Infrared and raman spectra of 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats). Experimental data and quantum chemistry calculations

Article abstract of DOI:10.1016/S0022-2860(01)00470-7

The infrared and Raman spectra in the range 4000-50 cm-@ were obtained for 5-amino-1,3,4-thiadiazole-2-sulfonamide. The molecular geometry was optimized by means of the DFT methods of quantum chemistry (B3LYP/6-31G**), resulting in a structure which agrees quite well with that obtained by X-ray diffraction. The wavenumbers corresponding to the normal modes of vibration were calculated using the same approximation and the associated force field converted to a set of local symmetry coordinates, with subsequent calculation of the potential energy distribution. An assignment of the observed bands is proposed on the basis of such calculations and the comparison with related molecules.

Full text of DOI:10.1016/S0022-2860(01)00470-7

Journal of Molecular Structure 570 ꢀ2001) 119±127
www.elsevier.com/locate/molstruc
Infrared and Raman spectra of 5-amino-1,3,4-thiadiazole-2-
sulfonamide ꢀHats). Experimental data and quantum
chemistry calculations
a
G.E. Cam Âõ , E.E. Chuf a n , J.C. Pedregosa , E.L. Varetti
a
a,1
b,1,*
a
Â
Area de Qu Âõ mica General e Inorg a nica ªDr. Gabino F. Puellesº, Facultad de Qu Âõ mica, Bioqu Âõ mica y Farmacia,
Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis, Argentina
CEQUINOR and LANAIS EFO -Centro de Qu Âõ mica Inorg a nica and Laboratorio Nacional de Investigaci o n y Servicios en Espectrofotometr Âõ a
b
Â
Optica, CONICETꢀUNLP), Departamento de Qu Âõ mica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata,
C. Correo 962, 1900 La Plata, Argentina
Received 2 October 2000; accepted 4 January 2001
Abstract
2
The infrared and Raman spectra in the range 4000±50 cm were obtained for 5-amino-1,3,4-thiadiazole-2-sulfonamide. The
1
pp
molecular geometry was optimized by means of the DFT methods of quantum chemistry ꢀB3LYP/6-31G ), resulting in a
structure which agrees quite well with that obtained by X-ray diffraction. The wavenumbers corresponding to the normal modes
of vibration were calculated using the same approximation and the associated force ®eld converted to a set of local symmetry
coordinates, with subsequent calculation of the potential energy distribution. An assignment of the observed bands is proposed
on the basis of such calculations and the comparison with related molecules. q 2001 Elsevier Science B.V. All rights reserved.
Keywords: 1,3,4-thiadiazole; 5-amino-1,3,4-thiadiazole-2-sulfonamide; Density functional calculations; Infrared; Raman
1
. Introduction
ties. Besides, it was proved that the metal complexes
of sulfonamides possess much stronger carbonic
anhydrase inhibitory properties than the sulfonamides
from which they were prepared [2±4]. Several studies
based on metal complexes which were synthesized in
our laboratories con®rmed this fact [5,6]. These
studies aroused our interest in the structural and spec-
troscopic characterization of synthetic acetazolamide
derivatives that could be used for elucidating the
versatility of the ligand.
Heterocyclic sulfonamides with the 1,3,4-thiadia-
zole ring are well known as inhibitors of the carbonic
anhydrase enzyme [1]. The acetazolamide ꢀ5-aceta-
mido-1,3,4-thiadiazole-2-sulfonamide) ꢀH acm) as a
therapeutically effective inhibitor of the enzyme, has
encouraged further synthesis of structural derivatives
with the aim of studying the effects of these changes
on its inhibitory activity and pharmacological proper-
2
The analysis of the vibrational spectra of the 1,3,4-
thiadiazole derivative compounds and their metal
complexes has been the most useful technique applied
to the understanding of the interaction between the
metal ions and the donor atoms of these molecules.
We have studied in previous works [7,8] the IR and
*
Corresponding author. Tel.: 154-221-4240-172;
fax: 154-221-4259-485.
Eꢀmail address: varetti@quimica.unlp.edu.ar ꢀE.L. Varetti).
