On the search of the influence of substituents in the structural and vibrational properties of p-substituted sulfinylanilines: Study of p-trifluoromethylsulfinylaniline

Article abstract of DOI:10.1016/j.jfluchem.2018.02.013

The study of substitution effects on the structural and vibrational properties of para substituted sulfinylanilines proceeds a step forward with the study of p-trifluoromethylsulfinylaniline, synthesized and characterized by NMR, Raman, FTIR and mass spec

Full text of DOI:10.1016/j.jfluchem.2018.02.013

Accepted Manuscript
Title: On the search of the influence of substituents in the
structural and vibrational properties of p-substituted
sulfinylanilines: study of p-trifluoromethylsulfinylaniline
Authors: Doly M. Chemes, Edgardo H. Cutin, Rosa M.S.
´
Alvarez, Norma L. Robles, Heinz Oberhammer
PII:
S0022-1139(17)30460-8
DOI:
Reference:
https://doi.org/10.1016/j.jfluchem.2018.02.013
FLUOR 9127
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Revised date:
Accepted date:
26-10-2017
23-2-2018
26-2-2018
´
Please cite this article as: Chemes DM, Cutin EH, Alvarez RMS, Robles
NL, Oberhammer H, On the search of the influence of substituents in the
structural and vibrational properties of p-substituted sulfinylanilines: study
of p-trifluoromethylsulfinylaniline, Journal of Fluorine Chemistry (2010),
https://doi.org/10.1016/j.jfluchem.2018.02.013
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On the search of the influence of substituents in the structural and vibrational
properties of p-substituted sulfinylanilines: study of p-
trifluoromethylsulfinylaniline
Doly M. Chemes, a Edgardo H. Cutin, a Rosa M. S. Álvarez b*, Norma L. Robles b* and Heinz
Oberhammer c
a Instituto de Química Física – Facultad de Bioquímica, Química y Farmacia, Universidad
Nacional de Tucumán. San Lorenzo 456, 4000 Tucumán, República Argentina.
b INQUINOA CONICET UNT. Facultad de Ciencias Exactas y Tecnología. Av.
Independencia1800, 4000 Tucumán, República Argentina.
c Institut für Physikalische und Theoretische Chemie, Universität Tübingen, 72076 Tübingen,
Germany
* nrobles@herrera.unt.edu.ar; * myshukoalvarez@gmail.com
Dedicated to Prof. Dr. Rüdiger Mews on occasion of his seventy-fifth birthday.
.
HIGHLIGHTS
Molecular properties of p-CF3ArNSO were determined by the NMR, Raman, FTIR, GC-Mass
methodologies.
PES scans and subsequent structural and vibrational characterization were performed by DFT
methods.
The energetically preferred molecular geometry has the NSO group in syn conformation and
coplanar with the aromatic ring.

GRAPHICAK ABSTRACT
IR
Raman
(cm-1)
Abstract
The study of substitution effects on the structural and vibrational properties of para substituted
sulfinylanilines proceeds a step forward with the study of p-trifluoromethylsulfinylaniline,
synthesized and characterized by NMR, Raman, FTIR and mass spectra. The experimental
spectra were compared and analyzed taking into account theoretical spectra obtained with
quantum chemical calculations at different levels of theory. The spectroscopic results reveal the
presence of a single form of this molecule which, according to the calculated molecular structure,
possesses the NSO group coplanar with the ring plane. In addition, the syn conformation of the
NSO group is also derived from both, experimental and theoretical data. The presence of the CF3
group in the para position of the aromatic ring influences the properties of the N=S=O group,
with the N=S bond more strongly affected than the S=O bond compared to results reported for
other para substituted sulfinylanilines.
Keywords: sulfinylaniline; vibrational spectroscopy; structural analysis

1. Introduction
Reactivity and structural/chemical properties of several organic N-sulfinylimines compounds of
the type R‒N=S=O have been subject of studies since the first reports of their synthesis by
Michaelis and co-workers 1, 2. By using various experimental techniques such as gas electron
diffraction, X-ray crystallography, UV-visible absorption spectroscopy, 17O NMR spectroscopy,
GC-Mass Spectrometry, and FTIR and Raman spectroscopies, as well as theoretical methods, it
was demonstrated that all R‒N=S=O compounds show syn conformation between the R‒N
single bond and the S=O double bond. The R group was benzene [3], ClC(O)S 4, CF3SS 5,
more recently CF3 and SF5 6 and many others, as it was reviewed by Romano and Della
Védova 7. The stability of this sterically unfavorable conformation, where the electron lone
pairs of nitrogen and sulfur eclipse each other, lies in the orbital interactions between each lone
pair and the opposite S‒O or N‒R antibonding σ* orbital. This anomeric effect is absent in the
anti form. As result, quantum chemical calculations predict the energy of anti conformation
about 8 kcal.mol-1 higher than syn for all mentioned compounds [7].
Particularly interesting are the N-sulfinylanilines since, due to the high reactivity of the aromatic
sulfinylamine function (Ar-N=S=O), they are used as ligands in organometallic chemistry [8]
and as precursors for obtaining cyclic sulfonamides with pharmacological properties [9-11]. The
study of the influence of substituents in the aromatic ring on the properties of the –N=S=O group
is therefore of significant relevance. Accordingly, we have focused on determining the structural
and vibrational characteristics of monosubstituted halogen sulfinylanilines such as o-, m and p-
fluorosulfinylaniline (FArNSO) [12-14], and m- and p-chlorosulfinylaniline (ClArNSO) [15, 16]
by using FTIR and Raman spectroscopies and quantum chemical predictions together with NMR
and GC-mass measurements. In these compounds, the syn conformation is characterized by a
fully planar molecular structure. This geometry not only favors the formation of an
intramolecular hydrogen bond between the oxygen and the H atoms in ortho position, but also
the electronic delocalization through the aromatic ring and the sulfinylimine group [17].
In the present work we address a conformational and vibrational analysis of para-
trifluoromethylsulfinylaniline, (p-CF3ArNSO). The inclusion of this compound in our series of
halogen substituted-sulfinylanilines is based on the popularity of the trifluoromethyl group in
pharma and agrochemical molecules, due to its capacity to exert significant changes on

