Spectroscopic and theoretical studies of some N,N-diethyl-2-[(4′- substituted)phenylsulfonyl]acetamides

Article abstract of DOI:10.1016/j.molstruc.2011.06.051

The analysis of the IR carbonyl band of the N,N-diethyl-2-[(4′- substituted)phenylsulfonyl]acetamides Et₂NC(O)CH₂S(O) ₂C₆H₄Y (Y = OMe 1, Me 2, H 3, Cl 4, Br 5, NO₂ 6) supported by B3LYP/6-3

Full text of DOI:10.1016/j.molstruc.2011.06.051

Journal of Molecular Structure 1002 (2011) 97–106
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectroscopic and theoretical studies of some
N,N-diethyl-2-[(40-substituted)phenylsulfonyl]acetamides
b
c
Elisângela Vinhato a, Paulo R. Olivato a, , Alessandro Rodrigues , Julio Zukerman-Schpector ,
⇑
Maurizio Dal Colle d
a Conformational Analysis and Electronic Interactions Laboratory, Instituto de Química, USP, CP 26077, 05513-970 São Paulo, SP, Brazil
b Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, UNIFESP, Diadema, Brazil
c Departamento de Química, Universidade Federal de São Carlos, UFSCAR, 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 carbonyl band of the N,N-diethyl-2-[(40-substituted)phenylsulfonyl]acetamides
Et2NC(O)CH2S(O)2AC6H4AY (Y = OMe 1, Me 2, H 3, Cl 4, Br 5, NO2 6) supported by B3LYP/6-31G(d,p) cal-
culations for 3, indicated the existence of three pairs (anti and syn) of cis (c) and gauche (g1 and g2) con-
formers in the gas phase, being the gauche conformers significantly more stable than the cis ones. The anti
geometry is more stable than the syn one, for each pair of cis and gauche conformers. The summing up of
the orbital (NBO analysis) and electrostatic interactions justifies quite well the populations and the mCO
frequencies of the anti and syn pairs of c, g1 and g2 conformers. The IR higher carbonyl frequency compo-
nent whose population is ca. 10%, in CCl4, may be ascribed to the least stable and most polar cis conformer
pair (in the gas phase) and the lower frequency component whose population is ca. 90%, to the summing
up of the populations of the two most stable and least polar gauche conformer pairs (g1 and g2) (in the gas
phase). The reversal of the cis(c)/gauche (g1 + g2) population ratio observed in chloroform ca. 60% (cis)/40%
(gauche) and the occurrence of the most polar cis(c) conformer only, in acetonitrile, strongly suggests the
coalescence of the two gauche components in a unique carbonyl band in solution. A further support to
this rationalization is given by the single point PCM solvation model performed by HF/6-31G(d,p)
method, which showed a progressive increase of the c/(g1 + g2) ratio going from gas to CCl4, to CHCl3
and to CH3CN. X-ray single crystal analysis of 4 indicates that this compound assumes, in the solid state,
the syn-clinal (gauche) conformation with respect to the [O@CACH2AS] moiety, and the most stable anti
geometry relative to the [C(O)N(CH2CH3)2] fragment. In order to obtain larger energy gain from the crys-
tal packing the molecules of 4 are linked in centrosymmetric dimers through two CAHꢀ ꢀ ꢀO interactions
(CAH[O–Ph]ꢀ ꢀ ꢀO[SO2]) forming a step ladder.
Article history:
Received 18 May 2011
Accepted 24 June 2011
Available online 14 July 2011
Keywords:
Conformational analysis
Infrared spectroscopy
Theoretical calculations
X-ray diffraction analysis
N,N-diethyl-2-[(40-
substituted)phenylsulfonyl]acetamides
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
along with crossed electrostatic and charge transfer interactions
between oppositely charged atoms, i.e. OðSO2Þ ! CðCOÞ and OðCOÞ
ðSO2Þ, the former interaction being the stronger one.
In the MeC(O)X series [8] there is a progressive decrease of the
!
Preceding spectroscopic (IR, 13C NMR, UV and UPS), X-ray dif-
fraction and theoretical studies of b-carbonyl-sulfones XC(O)CH2-
SO2R (X = Me, Ar, NR02, OR0 and SR0; R = Me, Et, Ar) [1–7] indicated
that these compounds, in the gas phase, in solution and in the solid
state prefer the gauche conformation between the C@O and CAS
bonds with respect to the cis conformer, excepting the thioester-
sulfones [6] for which only the gauche conformers are present both
in the gas phase and in solution.
S
experimental carbonyl oxygen lone pair (nO) ionization energy
going from ester (Ei = 10.45 eV) to thioester (Ei = 9.64 eV) to ketone
(Ei = 9.46 eV) to acetophenone (Ei = 9.34 eV) and to amide
(Ei = 9.20 eV) for X = OEt, SEt, Et, Ph, and NEt2, respectively, which
in turn is accompanied by a corresponding increase of the negative
charge on the carbonyl oxygen atom in this direction. Additionally,
there is a progressive decrease of the electron affinity of the
pꢁCO orbital going from thioester (Eae = 0.95 eV) to butanone
(Eae = 1.26 eV) to ester (Eae = 2.09 eV) and to amide (Eae = 2.26 eV).
Therefore, in spite of our previous work [4] which has shown
The stabilization of the gauche rotamers of b-carbonylsulfones
has been ascribed to pꢁCO rCꢁAS orbital interactions,
=rCAS and pCO=
⇑
Corresponding author. Address: Instituto de Química, Universidade de São
Paulo-USP, Av. Prof. Lineu Prestes, 748, Caixa Postal 26077, 05513-970 São Paulo,
SP, Brazil. Tel.: +55 11 3091 2167; fax: +55 11 3815 5579.
that the gauche conformer of the
than the cis one, the above data suggests a larger stabilization of
the cis conformer for the -sulfonyl-amides relative to the same
a-sulfonyl-amides is more stable
a
E-mail address: prolivat@iq.usp.br (P.R. Olivato).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.06.051

98
E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
conformation of the other
a
-sulfonyl derivatives, due to stronger
tracted with CH2Cl2 (3 ꢃ 10 mL). The combined organic layer was
nOðCOÞ
=
rꢁCASðOÞ2 orbital and OdCꢂO=Sdþ Coulombic interactions, which
dried over MgSO4 then the volatiles were removed and a solid
was obtained in 85–92% yield. The crude products were purified
by recrystallization. Suitable crystals for X-ray analysis were ob-
tained by vapour diffusion from chloroform/hexanes at room tem-
perature. The physical, 1H and 13C NMR, and elemental analysis of
compounds 1–6 are presented in Table 1. The starting N,N-diethyl-
2-[(40-substituted)phenylthio]acetamides were prepared as previ-
ously described [12].
ðSO2Þ
should operate in the cis conformation of the
a
-sulfonyl-amides
relative to the other a-sulfonyl derivatives. Moreover, the smaller
electron-affinity of the pꢁCO orbital for the acetamide (reference
compound) [8] suggests a smaller stabilization of the gauche con-
former of the sulfonyl-amides due to the weaker pCꢁO
=rCASO2 inter-
action with respect to the other
a-sulfonyl derivatives.
Aiming to throw more light on the nature of the different elec-
tronic interactions which may stabilize the cis and gauche conform-
ers of the
some
a
-sulfonyl-amides, this paper reports the IR study of
2.2. IR measurements
N,N-diethyl-2-[(40-substituted)phenylsulfonyl]acetamides
Et2NCðOÞCH2SðOÞ2AC6H4AY bearing in 40-position electron-
attracting, hydrogen and electron-donating substituents, i.e.
Y ¼ OMe 1; Me 2; H 3; Cl 4; Br 5; NO2 6 (Scheme 1) along with
density functional theory (DFT), ab initio-HF (for the PCM) and Nat-
ural Bond Orbital (NBO) calculations for 3 and X-ray diffraction
analysis of compound 4. 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 conjugation involving the 40-substituent at the
phenylsulfonyl group, and consequently should influence the
stabilization of the referred conformers.