Member of the Carrera del Investigador Cient Âõ ®co, CONICET,
1
R. Argentina.
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-2860ꢀ01)00470-7

120
G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
Table 1
Experimental and calculated geometrical parameters for 5-amino-
,3,4-thiadiazole-2-sulfonamide ꢀHats)
that there are few studies for 1,3,4-thiadiazole ring
derivatives comparing experimental data and
quantum chemistry calculations as a basis for the
assignment of the spectral features [9].
1
Parameter
Experimental [11]
Calculated
5-amino-1,3,4-thiadiazole-2-sulfonamide ꢀHats),
Ê
Bonds -A)
an acetazolamide derivative, has interesting pharma-
cological properties [10]. Its crystal structure is
known [11] but there is no data in the literature
regarding the infrared and Raman spectra. Therefore,
an experimental and theoretical study was made on
this substance in order to have a proper understanding
of its vibrational properties.
N3±H1
N3±H2
N3±C5
N4±C5
N4±N6
C5±S14
N6±C7
C7±S8
0.84
1.012
1.009
1.364
1.317
1.361
1.760
1.291
1.791
1.761
1.459
1.464
1.683
1.017
1.017
0.81
1.333
1.317
1.375
1.737
1.283
1.767
1.728
1.427
1.432
1.569
0.86
C7±S14
S8±O9
2. Experimental
S8±O10
S8±N11
N11±H12
N11±H13
The title compound was synthesized by acidic
0.81
hydrolysis of acetazolamide ꢀSigma) with hydro-
chloric acid [12]. Reagents used were of analytical
grade. Acetazolamide ꢀ4 g, 18 mmol) was added to a
37% hydrochloric acid solution ꢀ20 ml) at re¯uxwith
stirring for 2 h. The resulting solution was neutralized
Angles -degrees)
H1±N3±H2
H1±N3±C5
H2±N3±C5
H12±N11±H13
H12±N11±S8
H13±N11±S8
C5±N4±N6
N3±C5±N4
N3±C5±S14
N4±C5±S14
N4±N6±C7
N6±C7±S8
±
115.35
113.95
118.55
112.59
110.99
109.19
112.13
122.54
122.72
114.67
113.49
123.45
115.01
121.53
107.93
105.58
102.48
122.86
109.75
106.36
84.69
±
±
±
with NaHCO , the product was extracted with ethyl
3
±
±
acetate and the solvent was eliminated with vacuum.
After the usual workup and recrystallization 2.75 g
112.1
123.3
122.7
114.0
112.5
122.6
115.5
121.8
106.1
103.6
108.8
120.9
108.2
108.7
85.9
ꢀ15.3 mmol) of 5-amino-1,3,4-thiadiazole-2-sulfona-
mide ꢀHats) was isolated. The product was character-
ized by X-ray diffractometry; the powder pattern was
coincident with the corresponding one for Hats
crystals, obtained by the other method, used for the
structure resolution [11].
N6±C7±S14
S8±C7±S14
C7±S8±O9
FTIR spectra were recorded on a Nicolet Prot e g eÂ
60 spectrophotometer provided with a CsI beams-
C7±S8±O10
C7±S8±N11
O9±S8±O10
O9±S8±N11
O10±S8±N11
C5±S14±C7
4
21
plitter in the 4000±225 cm range, using thin KBr
pellets for the solid samples and KBr windows for the
samples dissolved in acetone. Spectral resolution was
21
21
better than 2 cm between 4000 and 2000 cm and
2
1
Dihedral angles -degrees)
S14±C7±S8±N11
S14±C7±S8±O9
better than 1 cm in the remaining ranges. The
Raman spectra were obtained with a Bruker 66 spec-
trophotometer provided with the FRA 106 Bruker
accessory, which used 1064 nm light for excitation.
