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The influence of micelle formation on the internal chemical shift of the aromatic protons of solutions of a cationic surfactant
The 'Influence of Micelle Formation on the Internal Chemical Shift of the Aromatic Protons of Solutions of a Cationic Surfactant R O N A L D E. A T K I N S O N , G A I L E. C L I N T , ANn T R E V O R W A L K E R Basic Research Department, -Procter ~ Gamble Limited Newcastle Technical Centre, Newcastle upon Tyne NE12 PTS, England
Received January 3, 1973; accepted June 13, 1973 The NMR spectrum of the aromatic protons from aqueous solutions of Me (CH2)~N+Me2CH2PhMeC1- (n = 7, 9) compounds is very concentration dependent. By comparing NMR and light scattering data it is shown that this effect is the result of micelle formation. EXPERIMENTAL METHODS
INTRODUCTION
Materials
Studies (1, 2) of the chemical shift of the I~F nucleus of surface active agents in aqueous solution have been used to investigate the nature of the micellar interior and the partition between monomeric and aggregated species. The corresponding chemical shifts for the hydrogen nucleus are usually small. However, it has been shown (3) that the proton signal from a phenyl group at the end of an alkyl chain in a surface active agent of the type Ph (CH2)nN+Me~Br - (n = 5 or 8) is a single peak and is displaced to higher fields by association to form micelles in aqueous solution. In the present study the N M R signal from the aromatic protons in compounds of the type Me (CH~)~N+Me2CH~PhMeC1 - (n = 7 or 9) in aqueous solution was found to be split into a symmetrical group of four bands indicating that the four protons are not equivalent. By comparing light scattering and N M R measurements it was shown that this splitting of the N M R signal was the result of micelle formation.
4-Methyl benzyl trimethyl ammonium chloride was prepared by stirring a solution of p-methyl benzyl chloride with excess trimethylamine in acetone for several hours. Recrystallization was carried out using acetone and petrol. Octyl dimethyl amine and decyl dimethyl amine were used in the preparation of the corresponding long chain compounds, CsHlvN+Me2CH2PhMeC1 and C10H21N+Me2CH2PhMeC1-. All materials used were analytically pure and did not exhibit a minim u m in the plot of surface tension against the logarithm of the concentration indicating the absence of highly surface active impurities. Light Scattering Measurements
Solutions of CsH17N+Me2CH2PhMeC1 - and C10H.~IN+Me2CH2PhMeC1- in D20 (10 moles m -3 NaC1) were clarified by filtration through Millipore filters (100 nm pore size) and the intensity of scattered light at various angles to the incident light (X = 546 nm) was measured at 308.2 4- 0.1 K using a Sofica model 32
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
Copyright (~ 1974 by AcademicPress, Inc. All rights of reproductionin any form reserved.
CHEMICAL SHIFT SURFACTANT 4200 P.G.D. instrument. The turbidities were calculated from the scattering at 90 ° on the basis of a benzene calibration. Corrections for depolarization of the scattered light were found to be negligible. Refractive index increments were determined at 308 K with a Rayleigh interferometer.
33
/
,
E
% ×
Nuclear Magnetic Resonance Measurements
10
N M R spectra were recorded using a PerkinElmer R12A spectrometer at a frequency of 60 MHz and a temperature of 308 K. To facilitate the recording of the signal from the aromatic protons without interference from solvent signals, solutions in D20 (99.7%) containing 10 moles m -3 NaC1 were used. In view of the solute aggregation the use of a reference solute was avoided, since partition between the micellar and solvent environments can occur. RESULTS
Light Scattering The turbidity (r) of CsH17N+M%CH~PhMe C1- and C10H21N+M%CH2PhMeC1 - solutions in D20 (10 moles m -3 NaC1) as a function of concentration (C) is shown in Fig. 1. Critical micelle concentrations (CMC) from these results are in good agreement with the values from surface tension measurements (Table I). Approximate values for the weight average aggregation number ((n)w) were obtained (Table I) from the light scattering data by extrapolating the reciprocal of the apparent micelle molecular weight to zero micellar concentration. The precise procedure (l) for the calculation of the concentration of monomer and aggregation numbers, which has been used for dilute solutions of nonionic surface active agent, cannot be used as the charge on the micelles leads to micellar interactions even for dilute solutions.