The IR spectra were recorded with a FT-IR Nicolet Magna 550
spectrometer, with 1.0 cmꢂ1 resolution, at a concentration of
1.0 ꢃ 10ꢂ2 mol mLꢂ1 in carbon tetrachloride, chloroform and ace-
tonitrile solutions, using a 0.519 mm sodium chloride cell, for the
fundamental carbonyl region (1800–1600 cmꢂ1). Thꢂe1spectra for
the carbonyl first overtone region (3600–3100 cm ) were re-
corded in carbon tetrachloride solution (1.0 ꢃ 10ꢂ2 mol mLꢂ1),
using a 1.00 cm quartz cell. The overlapped carbonyl bands (funda-
mental and first overtone) were deconvoluted by means of the
Grams/32 curve fitting program, version 4.04, Level II [13]. The
populations of the cis and gauche conformers were estimated from
the maximum of each component of the resolved carbonyl doublet,
expressed in percentage of absorbance, assuming equal molar
absorptivity coefficients for the referred conformers.
2. Experimental
2.1. Materials
2.3. X-ray measurements
All solvents for IR measurements were spectrograde and were
used without further purification. The N,N-diethyl-2-[(40-substi-
tuted)phenylsulfonyl]acetamides 1 and 4–6 are new compounds
and 1–6 were prepared through the oxidation [9] of the N,N-
Crystal data:
C
12H16ClNO3S; M ¼ 289:78, monoclinic, P21/c,
a = 8.1365(9), b = 19.885(2), c = 9.1290(9) Å, b = 103.621(5)o Å;
V = 1435.5(3) Å3, Z = 4, Dx = 1.341 Mg/m3, k (Mo K
R = 0.0386.
a) = 0.71073,
diethyl-2-[(40-substituted)phenylthio]acetamides. To
a solution
containing the proper amide–sulfide (1 mmol) in CH3OHð3 mLÞ at
0 °C, a solution of hydrogen peroxide (30% w/w in H2O) (5 mmol)
and selenium dioxide (1 mmol) in CH3OHð5 mLÞ was added. After
stirring for 8 h, brine solution was added and the product was ex-
2.3.1. Data collection and processing
X-ray diffraction data were collected on a CAD4 diffractometer
with /2h scan technique, with graphite monochromated Mo K
x
a
radiation, T = 290 K. Full matrix least-squares refinement on F2.
4172 reflections were collected (2hmax = 60.0°). During data collec-
tion, the intensity of three standard reflections was monitored
every 60 min of X-ray exposure time showing no significant decay.
Data were corrected for Lorentz-polarization effects. H-atoms were
located on stereochemical grounds and refined with fixed geome-
try each riding on a carrier atom with an isotropic displacement
parameter amounting to 1.2 (1.5 for methyl H atoms) times the va-
lue of the equivalent isotropic parameter of the atom they are at-
tached. The final R factors were R = 0.0386 for reflections with
I > 2r(I) and R = 0.0842 for all data. Programs used were Sir92
[14], SHELXL-97 [15], WinGx [16], PARST [17], ORTEP3 [18] and
DIAMOND [19].
(29)
H
O(1)
(34)
O
(33)
(13)
O
H
(12)
H
(24)
(2)
(4)
H
S
H
C
(26)
(27)
(7)
N
(9)
C
H
(31)
(21)
C
(3)
(22)
C
(15)
H
(20)
H
H
(5)
(8)
(6)
(28)
C
(23)
(10)
H
H
(19)
Y
(32)
H
(11)
(25)
(14)
C
H
H
(18)
(30)
(1')
H
H
(17)
(16)
2.4. Theoretical calculations
Y = OMe 1, Me 2, H 3, Cl 4, Br 5 and NO2 6
α= O(1)-C(2)-C(3)-S(4)
β = C(2)-C(3)-S(4)-C(22)
γ = C(2)-C(3)-S(4)-O(33)
γ’ = C(2)-C(3)-S(4)-O(34)
δ = C(3)-S(4)-C(22)-C(23)
θ = O(1)-C(2)-N(7)-C(9)
θ' = O(1)-C(2)-N(7)-C(8)
ω = C(2)-N(7)-C(9)-C(15)
ω' = C(2)-N(7)-C(8)-C(14)
φ = C(23)-C(22)-S(4)-O(33)
φ’ = C(23)-C(22)-S(4)-O(34)
All calculations were carried out (at 298 K) using methods and
basis sets implemented in the GAUSSIAN package of programs
(G03.E01) [20]. The hybrid Hartree–Fock density functional
B3LYP and ab initio Hartree–Fock methods [21] with the 6-
31G(d,p) basis set were used [22]. Full geometry optimizations
and analytical vibrational frequency calculations were performed
on all the cis and gauche orientations with respect to the carbonyl
group resultant from a systematic conformational search, allowing
complete relaxation of all internal parameters. Frequency analyses
were carried out to verify the nature of the minimum state of all
the stationary points obtained. To obtain an estimation of the sol-
vation effects on the relative stability of the most relevant minima,
single-point calculations were conducted on the gas phase
Scheme 1. Atoms labelling of N,N-diethyl-2-[(40-substituted)phenylsulfonyl]aceta-
mides and assignment of relevant dihedral angles.

E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
99
Table 1
Physical, 1H NMR, C NMR and elemental analysis data for N,N-diethyl-2-[(40-substituted)phenylsulfonyl]acetamides Et2NC(O)CH2SO2AC6H4AY 1–6.
13
Compd.
Y
Mp (°C)
1H and 13C NMRa
Molecular
formula
Analysis (%)
C
H
N
1
2
OMe 96–97
1H NMR: 7.85–7.82 (m, 2H), 7.03–6.99 (m, 2H), 4.17 (s, 2H), 3.87 (s, 3H), 3.49 (q, 2H,
J = 7.2 Hz), 3.34 (q, 2H, J = 7.2 Hz), 1.21 (t, 3H, J = 7.2 Hz), 1.10 (t, 3H, J = 7.2 Hz)
13C NMR: 164.00, 160.72, 130.81, 130.25, 114.17, 59.97, 55.59, 43.09, 40.75, 14.18, 12.68
C13H19NO4S
Calc.
54.72 6.71 4.91
Found 54.48 6.51 4.73
Calc. 57.97 7.11 5.20
Me
H
78–79
(85–
86)b
1H NMR: 7.81–7.78 (m, 2H), 7.36–7.33 (m, 2H), 4.18 (s, 2H), 3.49 (q, 2H, J = 7.2 Hz), 3.34 C13H19NO3S
(q, 2H, J = 7.2 Hz), 2.44 (s, 3H), 1.21 (t, 3H, J = 7.2 Hz), 1.09 (t, 3H, J = 7.2 Hz)
13C NMR: 160.64, 145.15, 136.01, 129.69, 128.63, 59.93, 43.16, 40.80, 21.70, 14.24, 12.72
1H NMR: 7.94–7.91 (m, 2H), 7.67–7.54 (m, 3H), 4.23 (s, 2H), 3.49 (q, 2H, J = 7.2 Hz), 3.36 C12H17NO3S
(q, 2H, J = 7.2 Hz), 1.22 (t, 3H, J = 7.2 Hz), 1.10 (t, 3H, J = 7.2 Hz)
Found 57.92 7.02 5.08
Calc. 56.45 6.71 5.49
3
81–82
(78–
80)c
13C NMR: 160.64, 138.94, 134.13, 129.06, 128.64, 59.82, 43.23, 40.90, 14.24, 12.70
Found 56.54 6.82 5.46
49.74 5.57 4.83
4
5
6
Cl
83–85
92–93
1H NMR: 7.88–7.83 (m, 2H), 7.55–7.51 (m, 2H), 4.20 (s, 2H), 3.48 (q, 2H, J = 7.2 Hz), 3.35 C12H16ClNO3S Calc.
