Synthesis, characterization and vibrational properties of p-fluorosulfinylaniline

Article abstract of DOI:10.1016/j.saa.2014.08.040

The reaction of p-fluoroaniline and SOCl₂ rendered p-fluorosulfinylaniline in good yield. The obtained dark yellowish liquid compound was characterized by NMR, UV-visible, FT-IR and Raman spectroscopies. The observed features were consistent wi

Full text of DOI:10.1016/j.saa.2014.08.040

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 300–305
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and vibrational properties
of p-fluorosulfinylaniline
⇑
Ana L. Páez Jerez, Andrea Flores Antognini, Edgardo H. Cutin, Norma L. Robles
INQUINOA (CONICET – UNT) Instituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, San Lorenzo 456, 4000 Tucumán, Argentina
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
A new fluorinated sulfinylaniline was
prepared in good yield.
IR, Raman and 1H NMR spectra
evidence the presence of a single syn
configuration.
ꢀ
The syn configuration adopted may be
explained through donor–acceptor
interactions.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2014
Received in revised form 5 August 2014
Accepted 21 August 2014
Available online 28 August 2014
The reaction of p-fluoroaniline and SOCl2 rendered p-fluorosulfinylaniline in good yield. The obtained
dark yellowish liquid compound was characterized by NMR, UV–visible, FT-IR and Raman spectroscopies.
The observed features were consistent with the existence of only one conformer, belonging to the CS
symmetry group. A tentative assignment of the vibrational modes was performed on the basis of exper-
imental spectra and quantum chemical calculations at different levels of theory (B3LYP and MP2 with
6-31+G(d), 6-311+G(d) and 6-311+G(df) basis sets). The conformational and vibrational properties of
p-fluorosulfinylaniline were in good agreement with experimental data reported for other substituted
sulfinylanilines and p-halogenanilines.
Keywords:
Halogen substituted sulfinylaniline
Vibrational spectroscopy
Quantum chemical calculations
Synthesis
Ó 2014 Elsevier B.V. All rights reserved.
Characterization
Introduction
N@S@O group makes these compounds interesting respect to
pre-resonant Raman properties due to
p orbitals and their related
The study of structural, conformational and vibrational proper-
ties of RAN@S@O compounds is of considerable interest. Even
though N-sulfinyl compounds can exist in two configurational
forms (syn and anti, see Scheme 1), the gas phase structures for
some members of this family showed only the presence of the ste-
rically unfavorable syn (Z-) conformer [1–7]. The presence of a
double bond character, an effect that can be used for sensing
molecular structure.
N-sulfinylaniline, O@S@NAC6H5, was first prepared by Michaelis
et al. in 1890 [8] but its exact geometrical structure was not con-
firmed until 1999 [9]. According to the results obtained by low tem-
perature X-ray crystallography, the ground state of O@S@NAC6H5 is
planar with syn (Z) configuration, in agreement with earlier results.
Although about 600 N-sulfinyl compounds are now known [10],
only a few N-sulfinyl-aromatic-imines have been characterized
and their reactivity has not been completely understood. While it
⇑
Corresponding author.
E-mail address: lisrobles@fbqf.unt.edu.ar (N.L. Robles).
http://dx.doi.org/10.1016/j.saa.2014.08.040
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

A.L. Páez Jerez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 300–305
301
Vibrational spectra
R
Fig. 1 shows the vibrational spectrum of p-fluorosulfinylani-
line. The FT-IR spectrum of this compound was recorded in the
region 4000–400 cmÀ1 at room temperature using a Perkin Elmer
GX1 Fourier Transform infrared instrument provided with KRS5
windows (4 cmÀ1 spectral resolution). The Raman spectrum of
the liquid was recorded at room temperature in the range
3350–50 cmÀ1 by employing a diode-pump, solid state 532 nm
green laser with 9.2 mW power at the sample for excitation in
a Thermoscientific DXR Smart Raman instrument equipped with
CCD detector. The resolution was between 2.7 and 4.2 cmÀ1 with
a grating groove density of 900 lines/mm. A confocal aperture of
N
S
N
S
R
O
O
syn
anti
Scheme 1.
is assumed that steric hindrance could lead to kinetic stabilization,
the electronic effects that substituents may cause on the aromatic
N-sulfinyl compounds have not been determined [11]. The study
of fluorinated substances is of considerable importance since they
are widely used in industries [12]. Due to the small size of the fluo-
rine atom and its high electronegativity, fluorinated compounds
show entirely different physical and chemical properties compared
to the other halogenated compounds [13]. In this context, we pres-
ent now the study of structural, conformational and vibrational
properties of p-fluorosulfinylaniline, a compound that will allow
us to assess the effect of an halogen atom in para position of an aro-
matic ring respect to N@S@O properties.
