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Measuring Interfacial Widths
A R T I C L E S
4.17 (t, J ) 4.4, 2H), 6.98 (d, J ) 9.2, 2H), 8.20 (d, J ) 9.2, 2H); 13
NMR (CDCl3) 61.1, 70.0, 114.5, 125.9, 141.7, 163.6; LRMS (EI) 183
(M+, 66), 139 (100); HRMS (EI) calcd for C8H9O4N 183.0532 (M+),
found 183.0536. See Supporting Information on pp S1-S4.
C
General Procedure for the Synthesis of 4a-e. Chlorosulfonic acid
was added to the solution of the corresponding alcohol in diethyl ether
at room temperature and stirred for 1 h. A 10% sodium carbonate
solution was added until the pH rose to 10. The water and any remaining
ether were then removed by rotary evaporation. The product was
separated from the mixture of solids with several acetonitrile extractions.
Evaporating the acetonitrile left solely the product of interest as a
sodium salt. The spectral data of the individual compounds are reported
below.
3-(4-Nitrophenoxy)propanol (3b). Compound 3b was prepared by
following the general procedure employing pNFB (0.998 g, 7.07 mmol),
1,3-propanediol (4.26 g, 56.0 mmol), and KOH (0.500 g, 8.91 mmol).
Purification of the reaction mixture gave 0.335 g (34%) of pNFB and
0.715 g (51%) of 3b as a yellow oil: Rf ) 0.25 (hexanes:EtOAc, 3:2);
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IR (NaCl) 3358 (s), 3115 (w), 2952 (w), 1510 (s), 1265 (s); H NMR
Sodium 2-(4-Nitrophenoxy)ethyl Sulfate (4a). Compound 4a was
prepared following the general procedure employing chlorosulfonic acid
(0.390 g, 3.35 mmol) and compound 3a (0.471 g, 2.57 mmol).
Evaporating the acetonitrile gave 0.618 g (82%) of 4a as an off-white
(CDCl3) 2.02 (dd, J ) 6.0, 6.0, 2H), 2.33 (s, 1H), 3.80 (t, J ) 6.0,
2H), 4.15 (t, J ) 6.0, 2H), 6.89 (d, J ) 9.2, 2H), 8.10 (d, 2H); 13C
NMR (CDCl3) 31.6, 59.1, 65.7, 114.3, 125.8, 141.2, 163.9. LRMS
(FAB) 198 ((M + H)+, 100); HRMS (FAB) calcd for C9H12O4N
198.0766 (M + H)+, found 198.0764. See Supporting Information on
pp S5-S8.
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solid: IR (KBr) 3517 (s), 3254 (s), 3115 (w), 1494 (s), 1250 (m); H
NMR (D2O) 4.22 (s, 4H), 6.90 (d, J ) 9.2, 2H), 8.00 (d, J ) 9.2, 2H);
13C NMR (D2O) 66.8, 67.0, 114.9, 126.1, 141.2, 163.6. See Supporting
Information on pp S25-S29.
4-(4-Nitrophenoxy)butanol (3c). Compound 3c was prepared by
following the general procedure employing pNFB (0.998 g, 7.07 mmol),
1,4-butanediol (3.19 g, 35.4 mmol), and KOH (0.500 g, 8.91 mmol).
Purification of the reaction mixture gave 0.437 g (44%) of pNFB and
0.621 g (44%) of 3c as a white solid: mp 78-80 °C; Rf ) 0.26
(hexanes:EtOAc, 3:2); IR (KBr) 3527 (s), 3115 (w), 2954 (w), 1508
Sodium 4-(4-Nitrophenoxy)butyl Sulfate (4c). Compound 4c was
prepared following the general procedure employing chlorosulfonic acid
(3.12 g, 26.8 mmol) and compound 3c (2.26 g, 10.7 mmol). Evaporating
the acetonitrile gave 2.67 g (80%) of 4c as a white solid: IR (KBr)
1
3498 (s), 3113 (w), 1501 (s), 1263 (m); H NMR (D2O) 1.65-1.71
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(m, 4H), 3.95 (t, J ) 5.6, 4H), 6.82 (d, J ) 9.2, 2H), 7.95 (d, J ) 9.2,
2H); 13C NMR (D2O) 24.7, 25.1, 68.5, 68.9, 114.7, 126.1, 140.8, 164.1.
