Spectroscopic and theoretical studies of some 2-ethylsulfinyl-(4′- substituted)-phenylthioacetates

Article abstract of DOI:10.1016/j.molstruc.2010.07.035

The analysis of the IR v_CO bands of the 2-ethylsulfinyl- (4′-substituted)-phenylthioacetates 4′-Y-C₆H ₄SC(O)CH₂S(O)Et (Y = NO₂ 1, Cl 2, Br 3, H 4, Me 5, OMe 6) supported by B3LYP/6-31G(d,p) calculatio

Full text of DOI:10.1016/j.molstruc.2010.07.035

Journal of Molecular Structure 981 (2010) 93–102
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectroscopic and theoretical studies of some
2-ethylsulfinyl-(40-substituted)-phenylthioacetates
a
a
a
Paulo R. Olivato a, , Mário L.T. Hui , Alessandro Rodrigues , Carlos R. Cerqueira Jr. ,
*
Julio Zukerman-Schpector b, Roberto Rittner c, Maurizio Dal Colle d
a Conformational Analysis and Electronic Interactions Laboratory, Institute of Chemistry, USP, CP 26077, 05513-970 São Paulo, SP, Brazil
b Departamento de Química, Universidade Federal de São Carlos, São Carlos, SP, Brazil
c Physical Organic Chemistry Laboratory, Chemistry Institute, State University of Campinas, Campinas, SP, Brazil
d Dipartimento di Chimica, Università di Ferrara, Ferrara, Italy
a r t i c l e i n f o
a b s t r a c t
The analysis of the IR vCO bands of the 2-ethylsulfinyl-(40-substituted)-phenylthioacetates 40-Y-
C6H4SC(O)CH2S(O)Et (Y = NO2 1, Cl 2, Br 3, H 4, Me 5, OMe 6) supported by B3LYP/6-31G(d,p) calculations
along with the NBO analysis for 1, 4 and 6 and X-ray analysis for 3, indicated the existence of four gauche
(q-g-syn, g3-syn, g1-anti and q-g2-syn) conformers for 1–6. The calculations reproduce quite well the
experimental results, i.e. the computed q-g-syn and g3-syn conformers correspond in the IR spectrum
(in solution), to the vCO doublet higher frequency component of larger intensity, while the computed
Article history:
Received 24 May 2010
Received in revised form 20 July 2010
Accepted 25 July 2010
Available online 4 August 2010
Keywords:
g1-anti conformer correspond to the
v
?
CO doublet lower frequency component (in solution). NBO analysis
Conformational analysis
Infrared spectroscopy
Theoretical calculations
2-Ethylsulfinyl-(40-substituted)-
phenylthioacetates
showed that the ns ? pCꢀ
, nO(CO)
rꢀC , nO(CO)
?
rCꢀ
1—C4
orbital interactions are the main factors
1@O2
1—S3
which stabilize the q-g-syn, g3-syn, g1-anti and q-g2-syn conformers for 1, 4 and 6. The nO(CO)
?
rCꢀ
1—S3
interaction which stabilizes the q-g-syn, g3-syn and q-g2-syn conformers into a larger extent than the
g1-anti conformer, is responsible for the larger vCO frequencies of the former conformers relative to the
latter one. The q-g-syn, g3-syn and q-g2-syn conformers are further stabilized by rC
?
pꢀCO (strong),
4—S5
pꢀCO
/
rꢀC , nO(CO)
?
rCꢀ
(weak) and pꢀCO
/
rCꢀ
(strong) orbital interactions. The g1-anti conformer
4—S5
6—H17½Etꢁ
4—S5
is also stabilized by rC4–S5
(weak), nO(SO)
?
pꢀCO (strong), pCO
/
rCꢀ
,
nO(CO)
?
rCꢀ
, pC9@C11[Ph] ?
rCꢀ
4—S5
6—H17½Etꢁ 4—H16
½a-CH2ꢁ
?
rCꢀ
(medium) and pꢀCO
/
rCꢀ
(strong) orbital interactions. The q-g-syn con-
4—S5
11—H23½o-Phꢁ
dꢂ
dþ
former is further stabilized by O
ꢃ ꢃ ꢃ S
attractive Coulombic interaction while the q-g2-syn conformer
ðCOÞ
ðSOÞ
is destabilized by the nS5ꢃ ꢃ ꢃOdꢂ repulsive Coulombic interaction. This analysis indicates the following
ðCOÞ
conformer stabilization order: q-g-syn; g3-syn > g1-anti ꢄ q-g2-syn. X-ray single crystal analysis of 3 indi-
cates that it assumes in the solid a distorted q-g2-syn geometry which is stabilized through almost the
same orbital and Coulombic interaction which takes place for the q-g2-syn conformer, in the gas, along
with dipole moment coupling and a series intermolecular CAHꢃ ꢃ ꢃO interactions.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
the diastereomer2 [9]. In general the stabilization of the gauche con-
formers has been attributed to the pCꢀO
/r
C–S and, to a minor extent,
rꢀC—S orbital interactions, while the larger stabilization of
the cis conformers of the -alkylsulfinylacetophenones and
Preceding spectroscopic (IR, 13C NMR, UV and UPS) and X-ray
studies supported by theoretical calculations on some b-carbonyl-
sulfoxides XC(O)CH2S(O)R have shown that the gauche conformer
to the pCO/
a
a-
phenylsulfinylamides relative to the
lacetones has been ascribed to the pPh-
a
-alkyl- and
a-aryl-sulfiny-
is the most stable for the
C6H4) [1–3] and -sulfinylesters (X = 4-Y-C6H4O; R = Et) [4], while
the cis conformer becomes the predominant for -sulfinylacetoph-
enones and -sulfinylamides (X = 4-Y-C6H4, Et2N; R = Alkyl, 4-Y-
C6H4 [5–8]. As for the -sulfinyl N-methoxy-N-methyl amides
a
-sulfinylketones (X = Me; R = Et, 4-Y-
pꢀCO and nN/pCꢀO conjugation,
a
which originates stronger intramolecular electrostatic and charge
transfer interactions between
d+@Odꢂ and d+@Odꢂ dipoles
(nO(CO)
rꢀS—O orbital interaction).
a
C
S
a
/
a
In the MeC(O)X series [10] there is a progressive increase of the
experimental carbonyl oxygen lone pair (nO) ionization energy
going from amide (Ei = 9.20 eV) to acetophenone (Ei = 9.34 eV) to
butanone (Ei = 9.46 eV) to thioester (Ei = 9.64 eV) and to ester
(Ei = 10.45 eV), for X = NEt2, Ph, Et, SEt and OEt, respectively, which
in turn is accompanied by a corresponding decrease of the negative
(X = N[Me][MeO]; R = 4-Y-C6H4) [9] the cis conformer prevails for
the diastereomer1, while the gauche conformer predominates for
* Corresponding author. Tel.: +55 11 3091 2167; fax: +55 11 3815 5579.