25 lm pinhole was used and 40 expositions of 8 s were accumu-
lated for the sample in order to achieve sufficient signal to noise
ratio.
Computational details
All quantum chemical calculations were performed using the
GAUSSIAN03 program [14]. The gradient corrected Density Func-
tional Theory (DFT) with the three-parameter hybrid functional
(B3) [15a] for the exchange part and the Lee–Yang–Parr (LYP)
correlation function [15b] has been employed, together with the
Rayleigh–Schrödinger perturbation theory developed by Møller
and Plesset at second order (MP2) [16]. 6-31+G(d), 6-311+G(d)
and 6-311+G(df) basis sets were used. Natural population analyses
NBO [17], as implemented in the GAUSSIAN03 program, were per-
formed. Gauge-including atomic orbital (GIAO) [18] and 1H chem-
ical shift calculations were done at the B3LYP/6-311+G(df) level of
theory.
Materials and methods
Experimental
Synthesis and characterization
According to the method proposed by Michaelis for the synthe-
sis of RAN@S@O compounds [8], p-fluorosulfinylaniline was pre-
pared using a 1:2:5 M relation of the corresponding fluorinated
aniline, thionyl chloride and benzene as the reaction solvent
respectively. p-fluoroaniline (3.52 g) and benzene (13.20 g) were
allowed to warm up at ca. 60 °C in a closed three neck round bot-
tom flask equipped with a Liebig condenser which was sealed with
a CaCl2 trap. Thionyl chloride (9.80 g) was added drop-to-drop to
the warming mixture. To prevent the interaction with air humidity,
the reaction was carried out in a nitrogen atmosphere. The mixture
was continuously stirred for 6 h at 85 °C and subsequently purified
by several distillation cycles in order to obtain a dark yellowish
liquid as the final product with ca. 95% yield. Its purity was con-
trolled by NMR, IR and Raman spectroscopies. The substance was
highly hygroscopic and corrosive. NMR spectra were recorded
using a Varian Unity 200 at 200 MHz for samples held at room
temperature and dissolved in CCl4 and CDCl3. 1H NMR: d = 7.06
(H8), 7.10 (H10), 7.89 (H7), 7.94 (H11) ppm.
Results and discussion
Quantum chemical calculations
Two stable conformers around the N@S double bond are
expected for p-fluorosulfinylaniline (see Scheme 1). However, cal-
culations reported for the parent sulfinylaniline [9] and some other
substituted sulfinylanilines [1–7] demonstrate that only the syn
form will be observed in the fluid phases. The potential energy
function for rotation around the N@S bond of p-fluorosulfinylani-
line was determined by structure optimizations at fixed dihedral
angles CAN@S@O in steps of 30°. Calculations at the B3LYP/6-
31+G(d) and MP2/6-31+G(d) approximations predicted
a syn
Table 1
Calculated geometric parameters for the p-fluorosulfinylaniline.a
B3LYP/6-311+G(df)
MP2/6-311+G(d)
CA F
CAH
C4AC3,5
C1AC2,6
C2,5AC3,6
C1AN
1.344
1.083
1.388
1.408
1.385
1.387
1.541
1.486
119.4
132.2
119.3
122.4
115.8
124.8
118.8
0.0
1.349
1.086
1.392
1.411
1.395
1.406
1.556
1.486
120.7
129.1
119.7
122.3
115.0
125.3
118.8
0.0
N@S
S@O
N@S@O
C1AN@S
C2AC1AC6
C3AC4AC5
C2AC1AN
C6AC1AN
FACAC
C1AN@S@O
Fig. 1. Experimental infrared and Raman spectra of p-fluorosulfinylaniline. Top:
infrared spectrum of a liquid sample held between KRS5 windows; bottom: room
temperature Raman spectrum of a liquid sample.
a
Bond lengths in Å and angles in degrees. Mean values are given for parameters
that are not unique. For numbering atoms see Fig. 2.