2 05
0
OOl
002
0 03
Concenirolion (g
FIO. 1. Light scattering results: the turbidity for CsH17N+Me2CH2PhMeC1- (O) and C~0H2,N+Me2CH2PhMeC1- (e) solutions in D20 (10 moles m-s NaC1) as a function of concentration. with reference to the signal from the water protons, is illustrated in Fig. 2. For dilute solutions ( < 0.03 g c m -3) a single band was obtained from the aromatic protons indicating that these are equivalent nuclei. At higher concentrations the spectrum split into a symmetrical group of four bands, the inner pair being stronger than the outer pair. This result suggests that the protons near to the quaternary nitrogen and those adjacent to the position substituted by the methyl group have different chemical shifts and are spin coupled. The internal chemical shift between the aromatic nuclei (zX6) was calculated (4) from the separation of the outer bands ( ~ 1 - ~4) and the TABLE CMC
VALUES
I
AND AOGa~EOATION CMC Surface tension
N M R Spectra The dependence upon concentration of the N M R spectrum of the aromatic protons of CsH17N+lV[%CH2PhMeC1- solutions in D20,
0'.04
cm-3~
CsH~,N+Me~CH~phMeCIC,0H2,N+Me2CH2PhMeCI-
NUMgERS (g crn-~) Light scattering
0 . 0 2 8 0.029 0.0061 0.0063
(n)w from light scattering
5 11
Journal of Colloid and Interface Science, Vol. 46, N o . 1, J a n u a r y 1 9 7 4
34
ATKINSON, CLINT, AND WALKER
separation of the inner bands ( 6 2 - ~). For concentrations less than 0.05 g cm -~ this calculation was imprecise due to the low intensity of the outer lines. Values of the intensity ratio (Ia) of the central to the outer bands were found to be in agreement with the values predicted from the separation of the lines Fib (61 -- 64) (62 -- 6a)-1] as shown in Fig. 2. A6 is shown as a function of the reciprocal concentration in aqueous solution for both CsH17N+Me2CH2PhMeC1 - and C10H21N+Me2CH~PhMeCI- in Fig. 3. The N M R spectrum from the aromatic protons of Me3N+CH2 PhMeCI- in D20 was found to be concentration dependent. At concentrations less than 0.2 g c m -3 a single band was observed and at higher concentrations a quartet was observed. A6, was found to be concentration dependent in other solvents and results for water and ethanol are shown in Fig. 4. Spectra of the aromatic protons recorded in other solvents showed that a decrease in solvent polarity led to an increase in the internal chemical shift of the aromatic protons (Table II).
(A) ~a 5.4
:Iib 52 20 g cm 5
TABLE
II
T H E CHEMICAL SHIFT OBSE!ZVED 2"OR C H a N + M e ~ C H ~ P h M e C 1 - IN DIFFERENT SOLVENTS.a Solvent
Dielectric constant
~(Hz)
Deuterochloroform CyclohexanoI Ethanol Methanol Ethylene glycol Dimethylsulfoxide Formic acid Deuterium oxide
4.8 15 24 32.6 37 44 58.5 78.25
19.1 18.6 15.1 5.4 1.8 6.0 0.5 0
a Conc. 0.1 g g-1 (solvent).
DI SCUSSION The minimum concentration (~0.03 g cm-~) at which splitting occurs in the N MR spectrum from the aromatic protons of CsH17N+Me2CH2PhMeC1 - corresponds to the CMC as determined by the light scattering and surface tension techniques, indicating that the splitting is associated with the micellar form of the surface active agent. The effect may be due to the location of the aromatic ring in the surface layer of the micelle, to the proximity of other aromatic groups or the polarization of zr electrons in the phenyl groups by the surface charge of the micelle. For molecules exchanging rapidly between two environments the chemical shift for particular nuclei is given by
(B)
Y'. 6iCj 4.6
J 6 ~ -----
~b 1614 g crn 5
)
E cj J
00275 g
cm-3
where C~ is the concentration of molecules in the environment j with chemical shift ~j. If the chemical shifts of the aromatic protons (1, 2) in the molecule 1
175
170
165
160
155
150
Me (CH2),,N+Me2CH2
145
2
MeC1-
b (Hz)
FI6. 2. N M R s p e c t r a for a r o m a t i c p r o t o n s o f CsH~TN+Me~CH2PhMeC1- solutions in D.oO (10 m o l e s m -3 NaC1).