E-mail address: prolivat@iq.usp.br (P.R. Olivato).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.07.035

94
P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
charge on the carbonyl oxygen atom in this direction. Moreover,
there is a progressive increase of the electron affinity of the pCꢀO
orbital going from amide (Eae = 2.26 eV) to ester (Eae = 2.09 eV) to
butanone (Eae = 1.26 eV) and to thioester (Eae = 0.95 eV).
saturated aqueous sodium chloride solution was added and then
the product was extracted with CH2Cl2. The organic layer was dried
over anhydrous magnesium sulphate. The solvent was removed
under vacuum without heating, and the obtained crude solid was
dissolved with dichloromethane and crystallized through the slow
addition of n-hexane, at room temperature. Suitable crystals for X-
ray analysis were obtained by vapour diffusion from chloroform/n-
hexane at room temperature for 3. The physical, 1H and 13C NMR,
and elemental analysis of the thioester-sulfoxides 1–6 are pre-
sented in Table 1. The starting 2-ethylthio-(40-substituted) phen-
ylthioacetates 40-Y-C6H4SC(O)CH2SEt were prepared as previously
described [12].
Therefore, it seems reasonable to expect a larger stabilization of
the gauche conformer for the
same conformation of the other
stronger pꢀCO
rC–S(O) orbital interaction which should operate in
the gauche conformation of the sulfinyl-thioesters, once the
nO(CO)
rꢀS—O orbital interaction should stabilize the cis conformation
a
-sulfinyl-thioesters relative to the
a-sulfinyl derivatives, due to
/
/
only into a minor extent due to the large ionization energy of the
carbonyl oxygen loner pair.
Aiming to throw more light on the nature of the different elec-
tronic interactions which may stabilize the cis and gauche conform-
2.2. IR measurements
ers of the
a-sulfinylthioesters, this paper reports the IR study of
some 2-ethylsulfinyl-(40-substituted)-phenylthioacetates [11] 40-
Y-C6H4SC(O)CH2S(O)Et bearing in 40-position electron-attracting,
hydrogen and electron-donating substituents, i.e. Y = NO2 1, Cl 2,
Br 3, H 4, Me 5, OMe 6 (Scheme 1) along with density functional
theory (DFT) and Natural Bond Orbital (NBO) calculations of 1, 4
and 6 and X-ray diffraction analysis of compound 3.
These compounds were chosen taking into account that the
orbital and Coulombic interactions, which could operate in their
cis and gauche conformers, should be affected by changes in the
nS/pꢀCO conjugation involving the 40-substituent at the phenylthio-
carboxy group, and consequently should influence the stabilization
of the referred conformers.
The IR spectra were recorded with a FTIR Nicolet Magna 550
FTIR spectrometer, with 1.0 cmꢂ1 resolution, at a concentration
of 1.0 ꢅ 10ꢂ2 mol dmꢂ3 in n-hexane, carbon tetrachloride, chloro-
form, and acetonitrile solutions, using a 0.519 mm sodium chloride
cell, for the fundamental carbonyl region (1800–1600 cmꢂ1). The
spectra for the carbonyl first overtone region (3600–3100 cmꢂ1
)
were recorded in carbon tetrachloride solution (1.0 ꢅ 10ꢂ2
mol dmꢂ3), using a 1.00 cm quartz cell. The overlapped carbonyl
bands (fundamental and first overtone) were deconvoluted by
means of the Grams/32 curve fitting program, version 4.04, Level
II [13]. The populations of the gauche and quasi-gauche conformers
were estimated from the maximum of each component of the re-
solved carbonyl doublet, expressed in percentage of absorbance,
assuming equal molar absorptivity coefficients for the referred
conformers.
2. Experimental
2.1. Materials
2.3. NMR measurements
1H NMR and 13C NMR spectra were recorded on a Varian Inova
300 spectrometer operating at 299.947 and 75.423 MHz, respec-
tively, for 0.1 mol/dm3 solutions in chloroform-d. 1H and 13C chem-
ical shifts are reported in ppm relative to TMS, as internal standard.
All solvents for IR measurements were spectrograde and were
used without further purification. The 2-ethylsulfinyl-(40-substi-
tuted)-phenylthioacetates 40-Y-C6H4SC(O)CH2S(O)Et (Y = NO2 1, Cl
2, Br 3, H 4, Me 5, OMe 6) are novel compounds and were prepared
as follows: to a stirred solution of the appropriate thioester-sulfide
(10 mmol) in glacial acetic acid (2.2 mL; 40 mmol) at 0 °C, a solu-
tion of hydrogen peroxide (10 mmol; 30%) was added slowly. The
reaction mixture was maintained below 10 °C until all the thioes-
ter-sulfide has been reacted (ca. 2 h), then, 13 mL of dichlorometh-
ane was added, and the solution was neutralized with an aqueous
solution of sodium bicarbonate. After stirring for 5–10 min, a
2.4. X-ray measurements
2.4.1. Data collection, structure solution and refinement
X-ray diffraction experiments were performed at room temper-
ature (T = 290 K) on a MACH3 four-circle diffractometer. MoK
a
radiation and /2h scanning mode were applied. Three standard
x
reflections showed no significant intensity fluctuation (ca. 0.4%)
throughout the experiments. The intensities were corrected for
(17)
(18)
(21)
H
H
H
(6)
(7)
(2)
Lorentz and polarization and
w-scan based absorption was applied.
O
C
C
The structure was solved by direct methods using SIR97 [14] and
refined against F2 with SHELXL97 program [15]. The hydrogen
atoms were added geometrically and refined with the riding mod-
el. Details of the data collection, structure solution and refinement
are shown in Table 2. The crystallographic data for the structure re-
ported in this paper have been deposited in the Cambridge Crystal-
lographic Data Centre as a supplementary publication no. CCDC
777718.
(24)
(22)
(9)
(19)
H
H
H
(12) (10)
C
S
(20)
H
(5)
(1)
O
(4)
(14)
(8)
Y
S
C
(3)
H
H
(13)
(11)
(16)
(15)
(25)
(23)
H
H
Y = NO2 1, Cl 2, Br 3, H 4, Me 5, OMe 6
2.5. Theoretical calculations
= O(2)-C(1)-C(4)-S(5)
= C(1)-C(4)-S(5)-C(6)
= C(1)-C(4)-S(5)-O(8)
= O(2)-C(1)-S(3)-C(9)
= C(1)-S(3)-C(9)-C(11)
= C(4)-S(5)-C(6)-C(7)
All calculations were carried out (at 298 K) using methods and
basis sets implemented in the Gaussian package of programs
(G03-E01) [16]. The hybrid Hartree–Fock density functional
B3LYP method [17] with the 6-31G(d,p) basis set was used [18].
Full geometry optimizations and analytical vibrational frequency
calculations were performed on all the gauche or quasi-gauche ori-
Scheme 1. Atoms labelling of 2-ethylsulfinyl-(40-substituted)-phenylthioacetates
and assignment of relevant dihedral angles.
entations of the
resultant from
a
-sulfur atom with respect to the carbonyl group
a systematic conformational search, allowing

P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
95
complete relaxation of all internal parameters. Frequency analy-
ses were carried out to verify the nature of the minimum state
of all the stationary points obtained and to calculate the
zero-point vibrational energies (ZPVE) corrections. The NBO 3.1
program [19] was used as implemented in the Gaussian 03 pack-
age, and the reported NBO delocalization energies (E2) are those
given by second-order perturbation theory.