(q, 2H, J = 7.2 Hz), 1.23 (t, 3H, J = 7.2 Hz), 1.10 (t, 3H, J = 7.2 Hz)
13C NMR: 160.44, 140.89, 137.40, 130.22, 129.44, 59.73, 43.22, 40.90, 14.29, 12.73
Found 49.58 5.73 4.84
43.12 4.83 4.19
Br
1H NMR: 7.79–7.76 (m, 2H), 7.72–7.68 (m, 2H), 4.19 (s, 2H), 3.48 (q, 2H, J = 7.2 Hz), 3.35 C12H16BrNO3S Calc.
(q, 2H, J = 7.2 Hz), 1.23 (t, 3H, J = 7.2 Hz), 1.10 (t, 3H, J = 7.2 Hz)
13C NMR: 160.43, 137.89, 132.35, 130.26, 129.61, 59.72, 43.24, 40.93, 14.30, 12.74
1H NMR: 8.41–8.38 (m, 2H), 8.14–8.11 (m, 2H), 4.27 (s, 2H), 3.49 (q, 2H, J = 7.2 Hz), 3.34 C12H16N2O5S
(q, 2H, J = 7.2 Hz), 1.26 (t, 3H, J = 7.2 Hz), 1.11 (t, 3H, J = 7.2 Hz)
Found 42.85 4.67 4.19
Calc. 47.90 5.37 9.33
NO2
129–
131
13C NMR: 160.18, 150.99, 144.41, 130.32, 124.12, 59.72, 43.24, 40.93, 14.30, 12.74
Found 47.85 5.17 9.23
a
b
c
1H and 13C chemical shifts in ppm relative to TMS and coupling constants in Hz at 300 MHz, in CDCl3.
From Ref. [10].
From Ref. [11].
optimized structures using the PCM model [23] as implemented in
the GAUSSIAN 03. The NBO 3.1 program [24] was used as imple-
mented in the GAUSSIAN 03 package, and the reported NBO delo-
calization energies (E2) are those given by second-order
perturbation theory.
frequency component becomes more intense than the lower fre-
quency one for 1–6. Moreover, in the highest relative permittivity
solvent, acetonitrile (e = 38), the lower frequency carbonyl doublet
component is absent, for the whole series, remaining a singlet
which corresponds to the higher carbonyl frequency component.
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 (Table 2) is not an evidence of the
existence of conformational isomerism, the occurrence of two car-
bonyl bands in the first overtone region for 1–5 and a single band
for 6, in carbon tetrachloride, at frequencies twice those of the
fundamental unless ca. 15 cmꢂ1 (which corresponds two times
the mechanical anharmonicity [26]) and with about the same
intensity ratios strongly indicates the occurrence of two stable
conformers, in carbon tetrachloride, for the series 1–5, and a un-
ique conformer for 6, precluding the existence of any vibrational
effect in the fundamental transition of the mCO stretching mode
[27,28]. The IR data suggests the occurrence of two conformers
in chloroform and one conformer in acetonitrile solutions for
1–5 derivatives.
3. Results and discussion
Table 2 collects the stretching frequencies and the absorbance
percentage of the carbonyl band components for compounds 1–6,
in solvents of increasing polarity. A doublet is shown in solvent of
low relative permittivity carbon tetrachloride (e = 2.2) [25] (fun-
damental and first overtone) for derivatives 1–5, being the lower
frequency carbonyl band component significantly more intense
(ca. 90%) than the higher frequency one, while only a singlet is ob-
served for derivative 6, in both regions. However, in a solvent of
higher relative permittivity, chloroform (e = 4.8), a carbonyl dou-
blet is present for the whole series (1–6), but a reversal carbonyl
doublet relative intensity is observed, i.e. the higher carbonyl
Aiming to estimate the geometries of the minimum energy con-
formations in the gas phase, B3LYP/6-31G(d,p) calculations for
compound 3, taken as the representative compound for the whole
series 1–6, were performed. Table 3 presents the relevant data for
compound 3 along with the X-ray dihedral angles for 4.
Table 2
Frequencies (m
, cmꢂ1) and intensities of the carbonyl stretching bands in the IR
spectra of N,N-diethyl-2-[(40-substituted)phenylsulfonyl]acetamides, Et2NC(O)CH2-
SO2AC6H4AY 1–6.
Compd.
Y
CCl4
CHCl3
CH3CN
The calculations for 3 show the existence of one pair of syn-peri-
planar (cis) and two pairs of syn-clinal (gauche) conformations: c, g1
and g2, respectively. The calculations for 3 show that each one of
the c, g1 and g2 conformers exists in a syn-anti equilibrium, being
the [AC(O)ANR2] group almost planar without any degree of pyra-
midalization. In fact, the h and h0 dihedral angles are close to 1° and
177°, due to the significant contribution of the ½ꢂOAC@Nþꢄ reso-
m
Pa
mb
P
m
P
m
P
1
2
3
4
5
6
OMe 1660
1651
8.6 3306
7.4 1648 62.3 1649 100
92.6 1638 37.7
7.4 1649 58.1 1649 100
92.6 1640 41.9
2.9 1648 66.4 1650 100
97.1 1639 33.6
6.6 1648 77.9 1649 100
93.4 1638 22.1
2.9 1648 73.7 1649 100
97.1 1639 26.3
1648 80.2 1649 100
1640 19.8
91.4 3287
8.9 3307
91.1 3289
10.7 3310
89.3 3291
6.8 3302
93.2 3290
6.1 3305
93.9 3290
–
Me
1660
1652
1662
1652
1662
1652
1660
1652
–
–
H
–
nance structure for the hybrid [8,29]. Moreover, the
x
and x0 dihe-
Cl
–
dral angles define the syn and anti conformations, that is, with both
methyl of the N,N-diethylcarboxamide group at the same half-
space defined by [AC(O)N] plane (for the syn conformer) or one
methyl in each half-space in relation to the referred plane (for
the anti conformer). The population ratio for each pair of conform-
Br
–
NO2
–
–
–
1652 100
3290 100
–
a
Relative intensity of each component of the carbonyl doublet, expressed in
percentage of absorbance.
ers of
a-sulfonyl-amide 3, c(anti)/c(syn), g1(anti)/g1(syn) and
b
g2(anti)/g2(syn) is ca. 3.7 which is very close to the previously,
First overtone.

100
E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
1
(a)
(c)
.8
.8
.6
.4
.2
0
.6
.4
.2
0
1700
1680 1660
1640 1620
1600 1580
1560
1700 1690 1680 1670 1660 1650 1640 1630 1620 1610
Wavenumber (cm-1)
Wavenumber (cm-1)
.05
.04
.03
.02
.01
0
(b)
(d)
1
.8
.6
.4
.2
0
-.01
-.02
3340
3320
3300
3280
3260
3240
1700 1690 1680 1670 1660 1650 1640 1630 1620 1610 1600
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 1. IR spectra of N,N-diethyl-2-phenylsulfonylacetamide (3) showing the carbonyl stretching band, in carbon tetrachloride [fundamental (a) and first overtone (b)],
chloroform (c) and acetonitrile (d).
Table 3
Relative energies (E, kJ molꢂ1), dipole moments ( , cmꢂ1), and selected dihedral angles (°) calculated for different cis(c) and gauche(g)
l, D), carbonyl harmonic frequencies (m
conformers of 3 at the B3LYP/6-31G(d,p) level and the X-ray geometrical data for 4-ClAC6H4ASO2CH2C(O)NEt2 4.