See Supporting Information on pp S30-S34.
(s), 1262, (s); H NMR (CDCl3) 1.45 (s, 1H), 1.75 (q, J ) 6.2, 2H),
1.91 (q, J ) 6.2, 2H), 3.72 (t, J ) 6.2, 2H), 4.08 (t, J ) 6.2, 2H), 6.92
(d, J ) 9.2, 2H), 8.17 (d, J ) 9.2, 2H); 13C NMR (CDCl3) 25.5, 29.1,
62.4, 68.6, 114.4, 125.9, 141.4, 164.0; LRMS (FAB) 212 ((M + H)+,
100), 140 (67); HRMS (FAB) calcd for C10H14O4N 212.0923 (M +
H)+, found 212.0928. See Supporting Information on pp S9-S12.
5-(4-Nitrophenoxy)pentanol (3d). Compound 3d was prepared by
following the general procedure employing pNFB (2.00 g, 14.1 mmol),
1,5-pentanediol (8.78 g, 84.3 mmol), and KOH (1.03 g, 18.3 mmol).
Purification of the reaction mixture gave 0.363 g (18%) of pNFB and
2.09 g (66%) of 3d as a yellow oil: Rf ) 0.20 (hexanes:EtOAc, 3:2);
Sodium 6-(4-Nitrophenoxy)hexyl Sulfate (4e). Compound 4e was
prepared following the general procedure employing chlorosulfonic acid
(1.30 g, 11.2 mmol) and compound 3e (1.34 g, 5.58 mmol). Evaporating
the acetonitrile gave 1.53 g (81%) of 4e as an off-white solid: IR (KBr)
1
3479 (s), 3117 (w), 1508 (s), 1259 (s); H NMR (D2O) 1.10-1.15 (s,
4H), 1.40-1.45 (m, 4H), 3.70-3.85 (m, 4H), 6.62 (d, J ) 8.4, 2H),
7.77 (d, J ) 8.4, 2H); 13C NMR (D2O) 24.8, 24.9, 28.2, 28.5, 69.0,
69.2, 114.5, 125.8, 140.5, 164.2. See Supporting Information on pp
S35-S39.
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IR (NaCl) 3361 (s), 3111 (w), 2940 (w), 1511 (s), 1265 (s); H NMR
(CDCl3) 1.27 (t, J ) 6.0, 1H), 1.50-1.60 (m, 2H), 1.60-1.65 (m, 2H),
1.80-1.90 (m, 2H), 3.68 (q, J ) 6.0, 2H), 4.05 (t, J ) 6.4, 2H), 6.92
(d, J ) 9.2, 2H), 8.27 (d, J ) 9.2, 2H); 13C NMR (CDCl3) 22.2, 28.7,
32.2, 62.6, 68.6, 114.3, 125.9, 141.3, 164.1. LRMS (FAB) 226 ((M +
H)+, 100), 69 (77); HRMS (FAB) calcd for C11H16O4N 226.1079 (M
+ H)+, found 226.1085. See Supporting Information on pp S13-
S16.
The neutral alcohol species 3a-f serve as excellent probes of
hydrophilic solid-liquid interfaces. The alcohol functional group can
hydrogen bond with silanol-terminated quartz surfaces allowing the
chromophore to probe local solvation environments different distances
away from the solid-liquid boundary. Surface-specific nonlinear optical
measurements described elsewhere show how different length rulers
sample regions of significantly different polarities, despite the fact that
the bulk dielectric properties of the solvents being studied can be quite
similar.17 In addition, preliminary studies have shown that the ionic
species 4a-e are also successful as probes of weakly interacting liquid-
liquid interfaces. Data comparing results from the shortest ruler with
those from the parent pNAs chromophore are discussed below.