3. Results and discussion
Table 3 lists the stretching frequencies and the absorbance
percentage of the analytically resolved carbonyl band for the 2-
ethylsulfinyl-(40-substituted)-phenylthioacetates 1–6 in solvents
of increasing relative permittivity [20], i.e. n-hexane (e = 1.9), car-
bon tetrachloride (e = 2.2), chloroform (e = 4.8), and acetonitrile
(e = 38). A carbonyl doublet is shown for the majority of the stud-
ied compounds, in all solvents, excepting 1 (CCl4 and CHCl3), 2 (n-
C6H14) and 3 (CH3CN), for which only a singlet is detected. In the
first overtone region of compounds 1, 2, 4–6, in CCl4, only singlets
are observed, excepting compound 3 for which a doublet is ob-
served. In general the doublet higher frequency component is sig-
nificantly more intense than the lower component along the
series 1–6, in all solvents. Therefore, the lack of the lower fre-
quency component in the carbonyl first overtone region for deriv-
atives 1, 2, 4–6, may be ascribed to the fact that the half-band
width of this band is twice larger than that of the carbonyl
stretching band, in the fundamental region. Thus, the low inten-
sity carbonyl band component is hidden under the higher inten-
sity carbonyl band component.
It should be pointed out that there is not any clear solvent ef-
fect on the intensity of each doublet component as the solvent
polarity varies. However, it may be noticed a discrete increase
of the intensity of the higher frequency component with respect
to the lower one, going from 6 to 1 or 2, in n-C6H14, CCl4 and
CHCl3. The solvent effect on the carbonyl band components for
3, as a prototype for compounds 1–6 is illustrated in Fig. 1.
Although the observed solvent effect is not an evidence of rota-
tional isomerism, the occurrence of two carbonyl bands in the
first overtone region of 3 at frequencies twice those of the funda-
mental unless ca. 25 cmꢂ1 (which corresponds two times the
mechanical anharmonicity [21]), and with practically the same
relative intensity ratios, may be taken as an evidence for the exis-
tence of two stable conformers [22,23] in solution for the whole
series 1–6 (see above).
Aiming to determine the geometries for the stable conforma-
tions of series 1–6, computations at the B3LYP/6-31G(d,p) level
of theory for the 2-ethylsulfinyl-(40-substituted)-phenylthioace-
tates 1, 4 and 6 were performed. Table 4 presents the relevant
data for these compounds which indicate the existence of four
stable conformations, i.e., quasi-gauche-syn (q-g-syn), g3-syn, g1-
anti, quasi-gauche2-syn (q-g2-syn). The q-g-syn and g3-syn con-
formers present almost the same computed carbonyl frequencies
of ca. 1702 cmꢂ1, 1696 cmꢂ1, 1695 cmꢂ1 for derivatives 1, 4 and 6,
respectively, while the g1-anti conformer present the lowest car-
bonyl frequency of ca. 1687 cmꢂ1, 1678 cmꢂ1, 1676 cmꢂ1 for
derivatives 1, 4 and 6, respectively. The q-g2-syn conformer pre-
sents the highest computed carbonyl frequency of ca.
1715 cmꢂ1, 1710 cmꢂ1, 1712 cmꢂ1 for derivatives 1, 4 and 6,
respectively. Furthermore, the summing up of molar fraction of
the q-g-syn and g3-syn conformers varies with the nature of the
40-substituent, i.e. from ca. 85% to 74% and to 65%, for derivatives
1 (NO2), 4 (H), 6 (OMe), respectively. Simultaneously, the molar
fraction of the g1-anti conformer increases in the same direction,
i.e. from ca. 12% to 24% and to 33%, for derivatives 1, 4 and 6,
respectively. The molar fraction of the least stable q-g2-syn

96
P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
Table 2
29.4%) for 1. The q-g-syn conformer displays the 2-sulfinyl (
a
Crystal data and structure refinement of 2-ethylsulfinyl-40-bromophenyl thioacetate
ffi+56°) substituent in a syn-clinal or quasi-gauche geometry with
respect to the carbonyl group. The syn and anti suffixes indicate
that the d dihedral angle [C(Ph)ASAC@O] is close to 0° and 180°,
respectively.
40-Br-C6H4SC(O)CH2S(O)Et (3).
Empirical formula
Formula weight
C10H11BrO2S2
307.22
290(2)
0.71073
The g3-syn conformer is the more stable (Erel. = 0.0 kJ molꢂ1
;
Temperature (K)
0
55.7%) for 1 and is the second (Erel. = 0.69 kJ molꢂ1; 31.8%) and
third (Erel. = 0.92 kJ molꢂ1; 26.3%) stable conformer for 4 and 6,
respectively. The g3-syn conformer displays the 2-sulfinyl
Wavelength (ÅA)
Crystal system, space group
Orthorhombic, P212121
0
Unit cell dimensions (AÅ)
a
b
4.9385(9)
28.760(2)
8.770(1)
(
a
ffi +75°) substituent in a syn-clinal or gauche geometry with re-
spect to the carbonyl group.
c
0
The g1-anti is the third stable conformer (Erel. = 3.9 kJ molꢂ1
;
1245.6(3)
Volume (AÅ3)
11.7%) and (Erel. = 1.42 kJ molꢂ1; 23.7%) for 1 and 4, respectively,
Z, Calc. density (Mg mꢂ3
)
4, 1.638
and is the second (Erel. = 0.41 kJ molꢂ1; 32.7%) stable conformer
Absorption coefficient (mmꢂ1
F(0 0 0)
)
3.613
for 6. The g1-anti conformer displays the 2-sulfinyl (
stituent in a syn-clinal or gauche geometry with respect to the car-
a
ffi +78°) sub-
616
Crystal size (mm)
Theta range for data collection (°)
Limiting indices
0.12 ꢅ 0.10 ꢅ 0.05
1.42–26.00
ꢂ6–6, 0–35, 0–10
2630, 2435
100.00%
bonyl group.
The q-g2-syn conformer is the least stable (Erel. ffi 7.1 kJ molꢂ1
;
Reflections collected
2.3%) conformer for 1, 4 and 6. The q-g2-syn conformer displays
Completeness to h = 26°
Absorption correction
Max and min transmission
Refinement method
W
-scan
the 2-sulfinyl (
a
ffi +60°) substituent in a syn-clinal or quasi-gauche
0.835, 0.655
geometry with respect to the carbonyl group, whose geometry is
similar to that of the q-g-syn conformer. Fig. 3 illustrates the com-
puted molecular structures of the q-g-syn, g3-syn, g1-anti and q-g2-
syn conformers of 4, taken as a prototype for compounds 1–6.
Table 5 shows the CHELPG charges at the selected atoms at the
B3LYP/6-31G(d,p) level for compounds 1, 4 and 6. Table 6 displays
the interatomic distances between some selected atoms and the
Full-matrix least-squares on F2
2435/1/137
Data/restraints/parameters
Goodness-of-fit on F2
1.022
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole (e ÅAꢂ3
r(I)]
0.0487, 0.1266
0.1267, 0.1642
0.481, ꢂ0.447
0
)
difference between these contacts and the sum of the van der
P
Waals radii ( v dW radii) (
D
l) for the same compounds.
conformer remains almost constant for derivatives 1, 4 and 6, of ca.