are the same for the monomeric molecule in aqueous solution but are changed by different amounts when the molecule is in the micelle
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
CHEMICAL SHIFT SURFACTANT
35
,o~
"o.|
10
o
o
'~lO
20
30
41o
1 (gqcm 5) ~FIG. 3. Internal chemical shift of aromatic protons (zX~) as a function of the reciprocal concentration : (O) CsH~TN+Me2CH=PhMeC1 - in D20 (10 moles m -3 NaCI), ( e ) C~0H21N+Me2CH2PhMeC1 - in D20 (10 moles m -3 NaC1).
then it may be shown that 1
where C is the total concentration of surface active ions. The concentration of monomeric
surface active ions for the micellar solutions (C*) is assumed to be given approximately by the value at the CMC. 2~m is a characteristic shift difference between the aromatic protons for the micelles and is shown as a function of C*/C in Fig. 5 for values of C up to 0.2 g cm-~. Similar values in the range 10-13 Hz were ob-
/ 2O
15r-
/ ~,
o12 Conceniration
~
o'4
(g crn-5)
FIG. 4. Internal chemical shift of aromatic protons (A~) as a function of concentration: (O) MeaN +CH2PhlV[eC1- in ethanol, (&) Me3N+CH2PhMeCI - in D20. Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
36
ATKINSON, CLINT, AND WALKER
t4 12
~
o
.....
I
.~
-g_
E t0 to
o
8 6
01t
012
0.5T
014
Cm C
Fro. 5. Internal chemical shift difference for the aromatic protons in the micellar environment (A6m): (O) CsH17N+Me2CH~PhMeC1-, (e) CloH~IN+IV[e~CH2PhMeC1-. rained for the two compounds suggesting that this analysis is essentially correct. In an alternative analysis of the data (5) the concentration of monomeric surface active ions can be obtained as a function of the total concentration if a value of A6,~ can be estimated. A value of (~}w can then be calculated from the gradient of In C* expressed as a function of In ( C - C*). Extrapolation of the results given in Fig. 3 below a concentration of 0.2 g cm-3 suggests that a value of 14 Hz is a reasonable estimate for ~Am which in the case of CsH~TN+Me2CH2PhMeC1- leads to a value of 5 for (n}~ in the concentration range 0.05-0.15 g cm-~. This value is the same as that obtained from light scattering data. However, the di~culty with this analysis is that the data at concentrations greater than 0.2 g cm-3 are not consistent with this value of A&~and larger values of A~m lead to lower values of (n)~. The assumption that there is a single characteristic shift difference for the aromatic protons may break down at concentrations greater than 0.2 g cm-3.
the solvent dielectric constant. The splitting of the spectrum increases with decreasing solvent dielectric constant. Solvent dependent spectra from aromatic protons have been observed previously. Farges and Dreiding (6) noted the isochrony of the aromatic protons (1 and 2) in the molecule 1
2
in carbon tetrachloride, deuterochloroform or trifluoroacetic acid solution, whereas they become nonequivalent in acetone or benzene. A change in solvent can influence the chemical shift of protons by a variety of mechanisms, which have been reviewed by Laszlo (7). By analogy with the results for homologues with longer alkyl chains, ion association (ion pair formation or cation association) may be responsible for the marked dependence of A~ for the aromatic protons of Me3N+CH2PhMeC1upon concentration, illustrated by the results for D20 and ethanol in Fig. 4.
Solutions of M e s N + C H ~ P h M e C I -
For solutions of MezN+CH2PhMeC1- in various solvents there is a correlation between the chemical shift of the aromatic protons and
REFERENCES 1. CORKILL, J. M . , GOODMAN, J. F., WALK, n, T., AND
Journal of Colloid and Interface Science, Vol. 46, No. 1, J a n u a r y 1974
WYEI~, J., Proc. Roy. Soc. A312, 243 (1969).
CHEMICAL SHIFT SURFACTANT 2.
MULLEK,N., ANDBII~KHAI~N,R. H., f. Phys. Chem.
72, 583 (1968). 3. ][NOUE,H., AND NAKAGAWA,T., J. Phys. Chem. 70, 1108 (1966). 4. E~ISLEY,J. W., FEENEY, J., AND SUTCLIFFE,L. H., "High Resolution NMR Spectroscopy," p. 319. Pergamon, Elmsford, NY, 1965.
37
5. MVLLEI~,N., AND PLATKO,F. E., Y. Phys. Chem. 75, 547 (1971). 6. FARGES,G., ANDDREIDING,A. S., Helv. Chim. Acta. 49, 552 (1966). 7. LASZ~O, P., in "Progress in NMR Spectroscopy" (J. W. E~SLE¥, J. FEENE¥, ANDL. H. SUTCL]FFE, Eds.), p. 231. Pergamon, Elmsford, N Y , 1967.