neighboring active centers as well as to increase lipophilicity of the molecules that contain it [18].
p-CF3ArNSO preparation was reported previously, as part of a study of the reactivity of N-
sulfinyl compounds with thioborane 19. Further studies, based on comparative analyses by 17O
and 13C NMR spectroscopy of several sulfinylanilines, were focused in the nature of the S-O
bond and the influence of substituents on its properties [20]. Now we present a more complete
approach of the structural properties of the p-CF3ArNSO molecule, for which FTIR, Raman and
NMR (1H and 13C) spectroscopies, together with measurements by GC-mass spectrometry, were
used. Quantum chemical calculations at various levels of theory supported the analysis of the
experimental data. A comparison with the results previously obtained for p-halogen substituted
sulfinylanilines allowed us to establish a correlation between specific vibrational frequencies and
hence to infer about the effect produced by the substituent at structural level according to its
inductive and mesomeric characteristics. It is well known that many efforts have been invested in
studying the biological aspects of new fluorine or trifluoromethyl-containing compounds [21].
Then, we expect that our results contribute to a better understanding of the reactivity of this kind
of molecules.
2. Results and discussion
Figure 1 presents the FTIR and Raman spectra in the 4000‒400 and 3500‒300 cm-1 spectral
ranges, respectively, of the green liquid obtained after purification. The absence of bands
attributable to the NH2 group (between 3500 and 3400 cm-1) indicates that the amine precursor
has been completely eliminated.

Figure 1. Experimental infrared (A) and Raman (B) spectra of p-CF3ArNSO.
2.1. Conformational analysis and structural characterization
The evaluation of the most stable conformations adopted by the p-CF3ArNSO molecule was
performed by exploring the potential energy surface (PES) as a function of two dihedral angles
that were modified independently. Figure 2 shows the relaxed PES scans done at the B3LYP/6-
311+G(df) level for the dihedral angles (C-N=S=O) and (C-C-N=S), varied from 0° to 180° in
steps of 30°. As it was observed for all N-sulfinylimines reported so far, the global minimum
obtained for the first scan corresponds to the syn conformation regarding the orientation of the C‒
N and the S=O bonds, (C-N=S=O) = 0°, while a considerably high barrier to rotation around the
N=S double bond was predicted. A previous PES study of HNSO, the simplest N-sulfinylimine,
indicated that the syn conformer is 4.58/4.97 kcal.mol-1 (B3LYP/MP2, respectively) than the anti
form, and that the interconversion between them solely involves a planar nitrogen inversion [22].
However, in a recent article on the generation and characterization of the OSNSO species,
conformational interconversions of the type syn-syn→ syn-anti and syn-syn → anti-anti were
analyzed by considering the explicit N=S bond rotation [23].The scan around the C-N bond of p-
CF3ArNSO indicated that the planar conformation was adopted by the whole molecule, since two

equivalent minima were obtained for the variable (C-C-N=S) = 0°/180°. The barrier to internal
rotation at the perpendicular conformation was calculated to be 5.06 kcal.mol-1.
Figure 2. Calculated relaxed PES scans for rotation around the N=S bond (A) and the C‒N bond (B).
A): the syn cornformation ( CNSO = 0°) of the NSO group is the most stable one; the second local
minimum predicted corresponds to the anti form ( CNSO = 180°). B): similarly, coplanarity between the
NSO group with the aromatic ring ( CCNS = 0° or 360°) is the preferred arrangement. Calculations were
performed at the B3LYP/6-311+G(df) level of theory.