302
A.L. Páez Jerez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 300–305
structure as global minimum and a local minimum for anti geom-
etry, about 10 kcal molÀ1 higher in energy. Subsequent full optimi-
zations and frequency calculations at these two minima resulted in
Vibrational spectroscopy
A tentative assignment of the 3N À 6 = 36 vibrational modes
expected for the title compound is presented in Table 2. The anal-
ysis of the experimental infrared and Raman spectra of a liquid
sample of p-fluorosulfinylaniline (see Fig. 1) was supported by the-
oretical calculations using B3LYP and MP2 methods with the 6-
311+G(d) and 6-311+G(df) basis sets. Reported data for the parent
sulfinylaniline [9,19] and the reactant p-fluoroaniline [20] were
also taken into account. Wojciechowski et al. demonstrated that
the MP2 method was very limited in predicting the experimental
vibrational wavenumbers of several modes in aromatic molecules
(aniline and phenol) despite the use of extended basis sets. The
same could be stated for p-fluorosulfinylaniline through the com-
parison of calculated wavenumbers obtained with B3LYP/6-
311+G(d) and MP2/6-311+G(d) approximations (see Table 2). The
same authors published a good concordance between DFT pre-
dicted wavenumbers for p-halogenanilines after applying suitable
scale factors, and the corresponding experimental values [21].
The same scale factors proposed in the study of p-halogenanilines
were applied to the B3LYP/6-311+G(df) calculated wavenumbers
for the title compound: 0.958, for the CAH stretchings and 0.983
for the remaining vibrational fundamentals (see Table 2). In addi-
tion, theoretical 15N substitution was used to help identifying the
vibrational modes expected for the N@S@O group. Figs. 4 and 5
show graphical comparisons between the experimental and theo-
retical spectra obtained for p-fluorosulfinylaniline. The theoretical
Raman spectrum was simulated considering irradiation of the sam-
ple with a 532 nm laser, according to the method reported [21].
So far, the vibrational modes belonging to the AN@S@O group
were analyzed for more than 600 compounds [10]. According to
the data reported in a review article summarizing the spectro-
scopic and vibrational properties of the RAN@S@O compounds,
the asymmetric stretching mode occurs in a wide spectroscopic
region: from 1145 cmÀ1 in Cd(N@S@O)2 to 1302 cmÀ1 in Si(CH3)3
N@S@O. Similarly, the corresponding symmetric mode was found
between 990 cmÀ1, in KAN@S@O and 1174 cmÀ1, in 2,6-diethyl-
sulfinylaniline [1]. Thus, it is obvious that the substitution at the
nitrogen atom plays an important role in determining the strength
of the considered bonds, which in turn accounts for the orbital
interactions manifested in this group, as it was discussed above.
On the other hand, an early study on the parent sulfinylaniline
described the stretching modes as two independent N@S and
S@O stretchings, placed at 1284 and 1155 cmÀ1, respectively
[22]. This assignment was achieved based on comparison with data
reported for SO2, therefore the last fundamental was assigned to
D
G° (anti–syn) = 7.54 and 6.29 kcal molÀ1 with the B3LYP/6-
311+G(df) and MP2/6-311+G(d) approximations, respectively.
Table lists the structural parameters of the syn form of
1
p-fluorosulfinylaniline.