2%. Fig. 2 presents a qualitative diagram which illustrates well this
trend. It should be pointed out that the calculations reproduce
quite well the experimental results. Actually, the q-g-syn and g3-
syn conformers which present very close computed frequencies
should correspond in the IR spectrum, in solution, to the carbonyl
doublet higher frequency component of larger intensity while the
g1-anti conformer should correspond to the carbonyl doublet lower
frequency component of smaller intensity. Moreover, in solution,
the intensity of the higher frequency carbonyl doublet component
changes from (100%, CCl4; 100%, CHCl3) for 1 to (90%, CCl4; 83%,
CHCl3) for 6 while the intensity of the lower carbonyl frequency
component changes from (0%, CCl4; 0%, CHCl3) for 1 to (10%,
CCl4; 17%, CHCl3) for 6. As expected, the least stable q-g2-syn con-
former of low molar fraction, in the gas, is not detected in solution.
Table 4 shows that the q-g-syn conformer is the more stable
(Erel. = 0.0 kJ molꢂ1; 42.0%) for 4 and (Erel. = 0.0 kJ molꢂ1; 38.6%)
In order to understand the nature of the orbital interactions
which act stabilizing the q-g-syn, g3-syn, g1-anti and q-g2-syn con-
formers for the title compounds, the NBO analysis [19] was per-
formed. Table 7 presents selected NBO interactions for 1, 4 and 6
[24]. It can be observed in this Table that the more important orbi-
tal interactions for q-g-syn, g3-syn, g1-anti and q-g2-syn conformers
are: (a) the LPS3
[O@CAS M –OAC@S+] conjugation, whose mean energy value is
ca. 31 kcal molꢂ1; (b) the LPO2 rCꢀ—S and LPO2 rꢀC—C (though
bond coupling) whose mean energy value is of ca. 35 kcal molꢂ1
?
pCꢀ
,
which corresponds to the
1@O2
?
?
and 18 kcal molꢂ1, respectively. Nevertheless, the LPO2
?
rꢀC—S
mean energy value which is ca. 36 kcal molꢂ1 for q-g-syn, g3-syn,
and q-g2-syn conformers is ca. 5 kcal molꢂ1 higher than the same
interaction for the g1-anti conformer.
The stronger LPO2
and q-g2) conformers relative to that for the anti (g1) conformer
originates an increase of the carbonyl bond order and thus in the
?
rꢀC—S orbital interaction for the syn (q-g, g3,
for 6, while is the second more stable (Erel. = 1.59 kJ molꢂ1
;
Table 3
Frequencies (
m
, cmꢂ1) and intensities of the carbonyl stretching bands in the IR spectra of 2-ethylsulfinyl-(40-substituted)-phenylthioacetates 40-Y-C6H4SC(O)CH2S(O)Et (1–6).
Comp.
Y
n-C6H14
CCl4
CHCl3
CH3CN
m
Pa
m
P
mb
P
m
P
m
P
c
1
2
3
4
5
6
NO2
Cl
–
–
–
1702
–
100.0
–
91.7
8.3
84.3
15.7
92.6
7.4
91.7
8.3
3384
–
3376
–
3377
3344
3373
–
3369
–
100.0
–
100.0
–
78.0
22.0
100.0
–
100.0
–
1700
–
100.0
–
91.7
8.3
92.2
7.8
88.9
11.1
82.6
17.4
83.6
16.4
1705
1695
1701
1682
1702
–
1699
1683
1696
1672
1698
1682
83.3
16.7
90.9
9.1
100.0
–
82.6
17.4
89.3
10.7
82.7
17.3
c
–
1704
–
100.0
1699
1682
1699
1687
1697
1682
1696
1674
1695
1675
1695
1666
1696
1675
1692
1665
1691
1668
1687
1667
Br
1704
1684
1702
1685
1700
1683
1700
1683
76.9
13.1
92.3
7.7
90.4
9.6
H
Me
OMe
92.6
7.4
90.1
9.9
3368
–
100.0
–
a
Intensity of each component of the carbonyl doublet expressed in percentage of absorbance.
First overtone.
Compound slightly soluble in this solvent.
b
c

P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
97
0.8
(a)
(d)
0.08
0.07
0.06
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.05
0.04
0.03
0.02
0.01
1730
1720
1710
1700
1690
1680
1670
1650
1660
1730 1720 1710 1700 1690
1680
1670
Wavenumbers / cm-1
Wavenumbers / cm-1
0.7
0.6
0.5
0.4
0.3
0.2
0.1
(e)
0.7
0.6
(b)
0.5
0.4
0.3
0.2
0.1
1730 1720 1710 1700 1690 1680 1670 1660 1650
1750 1740 1730 1720 1710 1700 1690 1680 1670 1660
Wavenumbers / cm-1
Wavenumbers / cm-1
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
(c)
3420
3400
3380
3360
3340
3320
3300
Wavenumbers / cm-1
Fig. 1. IR spectra of 2-ethylsulfinyl-40-bromophenylthioacetate (3) showing the analytically resolved carbonyl stretching band, in: n-hexane (a), carbon tetrachloride
[fundamental (b) and first overtone (c)], chloroform (d) and acetonitrile (e).
v
CO frequencies of the former conformers with respect to the latter
one. Fig. 4 illustrates the n(S3) , nO2(CO) and nO2(CO)
orbital interactions with their corresponding representa-
The syn (q-g, g3, q-g2) conformers for 1, 4 and 6 (Structure I,
Scheme 2) present short intramolecular contacts between the
/
pCꢀ
/
rCꢀ
/
1—O2
1—S3
rCꢀ
O(2)[CO]ꢃ ꢃ ꢃC(9)[Ph] atoms whose distances are shorter than the
1—C4
P
tions in the Valence Bond Theory. The NBO mean energy value of
v dW radii by
vant orbitals indicates the existence of the nO(CO)
D
l ffi ꢂ0.25 Å. The eigenvector analysis of the rele-
the rꢀC
orbital for syn (q-g, g3, and q-g2) indicate that it is more
/
pꢀPh charge trans-
1—S3
stable than the same orbital for g1-anti conformer by ca.
