we have called the Zeta method , requires the definition of the experimentally determined quantities for some reference substituent X° common to all of the data sets to be combined as values of the parameter ζ. The parameter ζ then accounts for the conditions or structural features which differentiate between the subsets. The reference substituent X° must be chosen so that it is sensitive to the conditions of interest. In all of the sets we have studied we have chosen the O H group as the reference substituent. As it is capable of acting as both a lone pair hydrogen acceptor and a hydrogen donor in hydrogen bonding it is well suited for parameterization of media effects. The correlation equation used in this method is obtained by simply adding the term Ζ ζ to the correlation equation used for the subsets. Based on our results above the general correlation equation may therefore be written as: 14

β ^

σ

*

+

Ζ > σ ^

+

*

σ

^

+

^

(27)

The data for all of the sets studied is given in Table 3. The segmental method was again used as the steric parameterization. Values of the transport parameter T for 4 substituted benzenesulfonamides (set 31) were correlated with equation 27. T is defined in a manner analogous to the definition of π by the equation: w

w

where k is obtained by extrapolating to pure water the capacity factor k' determined in water -methanol or water - acetonitrile mixtures by reversed phase high performance liquid chromatography. X is the substituent of interest, and Ζ is either a constant substituent or H. The best regression equation obtained is: w


6. CHARTON τ

87


= 0.779(^0.284)0^ + 4.35(±0.997)0^ + 8.62(±0.490)α - 0.148(±0.0384)μ - 0.360(±0.0559)«^ + 0.191 (±0.0830) (29)

ψ χ

χ

2

χ

2

ÎOOR , 95.52; Adj. 100R , 94.98; F, 136.4; S , 0.189; S°, 0.231; n, 38. Q, 22.6; C , 12.6; C , 50.0;C.,,4.30; C ^ , 10.5. cst

e

a

In this set the term in ζ is not significant. As the k values used to define τ have been extrapolated to pure water this is not surprising. Values of log k' for 3 - and 4 - substituted phenylacetylanilides (sets 32m and 32p respectively) in 50 % v/v aqueous methanol, 70 % v/v aqueous methanol, and (40 - 5 55) % v/v methanol - tetrahydrofiiran - water were correlated with equation 27. The best regression equations are for set 32m:


w

Logk = 1.60(±0.355)σ^ + 0.402(±0.137)σ^ - 2.60(±0.800)σ^ - 0.318(±0.0702^ - 0.309(±0.0659)« - 0.0760(±0.0197)« + 0.610(±0.115)υ + 0.310^0.123)^ + 1.14(±0.0459)ζ + 0.363(±0.0653) (30) x

//ΛΓ

ηΛΓ

1ΛΓ

Α/

2

2

100R , 95.17; Adj. 100R , 94.37; F, 103.0; S , 0.134; S°, 0.242; η, 57. Q, 37.8; C* 9.51; 6.18; C 7.53; C , 14.4; C , 7.34; C ^ , 7.31; C , 1.80; C , 8.08. and for set 32p: cst

F

0l

u2

m

c

Logk = 16.0(±3.74)σ^ + 17.5^4.63)0^ - 90.5(±27.8)o^ - 44.5(±10.2)0^ - 5.35(±1.34)μ^ + 7.72(±2.4\)η + 1.23(^.341)^ + 18.4(±4.75)υ^ + 24.0 (±6.73) + 1.18(^.0332)^ + 0.518(±0.0386) (31) x

Ηχ

2

2

100R , 98.97; Adj. 100R , 98.51; F, 182.5; S^, 0.0665; S°, 0.128; n, 30. C 14.7;C.,,16.1;C.,8.34; C , 8.20; C 4.93; C , 17.0; C , 22.1; C ^ , 7.11; C ^ , 1.14; C , 0.325. b

a

F

0 l

u2

c

We suspect that equation 31 is an artifact as its coefficients other than Ζ are so very much larger than those of equation 30. Values of log k' for substituted benzenes in these same solvent mixtures (set 33) were also correlated with equation 27 giving the regression equation: logfcp^=1.50(±0.461)o^+ 0.402(^.187)0^- 4.49(±1.14)o - 0.428(±0.0936) - 0.489(±0.079)«^- 0.0948(±0.026)«^ + 0.626^0.158)^ + 1.15(±0.091)ζ + 0.776(±0.090) (32) eAr

