Synthesis, characterization and vibrational studies of p-chlorosulfinylaniline

Article abstract of DOI:10.1016/j.molstruc.2016.06.067

p-Cholorosulfinylaniline was prepared by the reaction of p-chloroaniline and SOCl₂. The structural, conformational and configurational properties of the obtained liquid compound were studied by Raman and infrared spectroscopy in the liquid stat

Full text of DOI:10.1016/j.molstruc.2016.06.067

Accepted Manuscript
Synthesis, characterization and vibrational studies of p-Chlorosulfinylaniline
Doly M. Chemes, Diego J. Alonso de Armiño, Edgardo H. Cutin, Heinz Oberhammer,
Norma L. Robles
PII:
S0022-2860(16)30654-8
10.1016/j.molstruc.2016.06.067
MOLSTR 22686
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 15 March 2016
Revised Date: 24 June 2016
Accepted Date: 24 June 2016
Please cite this article as: D.M. Chemes, D.J. Alonso de Armiño, E.H. Cutin, H. Oberhammer, N.L.
Robles, Synthesis, characterization and vibrational studies of p-Chlorosulfinylaniline, Journal of
Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.06.067.
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ACCEPTED MANUSCRIPT
Graphical Abstract
1

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Synthesis, Characterization and Vibrational Studies of
p-Chlorosulfinylaniline
a
a
b
c
Doly M. Chemes, Diego J. Alonso de Armiño, Edgardo H. Cutin, Heinz Oberhammer
b
and Norma L. Robles*
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. Ayacucho 471, 4000 Tucumán, República Argentina.
c
Institut für Physikalische und Theoretische Chemie, Universität Tübingen, 72076
Tübingen, Germany.
ABSTRACT
2
p-Cholorosulfinylaniline was prepared by the reaction of p-chloroaniline and SOCl . The
structural, conformational and configurational properties of the obtained liquid compound
were studied by Raman and infrared spectroscopy in the liquid state. The assignment of the
vibrational spectra was carried out with the help of data obtained by quantum chemical
calculations at the harmonic oscillator approximation and using anharmonic vibrational
1
13
self-consistent field (VSCF) method as well. The H and C NMR chemical shifts of the
molecule were calculated by Gauge including orbital (GIAO) method (DFT/B3LYP
approximation using 6-311+G(df), 6-311++G(df,pd) and cc-pVTZ basis sets) and
compared to the experimental values. Natural Bond Orbital analysis provides an
explanation of the stability of the molecule and its electronic properties upon charge
delocalization.
Keywords p-Chlorosulfinylamine; vibrational spectroscopy; quantum chemical
calculations; conformational properties.
*
Corresponding Author: nrobles@herrera.unt.edu.ar
1

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1
. Introduction
The history of the discovery of N-sulfinylamines (R‒N=S=O) can be traced back to the
890’s, when they were synthesized and investigated by Michaelis et al. [1, 2]. As this
1
work proposed a general procedure for the cuantitative obtention of these compounds, it
constituted the initial step for the research of the structural properties, reactivity and
applications of N-sulfinylamines. To this day, numerous N-sulfinylamines are still obtained
through Michaelis’ method. Although more than 600 N-sulfinyl compounds are known [3],
only a few N-sulfinylamines were structurally characterized and their reactivity analyzed to
some extent. Gas electron diffraction studies for ClNSO [4], CH
3 3
NSO [5], SiH NSO [6],
FC(O)SNSO [7], SiMe NSO [8], CF SNSO [9] and CF SSNSO [10] resulted in the
3
3
3
presence of only the sterically unfavorable syn conformation of the R‒N=S=O skeleton (see
Scheme IA).
Scheme I. A) Syn and anti forms around the N=S bond; B) Charge delocalization structures
for p-, m- and o-chlorosulfinylaniline.
2