Compd. Conf.a Eb
Pc
l
mCO
Dihedral angles (°)e
d
0
/
a
b
c
c0
d
h
h0
x
x0
/
3
g1(anti)
g1(syn)
0
56.0 2.64 1657.3
86.2
86.6
ꢂ72.7
ꢂ77.4
3.9
ꢂ65.7
ꢂ66.3
75.5
49.6
49.1
ꢂ40.6
ꢂ39.5
55.3
179.9
179.4
90.4
87.9
ꢂ83.4
ꢂ85.0
91.9
1.9
2.2
1.3
ꢂ0.1
ꢂ0.5
ꢂ0.9
ꢂ173.5
ꢂ175.1
178.7
177.5
179.0
ꢂ86.1
77.3
ꢂ96.6
ꢂ97.1
ꢂ93.1
ꢂ99.8
ꢂ95.5
102.9
ꢂ24.3
ꢂ156.1
ꢂ159.8
164.4
3.59 13.1 2.68 1653.9
ꢂ26.8
g2(anti) 2.22 22.8 3.05 1647.2
g2(syn) 4.93 7.6 2.66 1644.6
c(anti) 12.11 0.4 6.50 1662.4
ꢂ170.5
ꢂ169.7
ꢂ175.4
ꢂ175.6
ꢂ86.9
32.0
30.2
76.2
76.3
162.6
ꢂ62.6
ꢂ86.0
77.3
ꢂ25.8
ꢂ158.2
c(syn)
14.82 0.1 6.48 1660.2
ꢂ86.5(2)
5.5
ꢂ62.8
55.1
91.6
179.2
92.2(3)
ꢂ26.1
ꢂ158.4
4
X-rayf
–
–
–
47.1(2) ꢂ69.0(1) 162.4(1)
72.5(2)
1.2(3) ꢂ175.4(2)
91.4(3) ꢂ40.7(2) ꢂ171.5(1)
a
Conformer designation; (g) and (c) refers to the gauche and cis conformers, respectively; syn refers to both N,N-diethyl methyl groups in the same half-space defined by
the [AC(O)N] plane and anti refers to the methyl groups above and the other bellow the referred plane.
b
Relative energy.
Molar fraction in percentage.
Scaling factor of 0.951.
See Scheme 1.
c
d
e
f
The other conformer found in the centrosymmetric dimmer of 4 presents the same dihedral angles but with opposite signals.
(HF) [30] and presently (B3LYP) [31], computed anti/syn ratio of ca.
4 for the N,N-diethylacetamide. In addition, each syn-anti pair for
the c, g1 and g2 conformers of 3 present almost equal calculated di-
pole moments whose mean values are: 6.5 D, 2.7 D and 2.9 D,
respectively (Table 3). The calculated carbonyl stretching frequen-
cies for the syn (c, g1 and g2) conformers are ca. 3 cmꢂ1 lower than
those of the anti (c, g1 and g2) conformers. Moreover the larger sta-
bility of the anti (c, g1 and g2) conformers of 3 relative to the syn
ones may be explained by the same factors which stabilize the anti
conformer into a large extent relative to the syn one for the parent
N,N-diethylacetamide [30].
Table 4 shows the Mülliken atomic charges [32] at selected
atoms at the B3LYP/6-31G(d,p) level for compound 3. Table 5 dis-
plays the interatomic distances between some selected atoms and
the difference between these contacts and the sum of the van der
Waals radii (Dl) for the same compound.

E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
101
Table 4
Mülliken charge (e) at selected atoms obtained at the B3LYP/6-31G(d,p) level for the N,N-diethyl-2-phenylsulfonyl-acetamide 3.
Conf.
O(1)[CO]
C(2)[CO]
S(4)
N(7)
H(29)[O–Ph]
H(12)[CH2]
H(20)[CH3]
H(11)[CH2]
H(16)[CH3]
O(33)[SO2]
O(34)[SO2]
g1(anti)
g1(syn)
g2(anti)
g2(syn)
c(anti)
c(syn)
ꢂ0.622
ꢂ0.622
ꢂ0.629
ꢂ0.629
ꢂ0.608
ꢂ0.608
0.786
ꢂ0.783
0.802
0.803
0.805
1.534
1.534
1.536
1.536
1.570
1.570
ꢂ0.684
ꢂ0.690
ꢂ0.692
ꢂ0.700
ꢂ0.702
ꢂ0.707
0.203
0.203
0.207
0.207
0.222
0.222
0.161
0.155
0.166
0.159
0.164
0.161
0.143
0.151
0.158
0.158
0.151
0.154
0.147
0.144
0.111
0.109
0.116
0.115
0.111
0.110
0.159
0.161
0.115
0.115
ꢂ0.704
ꢂ0.703
ꢂ0.698
ꢂ0.698
ꢂ0.707
ꢂ0.707
ꢂ0.690
ꢂ0.689
ꢂ0.695
ꢂ0.695
ꢂ0.678
ꢂ0.678
0.805
Table 5
Selected interatomic distances (Å) for the conformations for 3 at the B3LYP/6-31G(d,p) level, and the corresponding X-ray distances for 4.
Compd. Confa.
O(1)/
S(4)b
D
lc
O[SO2]
/
D
l
O(1)/
D
l
O(1)/
D
l
O(1)/
D
l
O(33)/
H(11)
D
l
O(34)/
H(16)
Dl
f
f
C(2)d,e
H(28)f
H(12)f
H(20)f
3
g1(anti) 3.461
g1(syn) 3.464
g2(anti) 3.307
0.14 3.130
0.14 3.126
ꢂ0.09
ꢂ0.09
ꢂ0.18
ꢂ0.19
0.02
0.02
ꢂ0.07
3.284
3.202
2.725
2.849
2.540
2.531
–
–
0
2.389
2.439
2.360
ꢂ0.33
ꢂ0.28
ꢂ0.36
ꢂ0.27
ꢂ0.35
ꢂ0.27
ꢂ0.32
2.841
2.657
2.849
2.604
2.858
2.624
0.12 2.465
ꢂ0.25
–
–
–
–
ꢂ0.06 2.490
ꢂ023
ꢂ0.01 3.034
0.13
ꢂ0.12
0.14
ꢂ0.10
–
–
–
–
–
–
–
–
–
2.520
2.494
–
ꢂ0.20
g2(syn)
c(anti)
c(syn)
X-ray
3.346
3.047
3.043
3.382(2)
0.02 3.029
0.13 2.445
ꢂ0.18 2.373
ꢂ0.19 2.448
ꢂ0.23
ꢂ0.27 3.247
ꢂ0.27 3.245
0.06 3.246(2)
–
–
–
–
g
g
g
4
–
–
2.40
–
2.64
ꢂ0.08
–
a
b
c
d
e
f
Conformer designation.
Sum of the van der Waals radii = 3.32 Å.
Difference between nonbonded atoms distance and the sum of their van der Waals radii.
Sum of the van der Waals radii = 3.22 Å.
Refers to the contact between the nearest sulfonyl oxygen atom [O(33) or O(34)] and carbonyl carbon atom.
Sum of the van der Waals radii = 2.72 Å.
Contact larger than the sum of the van der Waals radii.
g
The slightly smaller computed mean carbonyl stretching fre-
quency value of the syn (c, g1 and g2) conformers with respect to
those of the anti ones may be explained by the fact that both the
the c(anti, syn) conformations (ca. 6.5 D), whose populations are al-
most negligible in the gas phase, i.e. ca. 0.4% and 0.1%, respectively.