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
Received January 3, 1973; accepted June 13, 1973 The NMR spectrum of the aromatic protons from aqueous solutions of Me (CH2)~N+Me2CH2PhMeC1- (n = 7, 9) compounds is very concentration dependent. By comparing NMR and light scattering data it is shown that this effect is the result of micelle formation. EXPERIMENTAL METHODS
INTRODUCTION
Materials
Studies (1, 2) of the chemical shift of the I~F nucleus of surface active agents in aqueous solution have been used to investigate the nature of the micellar interior and the partition between monomeric and aggregated species. The corresponding chemical shifts for the hydrogen nucleus are usually small. However, it has been shown (3) that the proton signal from a phenyl group at the end of an alkyl chain in a surface active agent of the type Ph (CH2)nN+Me~Br - (n = 5 or 8) is a single peak and is displaced to higher fields by association to form micelles in aqueous solution. In the present study the N M R signal from the aromatic protons in compounds of the type Me (CH~)~N+Me2CH~PhMeC1 - (n = 7 or 9) in aqueous solution was found to be split into a symmetrical group of four bands indicating that the four protons are not equivalent. By comparing light scattering and N M R measurements it was shown that this splitting of the N M R signal was the result of micelle formation.
4-Methyl benzyl trimethyl ammonium chloride was prepared by stirring a solution of p-methyl benzyl chloride with excess trimethylamine in acetone for several hours. Recrystallization was carried out using acetone and petrol. Octyl dimethyl amine and decyl dimethyl amine were used in the preparation of the corresponding long chain compounds, CsHlvN+Me2CH2PhMeC1 and C10H21N+Me2CH2PhMeC1-. All materials used were analytically pure and did not exhibit a minim u m in the plot of surface tension against the logarithm of the concentration indicating the absence of highly surface active impurities. Light Scattering Measurements
Solutions of CsH17N+Me2CH2PhMeC1 - and C10H.~IN+Me2CH2PhMeC1- in D20 (10 moles m -3 NaC1) were clarified by filtration through Millipore filters (100 nm pore size) and the intensity of scattered light at various angles to the incident light (X = 546 nm) was measured at 308.2 4- 0.1 K using a Sofica model 32
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
Copyright (~ 1974 by AcademicPress, Inc. All rights of reproductionin any form reserved.
CHEMICAL SHIFT SURFACTANT 4200 P.G.D. instrument. The turbidities were calculated from the scattering at 90 ° on the basis of a benzene calibration. Corrections for depolarization of the scattered light were found to be negligible. Refractive index increments were determined at 308 K with a Rayleigh interferometer.
33
/
,
E
% ×
Nuclear Magnetic Resonance Measurements
10
N M R spectra were recorded using a PerkinElmer R12A spectrometer at a frequency of 60 MHz and a temperature of 308 K. To facilitate the recording of the signal from the aromatic protons without interference from solvent signals, solutions in D20 (99.7%) containing 10 moles m -3 NaC1 were used. In view of the solute aggregation the use of a reference solute was avoided, since partition between the micellar and solvent environments can occur. RESULTS
Light Scattering The turbidity (r) of CsH17N+M%CH~PhMe C1- and C10H21N+M%CH2PhMeC1 - solutions in D20 (10 moles m -3 NaC1) as a function of concentration (C) is shown in Fig. 1. Critical micelle concentrations (CMC) from these results are in good agreement with the values from surface tension measurements (Table I). Approximate values for the weight average aggregation number ((n)w) were obtained (Table I) from the light scattering data by extrapolating the reciprocal of the apparent micelle molecular weight to zero micellar concentration. The precise procedure (l) for the calculation of the concentration of monomer and aggregation numbers, which has been used for dilute solutions of nonionic surface active agent, cannot be used as the charge on the micelles leads to micellar interactions even for dilute solutions.