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Furthermore, vibrational studies combined with quantum chemical calculations for
CF NSO and SF NSO demonstrate the preference of the syn structure [11]. Quantum
3
5
chemical calculations (B3LYP/6-311+G(df)) predict energy differences ∆E = (Eanti – Esyn
)
of 7.1 kcal/mol for ClNSO, 6.3 kcal/mol for CH NSO, 3.1 kcal/mol for CF NSO and 3.9
3
3
kcal/mol for SF NSO. The HF/6-31G(d) method results in ∆E = 10.7 kcal/mol for
5
CF SNSO [9].
3
The strong preference of the sterically unfavorable syn structure has been rationalized by
orbital interactions. The nitrogen lone pair delocalize electronic density towards vicinal
antibonding σ* (S‒O) orbital, with a consequent decrease in the global energy of the
conformer involved. A similar effect is showed by the sulfur lone pair and adjacent
antibonding σ* (C‒N) orbital. These anomeric effects stabilize the syn conformation much
more strongly than the anti structure, by 18.3 kcal/mol in ClNSO, 17.4 kcal/mol in
CH NSO, 16.2 kcal/mol in CF NSO and by 16.6 kcal/mol in SF NSO. Thus, these strong
3
3
5
anomeric effects override the steric repulsion in the syn form. This steric repulsion is
evident from the bond angles at nitrogen and sulfur, which increase according to the
calculations by 7° to almost 10° when going from anti to syn conformation.
Several works with contradictory results concerning the structure of N-sulfinylaniline exist
in the literature [12]. The indication for the presence of a syn conformation, based on NMR
data [13, 14], was confirmed by an X-ray diffraction experiment [15]. This result for the
solid state was confirmed also for the free molecule by vibrational spectra and quantum
chemical calculations (B3LYP/6-311+G (df), and an energy difference ∆E of 8.1 kcal/mol
was reported [16]. Also in sulfinylaniline anomeric effects, which are much stronger in the
syn (25.4 kcal/mol) than in the anti structure (8.0 kcal/mol), stabilize the syn conformation.
H. Muchall rationalized the preference of the syn conformation with an intramolecular
C−H•••O bond involving the ortho hydrogen atom [17].
The inclusion of a substituent group/atom in N-sulfinylaniline leads to variation in the
molecular charge distribution, and consequently greatly affects the electronic, structural and
vibrational parameters.
The mass spectra of p-chlorosulfinylaniline were reported by Bowie et al [18].. Since no
report of the vibrational properties of this substance was attempted so far, in the present
investigation a conformational and vibrational analysis of p-chlorosulfinylaniline has been
3

