Structure of 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl 1,10- ditosylate by x-ray crystallography and 19F-NMR spectroscopy

Article abstract of DOI:10.1016/S0022-2860(98)00797-2

2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl 1,10-ditosylate and its precursors were synthesized and characterized by ¹H- and ¹⁹F-NMR spectroscopic methods and X-ray crystallography. These compounds are building blocks for the

Full text of DOI:10.1016/S0022-2860(98)00797-2

MOLSTR 10678
Journal of Molecular Structure 479 (1999) 75–81
Structure of 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl
19
1,10-ditosylate by X-ray crystallography and F-NMR
spectroscopy
Soma Dea, N.K. Lokanathb, M.A. Sridharb, J. Shashidhara Prasadb, K. Venkatesana,
Santanu Bhattacharyaa,1,
*
aDepartment of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
bSchool of Physics, Mysore University, Mysore 570 013, India
Received 29 July 1998; accepted 9 November 1998
Abstract
2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl 1,10-ditosylate and its precursors were synthesized and characterized by
1H- and 19F-NMR spectroscopic methods and X-ray crystallography. These compounds are building blocks for the syntheses of
the surfactants containing polyperfluoromethylene spacer. The molecule has extended all-trans conformation with molecular
ꢀ
symmetry 1 (Ci). There is a reasonably strong C–H…O interaction in the crystal and there are two F…F intermolecular contact
distances less than the sum of van der Waals radii. ᭧ 1999 Elsevier Science B.V. All rights reserved.
Keywords: X-ray crystallography; NMR spectroscopy; Surfactant; Polyperfluoromethylene spacer
1. Introduction
examine the role of the replacement of the polymethy-
lene spacer by the polyperfluoromethylene spacer.
This should be interesting because of the following
reasons, a) it is more hydrophobic and stiffer in nature
than a hydrocarbon chain [4,5]; b) larger Van der
Waals radii for F than that of H; which should
generate greater inter-chain contacts upon self-
assembly in a micellar or related aggregates [6–9];
c) enhanced thermal stability; d) chemical inertness
and e) biocompatibility. Indeed compounds with a
long perfluoroalkyl chain connected by a suitable
functional group show unusual surface properties
[10]. In addition surfaces coated with compounds
possessing perfluorinated chains become non-
wettable. For these reasons, various perfluorinated
compounds are receiving increased attention [11].
Unfortunately, very little reliable structural informa-
tion is available on such compounds. Therefore,
This group has been interested in the design of
novel gemini surfactants, see (1) below, owing to
their interesting physical and chemical properties
like low critical micellar concentration, high visco-
elasticity and an enhanced propensity for lowering
oil–water interfacial tension in comparison to their
conventional single-chain analogues e.g., cetyltri-
methylammonium bromide. It has been demonstrated
[1–3] that their micellar properties solely depend on
the nature and length of the spacer unit connecting the
two head groups. It has been deemed worthwhile to
* Corresponding author. Fax: 00 91 080 334 1683; e-mail:
sb@orgchem.iisc.ernet.in
1 Also at the Chemical Biology Unit, Jawaharlal Nehru Centre for
Advanced Scientific Research, Jakkur, Bangalore 560 064.
0022-2860/99/$ - see front matter ᭧ 1999 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(98)00797-2

76
S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
Table 1
before undertaking an elaborate program for their
synthesis, we sought to secure information on simple
structural perfluorocarbon derivatives in terms of
conformational details. In this article, the crystal
structure of 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadeca-
fluorodecyl 1,10-ditosylate (2) is reported, a precursor
for surfactant synthesis.