As expected the relevant a, b, c
, d, / and /0 dihedral angles of the
Oð1Þ ðꢅ ꢂ0:62eÞ ꢀ ꢀ ꢀ H½CH2ꢄðꢅ 0:16eÞ and Oð1Þ½COꢄðꢅ ꢂ0:62eÞ ꢀ ꢀ ꢀ
½ACðOÞCH2SðOÞ2APh] moiety are almost identical for each anti,
½COꢄ
H
½CH3ꢄðꢅ 0:15eÞ intramolecular contacts for the syn conformers are
syn pair for the (c, g1 and g2) conformers.
shorter than the
respectively, while the same contacts for the anti conformers are
shorter than the vdW radii by ( l ffi 0.12 Å),
l ffi ꢂ0.34 Å) and (
R
vdW radii by (
D
l ffi ꢂ0.28 Å) and (
D
l ffi ꢂ0.06 Å),
However, the SO2AC6H4AY fragment displays opposite dihedral
angles (a–d) between the g1 and g2 conformations (structures III
and IV, Scheme 3). In fact the SO2AC6H4AY moiety lies in the oppo-
site half-space of the [AC(O)N] plane for each (anti, syn) pair of g1
R
D
D
respectively (see structures I and II, Scheme 2). Therefore the
slightly larger summing up of the Od½CꢂOꢄ ꢀ ꢀ ꢀ Hdþ
attractive elec-
and g2 conformers which in turn makes their
gles of opposite signals, respectively, Fig. 2(a and b). Moreover, the
(anti, syn) pair of the g2 conformers present the angle which is ca.
a, b, c, d dihedral an-
½CH2;CH3ꢄ
trostatic interactions, which operate for syn conformers relative
to the anti ones, seems to be responsible for the discrete decrease
of the carbonyl bond order and consequently to the smaller car-
bonyl frequency for the syn conformers in comparison with the anti
a
12° smaller than that for (anti, syn) pair of the g1 conformers.
As for the (anti; syn) pair of the cis (c) conformers while one of
the sulfonyl oxygen atoms O[SO2] displays an anti-periplanar geom-
etry with respect to the carbonyl oxygen atom (c0 dihedral angle of
ca. 175°), similar to the previously studied sulfinyl-amides [28], the
other sulfonyl oxygen atom O[SO2] lies in a syn-clinal geometry rel-
ones by ca. 3 cmꢂ1
.
The larger stabilization of the anti (c, g1 and g2) conformers for
the -sulfonyl-amide 3 and of the anti conformer for the unsubsti-
a
tuted N,N-diethyl acetamide [30,31] with respect to the syn ones
along with the slightly smaller carbonyl frequency of the syn (c,
g1 and g2) conformers relative to the anti ones depends only on
ative to carbonyl carbon atom (c dihedral angle of ca. 55°). This
geometry gets closer the sulfonyl oxygen atom to both the car-
the N,N-diethylamide moiety irrespective of the nature of the
a-
bonyl carbon and the carbonyl oxygen atom (Fig. 2c).
carbonyl substituent.
The g1(anti, syn) and g2(anti, syn) conformations for 3 are the
more stable (55.8%; 13.1% and 22.9%; 7.63%, respectively) and the
less polar ones (ca. 2.7 D and ca. 2.9 D, respectively) relative to
3
2
2
3
3
syn
(I)
anti
(II)
(III)
(IV)
Scheme 3. The opposite dihedral angles between the SO2AC6H4AY fragment of the
anti, syn (g1 and g2) conformers of 3.
Scheme 2. Syn and anti geometries for the (c, g1 and g2) conformers of 3.

102
E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
(a)
(b)
g1 (anti)
g1 (syn)
g2 (anti)
g2 (syn)
(c)
c (anti)
c (syn)
Fig. 2. gauche [g1(anti) and g1(syn)] conformers (a), gauche [g2(anti) and g2(syn)] conformers (b) and cis [c(anti) and c(syn)] conformers (c) obtained at B3LYP/6-31G(d,p) level
for 3.
other for all the (anti, syn) pairs of the g1, g2 and c conformers,
excepting the
p( r( =
pꢁ)/ rꢁ) and OðSO2Þ rCꢁAH orbital interactions
Table 6
Comparison of significant NBO energies (kcal molꢂ1) of the corresponding interacting
orbitals for the anti and syn gauche (g1, g2) and cis (c) conformers of 3 at the B3LYP/6-
31G(d,p) level.
which are present for the gauche conformers only.
The most important orbital interaction is the LPN7
!
pꢁC2@O1
,
which corresponds to the [O@CAN $ ꢂOAC@Nþ] conjugation, pre-
sents mean energy value of ca. 70 kcal molꢂ1 for all the conformers.
In the carboxamide group there are also two other interactions
Orbitals
g1(anti) g1(syn) g2(anti) g2(syn) c(anti) c(syn)
LPN7
LPO1
LPO1
LPO33
LPO33
LPO34
LPO34
LPO33
LPO34
!
!
!
pꢁC2@O1
rꢁC2AN7
rꢁC2AC3
68.8
24.4
21.2
15.9
12.9
13.7
14.9
1.4
69.8
24.3
21.1
16.1
12.9
13.6
15.0
1.2
–
2.5
3.2
11.4
71.0
24.1
20.6
13.5
14.8
16.0
13.4
–
1.3
2.0
3.0
10.5
71.3
24.1
20.5
13.7
14.7
15.9
13.4
–
1.2
2.2
3.3
11.1
70.9
24.6
21.8
14.1
13.6
15.0
16.2
–
–
–
–
–
70.9
24.5
21.7
14.1
13.6
14.9
16.2
–
–
–
–
–
(through bond coupling) with high energies, i.e. LPO1
!
rꢁC2AN7 and
LPO1
!
rꢁC2AC3 whose mean energy values are of ca. 24 kcal molꢂ1
!
rꢁC3AS4
and 21 kcal molꢂ1, respectively, for g1, g2 and c conformers. The
!
!
!
!
!
rꢁS4AC22
rꢁC3AS4
rꢁS4AC22
rꢁC8AH11
rꢁC14AH16
sulfonyl oxygen lone pairs (LPO33 and LPO34) present also four
through bond coupling interactions: LPO33
!
rꢁC3AS4
,
LPO33
!
rꢁS4AC22, LPO34
!
rꢁC3AS4, LPO34
!
rꢁS4AC22, whose mean energy value
a
–
2.5
3.2
is ca. 15 kcal molꢂ1, for the referred conformers. Additionally, both
(anti, syn) pair of the g1 and g2 conformers present two short intra-
pC2@O1
rC3AS4
pꢁC2@O1
!
rꢁC3AS4
pꢁC2@O1
rꢁC3AS4
!
!
molecular contacts between the oppositely charged Oð33Þ
11.6
½SO2ꢄ
ðꢂ0:70eÞ ꢀ ꢀ ꢀ Hð11Þ½NCH2ꢄð0:15eÞ and Oð34Þ½SO2ꢄðꢂ0:69eÞ ꢀ ꢀ ꢀ Hð16Þ
½CH3ꢄ
a
Interaction energy smaller than 0.5 kcal molꢂ1
.
ð0:16eÞ atoms whose distances are shorter than the
RvdW radii
by
D
l ffi ꢂ0.23 Å (Tables 4 and 5). These electrostatic attractive
rꢁC8AH11 and
To rationalise the nature of the orbital interactions which stabi-
interactions are accompanied by the LPO33
!
rꢁC14AH16 orbital interactions (hydrogen bond) whose en-
lize the (anti, syn) pairs of the g1, g2 and c conformers for the title
compounds, the NBO analysis [24] was performed. Table 6 presents
selected NBO energy interactions between donor and acceptor
orbitals for the referred conformers of compound 3 taken as repre-
sentative for the whole series [33].
LPO34
!
ergy value is ca. 1.3 kcal molꢂ1 (Table 6). Therefore these weak
interactions contribute to the same extent for the stabilization of
both (anti, syn) pair of the g1 and g2 conformers.