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undertaken on the basis of a detailed characterization and a tentative assignment of the
vibrational spectra (FT-IR and Raman) supported by quantum chemical calculations at
different levels of theory. The effect of a halogen atom in para position of an aromatic ring
on the N=S=O properties has been analyzed.
2
2
. Experimental details
.1 Synthesis
p-Chlorosulfinylaniline was obtained with a 1:2:5 molar relation of the corresponding
chlorinated aniline (3.14 g; 18 mmol), thionyl chloride (9.80 g; 82.mmol) and benzene
(
13.20 g; 169 mmol) as the reaction solvent, respectively. The chlorinated aniline used as
precursor and the solvent were placed in a closed three neck round bottom flask equipped
with a Liebig condenser sealed with CaCl . Thionyl chloride was added drop wise to the 50
60 °C heated mixture. As the expected reaction product was expected to be an air
2
–
sensitive compound, the reaction was performed in nitrogen atmosphere.
The reaction mixture was continuously stirred and heated 8 hours at 80 – 85 °C until a dark
solution was obtained. The liquid mixture was then purified by several distillation cycles
until a dark green liquid with ca 93% yield was obtained. The purity of the substance was
1
13
checked by H and C NMR spectroscopy and GC-Mass spectrometry, together with IR
and Raman spectroscopy. In contact with air humidity, the substance hydrolyses rapidly. It
was also found to be a very corrosive compound for KBr windows, therefore KRS-5
windows had be used to register infrared spectra.
2
.2 FT-IR and Raman measurement
-1
FT-IR spectra of p-chlorosulfinylaniline was registered between in the 3500 – 400 cm
region at ambient temperature using a Perkin Elmer GX1 Fourier Transform infrared
spectrometer by placing the liquid sample between KRS-5 windows (spectral resolution: 1
-
1
cm ).
-
Raman spectra of a liquid sample were registered at room temperature in the 3500 – 50 cm
1
region by using a diode-pump solid state 532 nm green laser with 9.0 mW power at the
sample for excitation available in a Thermoscientific DXR Smart Raman instrument
-1
equipped with CCD detector (spectral resolution: 4 cm ; grating groove density of 900
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lines/mm). A confocal aperture of 25 µm slit was used and 40 expositions of 1 s were
accumulated for the sample to improve signal to noise ratio. The samples were held in
Pyrex capillaries at room temperature.
2.3. NMR and GC-MS measurements
1
13
NMR spectra were registered in CDCl at 200 MHz for H and 50 MHz for C on a Varian
3
Unity 200 spectrometer. The molecule was dissolved in chloroform-d solution (CDCl3).
The chemical shifts were reported in ppm relative to tetramethylsilane (TMS).
The GC/MS analysis was performed using a Model Trace GC Ultra gas chromatograph
coupled to a Polaris Q mass spectrometer with a ion-trap analyzer using a DB-5 capillary
column. Split-less injection was employed for the analysis. The oven was set initially at 60
°
C and kept at this temperature for 3 min. The temperature was afterwards increased at a
rate of 20 °C/min until a final 280 °C temperature was reached and kept for 5 min (total run
time: 20 min). Helium was used as carrier gas. The mass spectrometer was operated in the
electron ionization scan mode (range, m/z: 60 – 180). Quantification of the peaks was based
on peak area.
3
. Computational information
The theoretical predictions of the molecular structure, conformational properties, IR and
Raman spectroscopy were achieved by using the GAUSSIAN03 program [19]. Based on
the Density Functional Theory (DFT), the three-parameter hybrid functional for the
exchange part [20] and the Lee-Yang-Parr (LYP) correlation function [21] together with the
6
-311+G(df), 6-311++G(df, pd) and cc-pVTZ bases sets provide good approximations for
the quantum chemical calculations required to characterize the system in study. For the
study of the orbital interactions and nuclear magnetic shielding tensors, the natural
population analysis (NBO) [22] and Gauge-including atomic orbital (GIAO) method [23]
were used, respectively, as implemented in the GAUSSIAN03 program. In addition to these
calculations for the p-chlorosulfinylaniline, the B3LYP/6-311+G(df) method was applied
also to sulfinylaniline and to p-fluorosulfinylaniline for the sake of comparison.
In addition to these calculations, the recently implemented vibrational self-consistent field
(VSCF) ansatz in the QUMVIA software package [24] was used for the vibrational
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calculations. VSCF is a mean-field, variational iterative method for the calculation of the
vibrational wavefunction similar to the Hartree-Fock method in the electronic structure
theory. Following is a summary of the main postulates of this theoretical approach; further
details can be found elsewhere [25–28].
Neglecting rotational couplings, the vibrational Schrödinger equation for a molecule
depicted in rectilinear normal coordinates {q } may be formulated as:
i
ꢌ
ꢁ
ꢄꢂ
ꢀ
− ꢃ
+ ꢇꢈ ꢅꢉ ꢊꢋꢎ ꢏ ꢈ ꢅꢉ ꢊꢋ =ꢑꢒ ꢏ ꢈ ꢅꢉ ꢊꢋ
ꢐ ꢐ ꢐ
ꢂ
ꢂ
ꢄ
ꢅ
ꢆ
ꢆꢍꢁ
With
ꢌ
ꢏ ꢈ ꢅꢉ ꢊꢋ =ꢑꢓ ꢔ ꢈ ꢅꢉ ꢊꢋ
ꢐ
ꢆ,ꢐ
ꢆꢍꢁ
The vibrational wavefunction is represented as a Hartree product, i.e. a product of one-
dimensional, single-mode wavefunctions, usually called modals, that play a similar role as
orbitals do in the electronic structure theory. ψ is the vibrational wavefunction, φ are the
i,n
i
one-dimensional modals and q are the mass weighted normal coordinates. By using this
assumption and taking into account the variational principle, it is possible to obtain the
VSCF equations for each modal.
ꢕꢖ° ꢈꢅ ꢋ + ꢗ ꢈꢅ ꢋꢘꢔ ꢈꢅ ꢋ =ꢑꢙ ꢔ ꢈꢅ ꢋ
ꢆ
ꢆ
ꢆ
ꢆ
ꢆ
ꢆ
ꢆ
ꢆ
ꢆ
ꢌ
ꢌ
ꢗ ꢈꢅ ꢋ = ꢚꢓ ꢔ ꢝꢇ ꢈ ꢅꢉ ꢊꢋꢝ ꢓ ꢔ ꢟ
ꢆ
ꢆ
ꢛ
ꢞ
ꢛ
ꢛꢜꢆ
ꢛꢜꢆ
i
H ° is the core Hamiltonian for mode “i”, which involves the kinetic energy and the
diagonal potential; ν is the mean field potential. Since the solutions are required to
i
compute the mean field potential, the VSCF equations must be solved iteratively until self-
consistency is reached.
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Distributed Gaussian functions are employed as a basis set [29]. The nuclear potential
energy surface (PES) was approximated by using a quartic force field (QFF) with a 3-mode
coupling representation [30]. Third and forth order force constants were obtained by
numerical differentiation of Hessian matrices calculated analytically by using a different
electronic structure software (GAUSSIAN03, in this case) with the MP2/cc-pVDZ and
B3LYP/6-311++G(df, pd) approximations. By using a “very strict” convergence criterion,
the optimization of the molecular structures followed by the frequency calculation to obtain
the armonic frequencies and hessian matrices was achieved. These results were used to
build a set of distorted conformations along each normal mode using QUMVIA, and
Hessian matrices were calculated for each conformation using GAUSSIAN03. At last,
these Hessian matrices were used to calculate 3-mode coupling QFF using QUMVIA.
4
. Results and Discussion
.1 Molecular geometry, structural properties and NBO analysis
4
Calculations for the syn conformer of p-chlorosulfinylaniline depicted in Fig. 1 result in a
planar structure and calculated properties are listed in Table 1 (geometric parameters)
1
together with experimental values in Table 2 (vibrational frequencies), Table 3 ( H NMR
1
3
shifts) and in Table 4 ( C NMR shifts). B3LYP/6-311+G(df) calculations for the anti
conformer of sulfinylaniline and the p-fluoro and p-chloro derivatives result in non-planar
structures with the NSO group rotated out of the phenyl plane by φ(C‒N‒S=O) = 36.5°,
3
8
3.0° and 34.3°, respectively. The predicted energy differences ∆E = (Eanti – E ) are 7.5,
syn
.1 and 7.9 kcal/mole, respectively. The value for the parent compound differs slightly
from that reported in Ref. 16 (8.1 kcal/mol), since a planar structure for the anti conformer
was used. As in the case of the N-sulfinylamines (see Introduction), the adoption of the
sterically unfavorable syn conformation may be understood primarily with anomeric effects
lp(N) → σ* (S‒O) and lp(S) → σ* (N‒C). The interaction energies involved in these
delocalizations are higher in the syn structure by 18.8 and 18.3 kcal/mol, respectively. The
formation of an intramolecular C−HꢀꢀꢀO bond involving the ortho hydrogen atom proposed
in Ref.17 may contribute additionally to the stabilization of the syn conformer.
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4.2 Vibrational assignment
The experimental FT-IR and Raman spectra have been assigned on the basis of their
calculated vibrational frequencies and intensities. Table 2 lists the experimental and
theoretical wavenumbers together with a tentative assignment of the fundamental
transitions expected for p-chlorosulfinylaniline. The analysis of the experimental
vibrational spectra was performed taking into account vibrational spectra obtained by using
the harmonic oscillator (HO) approximation and also at the anharmonic vibrational self-
consistent field (VSCF) level of theory. Two potential energy surfaces (PES), B3LYP/6-
3
11++G (df,pd) and MP2/cc-pVDZ were used for HO and VSCF vibrational levels of
theory. To facilitate the identification of vibrational modes belonging to the N=S=O group
1
5
37
and C‒Cl bond, theoretical N and Cl substitution were used, together with data reported
for sulfinylaniline [14 – 16], p-fluorosulfinylaniline [31] and the reactant p-chloroaniline
[32]. Figures 2 and 3 show experimental and theoretical spectra of p-chlorosulfinylaniline.
Although HO-based calculations furnished us with quite useful theoretical predictions, a
better correlation was given by anharmonic vibrational frequency calculations at the VSCF
level of theory. Mean absolute deviations (MAD) over the entire spectra were of 38 and 48
-1
cm for HO//B3LYP/6-311++G(df,pd) and HO//MP2/cc-pVDZ PES, respectively, while
-1
only 24 and 23 cm for VSCF// B3LYP/6-311++G(df,pd) and VSCF// MP2/cc-pVDZ
levels of theory, respectively. Notice that VSCF calculations increased average accuracy by
a factor of almost two relative to the HO approximation. Moreover, although B3LYP PES
produced substantially better results than MP2 at the HO level, it is the later that produced
the best results at the VSCF approximation, despite the fact that a significantly bigger basis
set was used for B3LYP than for MP2. In other words, although B3LYP appears to produce
a better approximation for the potential energy function at the HO level, this apparent
advantage vanishes when anharmonicity is taken explicitly into account. Moreover, VSCF
calculations predicted modifications in the energy order of several vibrational states, a
result of the fact that anharmonicity affects different states by differing degrees, sometimes
modifying the assignments made by the HO approximation. In particular, C‒H stretching
modes are very good examples of this. As shown in Table 2, the energy order predicted for
these fundamentals at the VSCF level are ν > ν > ν > ν and ν > ν > ν > ν for MP2 and
2
1
4
3
2
1
3
4
B3LYP PESs, respectively. Notice that although in B3LYP states ν and ν do not exchange
3
4
8