104.58
139.20
11.00
104.32
139.88
6.86
S14±C7±S8±O10
Raman spectra of some sulfonamides and their
metallic complexes. A complete assignment was
dif®cult in these cases because the vibrational spectra
could not be interpreted in terms of localized vibra-
tions, because many atoms of the ring were involved
in several vibrational modes. It should be remarked
3. Calculations
The quantum chemical calculations were
performed with the Gaussian 98 set of programs
[13]. The geometric parameters were optimized and
vibrational properties were calculated using the

G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
121
Fig. 1. The molecular model of Hats.
density functional theory ꢀDFT), with the B3LYP
[
The harmonic force ®eld in cartesian coordinates
which resulted from the DFT procedure was trans-
formed to natural internal coordinates [16] through the
corresponding B matrix[17], calculated with a standard
program. The potential energy distribution was subse-
quently calculated with the resulting force ®eld.
pp
14,15] functionals and the 6-31G basis set.
Fig. 2. The infrared spectrum of solid Hats.

122
G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
Fig. 3. The Raman spectrum of solid Hats.
The force ®eld transformation and P.E.D. calcula-
and calculated molecular conformation, taking into
account that the calculation is made on an isolated
molecule whereas the experimental result corresponds
to interacting molecules in the crystal lattice.
tions were performed with the program fcartp [18].
The program moldraw [19] was used to represent
graphically the atomic displacements given by the
Gaussian programs for each vibrational mode,
allowing a qualitative understanding of the nature of
some vibrations.
4.2. Vibrational results
Representative infrared and Raman spectra of Hats
appear in Figs. 2 and 3, whereas the wavenumbers of
the observed spectral features are gathered in Table 2.
The Hats molecule has no symmetry elements. Its
36 normal modes of vibration were calculated, as well
as the corresponding infrared and Raman intensities.
The experimental and calculated wavenumbers are
compared in Table 3, being de®ned the one to one
correspondence after a careful comparison of wave-
numbers and relative intensities. The spectral features
corresponding to the n , n and n36 modes, predicted
4
. Results and discussion
4
.1. Structural results
An optimized molecular structure for Hats was
obtained as part of the DFT calculations. The corre-
sponding geometrical parameters are reproduced in
Table 1, whereas the molecular model appears in
Fig. 1. The theoretical results are compared in the
same table with the experimental data resulting from
an X-ray diffraction study [11]. The agreement
between these numbers is good, the larger difference
1
4
20
2
1
at 1066, 636 and 33 cm , could not be observed
presumably because of overlapping with more intense
bands or, in the case of n , because of experimental
3
6
Ê
being equal to 0.11 A for the S8±N11 bond and
around 28 for angles. As the dihedral angles show,
the agreement is also satisfactory for the experimental
limitations. The root mean square deviation ꢀRMSD),
calculated as a measure of the ®tting between theore-
tical and experimental wavenumbers, is equal to

G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
123
2
1
Table 2
Wavenumbers of observed bands in the infrared and Raman spectra
of solid Hats ꢀsh, shoulder; br, broad; vw, very weak)
[20] and a RMSD ˆ 67.8 cm were then obtained.
However, when the experimental wavenumbers corre-
sponding to the stretching and bending modes of the
NH2 groups, strongly affected by anharmonicity
effects, are not included in the comparison, values
a
a
Infrared
Raman
Assignment
3
3
3
3
3
2
2
1
1
1
1
431 ꢀ59)
324 ꢀ97)
307 sh
±
n
n
n
n
1
2
3
4
21
of RMSD equal to 25.3 cm without scaling and
37.6 cm after scaling, were obtained. Considering
3313 ꢀ6)
±
2
1
these values, we decided to use unscaled theoretical
wavenumbers to de®ne the band assignments below
1550 cm , as the assignment of the bands associated
with the NH groups present no dif®culties.