Subsequent full optimization and frequency calculation for the planar molecule in both the syn
and anti conformations were performed at the B3LYP/6-311+G(df) and MP2/cc-pVTZ levels of
theory. Since no imaginary vibrational frequencies were predicted, both forms correspond to
stable structures, but the syn form was the preferred one according to ΔE° (anti-syn) = 5.06/8.14
kcal.mol-1 and ΔG° (anti-syn) = 6.63 /8.52 kcal.mol-1 (B3LYP/MP2 methods, respectively).
The higher stability of the sterically unfavorable syn conformation of the N=S=O group is
explained by anomeric effects. The NBO analysis performed with the B3LYP/6-311+G(df)
approximation showed orbital interactions between the nitrogen and sulfur lone pairs with vicinal
antibonding orbitals. Figure 3 represents the lp (N) →σ* (S‒O) and lp (S) →σ* (C‒N) orbital
interactions that contribute with 15.33 and 5.61 kcal.mol-1, respectively, to the stabilization of the
syn conformation, while the contributions for the anti form amount only 9.90 and 1.01 kcal.mol-1,
respectively.

Figure 3. Relevant NBO orbital interactions calculated with B3LYP/6-311+G(df) approximation for syn
and anti conformations of p-CF3ArNSO.
The planar conformation predicted for the molecule facilitates a weak orbital interaction between
oxygen and the ortho hydrogen closest to it. This interaction is called anti-hydrogen bond, and a
distinctive consequence of it is the shortening of the C‒H bond involved and the consequent blue
shift of its stretching frequency. Additionally, the C---O distance is generally found to be in the
3.00 – 4.00 Å range 24. This interaction was already observed in the parent N-sulfinylaniline
17. According to MP2/cc-pVTZ calculation the overlap population for this O---H interaction is
+0.02 au, about 5% of the C‒H overlap (0.42 au). The O---H distance (2.27 Å) is shorter than the
Van der Waals distance of 2.60 Å while the C---O distance is predicted to be 3.05 Å.
As it was expected, the CF3 group attached in para position is freely rotating. In the equilibrium
orientation, one C‒F bond is perpendicular to the phenyl ring and the barrier of this 6-fold
potential with one C‒F bond in the plane of the phenyl ring is only 0.04 kcal/mol.
Figure 4 shows the optimized molecular structure of the most stable conformer. C‒H bond
lengths and O--H distance, calculated at the B3LYP/6-311+G(df) level are included. The
remaining structural parameters are presented in Table 1, together with those obtained with the
MP2/cc-pVTZ approximation.

Figure 4. Optimized molecular structure of p-trifluoromethylsulfinylaniline. All the CH distances,
calculated with the B3LYP/6-311+G(df) method, are included in order to show the shortening of the C2-
H1 bond as consequence of the anti-Hydrogen bond interaction.
2.2. Vibrational analysis
The vibrational analysis of p-CF3ArNSO was based on the evaluation of the experimental FTIR
and Raman bands and on the corresponding theoretical predictions. Experimental and calculated
vibrational behaviors for related systems such as the parent sulfinylaniline [3] and the reactant p-
trifluoromethlyaniline [25], as well as reported experimental and calculated data for p-FArNSO
[14] and p-ClArNSO [16 were also taken into account.
Figure 5 shows the spectral region between 1500 and 500 cm-1 of the experimental FTIR and
Raman and the calculated spectra (B3LYP/6-311++G(df,dp)) of p-CF3ArNSO. A tentative
assignment of all the fundamental vibrational modes expected for the title compound is presented
in Table 2. As can be seen in Table 2, vibrational frequencies calculated at B3LYP/6-
311++G(df,dp) and B3LYP/cc-pVTZ levels of theory show similar accuracy compared to the
experimental bands. Nevertheless, while both basis sets are of triple zeta level, the former is split
valence, which makes it significantly less expensive in terms of computational cost. In order to
check the performance of the variational approach attained with B3LYP, MP2 calculations were
also performed. It is well known that electronic self-interaction (among other deficiencies) may
sometimes be a serious problem in DFT-based calculations, so we consider good practice to