Moreover both (anti, syn) pairs of gauche conformers display
short contacts between the oppositely charged O½SO2ꢄðꢂ0:70eÞ ꢀ ꢀ ꢀ
The data from Table 6 show that the majority of the orbital
interactions present energy values which are very close to each
Cð2Þ½COꢄð0:80eÞ whose mean distances are shorter than the
RvdW

E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
103
radii by
conformers, respectively. However, the oppositely charged
Oð1Þ½COꢄðꢂ0:62eÞ ꢀ ꢀ ꢀ Sð4Þ½SO2ꢄð1:55eÞ distance is similar to the vdW
radii for the g2 pair of conformers while the same contact is slightly
larger than the vdW radii (
D
l ffi ꢂ0.19 Å and
D
l ffi ꢂ0.09 Å for the g2 and g1 pairs of
former (1747 cmꢂ1) is higher than the mean computed frequencies
of the (anti, syn) pairs of the g1 (1740 cmꢂ1) and g2 (1730 cmꢂ1
)
R
conformers.
The summing up of the orbital and electrostatic interactions
justifies quite well the populations and the frequencies of the syn
and anti (c, g1 and g2) conformers found in the gas phase for 3 (Ta-
ble 2). Considering that the syn and anti pair of each conformer pre-
sents the carbonyl frequency difference of only ca. 3 cmꢂ1, it seems
reasonable to expect in solution that these carbonyl frequencies
coalesce into a single band. Therefore in the non polar carbon tet-
rachloride solvent, it should be expected three carbonyl band com-
ponents which correspond to the highest frequency, most polar
and least stable cis conformer pair (1747 cmꢂ1; 6.5 D; 0.54%) fol-
lowed by two lower carbonyl components, which correspond to
the two most stables and significantly least polar gauche conformer
pairs (1740 cmꢂ1; 2.6 D; 68.9% for g1) and (1730 cmꢂ1; 2.9 D; 30.5%
for g2). However the IR data, in carbon tetrachloride (Table 1),
shows the existence of two conformers whose population ratio is
of ca. 10% for the higher frequency component and 90% for the low-
er one. The higher carbonyl frequency component, in CCl4 solution,
may be ascribed to the least stable most polar cis conformers (in
the gas) and the lower frequency component, in CCl4 solution, to
the summing up of the populations of the two most stable and
least polar gauche (g1 + g2) conformers in spite of the difference
of ca. 10 cmꢂ1 between them, in the gas phase. Moreover the rever-
sal of the cis(c)/gauche(g1 + g2) population ratio observed in chloro-
form of ca. 60% (cis)/40% (gauche) and the occurrence of only the
more polar cis(c) conformer in acetonitrile (100%) seems to give
support to the coalescence of the two gauche conformers in a un-
ique carbonyl band in solution. In fact a close look at the geome-
tries of g1 and g2 conformers [(structures III and IV, Scheme 3)
and Table 3], shows that they present almost opposite dihedral an-
R
D
l ffi 0.14 Å) for the g1 pair of conform-
ers. These short contacts are responsible for the stabilization of
both pair of gauche conformations (being stronger for the g2 rela-
tive to the g1 one) by the simultaneous occurrence of the
Od½SꢂO2ꢄ ꢀ ꢀ ꢀ Cdþ (strong) and O½dCꢂOꢄ ꢀ ꢀ ꢀ Sdþ (weak) Coulombic interac-
½COꢄ
½SO2ꢄ
tions. In spite of the suitable geometry of the O@CACAS@O frag-
ment for the g2 and g1 conformers for 3 the Od½SꢂO2ꢄ ꢀ ꢀ ꢀ Cdþ short
½COꢄ
contact do not display any detectable LPO½SO2ꢄ
!
pꢁC2@O1 orbital
interaction (0.5 kcal molꢂ1 or higher) as previously found for the
gauche conformers of the N-methoxy-N-methyl-2-phenylsulfonyl-
propanamides ðLP
!
pꢁC@O ¼ 0:70 kcal molꢂ1) [34], due to the
½SO2ꢄ
lower electron-affinity of the pꢁCðOÞNEt2 orbital of the amides with re-
spect to that of the pꢁCðOÞN½OMeꢄ½Meꢄ orbital of the N-methoxy-N-
methyl-amides.
The more pronounced Od½SꢂO2ꢄ ꢀ ꢀ ꢀ Cdþ (strong) and Od½CꢂOꢄ ꢀ ꢀ ꢀ Sdþ
½COꢄ
½SO2ꢄ
(weak) Coulombic interactions for the g2 pair of conformers with
respect to the g1 ones, are responsible for the decreasing of the car-
bonyl bond order, and thus, for the lower computed carbonyl
stretching frequency (1730 cmꢂ1) of the g2 conformers in compar-
ison with the computed carbonyl stretching frequency
(1740 cmꢂ1) for g1 ones.
Additionally, in the O@CACAS@O fragment there are also three
p( r(
pꢁ)/ rꢁ) interactions which has been ascribed for the gauche
conformer preference [35]. As pointed out above, the larger
a angle
for (anti, syn) pair of the g1 conformers (ꢅ86°) with respect to the
(anti, syn) pair of the g2 conformers (ꢂ75°) (Table 3) is responsible
for a little better overlap between
p( r(
pꢁ)/ rꢁ) orbitals, which in
turn originates slightly stronger pC2@O1
!
rꢁC3AS4
,
rC3AS4
!
pꢁC2@O1
,
pꢁC2@O1
!
rꢁC3AS4 interactions for the (anti, syn) pair of the g1 con-
gles (a–d) between them, therefore they display very close dipole
formers with respect to the g2 ones. The summing up of these
interactions for the g1 conformers is only ca. 1 kcal molꢂ1 larger
than that for the g2 conformers. On the other hand, the mean
values of the summing up of the energies of the selected orbital
interactions for both pairs of the g1 and g2 conformers are of ca.
191 kcal molꢂ1 (Table 6). Therefore, it seems reasonable to ascribe
the computed larger stabilization of the (anti, syn) pair of the g1
moments (ca. 2.6 D and 2.9 D) whose mean value 2.8 D is of ca.
3.7 D lower than that for the cis(c) conformer. Therefore the ob-
served solvent effect in solution strongly agrees with the larger sol-
vation of the most polar cis(c) conformer relative to the least polar
gauche (g1 and g2) conformers as the solvent relative permittivity
increases.
To give a further support to the observed strong solvent effect in
solution, a single point Polarisable Continuum Model (PCM) calcu-
lation was performed using the HF method [37] to estimate the
solvation effect (CCl4, CHCl3 and CH3CN) on the relative stability
of the obtained (anti, syn) (c, g1 and g2) minimum energy conforma-
tions in the gas phase for 3 (Table 7).
It should be pointed out that a close match was not found be-
tween the computed population ratio of the (c) (anti + syn)/
[g1(anti + syn) + g2(anti + syn)] and the experimental (IR) popula-
tion ratios. Nevertheless, a progressive increase of the referred
population ratio going from gas phase (1.8%)/(98.2%), to carbon tet-
rachloride (9.0%)/(91%), to chloroform (20.5%)/(79.5%) and to ace-
tonitrile (41.9%)/(58.1%) has been observed. Therefore, this trend
gives support to our rationalization which indicates that in the IR
spectra in solution ðCCl4; CHCl3Þ the pair of the most polar (anti,
syn) cis conformers correspond to the carbonyl high frequency
component and the least polar (anti, syn) pairs of the gauche (g1
and g2) conformers correspond to the carbonyl lower frequency
component. However, in acetonitrile only the pair of the most po-
lar (anti, syn) cis conformer is present.
conformers relative to the g2 ones to the p( r(
pꢁ)/ rꢁ) hyperconju-
gative interactions (
D
E ffi 1 kcal molꢂ1).