Crystal data and experimental crystallographic details
Empirical formula
Formula weight
Temperature
Crystal system, space group Triclinic, P1
Unit cell dimensions
C24H18F16O6S2
770.5
293 (2) K
˚
a ˆ 7.915 (3) A, a ˆ 91.93 (3)Њ
˚
˚
b ˆ 17.800 (5) A, b ˆ 104.94 (3)Њ
c ˆ 5.371 (3) A, g ˆ 99.49 (2)Њ
3
˚
Volume
718.8 (5) A
Z, calculated density
Absorption coefficient
F (000)
1, 1.780 Mg/m3
0.330 mmϪ1
386
Crystal shape
Crystal color
Rectangular
Colorless
Crystal size
0.3 × 0.25 × 0.2 mm
On the diffractometer:
u range for accurate cell
dimensions (Њ)
Index ranges
2.33–22.50Њ
0 Ͻ ˆ h Ͻ ˆ 8, Ϫ 19 Ͻ ˆ k Ͻ ˆ
18, Ϫ 5 Ͻ ˆ 1 Ͻ ˆ 5
Reflections collected/unique 2052/1885 [R(int) ˆ 0.0178]
Completeness to 2u ˆ 22.50 99.9%
Standard reflections
2. Experimental
Number
Interval
3
200
2.1. Materials
Decay
Ϫ 4.2
None
Perfluorosebacic acid was purchased from Aldrich
Chemical Co. Thin layer chromatography was
performed on silica gel-G purchased from Merck.
The plates were visualized by putting them in iodine
chamber. Column chromatography was done on silica
gel (60–120 mesh) obtained from Acme Synthetic
Chemicals. All the reagents and solvents were
obtained from commercial source and were purified,
dried or freshly distilled as required according to a
literature procedure [12].
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2s1]
R indices (all data)
Extinction coefficient
Max. shift/s
Full-matrix least-squares on F2
1885/0/218
1.025
R1 ˆ 0.0422, wR2 ˆ 0.1224
R1 ˆ 0.0466, wR2 ˆ 0.1260
0.012 (3)
0.001
Largest diff. Peak and hole 0.371 and Ϫ 0.276 e.AϪ3
2.2.1. Diethyl perfluorosebacate (4)
2.2. Synthesis
Perfluorosebacic acid 3 (1.5 g, 4.08 mmol) was
refluxed with excess dry EtOH in presence of one
drop of conc. H2SO4 for 24 h. After removal of
EtOH, the organic layer was dissolved in CHCl3 and
washed successively with water and NaHCO3 (sat.).
The product was passed through anhydrous Na2SO4
and upon concentration, a colorless liquid was
Melting points were recorded in open capillary
tubes and are uncorrected. H-NMR spectra (TMS
1
as an internal standard) were recorded on either a
JEOL-FX-90Q (90 MHz), a 200 MHz or a 270 MHz
1
Bruker NMR spectrometer. H-decoupled 19F-NMR
spectra were recorded in 400 MHz Bruker NMR spec-
trometer. Chemical shifts (d) are reported in ppm
downfield from the internal standard. IR spectra
were recorded in a Perkin Elmer Model 781 spectro-
meter and are reported in wave numbers (cmϪ1).
Microanalyses were performed on a Carlo Erba
elemental analyzer model 1106.
1
obtained (yield ca. 99%). IR (nujol) 1770 cmϪ1; H-
NMR (CDCl3, 90 MHz) d 1.33 (t, 6H), 4.4 (q, 4H);
19F-NMR (CDCl3, 376.5 MHz) d Ϫ86.51 (t), Ϫ 83.48
(br s), Ϫ83.3 (br s), Ϫ82.41 (br s); 13C-NMR (CDCl3,
22.5 MHz) d 13:75, 64.82; LRMS, EI, m/z (%) 547
(20).