perform wavefunction (post-Hartree-Fock) calculations in order to check for serious
discrepancies in the predictions, whenever possible. In this occasion, MP2 and DFT predictions
did not differ in any significant (qualitative) way, although DFT methods produced frequencies
that were better correlated with the experimental data than MP2 26.
Although the vibrational spectra of the parent sulfinylaniline have been extensively studied,
some controversies were detected a few years back regarding the coupling of N=S and S=O
bonds in the stretching vibrations. A detailed work published by Meij et al. on the Raman spectra
of sulfinylaniline [27] concluded that the stretching modes of the N=S=O group should be
described as two independent modes placed at 1284 cm-1 and 1155 cm-1 and assigned to the N=S
and S=O bonds, respectively. Romano et al. reported later the resonance Raman spectra and
quantum chemical calculations of this compound revealing a strong coupling between both
modes, which were defined as antisymmetric (at 1298 cm-1) and symmetric (at 1163 cm-1)
stretching vibrations [3]. More recently, our group reported the analysis of the vibrational spectra
and theoretical frequencies of p-FArNSO 14. This analysis pointed out that the bands centered
at 1303 cm-1 and 1030 cm-1in the IR spectrum could be attributed to the N=S=O antisymmetric
and symmetric stretching modes, respectively. A similar interpretation of the IR bands at 1297
cm-1 and 1031 cm-1 of p-chlorosulfinylaniline was later proposed [16]. A preliminar comparison
with results for m-, o-, and p- isomers of FArNSO [13,12,14] showed that the antisymmetric
stretching of the N=S=O group is the most affected vibration upon substitution at different ring
locations, with a frequency blue shift of up to 11 and 4 cm-1 for the meta and ortho isomers,
respectively. These shifts may be rationalized by taking into account the electronic effects
derived from the position of the substituent in the aromatic ring. As it was stated for this
fluorosulfinylaniline series, the small size of the fluorine atom may help in supplying the
aromatic ring with electronic density upon mesomeric delocalization of lone pair orbitals. In
contrast, it may withdraw electronic density from the aromatic ring due to its strong inductive
effect. In the present case, the CF3 group in para position of the aromatic ring would not
represent a source of electronic density towards the aromatic ring either through mesomeric or
inductive effects. The bands observed at 1289 and 1033 cm-1 in both vibrational spectra were
attributed to the antisymmetric and symmetric stretching modes of the N=S=O group (see Table
2). When comparing different p-substituted compounds, the evaluation of the contribution of the

electronic effects involved did not help to understand the frequency of the stretching vibrations.
In the series: p-FArNSO, p-CF3ArNSO and p-ClArNSO, the N=S distance was predicted to be
1.541, 1.539 and 1.507 Å, respectively (B3LYP/6-311++G(df,pd)). The corresponding
antisymmetric N=S=O stretching mode was assigned to the signals at 1303, 1289 and 1297 cm-1,
respectively (IR), suggesting this vibration to be sensitive to the substituent although it did not
show correlation with the bond lengths. The S=O bond distance was rather constant in this series,
being 1.486, 1.483 and 1.485 Å, respectively (B3LYP/6-311++G(df,pd)). The N=S=O
symmetric stretching mode was found to be similar for all studied substituted sulfinylanilines;
this mode was assigned to the signals centered at 1030, 1033 and 1031 cm-1, respectively in the
mentioned series. It is clear then that the effect exerted by the substituent was stronger in the
N=S bond of the N=S=O group than in the S=O one. The low sensitivity of the S=O bond to the
ring substitution in para position would be a consequence of the anti-H bond interaction in
which it is involved. The assignment of these stretching vibrations was further supported by
additional calculations: theoretical 15N substitution evidenced significant downshifts of the bands
attributable to the N=S=O antisymmetric and symmetric stretchings (1267 and 1017 cm-1,
respectively, with B3LYP/6-311++G(df,pd) ), allowing a confident identification of these modes
in the experimental spectra. The C‒N stretching appeared to be involved in several fundamental
stretching and bending vibrations, making difficult its assignment to a unique signal. However,
the C-N stretching was associated with the band observed at 730 cm-1 and calculated at 723 cm-1
based on the downshift, albeit small, predicted upon 15N substitution (720 cm-1).
Taking into account data reported for the p-trifluoromethylaniline, the assignment of the
fundamental vibrational modes belonging to the CF3 group in p-CF3ArNSO was straightforward.
In general, all benzene derivatives containing a trifluoromethyl group show a broad and strong
band near 1330 cm-1 in the infrared spectrum, while in the Raman its counterpart possesses
variable intensity [25]. In the present case, an intense and broad IR signal with maximum at 1326
cm-1 and a shoulder at ca 1314 cm-1 were assigned to the CF3 antisymmetric and symmetric
stretching modes, respectively. The totally symmetric CF3 stretching was observed at 1173 cm-1.
The features observed at 1328 and 1170 cm-1 in the Raman spectrum were associated to these
vibrations. In agreement with the assignment proposed for several other species containing the

CF3 functional group, the symmetric CF3 bending was associated to the medium intensity signal
centered at 792 cm-1 in the Raman spectra.
Figure 5. Experimental and theoretical spectra of p-trifluoromethylsulfinylaniline in the region between
1500 and 500 cm-1. Red lines: spectra calculated with the B3LYP/6-311++G(df,pd) approximation for the
isolated molecule in vacuum. Black lines: experimental spectra of the liquid sample at room temperature.
2.3. NMR analysis
Table 3 shows the experimental 1H and 13C chemical shifts of p-CF3ArNSO in CDCl3 (TMS was
used as internal reference) and the corresponding calculated values with the B3LYP/6-311+G(df)
approximation and the gauge-invariant atomic orbital (GIAO) method. According to reported
values for benzene derivatives and taking into account the theoretical predictions, the four