The higher stability of the statically unfavorable syn conforma-
tion observed for all sulfinylanilines reported hitherto may be
rationalized by orbital interactions. A Natural Bond Orbital (NBO)
analysis of the B3LYP/6-311+G(df) wavefunction of p-fluorosulf-
inylaniline suggests that the formal S@O double bond possesses
only r-bond character, and therefore three lone-pair orbitals exist
at the oxygen atom. Two of them (lp1 and lp2) show a pure p-type
nature and possess low occupancies due to strong delocalization
towards vicinal antibonding orbitals: lp2(O) ? r⁄ (NAS) and lp2
(O) ? p⁄ (NAS) with interaction energies of 19 and 62 kcal molÀ1
in the syn conformer. In the anti form these interaction energies
are lower, 18 and 55 kcal molÀ1, respectively. Even larger energy
differences, which stabilize the syn conformer, exist for interac-
tions between nitrogen and sulfur lone pair orbitals with vicinal
antibonding orbitals: lp (N) ? r⁄ (SAO) and lp (S) ? r⁄ (CAN)
with interaction energies of 15 and 10 kcal molÀ1. Corresponding
interaction energies in the anti form are only 8 and 1 kcal molÀ1
,
respectively. As these anomeric interactions decrease from syn to
anti configurations, the thermodynamic preference of the syn form
can be rationalized by higher stabilizing anomeric interactions.
Fig. 3 depicts the molecular orbitals involved in the relevant orbital
interactions.
Fig. 2. Molecular model of the syn conformer of p-fluorosulfinylaniline.
Fig. 3. Relevant NBO orbitals [B3LYP/6-311+G(df)] for the syn conformer of p-fluorosulfinylaniline.

A.L. Páez Jerez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 300–305
303
Table 2
Experimental and calculated wavenumbers (cmÀ1) and tentative assignments of the fundamental modes for p-fluorosulfinylaniline.
Mode
Approximate descriptiona
Experimentalb
IR (liq.)
Calculated
Raman (liq.)
B3LYP/6-311+G(df)
Calculated values
B3LYP/6-311+G(d)
MP2/6-311+G(d)
Scaled valuesc
m1
m2
m3
m4
m5
m6
m7
m8
CAH Stretch.
CAH Stretch.
CAH Stretch.
CAH Stretch.
CAC Stretch.
CAC Stretch.
CAC Stretch. + CAH Def.
CAC Stretch. + CAH Def.
N@S@O Asym. Stretch.
CAC Stretch. + CAH Def.
CAC Stretch.
CAF Stretch.
CAH Def.
CAH Def.
CAH Def. + CAC Def. i.p.
N@S@O Sym. Stretch.
CAH Def. + CAC Def. i.p.
CAH Def. o.o.p. + Ring torsion
CAH Def. o.o.p. + Ring torsion
Ring Def.
CAH Def. o.o.p.
CAN Stretch.
CAH Def. o.o.p.
CAH Def.
N@S@O Def. i.p.
Ring Def.
Ring Def.
Ring Def.
CAF Def. i.p.
3106 vw
3091 vw
3072 vw
–
1597 m
1587 m
1497 vs
–
1303 m
1283 m
1236 s
1227 sh
1167 s
1152 s
1097 m
1030 m
1013 w
–
–
3238 (1) [7]
3217 (1) [37]
3206 (1) [27]
3203 (1) [13]
1636 (73) [67]
1610 (6) [5]
1531 (37) [23]
1452 (1) [1]
1334 (5) [75]
1330 (2) [34]
1312 (16) [100]
1261 (67) [5]
1186 (15) [11]
1155 (100) [39]
1128 (19) [2]
1037 (6) [22]
1030 (3) [3]
1000 (<1) [<1]
979 (<1) [<1]
874 (40) [<1]
843 (4) [18]
837 (<1) [<1]
717 (14) [<1]
714 (<1) [<1]
648 (1) [5]
3102
3082
3071
3068
1609
1583
1505
1427
1311
1307
1290
1240
1166
1135
1109
1019
1012
983
962
859
829
823
705
702
637
594
3232 (2) [5]
3210 (2) [26]
3200 (1) [19]
3197 (2) [9]
1638 (95) [48]
1611 (7) [3]
1530 (47) [15]
1451 (1) [1]
1332 (5) [34]
1326 (1) [11]
1304 (24) [100]
1248 (83) [4]
1181 (27) [12]
1139 (100) [15]