2 kcal molꢂ1
This behaviour is responsible for the observed
slightly stronger nO2(CO) orbital interaction of the syn con-
formers with respect to the anti conformer.
fer for the referred conformers which should contribute for the
.
stabilization of the syn conformers. However, the LPO2 ?
pCꢀ
9@C11
/
rꢀ
interaction was not detected in the NBO analysis, probably because
its value should be slightly smaller than 0.5 kcal molꢂ1. On the
C1—S3

98
P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
other hand, the anti (g1) conformer (Structure II, Scheme 2) pres-
ent short intramolecular contacts between the oppositely
charged Hd+(16)ꢃ ꢃ ꢃCdꢂ(9)[Ph] atoms whose distances are shorter
P
than the v dW radii by
D
l values which vary from ꢂ0.28 Å to
ꢂ0.33 Å and to ꢂ0.34 Å for 1, 4 and 6, respectively. This trend is
in line with the pC9@C11
?
rCꢀ
orbital interaction whose value
4—H16
is the maximum (
tive 9 (highest HOMO of
tro derivative 1 whose
(lowest HOMO of
D
E = 0.64 kcal molꢂ1) for the methoxy deriva-
p
D
Ph orbital), and the minimum for the ni-
E value is smaller than 0.50 kcal molꢂ1
pPh orbital). A further short contact which takes
place in the anti (g1) conformer is between the oppositely charged
O
the
dꢂ(8)[SO]ꢃ ꢃ ꢃHd+(23)[o-Ph] atoms whose distances are shorter than
P
v dW radii by
D
l values which vary from ꢂ0.34 Å to
ꢂ0.35 Å and to ꢂ0.45 Å for 6, 4 and 1, respectively. This tendency
is in agreement with the progressive increase of the
(LPO8(3)
?
rCꢀ
; LPO8(1)
?
rCꢀ
) orbital interactions (hydro-
11—H23
11—H23
gen bond) whose energy values vary from (1.3; 1.0 kcal molꢂ1) to
(1.5; 1.0 kcal molꢂ1) and to (2.3; 1.6 kcal molꢂ1) for 6, 4 and 1,
respectively. Thus, the anti (g1) conformer is stabilized by both
pC9@C11[Ph]
?
rCꢀ
(weak) and LPO[SO]
?
rCꢀ
(med-
4—H16½a-CH2ꢁ
11—H23½o-Phꢁ
ium) orbital (hydrogen bond) and electrostatic interactions.
The q-g-syn, g3-syn, g1-anti and q-g2-syn conformers for 1, 4
and 6 which display very short S(5)ꢃ ꢃ ꢃC(1) contacts between
a-
sulfinyl sulfur and the carbonyl carbon atoms ( l mean value of
D
ca. ꢂ0.70 Å), are responsible for the stabilization of the referred
gauche conformers through the rC–S
/
pꢀCO
,
pCO
/ /
rꢀC—S and pꢀCO rꢀC—S
orbital interactions.
In general, the rC
/
pCꢀ
,
pCO
/
rꢀC—S and pꢀCO rCꢀ—S interac-
/
4—S5
1@O2
tions are stronger for the g3-syn and g1-anti conformers (
a
dihe-
dral angle of ca. 77°) and weaker for the q-g-syn and q-g2-syn
conformers ( dihedral angle of ca. 60°). In fact, there is a better
overlap between the relevant orbitals for the former conformers
a
with respect to the latter ones. Thus, the rC
?
pCꢀ
interac-
4—S5
1@O2
tion mean energy value is ca. 5.3 kcal molꢂ1 for g3-syn and g1-anti
conformers and ca. 3.8 kcal molꢂ1 for q-g-syn and q-g2-syn con-
formers for 1, 4 and 6 derivatives. In the same way, the unusual
pCꢀ
?
rCꢀ
interaction [25] mean energy value is ca.
1@O2
4—S5
7.2 kcal molꢂ1 for g3-syn and g1-anti conformers and ca.
5.0 kcal molꢂ1 for q-g-syn and q-g2-syn conformers for 1, 4 and
6 derivatives. The pC1@O2
?
rCꢀ
interaction mean energy value
p4)—/rS5*
(r) interaction series, i.e. ca.
is the weakest for the p*
(
2.2 kcal molꢂ1 for g3-syn and g1-anti conformers and ca.
1.4 kcal molꢂ1 for q-g-syn and q-g2-syn conformers, for 1, 4 and
6 derivatives.
It should be pointed out, that there is a slight progressive in-
crease of the rC
?
pCꢀ
mean interacting energy value, for
4—S5
1@O2
the four conformers, going from 6 to 1 which vary from 4.3 to
5.2 kcal molꢂ1. Actually, the electron-donating 40-methoxy sub-
stituent which destabilizes the pCꢀ
orbital gets it far apart from
1@O2
the rC
orbital, while the electron attracting 40-nitro substitu-
4—S5
ent which stabilizes the pCꢀ
orbital gets it closer to the rC
4—S5
1@O2
orbital. Therefore, the former substituent act decreasing the
orbital interaction energy while the latter substi-
rC
4—S5
?
pCꢀ
1@O2
tuent makes it stronger.
The geometry of g3-syn, g1-anti and q-g2-syn conformers allows
intramolecular contact between the oppositely charged
O
the
dꢂ(8)[SO]ꢃ ꢃ ꢃCd+(1)[CO] atoms whose distances are shorter than
P
v dW radii by
D
l mean values of ꢂ0.27 Å for 1, ꢂ0.16 Å
for 4 and ꢂ0.05 Å for 6. This contact becomes larger than the
P
v dW radii for the q-g-syn conformer as the sulfinyl oxygen
atom becomes far apart from the carbonyl carbon atom
(c
ffi 170°) (Table 4). Nevertheless, the weak LPO8(3)
?
pCꢀ
orbi-
1@O2
tal interaction of 0.5 kcal molꢂ1 is the only one detected for the
g3-syn conformer for the 40-nitro derivative 1 which possess the
shortest intramolecular contact (
D
l = ꢂ0.34 Å) and should have
the closest pꢀC
orbital energy with respect to that of the
1@O2

P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
99
g3-syn (∼32%)
q-g-syn (∼30%)
q-g2-syn (∼3%)
g3-syn (∼27%)
q-g-syn (∼42%)
q-g2-syn (∼2%)
g3-syn (∼56%)
g1-anti (∼12%)
q-g-syn (∼39%)
q-g2-syn (∼2%)
g1-anti (∼33%)
g1-anti (∼24%)
cm-1
cm-1
1695
1711 1696
1678
1715 1702 1687
cm-1
1712
1676
(c)
(a)
(b)
Fig. 2. Diagram showing the frequency and the relative intensity of the carbonyl band components for the q-g-syn, g3-syn, g1-anti and q-g2-syn conformers of 40-methoxy (a),
40-hydrogen (b), 40-nitro (c) 2-ethylsulfinyl-phenylthioacetates computed at the B3LYP/6-31G(d,p) level.
rC
O
orbital, as above discussed. It may be concluded that the
orbital overlap. Thus, the q-g-syn conformer is significantly stabi-
lized through the Coulombic Odꢂ(2)[CO]ꢃ ꢃ ꢃSd+(5)[SO] interaction.