The infrared and Raman bands of the solid
substance are generally not coincident in wavenum-
bers, with differences amounting up to 10 cm which
should be due to intermolecular interactions in the
crystal ꢀcorrelation effects). The same effect could
be the cause of the lack of correspondence between
calculated and experimental infrared intensities in a
172 ꢀ35)
088 ꢀ21)
876 br ꢀ46)
639 br ꢀ39)
605 ꢀ91)
580 ꢀ28)
498 ꢀ98)
450 ꢀ60)
3176 ꢀ2)
±
1605 1 1498 ˆ 3103
n NH, H-bonded
n NH, H-bonded
2
1
±
±
2
1601 ꢀ11)
1579 sh
1499 ꢀ9)
1452 ꢀ51)
1364 ꢀ7)
1348 ꢀ7)
1328 ꢀ6)
1164 ꢀ13)
1139 ꢀ50)
1098 ꢀ18)
n
n
n
n
5
6
7
8
2
1
ca. 1362 sh
1140 1 228 ˆ 1368
1
1
1
1
1
1
9
7
6
6
6
342 ꢀ100)
326 ꢀ50)
174 ꢀ62)
140 ꢀ50)
097 ꢀ17)
058 ꢀ20)
44 ꢀ39)
n
n
n
n
n
n
n
n
9
10
11
12
13
15
16
17
21
few cases, particularly for the 1174 and ca. 500 cm
bands. The relative intensities of the 584 and
21
34 cm bands appear inverted with respect to the
ca. 1063 sh ꢀ6)
951 ꢀ20)
797 ꢀ37)
±
5
95 ꢀ4)
calculated values, both in the infrared and Raman
spectra; for that reason an inversion of the experi-
mental/calculated correspondence is proposed.
The assignment of the spectral features to the
normal modes of vibration was de®ned basically by
the potential energy distribution ꢀTable 3). Such
values were calculated after transforming the original
force ®eld in Cartesian coordinates to the natural
internal coordinates de®ned in Table 4. However,
the assignment of some bands deserves some
comments, as follows:
98 ꢀca. 2)
75 ꢀ16)
50 ꢀ84)
395 1 315 ˆ 710
679 ꢀ21)
647 ꢀ34)
628 sh
n
n
n
n
n
n
n
18
19
21
22
23
24
25
±
5
5
84 ꢀ62)
34 vw
579 ꢀ10)
540 ꢀ0.4)
ca. 500 sh
ca. 500 sh
4
4
4
3
3
3
2
2
2
2
85 ꢀ24)
41 sh, br
16 ꢀ23)
95 ꢀ22)
39 ꢀ21)
15 sh
475 ꢀ5)
±
2 £ 228 ˆ 456
±
n
n
n
n
n
n
26
27
28
29
30
31
403 ꢀ20)
345 ꢀ5)
322 sh
294 ꢀ49)
274 ꢀ1)
±
The infrared NH stretching region, between 3500
2
and ca. 2300 cm , is complicated by broad bands
originated by the H-bonds existing in the crystal
85 ꢀ12)
77 ꢀ7)
1
53 ꢀ4)
157 1 111 ˆ 268
28 ꢀ10)
225 ꢀ8)
157 ꢀ4)
111 ꢀ100)
84 ꢀ65)
±
n
n
n
n
n
32
33
34
35
36
[
11]. In order to clear this spectral region, infrared
spectra of the substance dissolved in acetone were
obtained. The broad bands centered at 2876 and
2639 cm disappeared in such spectra, leaving
well-de®ned bands located at 3313, 3202 and
±
±
±
±
2
1
a
Relative apparent intensities ꢀband heights) in parentheses.