1123 (53) [3]
1029 (1) [2]
1023 (18) [19]
983 (<1) [<1]
965 (<1) [<1]
862 (53) [<1]
839 (6) [13]
825 (<1) [<1]
717 (20) [1]
711 (<1) [<1]
646 (2) [3]
3253 (2) [16]
3237 (<1) [59]
3229 (<1) [39]
3221 (1) [16]
1649 (49) [57]
1629 (4) [10]
1535 (87) [25]
1476 (<1) [3]
1413 (<1) [9]
1323 (3) [10]
1316 (20) [100]
1256 (100) [4]
1200 (61) [72]
1189 (17) [7]
1126 (10) [<1]
1030 (20) [<1]
1017 (8) [<1]
878 (<1) [<1]
857 (<1) [<1]
836 (15) [11]
804 (67) [<1]
789 (3) [<1]
707 (16) [4]
642 (<1) [2]
602 (2) [1]
498 (8) [<1]
489 (1) [1]
417 (3) [<1]
404 (1) [<1]
395 (15) [1]
388 (3) [1]
275 (5) [1]
249 (6) [1]
145 (1) [1]
110 (<1) [<1]
30 (<1) [<1]
3071 m
3063 m
–
1597 m
1587 sh
1497 m
–
1302 vs
1283 m
1236 w
m9
m10
m11
m12
m13
m14
m15
m16
m17
m18
m19
m20
m21
m22
m23
m24
m25
m26
m27
m28
m29
m30
m31
m32
m33
m34
m35
m36
1167 m
1151 s
1095 vw
1029 s
–
–
–
–
842 w
821 m
712 w
–
634 m
596 m
–
486 w
446 vw
–
393 vw
342 w
281 w
193 w
130 w
–
–
876 sh
843 s
822 m
702 m
681 m
635 w
598 w
535 m
484 vw
448 m
420 w
396 m
–
604 (1) [2]
603 (1) [2]
548 (3) [<1]
450 (5) [<1]
430 (<1) [<1]
425 (2) [<1]
401 (12) [1]
282 (3) [1]
268 (4) [<1]
135 (1) [<1]
117 (<1) [<1]
63 (<1) [<1]
539
442
423
418
394
277
263
133
544 (4) [<1]
448 (7) [<1]
428 (<1) [<1]
422 (2) [<1]
400 (16) [1]
281 (4) [1]
268 (5) [<1]
137 (1) [<1]
117 (<1) [<1]
64 (1) [<1]
Ring Def.
CAF Def. o.o.p.
Skeletal Def.
N@S@O Def. o.o.p.
Ring Def.
Ring Def.
–
–
–
–
115
62
Ring Def.
a
b
c
Stretch.: stretching; Def.: deformation; Asym.: antisymmetric; Sym.: symmetric; sh: shoulder; i.p.: in phase; o.o.p.: out of phase; and tors.: torsion.
s: Strong; vs: very strong; m: medium; w: weak; and vw: very weak.
Values scaled according to scaling factors in Ref. [21].
Fig. 5. Experimental and theoretical Raman spectra of p-fluorosulfinylaniline. Top:
theoretical gas phase Raman spectrum calculated at the B3LYP/6-311+G(df) level of
theory (532 nm excitation laser); bottom: room temperature spectrum of a liquid
sample.
Fig. 4. Experimental and theoretical infrared spectra of p-fluorosulfinylaniline. Top:
theoretical gas phase spectrum calculated at the B3LYP/6-311+G(df) level of theory;
bottom: room temperature infrared spectrum of a liquid sample.
the S@O symmetric stretching. However, a subsequent study of the
pre-resonant Raman spectra of sulfinylaniline concluded that both
stretching modes are actually coupled and appear at 1298 cmÀ1
(NSO asym) and 1163 cmÀ1 (NSO sym.), tough no frequency shift
was observed for the bands upon isotopic substitution of the
nitrogen atom [19]. In the vibrational spectra of p-fluorosulfinylan-
iline the bands at 1303 and 1030 cmÀ1 (IR) and 1302 and
1029 cmÀ1 (Raman) were assigned to the NSO asymmetric and
symmetric stretchings, respectively. The downshift of 6 cmÀ1 pre-
dicted for the 1037 cmÀ1 feature, while no changes were predicted

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A.L. Páez Jerez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 300–305
Table 3
strongest affected. However, the particular symmetry of the
N@S@O group in the stable syn conformer of p-fluorosulfinylani-
line breaks the expected equivalence of the aromatic protons,
therefore, each of the expected signals show to be rather complex.