4—S5
dꢂ(8)[SO]ꢃ ꢃ ꢃCd+(1)[CO] electrostatic interaction is the main factor
which contributes for the stabilization of the g3-syn, g1-anti and
q-g2-syn, whose strength follows the order 1 > 4 > 6, along with a
weaker contribution of the LPO8(3)
Similarly, the q-g2-syn conformer presents an
a
angle of ca. 60°,
ffi 70°
which is close to that of the q-g-syn conformer, but the
c
?
pCꢀ
orbital interaction.
and b ffi 178° dihedral angles for the q-g2-syn conformer are inter-
changed with respect to those of the q-g-syn conformer. This
geometry should also stabilize electrostatically the q-g2-syn con-
1@O2
A further short contact is found between the oppositely charged
O
dꢂ(2)[CO]ꢃ ꢃ ꢃHd+(17)[CH2] atoms whose distances are shorter than
P
the v dW radii by
D
l mean value of ca. ꢂ0.36 Å for q-g-syn, g3-
former through the Odꢂ(2)[CO]ꢃ ꢃ ꢃSd+(5)[SO] short contact, whose
P
syn, g1-anti conformers for 1, 4 and 6. The Odꢂ(2)[CO]ꢃ ꢃ ꢃHd+(17)[CH2]
interatomic distance is smaller than the
D
Scheme 2; Fig. 2) brings the sulfinyl sulphur lone pair close to
v dW radii by
contact is responsible for LPO2
?
rCꢀ
orbital interaction
l ffi ꢂ0.13 cmꢂ1. However, the q-g2-syn conformer (Structure III,
6—H17½Etꢁ
whose mean energy value is of ca. 1.2 kcal molꢂ1 for the referred
conformers. However, this contact is significantly larger than the
the negatively charged carbonyl oxygen atom (LPS5ꢃ ꢃ ꢃOdꢂ(2)[CO]
)
P
v dW radii for the q-g2-syn as the ethyl group becomes far apart
from the carbonyl oxygen atom. Thus, the electrostatic and orbital
(hydrogen bond) interactions contribute for the stabilization of the
q-g-syn, g3-syn, g1-anti conformers almost to the same extent.
It should be pointed out that appropriate geometry for the q-g-
which originates a strong repulsive Coulombic interaction between
them, leading to a significant destabilization of q-g2-syn conformer.
Moreover, this repulsive interaction seems to be responsible for an
increase of the carbonyl bond order and consequently to the rising
of the vCO stretching frequency of q-g2-syn conformer with respect
to the vCO frequencies of the g3-syn, g1-anti and q-g2-syn conform-
ers as found in the calculations (Table 4).
The mean summing up values of all selected orbital interaction
energies of the q-g-syn (96.2 kcal molꢂ1), g3-syn (102.0 kcal molꢂ1),
g1-anti (97.8 kcal molꢂ1) and q-g2-syn (97.7 kcal molꢂ1) conformers
for 1, 4 and 6 (Table 7) indicate that the g3-syn conformer is the
syn conformer (
a
ffi 55°; b ffi ꢂ80°;
c
ffi 170°) brings closer the
oppositely charged Odꢂ(2)[CO]ꢃ ꢃ ꢃSd+(5)[SO] atoms whose contact is
P
smaller than v dW radii by
D
l ffi ꢂ0.10 cmꢂ1. This geometry is
similar to that of the b-carbonyl-sulfoxides (a ffi 10°; b ffi ꢂ73°;
c
ffi 180°) [5–7], but do not allows the LPO2
?
rꢀS—O interaction as
the slightly larger
a
dihedral angle precludes the occurrence of this
q-g-syn
g3-syn
g1-anti
q-g2-syn
Fig. 3. Molecular structures of the conformers of 4 obtained at the B3LYP/6-31-G(d,p) level.

100
P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
Table 5
CHELPG charges (e) at selected atoms obtained at the B3LYP/6-31G(d,p) level for 40-Y-C6H4SC(O)CH2S(O)Et (1), (4), (6).
Comp.
1
Y
Conf.
O(2)[CO]
C(1)[CO]
S(3)
C(9)[Ph]
H(23)[Ph]
S(5)[SO]
O(8)[SO]
H(17)[CH2]
H(16)[
a-CH2]
NO2
q-g-syn
g3-syn
g1-anti
q-g2-syn
ꢂ0.385
ꢂ0.430
ꢂ0.392
ꢂ0.435
0.379
0.465
0.454
0.511
ꢂ0.267
ꢂ0.228
ꢂ0.191
ꢂ0.250
0.263
0.201
0.120
0.215
0.140
0.139
0.059
0.166
0.190
0.184
0.192
0.259
ꢂ0.425
ꢂ0.407
ꢂ0.380
ꢂ0.421
0.035
0.089
0.089
0.055
0.140
0.139
0.038
0.129
4
6
H
q-g-syn
g3-syn
g1-anti
q-g2-syn
ꢂ0.408
ꢂ0.451
ꢂ0.408
ꢂ0.459
ꢂ0.412
ꢂ0.457
ꢂ0.415
ꢂ0.467
0.405
0.505
0.462
0.543
ꢂ0.295
ꢂ0.269
ꢂ0.219
ꢂ0.297
ꢂ0.294
ꢂ0.262
ꢂ0.220
ꢂ0.306
0.261
0.223
0.138
0.254
0.124
0.128
0.046
0.153
0.185
0.185
0.165
0.249
ꢂ0.433
ꢂ0.410
ꢂ0.384
ꢂ0.425
ꢂ0.433
ꢂ0.410
ꢂ0.391
ꢂ0.426
0.040
0.103
0.085
0.053
0.133
0.132
0.035
0.125
OMe
q-g-syn
g3-syn
g1-anti
q-g2-syn
0.404
0.495
0.450
0.560
0.208
0.169
0.093
0.194
0.129
0.140
0.066
0.148
0.185
0.181
0.165
0.245
0.040
0.098
0.091
0.067
0.131
0.129
0.024
0.122
Table 6
Selected interatomic distances (Å) for the minimum energy conformations of 40-Y-C6H4SC(O)CH2S(O)Et (1), (4), (6) at the B3LYP/6-31G(d,p) level, and X-ray geometrical data for
40-Br-C6H4SC(O)CH2S(O)Et (3).