protons attached to the aromatic ring, labeled as H1, H4, H3 and H2 in Figure 4, showed signals
at 7.88, 7.84, 7.61, and 7.66 ppm, respectively, and appear as two doublets. The highest shielding
was experienced by H1 since it was closest to the S=O group; H4 was also affected, although in
a lesser extent, indicating that the NSO group was able of a 180° rotation to give an equivalent
conformation. This conformational interconversion was in agreement with the potential energy
scan presented in Fig. 2B. However, such H4 chemical shift was not predicted by the
calculations (see Table 3) due to the limitation of the theoretical method (no rotations are
allowed during calculation). The magnitude of the shielding experienced by the H atoms in ortho
position could also be related to the presence of the CF3 substituent, since experimental NMR
results previously obtained for p-FArNSO and p-ClArNSO have shown higher (7.94/7.89 ppm)
[14] and lower (7.12/7.07 ppm) [16] shielding, respectively, compared with the title molecule.
This behavior would be in line with the N=S bond length mentioned above. On the other hand,
the signals observed at 144.40, 126.98, 126.36, 127.71, 126.31, 126.89, and 131.57 ppm were
assigned to the carbon atoms from C1 to C7. The high chemical shifts observed for C1 and C7
with respect to the other carbon atoms were attributed to the shielding exerted by the nitrogen
and the fluorine atoms, respectively.
2.4. GC/MS analysis
Figure 6 shows the mass spectrum of the p-CF3ArNSO. The peak at m/z 207 was attributed to
the molecular ion [M+·], therefore the peak at m/z 208 was assigned to the protonated form of the
molecular ion [MH+·]. The feature at m/z 138 [M+·-69] was the base peak and was assigned to
the fragment resulting from the loss of the trifluoromethyl group; the intensity of this signal was
consistent with the high stability of the aromatic ion. The weaker peaks at m/z 191 [M+-16] and
188 [M+-19] were attributed to the loss of the O atom and a single fluorine atom, respectively.
Taking into account general fragmentation schemes reported for several substituted
arylsulphinylamines 28, the unstable species with 188 mass to charge ratio might subsequently
experience an SO loss, being the evidence of this fragmentation path the signal at 140 m/z. By
following these reported fragmentation schemes, the peak at m/z 63 might account for the
+
formation of a C5H3 species which would be originated by the C6H4N+ fragment (90 m/z), both
appearing with significant relative abundance in the spectra presented [28]. However, the peak

associated to this last species showed very low abundance in the spectra registered for p-
CF3ArNSO. Then, an alternative interpretation of the feature at 63 m/z in the spectrum of the
title molecule is proposed. Intramolecular interactions between oxygen and ortho hydrogen
atoms in p-CF3ArNSO would result reinforced upon loss of CF3, favoring the fragmentation and
subsequent loss of a HNSO+ specie. Since HNSO was recently suggested to be the most stable
isomer of S-nitrosothiols 29 its formation may be feasible. The base peak would be also
responsible for the feature at 110 m/z, assigned to the C5H4NS+ fragment that results from the
loss of the CO group after an intramolecular rearrangement, in concordance with the reported
fragmentation scheme for substituted arylsulphinylamines [28].
Figure 6. Mass spectrum of p-trifluoromethylsulfinylaniline, represented as relative abundance versus
mass to charge ratio (m/z). The peak at m/z 207 is attributed to the molecular ion [M+·]. The loss of the
CF3 group results in the base peak at m/z 138, indicating that the resulting aromatic fragment is stable by
charge delocalization.
3. Conclusions
By adjusting the general protocol for the synthesis of sulfinylanilines it was possible to obtain
the product p-trifluoromethylsulfinylaniline. This compound enlarges the series of para

substituted aromatic-NSO compounds studied by our group, already integrated by the p-
fluorosulfinylaniline and the p-chlorosulfinylaniline. Molecular properties were studied by 1H
and 13C NMR and GC/MS measurements. A vibrational characterization was performed by using
the FTIR and Raman spectroscopies and quantum-chemical calculations at different levels of
theory.
According to energy calculations for the possible conformers and taking into account the number
of vibrational bands observed in the experimental spectra, the presence of a single form of this
molecule in the liquid phase was assumed. As was already demonstrated by previous studies of
related sulfinylimines, the syn conformation of the NSO group was also the dominant form in
this case. In addition, calculations predicted coplanarity between the NSO group and the
aromatic ring, which was supported by the experimental 1H NMR analysis.
Special attention was paid to the vibrational assignment of the N=S=O group, since this has been
object of some discrepancies in the past. In the context of our serial studies, we proposed a
consistent and reliable assignment of the infrared and Raman features for this kind of
compounds: the vibrational stretches involving the NSO group are coupled in symmetric and
antisymmetric modes, but the former shows a higher character of S=O stretching while the
stretching of the N=S bond is dominant in the antisymmetric vibration. This interpretation was
based on the frequency shifts that were observed upon ring substitution in para position. This, in
turn, impacted on the experimentally observed chemical shifts of the protons attached to the
aromatic ring in ortho position. In addition, GC-MS spectrum showed features that would be
consistent with a molecular structure that favors the hydrogen-bonding interaction between the
oxygen and one of the ortho-H atoms.
4. Experimental Details
4.1.1. Synthesis: Obtaining p-CF3ArNSO was achieved by following the traditional method
proposed by Michaelis that consists in treating amines with thionyl chloride in benzene or ether
[1]. In the present case, a 1:3:7 molar relation of p-trifluoromethylaniline, thionyl chloride and
benzene was used. All the substances were purchased to Sigma-Aldrich Argentina and used
without further purification. p-Trifluoromethylaniline, (3.85 g, 24 mmol) and benzene (13.2 g,
170 mmol) were first placed in a three-neck round-bottom flask equipped with a Liebig