2
1
21
3103 cm
and 3392 cm . These bands should correspond to
and shoulders at 3420 cm
ꢀacetone)
21
2
08.6 cm , not taking into account the three unob-
1
21
the 3324, 3172, 3088 and 3431 cm bands of solid
1
served bands. It is usual to scale the theoretical wave-
numbers with a factor which eliminates the systematic
errors associated with the used calculation method
and basis set; accordingly, the calculated values
were scaled with the recommended factor 0.9613
Hats, respectively. The Raman spectrum show only
two bands in this region, located at 3313 and
21
3176 cm , which should correspond to the
symmetric stretching modes of the NH groups. The
bands due to the corresponding antisymmetric
2

124
G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
Table 3
Observed and calculated wavenumbers, infrared and Raman intensities, potential energy distribution and approximate description of the normal
modes of vibration for Hats
a
b
Mode Observed Calculated IR intensity
Raman intensity
P.E.D. ꢀcontributions $ 10 %)
Approximate description
1
2
3
4
5
6
7
8
9
1
3431
3324
3307
3172
1605
1580
1498
1450
1342
1326
3709
3637
3585
3514
1649
1583
1530
1498
1361
1344
48.46
49.83
84.37
53.89
209.02
37.29
150.27
93.11
183.05
56.82
70.34
67.74
217.57
143.66
19.74
8.35
36 S
49 S
64 S
51 S
55 S
67 S
1
3
1
3
5
6
1 64 S
1 50 S
1 36 S
1 50 S
1 26 S
1 22 S
2
4
2
4
7
8
n ꢀC)NH
n ꢀC)NH
2
antisymmetric
symmetric
2
n ꢀS)NH
n ꢀS)NH
d ꢀC)NH
2
antisymmetric
symmetric
2
1 17 S28
2
d ꢀS)NH
n C5±N4 ꢀring) 1 n N3±C5
n N6±C7
2
8.53
65.43
5.33
48 S13 1 34 S28
100 S15
49 S22 1 42 S23
30 S
2
n SO antisymmetric
0
6.38
9
1 21 S13 1 15 S17 1 20
28 1 11 S29
Complex
S
11
12
13
14
15
1174
1140
1097
±
1183
1133
1092
1066
1049
5.44
174.46
7.96
17.44
39.53
5.34
12 S13 1 62 S14
37 S22 1 37 S23
77 S10
n N4±N6 ꢀring)
2
n SO symmetric
Rocking ꢀS)NH
2
15.73
40.52
3.52
7.23
29 S
18 S
9
9
1 18 S13 1 10 S14 1 29 S19
1 17 S14 1 18 S16 1 17
2
Rocking ꢀC)NH 1 ring bend
Ring bending
1058
S18 1 14 S19 1 14 S31
16
17
18
19
20
944
795
675
650
±
860
779
654
640
636
180.42
0.34
14.18
11.38
6.28
15 S
8
1 13 S25 1 43 S34
n S8±N11 1 wagging ꢀS)NH
n C7±S14 ꢀring) 1 ring bend
n C5±S14
2
25 S16138 S19
2.61
84 S17 1 12 S29
152.28
66.2
8.91
11 S
15 S
8
6
1 31 S20 1 12 S21 1 48 S30
1 30 S 1 22 S20 1 11
Ring torsion 1 C5 bend. oop
5.48
8
2
Wag.ꢀS)NH 1 C5 bend.
S
21 1 35 S30 1 32 S34
1 24 S16 1 27 S18 1 13
20 1 10 S34
51 S20 1 43 S21 1 39 S33
oop 1 n SN
n C7±S14 ꢀring) 1 ring bend
21
628
618
81.41
3.26
22 S
8
S
23
22
24
25
534
584
500
485
586
552
501
477
10.43
139.09
151.5
0.5
Ring torsion
2.75
3.86
5.63
12 S
13 S
14 S
8
5
5
1 15 S18 1 48 S25
Wagging SO
2
1 27 S
1 29 S
7
1 24 S24
Wagging ꢀC)NH
2 2
1 dSO
117.59
7
1 13 S21 1 22
Complex
S24 1 17 S25
26
27
28
416
395
339
425
383
363
11.37
20.4
3.41
2.56
1.08
44 S26 1 20 S29 1 10 S32
20 S24 1 24 S29 1 19 S35
14 S24 1 19 S27 1 15 S29 1 10
Rocking SO
d SO 1 N3±C5 bend. ip
2
2
12.31
Complex
S33 1 22 S35
29
30
31
32
315
285
277
228
318
300
279
228
7.39
56.16
4.55
1.64
2
35 S27 1 19 S29
Twisting SO
2
5 7 2
11 S 1 24 S 1 106 S11 1 18 S30 Torsion ꢀC)NH
10.09
0.87
12 S18 1 38 S31
n C7±S8
Ring torsion 1 d CSN
2.41
13 S12 1 40 S21 1 13 S27 1 17
S
33 1 21 S35
90 S12 1 13 S24 1 25 S26 1 13
27 1 25 S32 1 26 S35
57 S12 1 45 S27 1 50 S32 1 21 S35 Tors.
S)NH
bend ip
3
3
4
157
111
162
124
12.56
16.45
0.96
1.53
Torsion ꢀS)NH
2
S
3
ꢀ
2
2
1 twist.SO 1 C7±S8
3
5
6
84
±
92
33
7.71
6.36
3.6
2.2
15 S12 1 63 S33 1 31 S35
17 S33 1 121 S36
C7 bend. oop. 1 d CSN
C7±S8 torsion
3
a
21
Infrared intensities in km mol
4
.