μΛΓ

Α/

2

2

100R , 90.61; Adj. 100R , 89.08; F, 50.67; S^, 0.180; S°, 0.338; n, 51. Q, 34.7; C , 9.30; C , 10.3;C.,,9.86; C , 14.4; C ^ , 11.3; C ^ , 2.18; C , 7.95. d

c

B l

c

Correlation with equation 26 of log k' values for substituted benzenes in aqueous methanol, acetonitrile, and tetrahydrofuran as the mobile phase (set 34) gave as the best regression equation: logk = 1.21(±0.391)o^ + 4.32(±1.72)o^ + 6.40(±0.801)α^ - 0.389(±0.0660^ - 0.837(±0.130)w + L06(±0242)v + 0.354(^.138)^ + 1.19(±0.162) (33) phx

flAr

lx


88


2

2

100R , 87.73; Adj. 100R , 86.35; F, 53.14; S , 0.280; S°, 0.376; n, 60. C 22.7; C , 8.14; C , 24.1;C.,,7.33; C , 19.9; C ^ , 15.8; C , 2.00. est

b

e

a

ul

c

Finally, we have correlated with equation 27 log k' values for a set of substituted benzenes in which the medium variation is in the column packing (set 35). The bonded phases studied were pentafluorophenyl dimethyl silane, heptafluoroisopropoxypropyl dimethyl silane, heptadecafluorodecyl dimethyl silane, and decyl dimethyl silane. The value for X = Bu when the bonded phase is decyl dimethyl silane was excluded as an outlier. The best regression equation obtained was: = 0

3 0 3

1 4 3

σ


*ρω- · (^· ) ^ + 0.279(±0.0998)υ^ + 1.27(±0.0743)ζ^-0.805(^.108)/^ + 0.725(±0.079φ 2

(34)

2

100R , 88.87; Adj. 100R , 88.07; F, 93.56; S^, 0.175; S°, 0.349; n, 90. C„ 11.8; C., 11.8;C.,,6.38; C , 10.8; C ^ , 13.2; Q, 31.2; C , 14.8. u l

c

These results demonstrate the validity of the application of the Zeta method to transport parameters. They also provide further evidence of the importance of μ as a parameter and the utility of the segmental parameterization of the steric effect. Discussion Parameters. The combination of the use of the dipole moment as a parameter and the use of the segmental model for parameterizing the steric effect have resulted in a very dramatic improvement in the quality of the model. The dipole moment should be required as a parameter whenever the permanent dipole moment of the unsubstituted substrate is significantly less than that of the largest moment of opposite sign of any substituent in the data set. This is a consequence of the additivity of group moments. It is not surprising that the dipole moment gives somewhat better results than does its square. As was noted above the use of the latter was derived for the case of random orientations of the interacting molecules. If the interaction is between oriented molecules μ is the preferred parameter. The dipole moments used for all of the members of set 12 were those of the corresponding PhX. The justification for this was the assumption that the actual variable was the C[sp ]-X bond moment of which the PhX dipole moment is a measure. An analogous approach was applied to sets 12 and 21. The required parameter was assumed to be the bond moment of the C[sp ]-X bond of which the M e X dipole moments are a measure, and were therefore used as parameters. The success of the model supports the assumption that the bond moment is the required parameter is justified. The need for a steric effect parameterization presumably results from different steric effects on solvation of the substituted substrate in the initial and final phases. It is noteworthy that generally in sets where the substituent is bonded to an sp hybridized carbon atom the steric effect occurs only at the first segment. By contrast, in sets where the substituent is bonded to an sp hybridized carbon atom no steric effect occurs at the first segment. 2