Comp
Y
Conf.a
S5ꢃ ꢃ ꢃC1
D
lc
O2ꢃ ꢃ ꢃS5
D
l
C1ꢃ ꢃ ꢃO8
D
l
C9ꢃ ꢃ ꢃO2
D
l
O2ꢃ ꢃ ꢃH17
–
D
l
O8ꢃ ꢃ ꢃH23
D
l
H16ꢃ ꢃ ꢃC9
D
l
H16ꢃ ꢃ ꢃC11
Dl
d
3
1
Br X-ray
NO2
2.699(7) ꢂ0.80 3.095(5) ꢂ0.23 3.124(8) ꢂ0.10 2.909(9) ꢂ0.31
q-g-s
g3-s
g1-a
2.822
2.783
2.837
2.763
ꢂ0.68 3.224
ꢂ0.72 3.336
ꢂ0.66 3.423
ꢂ0.74 3.218
ꢂ0.68 3.212
ꢂ0.69 3.360
ꢂ0.66 3.422
ꢂ0.73 3.185
ꢂ0.68 3.239
ꢂ0.69 3.358
ꢂ0.66 3.429
ꢂ0.73 3.161
3.32
ꢂ0.10 4.031
0.02 2.978
0.10 3.145
ꢂ0.10 3.245
ꢂ0.11 4.037
0.04 3.038
0.10 3.152
ꢂ0.14 3.305
ꢂ0.08 4.037
0.04 3.038
0.11 3.161
ꢂ0.16 3.307
3.22
0.71 2.987
ꢂ0.34 2.943
ꢂ0.18 4.030
ꢂ0.08 2.989
0.72 2.969
ꢂ0.28 2.954
ꢂ0.17 4.025
ꢂ0.02 2.978
0.82 2.967
ꢂ0.18 2.948
ꢂ0.06 4.022
0.09 2.970
3.22
ꢂ0.23 2.439
ꢂ0.28
ꢂ0.36
–
–
–
–
–
–
ꢂ0.28 2.356
0.81 2.331
ꢂ0.39 2.266
ꢂ0.45 2.617
ꢂ0.28 2.855
ꢂ0.05
ꢂ0.02
0.02
q-g2-s
ꢂ0.23
ꢂ0.25 2.409
ꢂ0.27 2.328
0.81 2.323
ꢂ0.24
ꢂ0.25 2.415
ꢂ0.27 2.324
0.80 2.324
–
–
–
–
4
6
H
q-g-s
g3-s
g1-a
2.824
2.806
2.839
2.770
ꢂ0.31
ꢂ0.39
–
–
–
–
ꢂ0.40 2.366
ꢂ0.35 2.574
ꢂ0.33 2.884
q-g2-s
–
–
–
–
OMe
q-g-s
g3-s
g1-a
2.819
2.806
2.840
2.772
ꢂ0.31
ꢂ0.40
–
–
–
ꢂ0.40 2.385
ꢂ0.34 2.565
ꢂ0.34 2.920
q-g2-s
ꢂ0.25
ꢂ
–
2.72
–
2.90
–
2.90
P
rv dWb 3.50
2.72
a
b
c
Conformer designation.
Sum of the van der Waals radii.
Difference between nonbonded atoms distance and the sum of the van der Waals radii.
Interatomic distance larger than the sum of the van der Waals radii.
d
Table 7
Comparison of significant NBO energies (kcal molꢂ1) of the corresponding interacting orbitals for the gauche(g) or quasi-gauche (q-g) conformers of 40-Y-C6H4SC(O)CH2S(O)Et (1),
(4), (6) at the B3LYP/6-31G(d,p) level.
Orbitals
Y = NO2 (1)
Y = H (4)
Y = OMe (6)
q-g-s
g3-s
g1-a
q-g2-s
q-g-s
g3-s
g1-a
q-g2-s
q-g-s
g3-s
g1-a
q-g2-s
LPS3
LPO2
LPO2
LPO2
rC
?
?
?
?
pCꢀ
30.7
36.7
17.7
1.3
3.9
1.4
4.7
–
30.5
36.5
18.2
1.3
6.1
2.0
7.2
0.5
–
28.9
31.5
18.3
0.8
5.1
2.3
7.2
–
30.7
37.2
18.8
31.8
35.7
18.1
1.5
3.2
1.3
4.2
–
32.2
35.3
18.5
1.3
5.4
2.0
7.2
–
30.5
30.5
18.5
0.9
5.0
2.3
7.2
–
32.0
36.2
19.2
–
32.0
35.5
18.1
1.4
3.3
1.4
4.8
–
32.2
35.0
18.5
1.4
5.4
2.0
7.3
–
30.8
30.3
18.6
0.8
4.9
2.4
7.3
–
31.9
36.2
19.3
–
1 @O2
rCꢀ
rCꢀ
rCꢀ
1 —S3
1 —C4
6 —H17
a
–
?
pCꢀ
5.0
1.5
5.2
–
4.2
1.3
4.8
–
3.8
1.2
4.5
–
4—S5
1@O2
pC1@O2
?
?
rCꢀ
4 —S5
pCꢀ
rCꢀ
1@O2
4—S5
LPO8(3) ? pꢀC
LPO8(3) ? rꢀC
LPO8(1) ? rꢀC
1@O2
–
2.3
1.6
–
–
–
1.5
1.0
–
–
–
–
1.3
1.0
0.6
–
11 —H23
11 —H23
4—H16
–
–
–
–
–
–
–
–
–
pC9@C11
?
rCꢀ
–
–
–
–
–
–
–
–
–
a
Interaction energy lower than 0.5 kcal molꢂ1
.
most stable, followed by g1-anti and q-g2-syn conformers, being the
q-g-syn conformer the slightly less stable. The q-g-syn conformer is
further stabilized through the Odꢂ(2)[CO]ꢃ ꢃ ꢃSd+(5)[SO] attractive Cou-
lombic interaction while the q-g2-syn conformer is destabilized by
the LPS5ꢃ ꢃ ꢃOdꢂ(2)[CO] repulsive Coulombic interaction. This analysis
is in line with the computed relative conformer population which
indicates that both the q-g-syn and g3-syn conformers are the more
stables, followed by the g1-anti conformer, while the q-g2-syn is the
least stable (Fig. 2 and Table 4).
The computed population of the q-g-syn, g3-syn and g1-anti con-
formers changes going from the electron attracting 40-nitro deriv-
ative
1
to the electron-donating 40-methoxy derivative 6.
Nevertheless, the low population of the q-g2-syn remains practi-
cally constant going from 1 to 6 (Table 4). It should be pointed
out that there is not a straightforward explanation to justify the
facts: that the q-g-syn conformer population increases going from
1 (29.4%) to 6 (39%), the g3-syn conformer decreases its population
going from 1 (39%) to 6 (27%) while the g1-anti population

P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
101
Fig. 4. n(S3)
/
pꢀ
(a), nO2(CO)
/
rꢀ
(b) and nO2(CO)
/ (c) orbital interactions with their corresponding representations in the Valence Bond Theory.
rꢀ
C1 —C4
C1—O2
C1—S3
Table 8
0
Intermolecular hydrogen-bond geometry (ÅA, °) for the single crystal of 2-ethylsulfi-
nyl-40-bromophenylthioacetate 40-Br-C6H4SC(O)CH2S(O)Et (3).
DAHꢃ ꢃ ꢃA
DAH
Hꢃ ꢃ ꢃAa
Dꢃ ꢃ ꢃA
DAHꢃ ꢃ ꢃA
i
C4AH4Aꢃ ꢃ ꢃO8
0.97
0.96
0.97
0.97
0.93
2.58
2.65
2.58
2.48
2.64
3.546(9)
3.563(11)
3.323(9)
3.273(8)
3.500(11)
175
158
134
139
154
i
C7AH7Bꢃ ꢃ ꢃO8
C6AH6Bꢃ ꢃ ꢃO8
C4AH4Bꢃ ꢃ ꢃO8
ii
ii
iii
C
10AH10ꢃ ꢃ ꢃO2
Symmetry operations: i = ꢂx + 1/2 + 1, ꢂy + 1, +z ꢂ 1/2
ii = x ꢂ 1, y, z
iii = x + 1, y, z
Fig. 5. X-ray crystal structure of 2-ethylsulfinyl-40-bromophenylthioacetate (3)
with the heavy atoms labelling. Displacements ellipsoids are drawn at 50%
probability level and H atoms are shown as spheres of arbitrary radii.
a
Sum of the van der Waals radii: 2.72 Å.
increases going from 1 (12%) to 6 (33%). Actually, the different orbi-
tal and electrostatic interactions which stabilize the referred con-
formers may act in opposite directions making difficult to
rationalize these trends (see above).