Raman activities in A ꢀamu) n, stretching; d, bending; ip., in plane; oop., out of plane.
b
21
Ê

G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
125
Table 4
Natural internal coordinates for Hats. Atom numbers as in Fig. 1
a
Coordinate
Description
2
NH group
S
S
S
S
S
S
S
S
S
S
S
S
1
2
3
4
5
6
7
8
9
ˆ r ꢀ1±3)
NH stretching
NH stretching
NH stretching
NH stretching
ˆ r ꢀ2±3)
ˆ r ꢀ11±12)
ˆ r ꢀ11±13)
ˆ a ꢀ1±3±2)
NH
ꢀS)NH
NH wagging
ꢀS)NH wagging
NH rocking
ꢀS)NH rocking
NH torsion
ꢀS)NH torsion
2
deformation
ˆ a ꢀ12±11±13)
ˆ a ꢀ1±3±5) 1 a ꢀ2±3±5)
ˆ a ꢀ12±11±8) 1 a ꢀ13±11±8)
ˆ a ꢀ1±3±5) 2 a ꢀ2±3±5)
2
deformation
2
2
2
10 ˆ a ꢀ12±11±8) 2 a ꢀ13±11±8)
11 ˆ t36 1 t37 1 t38 1 t39
2
2
12 ˆ t46 1 t47 1 t48 1 t49 1 t50 1 t51
2
Ring
S
S
S
S
S
S
4
S
13 ˆ r ꢀ5±4)
CN stretching
NN stretching
NC stretching
CS stretching
CS stretching
Ring bending
14 ˆ r ꢀ4±6)
15 ˆ r ꢀ6±7)
16 ˆ r ꢀ7±14)
17 ˆ r ꢀ5±14)
18 ˆ a ꢀ5±14±7) 1 a a ꢀ4±5±14) 1 a a ꢀ6±7±14) 1 b a ꢀ5±
±6) 1 b a ꢀ4±6±7)
19 ˆ ꢀa 2 b) a ꢀ4±5±14) 2 ꢀa 2 b) a ꢀ6±7±14) 1 ꢀ1 2 a) a
Ring bending
Ring torsion
Ring torsion
ꢀ
5±4±6) 2 ꢀ1 2 a) a ꢀ4±6±7)
S
20 ˆ b t ꢀ7±14±5±4) 1 b t ꢀ6±7±14±5) 1 a t ꢀ14±5±4±
) 1 a t ꢀ4±6±7±14) 1 t ꢀ5±4±6±7)
21 ˆ ꢀa 2 b) t ꢀ4±6±7±14) 2 ꢀa 2 b) t ꢀ14±5±4±
) 1 ꢀ1 2 a) t ꢀ6±7±14±5) 2 ꢀ1 2 a) t ꢀ7±14±5±4)
6
S
6
2
SO group
S
S
S
22 ˆ r ꢀS8yO9)
SO stretching
SO stretching
SO deformation
23 ˆ r ꢀS8yO10)
24 ˆ 4 a ꢀ9±8±10) 2 g ꢀ7±8±9) 2 g ꢀ7±8±10) 2 c ꢀ11±8±
2
9) 2 c ꢀ11±8±10)
S25 ˆ g ꢀ7±8±9) 1 g ꢀ7±8±10) 2 c ꢀ11±8±9) 2 c ꢀ11±8±10)
S26 ˆ g ꢀ7±8±9) 2 g ꢀ7±8±10) 1 c ꢀ11±8±9) 2 c ꢀ11±8±10)
S27 ˆ g ꢀ7±8±9) 2 c ꢀ11±8±9) 1 c ꢀ11±8±10) 2 g ꢀ7±8±10)
SO
SO
SO
2
2
2
wagging
rocking
twisting
Other coordinates
S
S
S
S
S
S
S
S
28 ˆ r ꢀN3±C5)
NC stretching
29 ˆ a ꢀN3±C5±N4) 2 a ꢀN3±C5±S14)
30 ˆ e ꢀN3±C5±N4/S14)
In plane deformation
Out of plane deform
CS stretching
31 ˆ r ꢀC7±S8)
32 ˆ a ꢀN6±C7±S8) 2 a ꢀS8±C7±S14)
33 ˆ e ꢀS8±C7±N6/S14)
In plane deformation
Out of plane deform.