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places, they are predicted to be almost degenerate in energy, so the tendency is similar in
both PES. It is also noteworthy the fact that the absolute transition frequencies for these
states is greatly improved, with absolute deviations (only considering C‒H stretching
-1
-1
modes) going from 186 cm at the HO approximation to only 10 cm at VSCF level of
-1
theory for the MP2 PES and from 141 to 32 cm for B3LYP PES, where the frequencies in
this region are somewhat underestimated. Other vibrational states also exchange places.
Particularly pairs of states ν and ν are predicted to exchange places in both PES, while a
1
7
18
similar trend is predicted by VSCF//MP2 calculations for pairs ν23/ ν24, and pairs ν26/ ν27
and ν / ν by VSCF//B3LYP. The lower portion of the spectra exhibits an interesting
3
2
33
feature, since the anharmonic transitions were predicted to have higher frequencies than
their harmonic counterparts. This may be understood taking into account that potential
energy surfaces along low frequency normal modes are usually flatter near the equilibrium
geometry than in other more displaced geometries. As a consequence, quadratic
approximations are too flat compared to the real, fully anharmonic PES. In general terms,
VSCF calculations proved to be very useful for the assignment of the vibrational spectra. In
comparison with common ad-hoc methodologies, which ordinarily use empirical scaling
factors, the VSCF methodology allows the prediction of overall absolute frequencies of
similar or better accuracy with respect to experimental values. In addition, it is able to
handle more complicated assignments, as in the C‒H stretchings mentioned above or the
lower part of the spectra, where the trend of anharmonicity is opposite to the effect of
scaling factors. For these reasons, we conclude that the use of anharmonic variational
methods is a very good alternative in comparison with the use of current ad-hoc scaling
factors.
We now address some issues regarding the –N=S=O moiety. Previous analysis showed a
marked correlation between the stretching vibrations of this group and the atom bonded to
the N atom. An early study on the parent sulfinylaniline described the stretching modes as
-1
-1.
two independent modes placed at 1284 cm and 1155 cm for N=S and S=O respectively
14]. Later, the study of the pre-resonant Raman spectra of sulfinylaniline evidenced a
strong coupling of the N=S and S=O stretching modes [16]. According to the data reported
[
-1
-1
for p-fluorosulfinylaniline, the signals centered at 1303/1302 cm and 1030/1029 cm in
the IR and Raman spectra were attributed to the asymmetric and symmetric stretching
9