3

2

3


6. CHARTON

89


The n and i parameters seem to be much more effective than the a and i° parameters respectively. We believe that in the case of the a parameter this is due to the existence of a leveling effect in the systems studied. When either the initial or the final phase is aqueous the concentration of water is not less than 55 molar. In this phase any substratewater hydrogen bond that can form will do so. Parameters which are derived from equilibrium constants measured for dilute solutions in nonpolar solvents will not be useful in modelling the hydrogen bonding in an aqueous phase. There is a hydrogen bonding problem which we have not yet addressed entirely. The aromatic ring is capable of hydrogen bonding. Some or all of the electrical effect parameters are significant in all of the data sets studied. Their purpose is most likely to account for fact that there is a solvent effect on the dipole moment. The group dipole moments we have used as parameters were obtained from gas phase data when possible, otherwise they were obtained in nonpolar solvents. The values of the group moments in water are probably very different from these. When the G group of X G is composed of sp hybridized C atoms the electrical effect parameters may also account for the effect of X on charge transfer and hydrogen bond acceptor interactions of G We may obtain further insight into the parameterization by comparing predicted and observed signs of the coefficients of the regression equations obtained for correlations of log Ρ values. In partition studies water is the initial phase and the organic solvent is the final phase. The interaction between the substrate and the initial phase should be given by: H

H


H

2

Q +

H

L

-

X

+

W°1X

n

+

2W nX

D

+

W°dX +

V *

R

+

W°eX

B

+

DW»DX

M

+

W*X

B

+

AW»AX

A

+

W«X

S

W^X

+

H

1W"HX 35

Κ

( >

while that in the final phase should be given by: L

+

Qx • o°ix +

Η

η

+

2θ ηΧ

D

+

o°dx +

V *

B

N

DO DX

R

+

o°*x +

B

M

o*x

N

+

AO AX

+

S

A

o*x

G *X

+

+

H

N

w HX

B

36

0

( )

where W designates the aqueous phase and Ο the organic phase. Then from equation 1: Qx

•

L

L

D

D

+

R

-

R

( O- W>°IX+( O- W)°JX ( O

M

M

A

A

w)°^( o- w)*x^ o- w)«x

Thus, any coefficient V of an independent variable ν in the IMF equation is given by: v

'

V

o '

V

38

w

< >

Properties of a number of solvents are given in Table 4. They include values of α, μ, n , rin, and the molarity of the pure solvent, M . Also tabulated are values of M a , Μ μ, M n , and M ^ . These values suggest that H , H , and M are much larger than H , H , and MQ. It follows then that the signs of the coefficients H , , H , and M should be negative in all of the sets studied. This is indeed the case. Polarizability should be H

S v

S v

1 0

H

S v

1 W

2 0

2 W

w

2


8ν

90


much more important in the organic phase than in the aqueous phase. This should also be true of the coefficient B which is also a measure of polarizability. Thus the values of A and B should all be positive. Again this is the case in all the sets studied. It is interesting to note that steric effect coefficients Sj are all positive for these sets. This presumably results from steric shielding of the substituent X by the group Y which decreases the extent of hydrogen bonding and of dipole - dipole and dipole -induced dipole interactions in the water phase, resulting in an increased concentration of substrate in the organic phase. L , D, and R, the coefficients of the electrical effect parameters are also positive in all cases. Why this should be the case is unclear. C G

C Y


Table 4, Solvent properties. Solvent

n„

n„

a

M inS\f w

—

water

55.6

2

2

1.88

0.018

c-hexane

9.25

0

0

0

0.257

0.00245

chloroform

12.4

1

0

1.04

0.191

0.067 0.665

PGDP

2.56

0

4

2.4

1.012

1-octanol

6.35

1

1

1.62

0.390

1.72

hexane

7.66

0

0

0

0.278

0.00406

Solvent

M

Transport Parameter Dependence on Intermolecular Forces - ACS

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