One unusual aspect of the characterization warrants mention here.
Fast atom bombardment (FAB) mass spectrometry provides unambigu-
ous identification of the neutral alcohol species (3a-f). The ionic
sulfates, however, need to be identified by using electrospray mass
spectrometry. Mass spectra of species 4a, 4c, and 4e recorded using
anion detection show dominant features corresponding to the monomer
anion (r-) mass (Figure 2). Careful inspection of the spectra show small,
additional features at higher masses corresponding to [r2Na1]- up to
hexamer clusters ([r6Na5]-). These aggregates provide evidence that
samples are, in fact, the sodium salt. Except for species 4a, these larger
clusters have very small intensities relative to that of the parent
monomer anion. In the 4a anion spectrum, the dimer [r2Na1]- has ∼50%
of the intensity of the monomer anion.
6-(4-Nitrophenoxy)hexanol (3e). Compound 3e was prepared by
following the general procedure employing pNFB (2.00 g, 14.1 mmol),
1,6-hexanediol (8.30 g, 70.2 mmol), and KOH (1.03 g, 18.3 mmol) at
50-60 °C. Purification of the reaction mixture gave 0.321 g (16%) of
pNFB and 0.213 g (63%) of 3e as a white solid: mp 80-83 °C; Rf )
0.31 (hexanes:EtOAc, 3:2); IR (KBr) 3516 (s), 3115 (w), 2930 (w),
1500 (s), 1258 (s); 1H NMR (CDCl3) 1.28 (s, 1H), 1.40-1.65 (m, 6H),
1.80-1.85 (m, 2H), 3.65 (s, 2H), 4.03 (t, J ) 6.4, 2H), 6.91 (d, J )
9.2, 2H), 8.17 (d, J ) 9.2, 2H); 13C NMR (CDCl3) 25.5, 25.7, 28.9,
32.6, 62.8, 68.7, 114.4, 125.9, 141.3, 164.1; LRMS (FAB) 240 ((M +
H)+, 99), 55 (100); HRMS (FAB) calcd for C12H18O4N 240.1236 (M
+ H)+, found 240.1233. See Supporting Information on pp S17-S20.
8-(4-Nitrophenoxy)octanol (3f). Compound 3f was prepared by
following the general procedure employing pNFB (0.998 g, 7.07 mmol),
1,8-octanediol (6.20 g, 42.4 mmol), and KOH (0.500 g, 8.91 mmol) at
50-60 °C. Purification of the reaction mixture gave 0.345 g (35%) of
pNFB and 0.923 g (49%) of 3f as a white solid: mp 86-88 °C; Rf )
0.35 (hexanes:EtOAc, 3:2); IR (KBr) 3516 (s), 3111 (w), 2929 (w),
1499 (s), 1260 (s); 1H NMR (CDCl3) 1.24 (t, J ) 5.6, 1H), 1.30-1.60
(m, 10H), 1.75-1.85 (m, 2H), 3.63 (q, J ) 5.6, 2H), 4.02 (t, J ) 6.4,
2H), 6.91 (d, J ) 9.2, 2H), 8.17 (d, J ) 9.2, 2H); 13C NMR (CDCl3)
25.6, 25.8, 28.9, 29.2, 29.3, 32.7, 63.0, 68.8, 114.4, 125.9, 141.3, 164.2;
LRMS (FAB) 268 ((M + H)+, 56), 69 (100); HRMS (FAB) calcd for
C14H22O4N 268.1549 (M + H)+, found 268.1546. See Supporting
Information on pp S21-S24.
Spectral patterns change dramatically in the positive ion spectra.
Data for 4a, 4c, and 4e show long progressions out to the detection
limits of the instrument (2000 amu, see Figure 3). These progressions
correspond to aggregates of anion:sodium complex with an additional
sodium ion [rnNan+1]+. The progression extends out to the hexamer
(17) Steel, W. H.; Zhang, X.; Walker, R. A. In preparation.
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J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002 4827