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modes of the N=S=O group, respectively [31]. Consequently, in the present work the
-1
-1
signals observed at 1297 and 1031 cm in the infrared spectra and at 1296 and 1031 cm in
the Raman spectra were assigned to the asymmetric and symmetric stretching respectively
of p-chlorosulfinylaniline. The vibrational spectra evidenced no significant influence of the
chlorine atom in the vibrational modes of the N=S=O group compared to the corresponding
signals for p-fluorosulfinylaniline. Preliminary calculations performed for o- and m-
chlorosulfinylaniline indicate that the effect of the chlorine atom on the frequencies of the
N=S=O group depends on its place in the aromatic ring. The asymmetric stretching of the
-1
-1
N=S=O group in o-chlorosulfinylaniline was calculated at 1320 cm , 4 cm lower in
frequency terms, with respect to p-fluorosulfinylaniline, while the corresponding mode for
-1
the meta substituted compound was predicted at 1308 cm at the B3LYP/6-311++G(df,pd)
level. The resonance structures depicted on Scheme IIB(should be Scheme IB) show the
effective charge delocalization for the chlorine atom in ortho, meta and para position. The
assignment proposed may be rationalized linking the shortening and elongation of the N=S
and S=O bonds with the partial contribution of these structures to the resonance hybrid.
-1
The in-plane bending of the N=S=O group was attributed to the signals at 618 cm in the
vibrational spectra while the out-of-plane bending mode for this group was assigned to the
-1
signal centered at 486 cm in the infrared spectrum. This is not completely comparable to
the assignment proposed for the corresponding modes in p-fluorosulfinylaniline, for which
-1
-1
signals at -634 cm and 281 cm (Raman) were observed [31].
Depending on the configuration and conformation of the aromatic compound the C‒Cl
-1
stretching vibration was observed in the region between 850 and 550 cm [30]. For this
-1
molecule the band at 836 cm (Raman) was assigned to the C‒Cl stretching while the C‒Cl
-1
in–plane bending vibration was assigned at 354 cm in the Raman spectra, in agreement
with harmonic and anharmonic calculations (see Table 2). The C‒N stretching mode was
-1
observed at 785 cm in the infrared spectrum of the p-fluoro derivative [31], while in this
-1
study, this vibration was assigned to the band observed at 770cm in the infrared and
Raman spectrum.
-1
We finally focus on the bands centered at 1484 cm which were labeled as ν in this work.
7
These bands are actually complex bands, with two weaker features centered at 1479 and
-1
-1
1
473 cm in IR and only one companion observed at 1473 cm in Raman spectra. When
10