2 05
0
OOl
002
0 03
Concenirolion (g
FIO. 1. Light scattering results: the turbidity for CsH17N+Me2CH2PhMeC1- (O) and C~0H2,N+Me2CH2PhMeC1- (e) solutions in D20 (10 moles m-s NaC1) as a function of concentration. with reference to the signal from the water protons, is illustrated in Fig. 2. For dilute solutions ( < 0.03 g c m -3) a single band was obtained from the aromatic protons indicating that these are equivalent nuclei. At higher concentrations the spectrum split into a symmetrical group of four bands, the inner pair being stronger than the outer pair. This result suggests that the protons near to the quaternary nitrogen and those adjacent to the position substituted by the methyl group have different chemical shifts and are spin coupled. The internal chemical shift between the aromatic nuclei (zX6) was calculated (4) from the separation of the outer bands ( ~ 1 - ~4) and the TABLE CMC
VALUES
I
AND AOGa~EOATION CMC Surface tension
N M R Spectra The dependence upon concentration of the N M R spectrum of the aromatic protons of CsH17N+lV[%CH2PhMeC1- solutions in D20,
0'.04
cm-3~
CsH~,N+Me~CH~phMeCIC,0H2,N+Me2CH2PhMeCI-
NUMgERS (g crn-~) Light scattering
0 . 0 2 8 0.029 0.0061 0.0063
(n)w from light scattering
5 11
Journal of Colloid and Interface Science, Vol. 46, N o . 1, J a n u a r y 1 9 7 4
34
ATKINSON, CLINT, AND WALKER
separation of the inner bands ( 6 2 - ~). For concentrations less than 0.05 g cm -~ this calculation was imprecise due to the low intensity of the outer lines. Values of the intensity ratio (Ia) of the central to the outer bands were found to be in agreement with the values predicted from the separation of the lines Fib (61 -- 64) (62 -- 6a)-1] as shown in Fig. 2. A6 is shown as a function of the reciprocal concentration in aqueous solution for both CsH17N+Me2CH2PhMeC1 - and C10H21N+Me2CH~PhMeCI- in Fig. 3. The N M R spectrum from the aromatic protons of Me3N+CH2 PhMeCI- in D20 was found to be concentration dependent. At concentrations less than 0.2 g c m -3 a single band was observed and at higher concentrations a quartet was observed. A6, was found to be concentration dependent in other solvents and results for water and ethanol are shown in Fig. 4. Spectra of the aromatic protons recorded in other solvents showed that a decrease in solvent polarity led to an increase in the internal chemical shift of the aromatic protons (Table II).
(A) ~a 5.4
:Iib 52 20 g cm 5
TABLE
II
T H E CHEMICAL SHIFT OBSE!ZVED 2"OR C H a N + M e ~ C H ~ P h M e C 1 - IN DIFFERENT SOLVENTS.a Solvent
Dielectric constant
~(Hz)
Deuterochloroform CyclohexanoI Ethanol Methanol Ethylene glycol Dimethylsulfoxide Formic acid Deuterium oxide
4.8 15 24 32.6 37 44 58.5 78.25
19.1 18.6 15.1 5.4 1.8 6.0 0.5 0
a Conc. 0.1 g g-1 (solvent).
DI SCUSSION The minimum concentration (~0.03 g cm-~) at which splitting occurs in the N MR spectrum from the aromatic protons of CsH17N+Me2CH2PhMeC1 - corresponds to the CMC as determined by the light scattering and surface tension techniques, indicating that the splitting is associated with the micellar form of the surface active agent. The effect may be due to the location of the aromatic ring in the surface layer of the micelle, to the proximity of other aromatic groups or the polarization of zr electrons in the phenyl groups by the surface charge of the micelle. For molecules exchanging rapidly between two environments the chemical shift for particular nuclei is given by
(B)
Y'. 6iCj 4.6
J 6 ~ -----
~b 1614 g crn 5
)
E cj J
00275 g
cm-3
where C~ is the concentration of molecules in the environment j with chemical shift ~j. If the chemical shifts of the aromatic protons (1, 2) in the molecule 1
175
170
165
160
155
150
Me (CH2),,N+Me2CH2
145
2
MeC1-
b (Hz)
FI6. 2. N M R s p e c t r a for a r o m a t i c p r o t o n s o f CsH~TN+Me~CH2PhMeC1- solutions in D.oO (10 m o l e s m -3 NaC1).
are the same for the monomeric molecule in aqueous solution but are changed by different amounts when the molecule is in the micelle
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
CHEMICAL SHIFT SURFACTANT
35
,o~
"o.|
10
o
o
'~lO
20
30
41o
1 (gqcm 5) ~FIG. 3. Internal chemical shift of aromatic protons (zX~) as a function of the reciprocal concentration : (O) CsH~TN+Me2CH=PhMeC1 - in D20 (10 moles m -3 NaCI), ( e ) C~0H21N+Me2CH2PhMeC1 - in D20 (10 moles m -3 NaC1).