condenser which was sealed with a CaCl2 trap. Then, thionylchloride (9.80 g, 82 mmol) was
added drop wise to the mixture. To prevent the interaction with air humidity, the loading of the
three components was carried out under nitrogen atmosphere. Since a vigorous reaction took
place while thionyl chloride was added, the mixture was continuously stirred. Then, the flask
was closed and the mixture was heated for 8 hours at 80‒85 °C. The evolution of the reaction
was followed by IR spectroscopy: the complete disappearance of the bands between 3400 and
3500 cm-1, attributed to the NH2 group of the reagent, was determinant. Once the reaction was
over, the dark liquid obtained (yield: 4.54 g (92%)) was subsequently purified by several
distillation cycles in order to get the pure final product (yield: 4.24 g (86%)). The resulting green
liquid is highly hygroscopic and corrosive. It was subjected to elemental analyses and further
purity control was performed by using several experimental techniques, as it is detailed.
4.1.2. Elemental analysis: These studies were conducted using an EXCETER CE-440 analyzer.
According to the molecular formula of p-CF3ArNSO the following abundances (expressed in %)
are expected: C, 40.58; H, 1.93; N, 6.76. The elemental analyses for the obtained compound
gave the following abundances (in %): C, 40.64; H, 1.69; N, 7.13, which indicated a yield of ca.
98%.
4.1.3. Spectroscopic measurements: FTIR spectra of p-CF3ArNSO between 3500 and 400 cm -1
were recorded with a Perkin-Elmer GX1 Fourier Transform infrared instrument (1 cm-1 spectral
resolution). A film of the liquid sample was placed between KRS-5 windows. A DXR Smart
Raman instrument (Thermo Fisher Scientific) equipped with a diode-pump, solid state laser
emitting at 532 nm was used for the Raman measurements (5 cm-1 of spectral resolution). The
liquid sample was handled in glass tubes of 0.5 cm of internal diameter. Spectra between 3500
and 50 cm-1 were acquired from accumulation of 60 expositions of 1 s each one with a laser
power of 9 mW at the sample. All FTIR and Raman measurements were carried out at room
temperature.
1H and 13C NMR spectra were recorded at 200 and 50 MHz, respectively, for the p-
trifluoromethylsulfinylaniline dissolved in CDCl3. Tetramethylsilane (TMS) was used as internal
standard for chemical shift calibration.

The GC-MS analysis was carried out using a Model Trace GC Ultra gas chromatograph coupled
to a Polaris Q mass spectrometer with an ion-trap analyzer with a DB-5 capillary column. Split-
less injection and helium as carrier gas were used for this study. The initial temperature of the
oven was 60°C. After maintaining that temperature for 3 min, the temperature was increased at a
rate of 15°C/min to reach a final value of 250°C, which was then maintained for 5 min. The total
run time was 20 min. The signal observed at 4.38 min (98% relative area) in the total-ion
chromatogram accounts for the presence of the molecule under study. Quantification of the
peaks was based on peak area. On the other hand, the mass spectrometer was operated in the
electron ionization scan mode (range, 40‒160 m/z). The molecular ion was assigned to the peak
with m/z 207.
4.2. Computational Details
GAUSSIAN 03 program package [30] was used for geometry optimization, conformational
properties, 15N isotopic substitution and vibrational frequency calculations of p-CF3ArNSO.
Based on the Density Functional Theory (DFT), the three-parameter hybrid functional for the
exchange part 31 and the Lee-Yang-Parr (LYP) correlation function (B3LYP) 32 was used.
Calculations at the level of Rayleigh-Schrödinger perturbation theory developed by Møller and
Plesset at second order (MP2) 33 were also performed. Both methods were used with the 6-
311+G(df), 6-311++G(df,pd) and cc-pVTZ bases sets. The methods provided good
approximations for the quantum chemical calculations required to characterize the system under
study. In addition, by using the same approximations, a natural population analysis (NBO) 34
was performed. On the other hand, the 1H and 13C NMR chemical shielding were evaluated for
p-CF3ArNSO by using the GIAO method 35at the B3LYP/6-311+G(df) level of theory.
Acknowledgments
This work was partially supported by CONICET, National University of Tucumán, Grant PICT
1167-2015 and Grant PIP 0404/2013. D.M.C. is scientific support personnel of CONICET.