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comparing equivalent bands of p-fluorosulfinylaniline [31], we observed a similar set of
bands in the same region. Since the mass and NMR spectra would not evidence the
presence of relevant amount of impurities, it is possible to attribute these signals to
overtones and/or combination bands, borrowing intensity from ν dipole-allowed transition
7
through Fermi resonance. The exact identity of the resonant overtones or combination
bands is quite hard to determine, because of the high density of "dark" vibrational states in
this region and the low symmetry of the molecule. More accurate vibrational structure
calculations considering vibrational correlation explicitly, as in the vibrational
configuration interaction approach (VCI) [26] are now in development by our research
group. We trust they shall be able to provide a more solid foundation about these interesting
spectra features in the near future.
4.3 NMR profile
Nuclear magnetic resonance (NMR) spectroscopy has evolved as one of the most powerful
analytical techniques. It allows the visualization of single atoms and molecules in various
media in solution as well as in solid state. NMR is nondestructive and gives molar response
that allows structure elucidation and quantification simultaneously. The experimental and
1
13
3
theoretical data of the spectra of H and C NMR in chloroform-d (CDCl ) solution solvent
are show in Table 3 and 4. The atom positions were arranged based on number of Fig. 1.
The assignment proposed for the title molecule was performed on the basis of data reported
for substituted aromatic molecules with electron withdrawing groups in para position [31]
and the unsubstituted sufinylaniline [14]. For the calculation of nuclear magnetic shielding
tensor with the gauge-including atomic orbital (GIAO) method [23] an optimized structure
at the B3LYP/6-311+G(df) level of theory was used. As it is well known, the chemical
shifts of aromatic protons and carbon atoms of organic compounds are usually observed in
the 7.00 – 8.00 ppm and 100 – 150 ppm range, respectively. Therefore, the signals centered
1
at 7.12, 7.78 , 6.58 and 6.62 ppm in the H NMR spectra were assigned to the four aromatic
1
3
protons of p-chlorosulfinylaniline. Meanwhile, the C NMR spectrum showed signals at
28.53 (C (1)), 128.58 (C (2)), 128.43 (C (3, 5, 6)) and 128.44 ppm (C (4)). These results
1
confirmed that the presence of electron withdrawing groups/atoms lead to deshielding of
the protons in resonance and the consequent increase of the chemical shift values, therefore
11

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the influence of the chlorine atom and the N=S=O group must be considered. The increase
in chemical shift observed for C1 and C4 with respect to the other carbon atoms might be
attributed to the presence of the chlorine and the N=S=O group attached to the aromatic
ring. The assignment proposed took into account the well known fact that electron
withdrawing atoms/groups attract electronic density, with the consequent de-shielding of
nearby nuclei and the increment of their chemical shift value.
4
.4 GC/MS profile
It is well known that aromatic halogenated compounds generally show an intense signal for
the molecular ion. This fact, together with the common feature of isotopic patterns of
chlorinated molecules in the mass spectra made the assignment of the observed signals
quite straightforward. In agreement with a previous analysis of the mass spectra of
chlorosulfinylaniline [32], the intense signal at 5.77 min (93.4 % relative area and 173
molecular weight) in the total-ion chromatogram and the accompanying peak found at 175
3
5
37
m/z were attributed to the Cl/ Cl substituted molecular ion, respectively (see Fig 4).
Therefore the peak at m/z 174 was assigned to the protonated form of the base peak at m/z
1
73. Another common feature of halogen substituted aromatic compounds is the presence
of a signal accounting for the halogen loss, observed in our experience at 138 m/z.
The additional peak found at time retention 5.16 min (0.38 % relative area and m/z 127)
was assigned to the reactant p-chloroaniline, while the signals at m/z 110 and 63 were
+
.
attributed to the [C6H4Cl] and [H‒N=S=O] fragments, respectively. Fig. 5 depicts a
scheme of the fragmentation pattern with the most relevant fragments of interest.
5
. Conclusions
It is well known that the presence of substituents attached to a parent unsubstituted
compound of acknowledged properties may modify those characteristics to such an extent
that may compel us to evaluate the resulting compound as new specie. p-
Chlorosulfinylaniline was obtained through the reaction of p-chloroaniline and SOCl and
2
characterized by using nuclear magnetic resonance spectroscopy, gas chromatography/
mass spectrometry, vibrational spectra and quantum chemical calculations with the purpose
12