X-ray single crystal analysis, performed for 3 (Fig. 5) shows that
the dihedral angles a, b, c, d, u (Table 4) indicate that this com-
H
O
H
O
S
C
C
S(O)Et
C
C
S(O)(Et)
H
S
Y
H
pound exists in the solid state in a geometry which is reasonably
close to the less stable q-g2-syn gas conformation for derivatives
Y
1, 4 and 6. However, the
(74.6°) deviates significantly from the same angle for 1, 4 and 6,
in the gas phase (
ffi ꢂ173°). It should be noted, that in the solid
of 3, the difference between the intramolecular contacts and the
sum of the van der Waals radii (
l) (Table 6) for S5ꢃ ꢃ ꢃC1 (ca.
ꢂ0.80 Å), O2ꢃ ꢃ ꢃS5 (ca. ꢂ0.23 Å), C1ꢃ ꢃ ꢃO8 (ca. ꢂ0.10 Å), C9ꢃ ꢃ ꢃO2 (ca.
l) values found in
e dihedral angle in the crystal for 3
II
I
e
D
ꢂ0.32 Å) are similar to the corresponding (
D
the gas phase for 1, 4 and 6. Therefore, these short contacts stabi-
lize almost into the same extent the distorted q-g2-syn conformer
of 3 in the solid through the same orbital and Coulombic interac-
tions which take place for the q-g2-syn conformer in the gas phase
for 1, 4 and 6.
In order to obtain a larger energy gain from crystal packing, the
slightly distorted q-g2-syn geometry of 3 is stabilized in the solid
through dipole moment coupling along with a series of CAHꢃꢃꢃO
interactions whose HꢃꢃꢃO interatomic distances are close or shorter
than the sum of their van der Waals radii as shown in Table 8.
III
Scheme 2. Relevant intramolecular short contact in syn (q-g, g3, q-g2) conformers
(I), anti (g1) conformer (II) and q-g2-syn conformer (III) of 2-ethylsulfinyl-(40-
substituted)-phenylthioacetates 40-Y-C6H4SC(O)CH2S(O)Et.

102
P.R. Olivato et al. / Journal of Molecular Structure 981 (2010) 93–102
C.R. Cerqueira Jr. The LCCA-Laboratory of Advanced Scientific
4. Conclusions
Computation of the University of São Paulo is acknowledged for
access to resources. M.D.C. thanks the University of Ferrara (Nano
& Nano Project) for financial support. Professor G. Distefano’s
assistance during the execution of this work is also gratefully
acknowledged.
The preferred conformations of some 2-ethylsulfinyl-(40-substi-
tuted)-phenylthioacetates bearing as substituents NO2 1, Cl 2, Br 3,
H 4, Me 5, OMe 6 were determined by vCO IR analysis, B3LYP/6-
31G(d,p) calculations along with the NBO analysis for 1, 4 and 6
and X-ray analysis for 3. Theoretical data indicated the existence of
four gauche conformers, i.e. the q-g-syn, g3-syn, g1-anti and q-g2-syn
conformers for 1, 4 and 6 derivatives. The q-g-syn and g3-syn con-
formers present almost the same computed vCO frequencies while
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.07.035.
the g1-anti conformer presents the lowest
v
CO frequency. The q-g2-
syn conformer shows the highest computed
v
CO frequency. The cal-
culations reproduce quite well the experimental results. In fact the
q-g-syn and g3-syn conformers correspond in the IR spectrum (in
solution) to the vCO doublet higher frequency component of larger
intensity while the g1-anti conformer correspond to the vCO doublet
lower frequency component of smaller intensity.
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The NBO analysis showed that the q-g-syn, g3-syn, g1-anti and q-
g2-syn conformers for 1, 4 and 6 are strongly stabilized by
LPS3
?
pCꢀ
(conjugative), LPO2
?
rCꢀ
and LPO2 ?
rCꢀ
1@O2
1—S3
1—C4
(through bond coupling) interactions whose mean energy values
are of ca. 31 kcal molꢂ1, 35 kcal molꢂ1 and 18 kcal molꢂ1, respec-
tively. The LPS3
?
pꢀ
and LPO2
?
rꢀ
orbital interactions sta-
C1—O2
C1—C4
bilize all the conformers into the same extent while the (q-g, g3
and q-g2)-syn conformers are more stabilized than the g1-anti con-
former by ca. 5 kcal molꢂ1 through the LPO2
?
rCꢀ
orbital interac-
1—S3
tion. The stronger LPO2
?
rCꢀ
interaction for the (q-g, g3 and q-g2)-
1—S3
syn conformers relative to that of the g1-anti conformer originates an
increaseof thecarbonylbond order andthus in the
the former conformers relative to the latter one.
vCO frequenciesof
The q-g-syn, g3-syn and q-g2-syn conformers are further stabi-
lized by rC
?
pCꢀ
/
(strong), pC1@O2/ ?
rꢀC , LPO2 rꢀC
4—S5
4—S5
6—H17½Etꢁ
(weak) and pꢀC
rꢀC1—O2 (strong) orbital interactions. The g1-anti
1@O2
4—S5
conformer is stabilized by rC
?
pCꢀ
(strong), ? pC1@O2
(weak),
rCꢀ
/ (strong) orbital
1@O2 4—S5
/
4—S5
1@O2
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rCꢀ
LPO8[SO])
,
LPO2[CO]
?
?
rCꢀ
,
pC9@C11[Ph] ?
rCꢀ
4—S5
6—H17½Etꢁ
4—H16
½a-CH2ꢁ
rCꢀ
(medium) and pꢀC
11—H23½o-Phꢁ
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energies of the q-g-syn, g3-syn, g1-anti and q-g2-syn conformers for
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lowed by g1-anti and q-g2-syn conformers, being the q-g-syn con-
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X-ray single crystal analysis, performed for 3 shows that this
compound assumes a geometry reasonably close to the less stable
q-g2-syn conformation in the gas phase for 1, 4 and 6.
In the solid, 3 presents similar S5ꢃ ꢃ ꢃC1, O2ꢃ ꢃ ꢃS5, C1ꢃ ꢃ ꢃO8, C9ꢃ ꢃ ꢃO2
intramolecular short contacts found in the gas phase for 1, 4 and
6. These contacts stabilize the distorted q-g2-syn conformer of 3
through the same orbital and Coulombic interactions which take
place for the q-g2-syn conformer in the gas phase for 1, 4 and 6.
The energy gain for the crystal packing of 3 is obtained through di-
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Acknowledgments
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[24] Occupancies for donor and acceptor orbitals for the q-g-syn, g3-syn, g1-anti and
q-g2-syn conformers of the 2-ethylsulfinyl-(40-substituted)-phenylthioacetates
1, 4 and 6 are presented in Table S1 (Supplementary information).
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The Brazilian authors thank the Fundação de Amparo à Pesqu-
isa do Estado de São Paulo (FAPESP) for financial support of this
research and for a fellowship to A.R., the Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq) for fellowships
to P.R.O., J.Z.-S. and R.R. and for scholarships to M.L.T. Hui and