then it may be shown that 1
where C is the total concentration of surface active ions. The concentration of monomeric
surface active ions for the micellar solutions (C*) is assumed to be given approximately by the value at the CMC. 2~m is a characteristic shift difference between the aromatic protons for the micelles and is shown as a function of C*/C in Fig. 5 for values of C up to 0.2 g cm-~. Similar values in the range 10-13 Hz were ob-
/ 2O
15r-
/ ~,
o12 Conceniration
~
o'4
(g crn-5)
FIG. 4. Internal chemical shift of aromatic protons (A~) as a function of concentration: (O) MeaN +CH2PhlV[eC1- in ethanol, (&) Me3N+CH2PhMeCI - in D20. Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974
36
ATKINSON, CLINT, AND WALKER
t4 12
~
o
.....
I
.~
-g_
E t0 to
o
8 6
01t
012
0.5T
014
Cm C
Fro. 5. Internal chemical shift difference for the aromatic protons in the micellar environment (A6m): (O) CsH17N+Me2CH~PhMeC1-, (e) CloH~IN+IV[e~CH2PhMeC1-. rained for the two compounds suggesting that this analysis is essentially correct. In an alternative analysis of the data (5) the concentration of monomeric surface active ions can be obtained as a function of the total concentration if a value of A6,~ can be estimated. A value of (~}w can then be calculated from the gradient of In C* expressed as a function of In ( C - C*). Extrapolation of the results given in Fig. 3 below a concentration of 0.2 g cm-3 suggests that a value of 14 Hz is a reasonable estimate for ~Am which in the case of CsH~TN+Me2CH2PhMeC1- leads to a value of 5 for (n}~ in the concentration range 0.05-0.15 g cm-~. This value is the same as that obtained from light scattering data. However, the di~culty with this analysis is that the data at concentrations greater than 0.2 g cm-3 are not consistent with this value of A&~and larger values of A~m lead to lower values of (n)~. The assumption that there is a single characteristic shift difference for the aromatic protons may break down at concentrations greater than 0.2 g cm-3.
the solvent dielectric constant. The splitting of the spectrum increases with decreasing solvent dielectric constant. Solvent dependent spectra from aromatic protons have been observed previously. Farges and Dreiding (6) noted the isochrony of the aromatic protons (1 and 2) in the molecule 1
2
in carbon tetrachloride, deuterochloroform or trifluoroacetic acid solution, whereas they become nonequivalent in acetone or benzene. A change in solvent can influence the chemical shift of protons by a variety of mechanisms, which have been reviewed by Laszlo (7). By analogy with the results for homologues with longer alkyl chains, ion association (ion pair formation or cation association) may be responsible for the marked dependence of A~ for the aromatic protons of Me3N+CH2PhMeC1upon concentration, illustrated by the results for D20 and ethanol in Fig. 4.
Solutions of M e s N + C H ~ P h M e C I -
For solutions of MezN+CH2PhMeC1- in various solvents there is a correlation between the chemical shift of the aromatic protons and
REFERENCES 1. CORKILL, J. M . , GOODMAN, J. F., WALK, n, T., AND
Journal of Colloid and Interface Science, Vol. 46, No. 1, J a n u a r y 1974
WYEI~, J., Proc. Roy. Soc. A312, 243 (1969).
CHEMICAL SHIFT SURFACTANT 2.
MULLEK,N., ANDBII~KHAI~N,R. H., f. Phys. Chem.
72, 583 (1968). 3. ][NOUE,H., AND NAKAGAWA,T., J. Phys. Chem. 70, 1108 (1966). 4. E~ISLEY,J. W., FEENEY, J., AND SUTCLIFFE,L. H., "High Resolution NMR Spectroscopy," p. 319. Pergamon, Elmsford, NY, 1965.
37
5. MVLLEI~,N., AND PLATKO,F. E., Y. Phys. Chem. 75, 547 (1971). 6. FARGES,G., ANDDREIDING,A. S., Helv. Chim. Acta. 49, 552 (1966). 7. LASZ~O, P., in "Progress in NMR Spectroscopy" (J. W. E~SLE¥, J. FEENE¥, ANDL. H. SUTCL]FFE, Eds.), p. 231. Pergamon, Elmsford, N Y , 1967.
Journal of Colloid and Interface Science, Vol. 46, No. 1, January 1974