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of adding one more step in the knowledge of the influence that the presence of halogen
substituents exert on sulfinylanilines. Compared to the parent sulfinylaniline and p-
fluorosulfinylaniline, the closest analogue so far reported, the vibrational fundamentals
modes of the sulfinyl group, as well as the C‒N and C‒Cl stretching modes do not account
for differences of considerable interest. However, taking into account preliminary
theoretical calculations performed for the m- and o- isomers, it is expected that more
significant changes would be observed in relation with the position of the substituent in the
aromatic ring. These changes would reflect, as in the p-, m- and o-fluorosulfinylaniline [31,
3
3, 34] series, the joint action of electronic effects from the N=S=O and chlorine
substituents.
With regard to the theoretical approaches employed in the analysis of the vibrational
spectra, it is interesting to highlight that the vibrational self-consistent field method was
found to be a very valuable tool for the assignment of the vibrational spectra. Its predictions
not only significantly improved the overall accuracy of the theoretical spectra, but they also
showed that the effects of anharmonicity cannot be mimicked by using simple ad-hoc
scaling factors. Considering the relative ease of use and good cost-benefit ratio of VSCF
methodology, when analytical hessians are available, we propose that a more extended use
of such is advisable.
-1
We also identified a set of bands centered at 1484, 1479 and 1483 cm in p-
-1
chlorosulfinylaniline spectra and at 1479, 1496 and 1513 cm at p-fluorosulfinylaniline,
which we propose are possible Fermi resonances. A more detailed study must await,
however, the availability of more advanced post-VSCF methods suitable for the study of
molecules of this size, which are in active development by our group.-
Acknowledgements
Authors acknowledge CONICET (Consejo Nacional de Investigaciones Científicas y
Técnicas), UNT (Universidad Nacional de Tucumán) and DAAD (Deutscher Akademischer
Austauschdienst, Germany) for the financial support. Authors also kindly acknowledge
staff from LISA (Laboratorio de Investigación y Servicios Analíticos) for NMR and
GC/MS measurements.
13

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Figure Captions
Fig. 1. Molecular model of the syn conformer of p-chlorosulfinylaniline.
Fig 2. Experimental and theoretical infrared spectra ofp-chlorosulfinylanilie. Top:
theoretical gas phase spectrum calculated at the B3LYP/6-311++G(df,pd) level of theory;
bottom: room temperature infrared spectrum of a liquid sample held between KRS-5
windows.
Fig. 3. Experimental and theoretical Raman spectra of p-chlorosulfinylaniline. Top:
theoretical gas phase Raman spectrum calculated at the B3LYP/6-311++G(df,pd) level of
theory (532 nm excitation laser); bottom: room temperature spectrum of a liquid sample.
Fig. 4. Mass spectra (mass numbers (m/z) versus relative abundance) obtained for p-
chlorosulfynilaniline.
Fig. 5. Major fragmentation patterns of m/z peaks for p-chlorosulfinylaniline.
Scheme I. A) Syn and anti forms around the N=S bond; B) Charge delocalization structures
for p-, m- and o-chlorosulfinylaniline.

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Table 1. Calculated geometric parameters for the p-chlorosulfinylaniline.
Structural
p-chlorosulfinylaniline
a
parameters
B3LYP/
B3LYP/
6
-311++G(df,pd) cc-pVTZ
C‒Cl
1.748
1.080
1.408
1.385
1.391
1.387
1.507
1.485
119.4
132.2
119.3
121.1
124.8
116.0
119.5
0.0
1.746
C‒H
1.078
1.407
1.385
1.390
1.389
1.536
1.479
119.8
131.8
119.1
121.1
1.249
116.1
119.5
0.0
C1‒C2(6)
C2(5)‒C3(6)
C4‒C3(5)
C1‒N
N=S
S=O
N=S=O
C1‒N=S
C2‒C1‒C6
C3‒C4‒C5
C2‒C1‒N
C6‒C1‒N
Cl‒C‒C
C1‒N=S=O
a
Bond lengths in Å and angles in degrees. Mean values are given for parameters that are
not unique. For numbering atoms see Fig. 1.