S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
77
Table 2
2
˚
Atomic coordinates and equivalent isotropic displacement parameters (A ). Ueq is defined as one third of the trace of the orthogonalized Uij
tensora
x
y
z
Ueq
C (1)
C (2)
C (3)
C (4)
C (5)
C (6)
C (7)
S (8)
14119 (6)
12659 (4)
12795 (5)
11460 (4)
9966 (4)
9789 (5)
11151 (5)
8259 (10)
8845 (3)
7493 (3)
6714 (3)
7048 (4)
5365 (4)
5823 (3)
4675 (3)
3906 (4)
4672 (2)
3390 (3)
2248 (4)
2765 (3)
1533 (3)
781 (4)
4296 (3)
3981 (2)
3375 (2)
3082 (2)
3402 (17)
4010 (2)
4296 (2)
3033.9 (5)
2482.1 (15)
3631.8 (15)
2606.7 (12)
1953.4 (17)
1614.2 (17)
1152.7 (12)
2164.8 (11)
1134.7 (16)
606 (11)
1581.2 (12)
707.4 (16)
234.3 (13)
1217.6 (13)
246.5 (17)
Ϫ215.2 (14)
734.9 (14)
1998 (9)
3210 (7)
4707 (9)
5799 (7)
5393 (6)
3894 (7)
2836 (7)
6779.7 (15)
8482 (4)
7612 (5)
4387 (4)
3097 (6)
1045 (6)
Ϫ625 (4)
Ϫ305 (4)
2043 (5)
3444 (4)
3632 (4)
Ϫ14 (6)
0.0964 (15)
0.0614 (9)
0.0730 (11)
0.0635 (10)
0.0443 (7)
0.0631 (9)
0.0714 (11)
0.0531 (3)
0.0704 (7)
0.0743 (8)
0.0517 (6)
0.0494 (8)
0.0466 (7)
0.0714 (6)
0.0696 (6)
0.0439 (7)
0.0691 (6)
0.0733 (6)
0.0440 (7)
0.0780 (7)
0.0904 (8)
0.0464 (7)
0.0937 (9)
0.1031 (10)
O (9)
O (10)
O (11)
C (12)
C (13)
F (14)
F (15)
C (16)
F (17)
F (18)
C (19)
F (20)
F (21)
C (22)
F (23)
F (24)
Ϫ1529 (4)
Ϫ1511 (5)
1018 (6)
2715 (4)
2298 (5)
1517 (3)
143 (3)
2
a Coordinates are fractional × 104; isotropic thermal parameters are Ueq (A ). The ESD values are given in parentheses.
˚
2.2.2. 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-
2.2.3. 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-
hexadecafluorodecane-1,10-diol (5)
hexadecafluorodecyl 1,10-ditosylate (2)
To an ice-cold solution of 4 (1.1 g, 2.01 mmol) in
dry THF (15 mL), LiAlH4 (0.306 g, 8.06 mmol) was
added and stirred at 0ЊC for 1 h. Then the mixture was
refluxed for 12 h. After this the reaction mixture was
cooled and carefully quenched with cold EtOAc first
and then with water. The organic layer was extracted
with CHCl3 and passed through anhydrous Na2SO4.
The solution was concentrated by rotary evaporation
to leave a colorless solid (yield 90%). The solid was
highly soluble in acetone, but sparingly soluble in
CHCl3. So, it was recrystallized from a mixture of
acetone CHCl3. Mp 128ЊC (sharp); IR (nujol) 3300,
Alcohol 5 (0.26 g, 0.563 mmol) dissolved in pyri-
dine (1.4 mL) was treated with tosyl chloride
(0.644 g, 3.376 mmol) at 0ЊC. Diethyl ether (25 mL)
was added and the solution was washed successively
with 1.5 M HCl, 3% NaHCO3 and water. The organic
layer was dried over anhydrous Na2SO4 and concen-
trated under vacuum. A white solid was obtained. It
was purified by passing through a silica gel (60–120
mesh) column using 10:1–7:1 hexane/EtOAc as the
eluent to obtain a colorless crystal (yield 80%). Mp
77–78ЊC; TLC (10:1 hexane/EtOAC, Rf 0.2); IR
(nujol) 1590, 1235 cmϪ1
;
1H-NMR (CDCl3,
1
1700 cmϪ1; H-NMR (CD3COCD3, 90 MHz) d 4.2
90 MHz) d 2.43 (s, 6H), 4.43 (t, 4H), 7.36 (d, 4H),
7.8 (d, 4H); 19F-NMR (CDCl3, 376.5 MHz) d Ϫ124.1
(s), Ϫ123.0 (s), Ϫ120.5 (s); 13C-NMR (CDCl3,
22.5 MHz) d 21.6, 62.72, 63.94, 65.27, 128.17,
130.16, 132.04, 146.08. Elemental Analysis-found:
(m, 4H), 5.18 (t, 2H); 19F-NMR (CD3COCD3,
376.5 MHz) d Ϫ93.1 (br s), Ϫ91.55 (s). Elemental
Analysis-found: C ˆ 25.44%, H ˆ 1.3%; calculated
C ˆ 25.5%, H ˆ 1.39% with 0.5 H2O.