As expected for the geometry of the O@CACAS@O fragment, the
summing up of the orbital interaction energies (ca. 176 kcal molꢂ1
)
for the (anti, syn) pair of the cis (c) conformers is significantly lower
than that found for the (anti, syn) pair of the gauche conformers by
ca. 15 kcal molꢂ1. Moreover the c(anti, syn) geometries, whose c0
dihedral angle are ca. ꢂ175° (Table 3), allows a short Oð1Þ
½COꢄ
ðꢂ0:61eÞ ꢀ ꢀ ꢀ Sð4Þ½SO2ꢄð1:57eÞ contact whose distance is shorter than
the
R
vdW radii by (
D
l ffi ꢂ0.27 Å). Similarly to the N,N-diethyl-2-
[(40-substituted)phenylsulfinyl]acetamides [30], this short-range
contact should stabilize the cis conformation through the
Od½CꢂOꢄ . . . Sdþ electrostatic and charge transfer interactions. Never-
½SO2ꢄ
theless, the contact between one of the negatively charged sulfonyl
oxygen atom, whose dihedral angle
negatively charged carbonyl oxygen atom i.e.
ꢀ ꢀ ꢀ Oð1Þ½COꢄðꢂ0:61eÞ, presents an intramolecular distance of 3.09 Å
which is close to the vdW radii (3.04 Å). This short contact orig-
c
is ca. 55° (Table 3), and the
O½SO2ꢄðꢂ0:71eÞ
R
inates
C
a strong Repulsive Field Effect [36] between the
dþ@OdꢂandðOÞSdþ@Odꢂ dipoles which should overcome the
Table 8 presents the frequency shifts for the higher (
Dmc) and
Od½CꢂOꢄ . . . Sdþ attractive interaction. Therefore the balance of these
lower ( g) carbonyl doublet components of compounds 1–6, in
Dm
½SO2ꢄ
interactions should act not only destabilizing the anti and syn pair
of the cis conformers, but also increasing the carbonyl bond order
and thus its frequency in comparison to that of the (anti, syn) pair
of the gauche (g1 and g2) conformers. In fact the mean computed
carbonyl frequency value for the (anti, syn) pair of the cis con-
carbon tetrachloride, relative to the mCO frequency of the parent
N,N-diethylacetamide [30].
The significantly positive (ca. +10 cmꢂ1) (
D
m
c) frequency shifts
are in a good agreement with the strong inductive effect (ꢂI ) of
r
the a-phenylsulfonyl substituent, whose rI value is 0.57 [38], along

104
E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
Table 7
Single point PCM solvent effect on the minimum energy gas phase for the gauche and cis conformations of 3 at the HF/6-31G(d,p) level; relative energies (E, kJ molꢂ1), dipole
moments (
l, D) and frequencies (
m
, cmꢂ1).
Conf.a
Gas phase
CCl4
CHCl3
CH3CN
d
Eb
Pc
l
mCO
E
P
l
E
P
l
E
P
l
g1(anti)
g1(syn)
g2(anti)
g2(syn)
c(anti)
c(syn)
0
4.35
3.60
7.70
9.41
67.7
11.5
16.0
3.0
1.5
0.3
2.77
2.77
3.69
3.69
6.88
6.89
1663.8
1662.6
1657.1
1657.1
1673.1
1672.2
0
59.2
12.0
17.0
2.7
7.0
2.1
3.03
3.02
4.05
4.11
7.55
7.56
0
49.6
9.6
17.5
2.7
15.6
5.0
3.20
3.18
4.32
4.41
8.02
8.02
0.04
1.89
4.23
6.98
0
33.8
6.2
16
2.1
34.4
7.5
3.35
3.31
4.5
4.71
8.52
8.51
3.93
3.05
7.69
5.31
8.20
4.07
2.57
7.21
2.86
5.74
13.01
3.76
a
Conformer attribution.
Relative energy.
Molar fraction in percentage.
Scaling factor of 0.87.
b
c
d
Table 8
Carbonyl frequency shifts (Dm
, cmꢂ1) for the cis and gauche rotamers of the N,N-
diethyl-2-[(4-substituted)phenylsulfonyl]acetamides 1–6, in carbon tetrachloride.
a,b
Compd.
Y
D
mca,b
Dmg
1
2
3
4
5
6
OMe
Me
H
Cl
Br
+9.4
+9.3
+11.2
+11.2
+9.8
–
+0.4
+1.3
+1.6
+1.7
+1.6
+1.7
NO2
a
D
mc and
D
mg refers to the difference: m[Et2NC(O)CH2SO2–C6H4–Y]–[Et2NC(O)CH3], for the
cis and gauche rotamers, respectively.
b
Parent compound (m
CO = 1650.9 cmꢂ1, CCl4) [30].
with the Od½CꢂOꢄ . . . Odꢂ short contact which is responsible for a
½SO2ꢄ
strong Repulsive Field Effect between the
C
dþ@Odꢂ and
ðOÞSdþ@Odꢂ dipoles in the (anti, syn) pair of the cis conformers.
These effects operate increasing the carbonyl bond order and thus
the carbonyl frequency for the higher doublet frequency compo-
nent which corresponds to the cis conformers. On the other hand,
the slight positive (ca. +1.4 cmꢂ1) (
rates the existence of the rC3AS4
tal) and OdðSꢂO2Þ . . . CðdCþOÞ; OðdCꢂOÞ . . . Sdþ
D
m
g) frequency shifts corrobo-
rꢁC3AS4 (orbi-
(Coulombic) interactions
!
pꢁC2@O1
;
pC2@O1
!
Fig. 3. The molecular structure of compound 4 showing atom labelling scheme and
displacement ellipsoids at the 50% probability level (arbitrary spheres for the H-
atoms).
ðSO2Þ
which act in the (g1 and g2) gauche conformers decreasing the car-
bonyl bond order and thus its frequency. However the balance of
the inductive (ꢂI ) effect, which act in opposition to the orbital
r
intramolecular short contacts between the oppositely charged
and electrostatic effects, leads to a slight increase of the carbonyl
frequency of the gauche conformers (lower carbonyl frequency
component) relative to the carbonyl frequency of the parent
compound.
atoms: O½dSꢂO2ꢄ ꢀ ꢀ ꢀ Cd½CþOꢄ; O½dCꢂOꢄ ꢀ ꢀ ꢀ S½dSþO2ꢄ; O½dCꢂOꢄ ꢀ ꢀ ꢀ Hdþ
and Od½SꢂO2ꢄ ꢀ ꢀ ꢀ
½NCH2ꢄ
Hd½NþCH2ꢄ, whose interatomic distances are close or shorter than the
R
0.06 Å,
vdW radii by
D
l [O(33)ꢀ ꢀ ꢀC(1)] = ꢂ0.07 Å,
D
l = [O(1)ꢀ ꢀ ꢀS(4)] =
D
l
[O(1)ꢀ ꢀ ꢀH(12)] = ꢂ0.32 Å and
Dl
[O(33)ꢀ ꢀ ꢀH(11)] =
Moreover, Table 2 shows that there is a progressive increase of
the population of the lower carbonyl frequency doublet compo-
nent, which has been ascribed to the summing up of the g1 and
g2 conformers, with respect to the population of the higher fre-
quency component (c) conformer, in chloroform, going from the
electron-attracting 40-nitro-(6) (20%) to the electron-donating 40-
methoxy-(1) (40%) substituents. This trend is in line with the
ꢂ0.08 Å, respectively (Table 5). Therefore, these short contacts
originate attractive electrostatic interactions which contribute to
the stabilization of the syn-clinal (gauche) conformation for 4 in
the solid. Furthermore in order to obtain larger energy gain from
the crystal packing, as shown in Fig. 4, the molecules of 4 are linked
in centrosymmetric dimers through two CAH ꢀ ꢀ ꢀ O interactions
ðCAH½OAPhꢄ ꢀ ꢀ ꢀ O½SO2ꢄÞshown in dotted black lines, forming a step lad-
der parallel to the a direction, in turn these chains are held to-
increasingdþ contribution of the rC3AS4
!
pꢁC2@O1 (orbital) and
ꢀ ꢀ ꢀ CðCOÞ (Coulombic) interactions in this direction, which in
dꢂ
O
ðSO2Þ
gether by the C23AH28ꢀ ꢀ ꢀO1 interaction (CAH½OAPhꢄ ꢀ ꢀ ꢀ O
)
turn contributes for the progressive stabilization of both g1 and
g2 conformers (see Table 6).