SN stretching
34 ˆ r ꢀS8±N11)
35 ˆ 4 a ꢀ7±8±11) 2 g ꢀ7±8±9) 2 g ꢀ7±8±10) 2 c ꢀ11±8±
CSN deformation
9) 2 c ꢀ11±8±10)
S
36 ˆ t40 1 t41 1 t42 1 t43 1 t44 1 t45
Torsion around C7±S8
a
a ˆ cos 1448; b ˆ cos 728.

126
G.E. Cam Âõ et al. / Journal of Molecular Structure 570 -2001) 119±127
Table 5
Wavenumbers of vibrational modes of the SO
2
NH
2
moiety in Hats and in the related molecules CH
3
SO
2
NH
2
and CF
3
SO
2
NH
2
Vibrational mode
Hats
CH SO NH [21] CF SO NH
3
2
2
3
2
2
[22]
ꢀ
ꢀ
ꢀ
S)NH
S)NH
S)NH
2
2
2
antisymm. stretch.
symmetric stretch.
deformation
3307
3172
1580
1342
1140
1097
3320
3245
1576
1315
1145
1166
689
3392
3280
1522
1357
1153
1046
432
SO
SO
2
antisymm. stretch.
symmetric stretch.
2
ꢀ
S)NH
S)NH
2
rocking
ꢀ
2
wagging
636 ꢀcalc.)
584
SO
SO
SO
2
2
2
wagging
deformation
twisting
493
533
628
495
500, 395
315
345 ꢀcalc.)
394 ꢀcalc.)
311
CS stretching
277
778
318
±
CSN deformation
ꢀS)NH
228, 84
157
337
306 ꢀcalc.)
2
torsion
stretchings should be, therefore, those located at 3431
The approximate descriptions offered in Table 3 take
into account the main contributions of the coordinates
de®ned in Table 4 to the normal modes of vibration. In a
few cases, however, the normal modes are represented
byacomplexmixtureofthesecoordinatesandaredesig-
nated as such. The present study shows how the modern
techniques of the quantum chemistry allow an under-
standingof the vibrational properties of some molecules
which could not be achieved at a comparative level with
the traditional method of spectral comparison with
related molecules.
21
and 3307 cm . Such an assignment gives a splitting
21
between both stretching modes of 107 cm for the
ꢀ
21
C)NH and 135 cm for the ꢀS)NH group, near the
2 2
2
1
1
24 cm value predicted by the calculation for both
21
groups. The band observed at 3088 cm in the infrared
spectrum is assigned to a combination of fundamentals.
The assignment of the intense Raman bands located
2
1
at 111 and 84 cm is dubious because the crystal
lattice modes are also expected in this low wavenum-
bers region. No experimental data is available at
present to remove this uncertainty.
The comparison with the spectra of related mole-
cules did not offer much help to con®rm the assign-
ments based on the calculated P.E.D. The vibrational
modes having strong contributions of the ring vibra-
tions have wavenumbers which are generally far from
the corresponding values reported for the parent ring,
Acknowledgements
The research grants of CONICET and ANPCYT
are gratefully acknowledged.
1
,3,4-thiadiazole [9], a fact which should be attributed
to the strong coupling of these vibrations with those of
the substituents in C5 and C7. An extreme example of
such disagreement is the rather localized N4±N6
stretching vibration to which is assigned the
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174 cm band in Hats, whereas in 1,3,4-thiadiazole
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