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Table 2. Experimental and calculated wavenumbers of the p-chlorosulfinylaniline and
tentative assignments of main fundamental vibrational modes.
b
Experimental
Theoretical
B3LYP/6-311++G(df,pd)
a
MP2/cc-pVDZ
Mode
Approximate description
IR
liq.)
Raman
(liq.)
HO
VSCF
HO
VSCF
(
ν1 C–H Stretch.
ν2 C–H Stretch.
ν3 C–H Stretch.
ν5 C–C Stretch.
ν6 C–C Stretch.
ν7 C–C Stretch. + C–H Def.
3091w
-
-
3224 (2 [4]
3039
3063
3023
1594
1563
3273(4)[27]
3083
3075vw 3210(1)[16]
3252(<1)[95] 3100
3243(<1)[51] 3054
1638(29)[95] 1613
1610(<1)[13] 1585
3071vw 3071vw 3202(<1)[77]
1583s 1582s 1620(67)[64]
1563vw 1563vw 1586(3)[3]
1484s 1484w 1514(29)[11]
1495 1511(100)[23 1492
ν
ν
8
C–C Stretch.
C–H Def. i.p.
1406w
1336w
-
-
1440(3)[<1]
1330(<1)[<1]
1425
1319
1306
1489(2)[4]
1405(5)[2]
1305(4)[17]
1462
1385
1295
9
ν
ν
10 N=S=O Asym. Stretch.
11 C–C Stretch.
1297s 1296vs 1324(6)[100]
1273s 1272w 1305(17)[38]
1234vw
1176s
1162 vs 1161s 1133(21)[1]
1102s 1102w 1101(89)[17]
1087s 1087m 1039(4)[12]
1031w 1031s 1028(26)[7]
1013s 1013w 1005(<1)[<1]
1290 1297(41)[100 1279
1204(52)[80] 1200
1188(4)[2] 1184
ν12 C–H Def. i.p.
ν13 C–H Def.
ν14 C–H Def.
ν15 C–Cl Stretch.
ν16 Ring Def.
ν17 N=S=O Symm. Stretch.
ν18 C–H Def. o.o.p.
ν19 C–H Def. o.o.p.
-
-
1202(3)[15]
1160(100)[18]
1199
1146
1133
1091
1029
1017
1025
1016
899
882
782
717
667
627
551
560
429
430
364
344
242
244
126
108
79
1129(68)[27] 1118
1117(17)[<1] 1117
1022(52)[4]
990(19)[8]
957(<1)[<1]
931(<1)[<1]
838(39)[1]
833(35)[2]
773(26)[7]
671(31)[8]
639(<1)[<1]
620(4)[2]
554(4)[<1]
519(5)[<1]
413(3)[<1]
407(13)[<1]
348(21)[4]
342(2)[<1]
240(5)[<1]
234(5)[<1]
139(1)[2]
1015
979
992
979
867
864
768
666
707
615
551
546
423
411
348
343
239
239
139
106
72
-
963w 984(<1)[<1]
ν
ν
ν
ν
20 C–Cl Stretch.
21 C–H Def. o.o.p.
22 C–N Stretch.
23 Ring Def.
836vs
815vw
770w
-
-
864(44)[<1]
844(1)[<1]
784(3)[6]
770w
679vs 684vw 734(<1)[<1]
665m
618w 618vw
551vw 551w
529w
ν24 Ring Def.
664w
673(16)[1]
631(5)[1]
ν25 N=S=O Def. i.p.
ν26 C–H Def. o.o.p.
ν27 C–H Def. o.o.p.
ν28 N=S=O Def. o.o.p.
ν29 Skeletal Def.
554(<1)[2]
548(3)[<1]
427(1)[<1]
425(10)[<1]
361(9)[<1]
345(7)[<1]
242(2)[<1]
238(2)[<1]
124(1)[<1]
99(<1)[<1]
57(<1)[<1]
-
-
-
486vw
419m
ν30 C–Cl Def. i.p.
-
-
-
-
-
-
-
354vw
340vw
ν
ν
ν
ν
31 Skeletal Def.
32 C – Cl Def. i.p. + N=S=O Def. i.p.
33 Torsion N=S=O
-
-
-
-
-
34 Def. C‒N=S
ν35 Torsion Skeletal
ν36 a Torsion Skeletal
99(<1)[<1]
52(<1)[<1]
Stretch.: stretching; Def.: deformation; Asym.: antisymmetric; Sym.: symmetric; i.p.: in phase; o.o.p.:
out of phase; tors.: torsion; s: strong; vs: very strong; m: medium; w: weak; vw: very weak.
b

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1
Table 3. Experimental and calculated H NMR chemical shifts for p-chlorosulfinylaniline
(
200 MHz, CDCl , TMS).
3
a
H
δ [ppm],multiplicity J [Hz]
δ [ppm],
a
b
Experimental
Theoretical
C(2)H
C(3)H
C(5)H
C(6)H
7.12, m J1,2=6.36
7.07, m J =6.36
8.78
7.31
7.06
7.03
2
,1
6.62,m J =6,78
3
,4
6.58, m J =6,78
4
,3
a
b
For atom numbering see Fig. 1. Calculated chemical shifts (GIAO method) using
B3LYP/6-311+G(df) approximation.

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1
3
Table 4. C NMR experimental (CDCl , 50 MHz) and calculated data of p-
3
chlorosulfinylaniline.
a
C
Chemical shift (δ) (ppm)
Experimental
128.53
b
Theoretical
128.86
133.56
132.95
151.14
132.04
133.26
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
129.58
128.43
128.44
128.43
128.43
a
For atom numbering see Fig. 1.
b
Calculated chemical shifts (GIAO method) using B3LYP/6-311+G(df) approximation.

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5