½COꢄ
shown in orange.1 Details of these (CAH ꢀ ꢀ ꢀ O interactions are given
in Table 9. It is worth noting that in the very close structure, namely
X-ray single crystal analysis of 4 indicates that this compound
assumes, in the solid state, the syn-clinal (gauche) conformation
with respect to the [CðOÞCH2SO2AC6H4ACl] moiety, and the most
stable anti geometry relative to the [C(O)N(CH2CH3)2] fragment
N,N-diethyl-phenylsulfonylacetamide (CSD code SAVJOO [39]), the
a
angle is of 89.6° but the rest of the molecule is in another conforma-
tion, as can be seen in Fig. S1. On the other hand, the packing of both
(see Table 3 and Fig. 3). In fact, all the dihedral angles (a
–/0) of
the X-ray single molecule structure are close in absolute values
to those found for the (g1 and g2) gauche conformers for 3, in the
gas phase. Moreover, this geometry in the solid leads to some
1
For interpretation of color in Figs. 1–4, the reader is referred to the web version of
this article.

E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
105
a
b
c
Fig. 4. The supramolecular arrangement showing the formation of step ladder chains parallel to the a direction, made of two centrosymmetric CAHꢀ ꢀ ꢀO interactions (black
dashed lines). These are, in turn, held together by another CAHꢀ ꢀ ꢀO interaction showed as orange dashed lines. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
an opposite dihedral angle relationship between the g1 and g2 con-
Table 9
formations. The (anti, syn) pair of the g2 conformers present the
a
Summary of intermolecular interactions (D–Hꢀ ꢀ ꢀA; Å, °) operating in the crystal
structures of 4.
angle which is ca. 12° smaller than that for (anti, syn) pair of the
g1 conformers.
DAHꢀ ꢀ ꢀA
DAH (Å)
Hꢀ ꢀ ꢀA (Å)
Dꢀ ꢀ ꢀA (Å)
DAHꢀ ꢀ ꢀA (°)
The summing up of the orbital (NBO analysis) and electrostatic
interactions justifies quite well the populations and the frequen-
cies of (anti, syn) pairs of the c, g1 and g2 conformers found in the
gas phase.
C24AH29ꢀ ꢀ ꢀO33i
C8AH11ꢀ ꢀ ꢀO34ii
C23AH28ꢀ ꢀ ꢀO1iii
0.93
0.97
0.93
2.64
2.67
2.46
3.349 (2)
3.222 (3)
3.122 (2)
133
117
128
Symmetry codes: (i) 2 ꢂ x; ꢂy; z ꢂ 1; (ii) 1 ꢂ x; ꢂy, 1 ꢂ z; (iii) x; ꢂy + 1/2; z + 1/2.
The IR higher carbonyl frequency component whose population
is ca. 10%, in CCl4 solution, may be ascribed to the least stable and
most polar cis conformer pair (in the gas) and the lower frequency
component whose population is ca. 90%, to the summing up of the
populations of the two most stable and least polar gauche con-
former pairs (g1 and g2), in spite of the difference of ca. 10 cmꢂ1 be-
tween them in the gas phase. Moreover, the reversal of the cis(c)/
gauche (g1 + g2) population ratio observed in chloroform ca. 60%
(cis)/40% (gauche) and the occurrence of the more polar cis(c) con-
former only in acetonitrile (100%) strongly suggests the coales-
cence of the two gauche components in a unique carbonyl band
in solution. The lower dipole moment values (2.6 D and 2.9 D)
for the g1 and g2 conformers which are ca. 3.7 D lower than the c
conformers, strongly agree with the larger solvation of the most
polar c conformer relative to the least polar g1 and g2 conformers
as the solvent polarity increases. A further support to this rational-
ization is given by the single point PCM solvation model performed
at the HF method for the (anti, syn) pairs of the c, g1 and g2 con-
formers, which showed a progressive increase of the c/g1 + g2 ratio
going from gas (1.8%/98.2%) to CCl4 (9%/91%), to CHCl3 (20.5%/
79.5%) and to CH3CN (41.9%/58.1%).
molecules are very close to one another (Figs. 4 and S2) that is both
form step ladders that are connected through CAHꢀ ꢀ ꢀO interactions.
The fact that the pair of syn-clinal (gauche) conformations found
in the centrosymmetric dimers in the solid of 4 (Table 3) present
dihedral angles which are very close to those found for the (g1
and g2) gauche conformers for 3, in the gas phase (Table 3), seems
to be a further evidence that in solution these two conformers
should present even closer geometries whose carbonyl frequencies
should be nearly coincident.
4. Conclusions
The preferred conformations of N,N-diethyl-2-[(40-substi-
tuted)phenylsulfonyl]acetamides, bearing as substituents OMe 1,
Me 2, H 3, Cl 4, Br 5, NO2 6 were determined by mCO IR analysis,
B3LYP/6-31G(d,p) calculations (for 3), HF/6-31G(d,p) PCM (for 3)
and X-ray diffraction (for 4). Theoretical data showed the existence
of three pairs of (anti, syn) cis(c) (least stable), gauche (g1 and g2)
(most stable) conformers. The anti (c, g1 and g2) conformers, with
respect to the geometry of the ½CðOÞNEt2ꢄ fragment, prevails over
the syn ones by ca. 3.7 times. The SO2AC6H4AY fragment displays
X-ray single crystal analysis of 4 indicates that this compound
assumes, in the solid, the syn-clinal (gauche) conformation, and
the most stable anti geometry relative to the [C(O)N(CH2CH3)2]

106
E. Vinhato et al. / Journal of Molecular Structure 1002 (2011) 97–106
fragment. The short intramolecular contacts: Od½SꢂO2ꢄ ꢀ ꢀ ꢀ C½dCþOꢄ; O½dCꢂOꢄ ꢀ ꢀ ꢀ
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and Od½SꢂO2ꢄ ꢀ ꢀ ꢀ H½dNþCH2ꢄ, originate attractive elec-
½NCH2ꢄ
trostatic interactions which contribute to the stabilization of the
syn-clinal (gauche) conformation of 4. In order to obtain larger en-
ergy gain from the crystal packing the molecules of 4 are linked in
centrosymmetric dimers through two CAHꢀ ꢀ ꢀO interactions
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Acknowledgements
The Brazilian authors thank the Fundação de Amparo à Pesquisa
do Estado de São Paulo (FAPESP) for financial support of this re-
search and for a fellowship to (E.V.), the Conselho Nacional de
Desenvolvimento Científico and Tecnológico (CNPq) for a scholar-
ship to (E.V.) and fellowships to (P.R.O and J.Z.-S.). The Italian
author thanks the University of Ferrara (nano & nano project) for
financial support.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.06.051.
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[31] Computed data at B3LYP/6-31G(d,p) level for the anti-syn conformations of the
N,N-diethylacetamide are presented in Table S1 (Supplementary information).
[32] CHELPEG charges are presented in Table S2 but the hydrogen charge value at
the methylene and methyl groups are too low or negative, therefore, we have
used the Mülliken charges in the present paper.
[33] Occupancies for donor and acceptor orbitals for the (anti,syn) pairs of the g1,g2
and c conformers of 3 are presented in Table S3.
[34] P.R. Olivato, N.L.C. Domingues, A.K.C.A. Reis, E. Vinhato, M.G. Mondino, J.
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and the results presented in Table S4 show that the computed population ratio
of the (c) (anti + syn)/[g1(anti + syn) + g2(anti + syn)] increases only slightly
with the increasing solvent polarity.
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