Taking into account the theoretical 1H NMR spectrum obtained, H7
and H11 (see Fig. 2) show to be the most influenced by the pres-
ence of the electron withdrawing N@S@O group, therefore, the sig-
nals observed at 7.94 and 7.89 ppm were assigned to those
protons, respectively. Therefore, the remaining features observed
belong to the H8 and H10 atoms.
Tentative assignments of 1H NMR experimental and calculated chemical shifts for
p-fluorosulfinylaniline.
Atomsa
Chemical shift (d) (ppm)
Experimental
Theoreticalb
H8
H10
H7
7.06
7.10
7.89
7.94
6.785
6.873
7.206
8.911
H11
a
For atom numbering see Fig. 2.
Calculated chemical shifts (GIAO method) using B3LYP/6-311+G(df)
b
approximation.
Conclusions
A new member of the sulfinylaniline family of compounds has
been prepared by reacting p-fluoroaniline and SOCl2. The obtained
highly reactive and corrosive liquid compound was characterized
by using 1H NMR and vibrational spectra. Although at least two
stable conformers might be expected (syn and anti with respect
to the CAN and S@O bonds), all experimental spectra evidence
the presence of a single conformer, since no additional signals were
observed to account for several forms in equilibrium at room tem-
perature. Theoretical calculations using B3LYP and MP2 methods
confirmed that only the syn conformer is present in the fluid
phases, predicting a local C1 symmetry for the N@S@O group,
although a global CS symmetry may be safely assumed in agree-
ment with the properties observed for the parent sulfinylaniline.
The unexpected syn configuration adopted by all R-N@S@O com-
pounds reported so far might be rationalized in terms of orbital
interactions. In fact, larger interaction energies were predicted
for the syn configuration of p-fluorosulfinylaniline compared to
the anti structure, according to Natural Bond Orbital analysis. Thus,
the thermodynamic preference of the syn form can be rationalized
as a result of the influence of stabilizing anomeric interactions.
for neither the 1186 cmÀ1 nor the 1155 cmÀ1 bands, allowed us to
propose these assignments.
It is interesting to note that no remarkable influence of this
group was revealed in both, the experimental and theoretical
vibrational spectra between the p-fluorosulfinylaniline and the
parent unsubstituted compound. However, calculations performed
for o- and m-fluorosulfinylaniline, indicate that the influence of a
fluorine atom depends on its position in the aromatic ring and on
the vibrational mode considered. Thus, the asymmetric stretching
of the N@S@O group in o-fluorosulfinylaniline was calculated at
1335 cmÀ1, in close agreement with that belonging to the title mol-
ecule (1334 cmÀ1), while the corresponding mode for the meta
substituted compound was predicted at 1348 cmÀ1 (B3LYP/
6-311+G(df). In turn, the symmetric N@S@O stretching was calcu-
lated at 1037, 1059 and 1056 cmÀ1 for p-, o- and m-sulfinylaniline,
respectively [23].
The in-plane deformation of the N@S@O group was assigned to
the signal placed at 635 and 634 cmÀ1 in the infrared and Raman
spectra, respectively.
Data reported for the p-fluoroaniline allowed a straight assign-
ment of the signal belonging to the CAF stretching in the title com-
pound [20]. This signal was observed as a strong feature at
1225 cmÀ1 in the IR spectrum, therefore it was safely attributed
to the shoulder ca. 1227 cmÀ1 in the infrared spectrum of p-fluoro-
sulfinylaniline. It is worth mentioning that this fundamental mode
has shown to be sensitive towards substitution of the benzene ring,
since it was found at 1270 and 1288 cmÀ1 in the infrared spectrum
of o-fluoroaniline and m-fluoroaniline, respectively [24]. The study
of the corresponding o-fluorosulfinylaniline and m-fluorosulfiny-
laniline will allow us to determine if the N@S@O group exerts a
similar influence on the CAF stretching on these compounds [23].
Acknowledgments
Authors acknowledge Prof. Dr. Heinz Oberhammer, University
of Tübingen, for valuable discussion. Authors also acknowledge
CONICET (Consejo Nacional de Investigaciones Científicas y Técni-
cas) and UNT (Universidad Nacional de Tucumán) for the financial
support.
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