78
S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
Table 3
Table 3 (continued)
˚
Bond lengths [A] and angles [Њ]
C2–C7–H7
C6–C7–H7
O9–S8–O10
O9–S8–O11
O10–S8–O11
O9–S8–C5
O10–S8–C5
119.2
119.2
C1–C2
C1–H1B
C1–H1C
C2–C3
C2–C7
C3–C4
C3–H3
C4–C5
C4–H4
C5–C6
C5–S8
C6–C7
C6–H6
C7–H7
S8–O9
S8–O10
1.507 (5)
0.9600
0.9600
120.63 (17)
108.38 (14)
102.92 (14)
108.86 (15)
110.73 (15)
103.87 (13)
117.47 (18)
107.9 (2)
110.1
110.1
110.1
110.1
108.4
107.1 (2)
110.6 (2)
107.2 (2)
108.7 (2)
107.7 (2)
115.3 (3)
107.6 (2)
109.0 (2)
109.6 (2)
108.9 (2)
107.5 (2)
116.9 (2)
106.8 (3)
108.0 (2)
108.4 (2)
108.3 (2)
108.7 (2)
116.2 (2)
107.2 (3)
108.0 (2)
108.6 (2)
108.7 (3)
107.8 (3)
116.2 (3)
1.368 (5)
1.372 (5)
1.376 (5)
0.9300
1.366 (5)
0.9300
1.375 (5)
1.752 (3)
1.379 (5)
0.9300
O11–S8–C5
C12–O11–S8
O11–C12–C13
O11–C12–H12A
C13–C12–H12A
O11–C12–H12B
C13–C12–H12B
H12A–C12–H12B
F15–C13–F14
F15–C13–C12
F14–C13–C12
F15–C13–C16
F14–C13–C16
C12–C13–C16
F18–C16–F17
F18–C16–C13
F17–C16–C13
F18–C16–C19
F17–C16–C19
C13–C16–C19
F21–C19–F20
F21–C19–C22
F20–C19–C22
F21–C19–C16
F20–C19–C16
C22–C19–C16
F24–C22–F23
F24–C22–C19
F23–C22–C19
F24–C22–C22 (xꢀyꢀzꢀ)
F23–C22–C22 (xꢀyꢀzꢀ)
0.9300
1.417 (3)
1.421 (3)
1.594 (2)
1.429 (4)
1.512 (4)
0.9700
S8–O11
O11–C12
C12–C13
C12–H12A
C12–H12B
C13–F15
C13–F14
C13–C16
C16–F18
C16–F17
C16–C19
C19–F21
C19–F20
C19–C22
C22–F24
C22–F23
C22–C22 (xꢀyꢀzꢀ)
C2–C1–H1A
C2–C1–H1B
H1A–C1–H1B
C2–C1–H1C
H1A–C1–H1C
H1B–C1–H1C
C3–C2–C7
C3–C2–C1
C7–C2–C1
C2–C3–C4
C2–C3–H3
C4–C3–H3
C5–C4–C3
C5–C4–H4
C3–C4–H4
C4–C5–C6
C4–C5–S8
C6–C5–S8
C5–C6–C7
C5–C6–H6
C7–C6–H6
C2–C7–C6
0.9700
1.343 (4)
1.352 (4)
1.541 (4)
1.330 (3)
1.349 (3)
1.546 (4)
1.332 (3)
1.334 (4)
1.542 (4)
1.329 (4)
1.334 (4)
1.541 (6)
109.5
109.5
109.5
109.5
109.5
109.5
118.2 (3)
121.2 (4)
120.6 (4)
121.4 (3)
119.3
119.3
119.5 (3)
120.3
ꢀ ꢀꢀ
C19–C22–C22 (xyz)
C ˆ 37.75%, H ˆ 2.5%; calculated C ˆ 37.42%, H ˆ
2.35%.