N.L.R., E.H.C., and R.M.S.A. are career researchers of CONICET. The authors gratefully
knowledge the reviewers and Prof. Dr Thrasher for their helpful advice.
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Table 1. Calculated geometric parameters for p-trifluoromethylsulfinylanilinea.
Structural
B3LYP/
B3LYP/
MP2/
parameters
6-311++G(df,pd)
cc-pVTZ
cc-pVTZ
C(1)‒C(2)
C(1)‒C(6)
C(2)‒C(3)
C(6)‒C(5)
C(3)‒C(4)
C(5)‒C(4)
C(4)‒C(7)
C(1)‒N
N=S
S=O
C(2)‒H(1)
O••••H(1)
C(7)‒F(1,3)
C(7)‒F(2)
N=S=O
1.407
1.404
1.386
1.383
1.393
1.395
1.507
1.390
1.539
1.483
1.079
2.341
1.346
1.352
119.6
132.2
119.4
119.7
120.3
119.7
127.7
115.8
115.5
112.2
112.1
0.0
1.405
1.403
1.389
1.386
1.393
1.395
1.499
1.399
1.549
1.480
1.078
2.274
1.340
1.344
121.1
129.3
119.8
119.5
120.4
119.6
124.8
115.4
112.2
112.0
111.8
0.0
1.405
1.403
1.389
1.386
1.393
1.395
1.499
1.399
1.549
1.480
1.078
2.274
1.340
1.344
121.1
129.3
119.8
119.5
120.4
119.8
124.8
115.4
111.2
112.0
111.8
0.0
C(1)‒N=S
C(2)‒C(1)‒C(6)
C(3)‒C(2)‒C(1)
C(3)‒C(4)‒C(5)
C(6)‒C(5)‒C(4)
C(2)‒C(1)‒N
C(6)‒C(1)‒N
C(4)‒C(7)‒F(2)
C(4)‒C(7)‒F(1)
C(4)‒C(7)‒F(3)
C(1)‒N=S=O
a Bond lengths in Å and angles in degrees. For atom numbering see Fig. 4.

Table 2. Experimental and calculated vibrational frequencies of p-trifluoromethylsulfinylaniline. Tentative assignment of
fundamental vibrational modes.
Experimental b (cm-1)
Theoretical values c (cm-1)
Mode
Approximate description a
B3LYP/6-311++G(df, pd)
IR
(liq)
Raman
(liq)
B3LYP/cc-pVTZ
MP2/cc-pVTZ
Calculated values
3229 (1)[8]
Scaled values d
3093
3077
3068
3065
1619
1571
1506
1423
1324
1311
1298
1289
1190
1158
1143
1111
1110
1065
1025
1014
996
ν1
ν2
ν3
ν4
ν5
ν6
ν7
ν8
ν9
C–H Stretch.
C–H Stretch.
C–H Stretch.
C–H Stretch.
-
-
3234 (1)[8]
3264 (1)[17]
3248 (<1)[54]
3239 (<1)[28]
3232 (<1)[16]
1653 (1)[54]
1614(<1)[3]
1535(<1)[27]
1485 (1)[5]
1425(3)[1]
3092 vw
3061 vw
3039 w
1612 m
1576 w
1503 vw
1413m
1326 vs
1314 sh
-
1289 m
1184 sh
1173 vs
1130 vs
1108 s
-
3084 w
3065 sh
-
1612 m
1577 sh
1503 m
-
1328 sh
-
1305 vs
1289 s
-
3212 (<1)[33]
3202 (<1)[17]
3199 (<1)[11]
1647 (<1)[100]
1598 (1)[2]
3211 (<1)[37]
3202 (<1)[20]
3197 (<1)[12]
1649 (<1)[98]
1601 (<1)[<1]
1536 (<1)[32]
1450 (4)[1]
1349 (5)[15]
1334 (12)[100]
1323 (100)[20]
1314 (14)[99]
1211 (3)[20]
1183 (57)[30]
1173 (4)[18]
1135 (63)[2]
1130 (29)[1]
1084 (38)[7]
1050 (1)[14]
1035 (9)[4]
C=C Stretch.
C=C Stretch. + C–H Def.
C=C Stretch.+ C–H Def.
C=C Stretch.+ C–H Def.
CF3 Asym. Stretch.
CF3 Sym. Stretch.
C=C Stretch + C–H Def.
N=S=O Asym. Stretch.
C–C Stretch. + C–H Def. i.p
CF3 Asym Stretch.
C–C Stretch.
C–H Def. +C–C Stretch.
C–H Def. +C–C Stretch.
C=C Stretch. +C–H Def.
N=S=O Sym. Stretch.
C–H Def.
1532(<1)[32]
1448 (4)[1]
1347 (4)[13]
1334 (7)[99]
1320 (100)[36]
1311 (23)[93]
1211 (2)[28]
1178 (57)[4]
1163 (10)[32]
1130 (49)[<1]
1129 (57)[3]
1083 (43)[7]
1043 (2)[13]
1032 (10)[7]
1013 (<1)[<1]
995(<1)[<1]
881 (20)[<1]
860(1)[<1]
ν10
ν11
ν12
ν13
ν14
ν15
ν16
ν17
ν18
ν19
ν20
ν21
ν22
ν23
ν24
ν25
ν26
1366(100)[20]
1326(1)[1]
1317(10)[100]
1222(46)[2]
1212(6)[25]
1199(3)[20]
1190(56)[3]
1127(8)[<1]
1094(22)[4]
1035(11)[1]
1022(<1)[<1]
979(<1)[<1]
963(<1)[<1]
867(15)[<1]
852(<1)[<1]
804 (<1)[10]
742(<1)[<1]
1170 vs
-
1108 vw
-
1069vs
1033m
1015 m
1007sh
-
849 vs
830 sh
-
1069 m
1033 m
1015w
-
971 w
-
C–H Def. o.o.p.
C–H Def. o.o.p.
C–H Def. o.o.p.
C–H Def. o.o.p.
1011 (<1)[10]
1001 (<1)[<1]
886 (7)[<1]
978
866
-
845
789
748
860 (<1)[<1]
805 (<1)[15]
768 (<1)[<1]
Ring Def.
810 w
792 m
803 (<1)[17]
761 (<1)[<1]
CF3 Sym. Def.
-