2.3. X-ray crystallography
120.3
120.5 (3)
119.9 (2)
119.6 (2)
118.8 (3)
120.6
Single crystals suitable for X-ray diffraction
analysis were grown from CHCl3/MeOH mixture at
room temperature by slow evaporation. Crystal data
and details of the experimental crystallographic work
for 2 are recorded in Table 1. Diffraction data were
120.6
121.6 (3)

S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
79
Table 4
2
2
2 2
˚
Anisotropic displacement parameters (A ). The anisotropic displacement factor exponent takes the form: Ϫ2p [h a U11 ϩ … ϩ 2hkabU12]
U11
U22
U33
U23
U13
U12
C1
C2
C3
C4
C5
C6
C7
S8
0.087 (3)
0.050 (2)
0.049 (2)
0.049 (2)
0.0396 (16)
0.0507 (19)
0.075 (3)
0.0430 (5)
0.0676 (15)
0.0587 (14)
0.0385 (11)
0.0422 (17)
0.0477 (17)
0.0696 (13)
0.0638 (12)
0.0476 (17)
0.0560 (12)
0.0655 (13)
0.0468 (17)
0.0684 (13)
0.0625 (13)
0.0479 (17)
0.0674 (14)
0.0735 (15)
0.0105 (3)
0.063 (2)
0.072 (2)
0.060 (2)
0.0466 (17)
0.064 (2)
0.095 (3)
0.065 (2)
0.106 (3)
0.084 (3)
0.0432 (16)
0.075 (2)
0.071 (2)
0.0492 (5)
0.0528 (14)
0.0811 (17)
0.0591 (13)
0.0536 (18)
0.0441 (17)
0.0659 (13)
0.0661 (12)
0.0389 (16)
0.0663 (12)
0.0785 (14)
0.0427 (16)
0.0745 (14)
0.1021 (17)
0.0419 (16)
0.0760 (15)
0.128 (2)
Ϫ0.003 (3)
Ϫ0.0036 (18)
0.018 (2)
0.052 (3)
0.0204 (17)
0.033 (2)
0.0203 (18)
0.0100 (13)
0.0146 (17)
0.019 (2)
0.0149 (4)
0.0158 (12)
0.0304 (13)
0.0115 (10)
0.0162 (14)
0.0165 (14)
0.0372 (10)
0.0012 (10)
0.0137 (13)
0.0012 (9)
0.0391 (11)
0.0125 (14)
0.0392 (11)
Ϫ0.0144 (12)
0.0169 (14)
Ϫ0.0080 (11)
0.0601 (15)
Ϫ0.028 (3)
Ϫ0.0123 (17)
0.0101 (18)
0.0094 (16)
Ϫ0.0005 (13)
0.0117 (17)
Ϫ0.0023 (19)
Ϫ0.0056 (4)
Ϫ0.0066 (13)
Ϫ0.0005 (13)
Ϫ0.0010 (9)
0.0009 (14)
0.0001 (14)
Ϫ0.0096 (10)
Ϫ0.0062 (10)
0.0029 (14)
Ϫ0.0023 (10)
Ϫ0.0164 (10)
0.0038 (13)
Ϫ0.0194 (11)
Ϫ0.0110 (11)
0.0004 (14)
Ϫ0.0262 (13)
Ϫ0.0313 (13)
0.0251 (19)
0.0024 (14)
0.0200 (19)
0.0269 (19)
Ϫ0.0021 (4)
0.0232 (13)
Ϫ0.0261 (14)
Ϫ0.0048 (10)
0.0019 (15)
0.0048 (14)
Ϫ0.0161 (10)
0.0287 (10)
0.0032 (13)
0.0330 (11)
Ϫ0.0304 (11)
0.0078 (13)
Ϫ0.0323 (12)
0.0528 (13)
0.0005 (14)
0.0542 (14)
Ϫ0.0684 (17)
0.064 (2)
0.0628 (6)
0.0849 (17)
0.0826 (17)
0.0527 (13)
0.0517 (18)
0.0475 (17)
0.0798 (14)
0.0652 (12)
0.0444 (16)
0.0735 (13)
0.0744 (13)
0.0415 (16)
0.0879 (15)
0.0809 (15)
0.0489 (17)
0.1109 (18)
0.1038 (18)
O9
O10
O11
C12
C13
F14
F15
C16
F17
F18
C19
F20
F21
C22
F23
F24
measured on a Rigaku AFC75 Diffractometer with
Corporation [13]. Statistical tests favored the choice
of the space group P 1. As the number of molecules
˚
ꢀ
monochromated Mo radiation (l ˆ 0.71073 A). The
ꢀ
ꢀ
intensities of three control reflections (2 6 0, 2 3 0 and
with unit cell is one, the molecular symmetry must be
ꢀ
ꢀ
ꢀ
2 5 1) monitored every 150 reflections were used for
checking the stability of the crystal. The small
deterioration was corrected and data reduced using
the program developed by Molecular Structure
1 (Ci) and it must coincide with a centre of inversion
in the unit cell. The structure was solved by using
direct method SHELXS-86 [14] and refined by the
full-matrix least squares method using SHELXL-97
[15]. All the hydrogen atoms were fixed at the stereo-
˚
chemically expected positions (C–H ˆ 0.93 A) and
Table 5
2
a
˚
Hydrogen coordinates and isotropic displacement parameters (A ) .
refined as riding hydrogens. The final atomic positions
and selected molecular dimensions are recorded in
Tables 2–5. Fig. 1 portrays on ORTEP diagram [16]
x
Y
z
Ueq
H (1A)
H (1B)
H (1C)
H (3)
H (4)
H (6)
H (7)
H (12A)
H (12B)
14160
15238
13888
13812
11572
8767
11046
7379
8014
3934
4390
4766
3157
2668
4225
4712
1580
2102
661
0.145
0.145
0.145
0.088
0.076
0.076
0.086
0.059
0.059
3293
1269
4991
6806
3600
1843
4323
2310
a Coordinates are fractional × 104; isotropic thermal parameters
2
˚
Scheme 1.
are Ueq (A ). The ESD values are given in parentheses.

80
S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
Fig. 1. ORTEP [16] plot of 2 with the atom-numbering scheme.
of the molecule with atom numbering. The molecular
packing looking down the c-axis is presented in
Fig. 2.
report of X-ray results on polyfluoromethylene
system, as seen from the Cambridge Database [17].
In the crystal lattice, molecules translated along the
c-axis (x, y, z-1) are linked by a reasonably strong
˚
C–H…O hydrogen bond [O9…H12 ˆ 2.400 A and
C12–H12B…O9 ˆ 146.5Њ]. It is noteworthy that with
an excess of F acceptors, there is no trace of inter-
molecular C–H…F hydrogen bonding although there
is a short intramolecular F18…H12B contact of
3. Results and discussion
The target molecule (2) has been synthesized
according to a procedure summarized in Scheme 1.
The details of each synthetic step have been presented
in the Experimental.
The molecule adopts an extended conformation. It
also reveals that bond lengths and angles are normal
with the exception of C–C–C and F–C–F angles
which have average values of 116.2(1) and
107.2(1)Њ respectively. The widening of the C–C–C
angle from the expected value is accompanied by a
decrease in the F–C–F angle. However, there are no
˚
2.454 A. There are two intermolecular F…F contacts
˚
less than the sum of van der Waals radii of 2.84 A
˚
˚
(F21…F23: 2.670 A; F17…F17: 2.808 A). There are
at least ten intermolecular F…F, F…H, O…H and
˚
F…C contacts less than 3.0 A which may partly
account for the high crystal density (1.78 Mg/ m3).
It is to be expected that the energy contribution from
electrostatic interaction arising from F…H would also
contribute to the stability of the crystal structure.

S. De et al. / Journal of Molecular Structure 479 (1999) 75–81
81
Fig. 2. Molecular packing looking down the c-axis.
[8] M.P. Krafft, F. Giulieri, J.G. Riess, Angew. Chem. Int. Ed.
Engl. 32 (1993) 741.
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