ν27
ν28
ν29
ν30
ν31
ν32
ν33
ν34
ν35
ν36
ν37
ν38
ν39
ν40
ν41
ν42
ν43
ν44
ν45
C–N Stretch.
730 m
680 m
656m
618m
-
-
736 (1)[<1]
664 (3)[4]
630 (3)[1]
723
653
619
594
564
525
510
443
414
400
318
312
278
183
178
110
82
737 (1)[<1]
666 (3)[4]
632 (2)[1]
739(3)[1]
661(4)[2]
C–H Def.i.p.+ N=S=O Def.i.p.
N=S=O Def.i.p. + C–H Def.i.p.
C–H Def. o.o.p.
CF3 Asym. Def.
C–H Def. o.o.p.
CF3 Asym. Def.
C–H Def. o.o.p.
C–H Def. o.o.p.
C–H Def. i.p.
C–H Def. o.o.p.
N=S=O Def. o.o.p.
C–H Def. i.p.
Ring Def.i.p.
Ring Def. o.o.p.
656w
619 w
619 (2)[2]
608(3)[<1]
587(<1)[<1]
533(<1)[<1]
520(1)[<1]
453(1)[<1]
416(<1)[<1]
408(<1)[<1]
322(1)[<1]
311(3)[1]
284(1)[<1]
186(1)[1]
182(<1)[1]
116 (<1)[1]
80(<1)[1]
604 (3)[<1]
574 (<1)[<1]
534 (<1)[<1]
519 (<1)[1]
451 (1)[<1]
421 (<1)[<1]
407 (1)[<1]
323 (2)[<1]
317 (4)[<1]
283 (1)[<1]
186 (1)[1]
181 (<1)[<1]
112 (<1)[1]
83 (<1)[<1]
49 (<1)[<1]
18 (<1)[1]
607 (3)[<1]
575 (<1)[<1]
536 (<1)[<1]
521 (<1)[1]
454 (1)[<1]
423 (<1)[<1]
408 (1)[<1]
326 (2)[<1]
319 (3)[<1]
284 (1)[<1]
188 (1)[1]
184 (<1)[<1]
114 (<1)[<1]
84 (<1)[<1]
50 (<1)[<1]
19 (<1)[1]
598 m
-
-
-
-
516 vw
453vw
449vw
-
-
406vw
406vw
-
-
-
-
-
-
-
-
-
-
-
281w
183 vw
-
C‒N=S Def.
116 sh
N=S=O Def. i.p. + C–H Def. o.o.p.
N=S=O Def. i.p. + C–H Def. o.o.p.
Torsion CF3
-
-
-
48
18
41 (<1)[<1]
15 (<1)[1]
a Stretch.: stretching; Def.: deformation; Asym.: antisymmetric; Sym.: symmetric; i.p.: in phase; o.o.p.: out of phase; sh:
shoulder.b s: strong; vs: very strong; m: medium; w: weak; vw: very weak. c Relatives infrared intensities in parentheses,
normalized to 100% ;Relative Raman activities between brackets, normalized to 100%. d Values scaled according to the scaling
factors in Ref. [26].

1
Table 3. Experimental and calculated chemical shifts for H (200 MHz) and 13C (50 MHz) of p-
trifluoromethylsulfinylaniline dissolved in CDCl3. TMS was used as internal reference.
Assignment a
Chemical shift (δ) (ppm)
Experimental Theoretical b
H1
H2
H3
H4
C2
C3
C4
C5
C6
C7
C1
7.88
7.84
8.90
7.51
7.66
7.51
7.61
7.19
126.98
126.36
127.71
126.31
126.89
131.57
144.40
132.69
130.54
133.96
129.84
132.25
139.16
152.94
a For atom numbering see Fig. 4.
b Calculated chemical shifts (GIAO method) using B3LYP/6-311+G(df) approximation.