Conformational properties of ortho-nitrobenzenesulfonamide in gas and crystalline phases. Intra- and intermolecular hydrogen bond

Article abstract of DOI:10.1007/s11224-010-9725-4

A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four confor

Full text of DOI:10.1007/s11224-010-9725-4

Struct Chem (2011) 22:373–383
DOI 10.1007/s11224-010-9725-4
ORIGINAL RESEARCH
Conformational properties of ortho-nitrobenzenesulfonamide
in gas and crystalline phases. Intra- and intermolecular hydrogen
bond
Nina I. Giricheva
Yulia S. Medvedeva
Anna V. Bardina Vyacheslav M. Petrov
•
Georgiy V. Girichev
•
•
Sergey N. Ivanov
•
•
Received: 8 December 2010 / Accepted: 17 December 2010 / Published online: 5 January 2011
Ó Springer Science+Business Media, LLC 2010
A combined gas-phase electron diffraction and quantum
chemical (B3LYP/6-311?G**, B3LYP/cc-pvtz, MP2/
cc-pvtz) study of molecular structure of 2-nitrobenzene-
sulfonamide (2-NBSA) was carried out. Quantum chemical
calculations showed that 2-NBSA has four conformers, two
of which are stabilized by intramolecular hydrogen bond.
The latter (with the S–N bond in a close to orthogonal
position around the phenyl ring and differing from each other
by staggered or eclipsed positions of the N–H and S=O bonds
in the SO NH group) presented in a saturated vapor over
Keywords 2-Nitrobenzenesulfonamide ꢀ Conformer ꢀ
Transition state ꢀ Molecular structure ꢀ Internal rotation ꢀ
Pyramidal inversion ꢀ Hydrogen bond ꢀ Gas electron
diffraction ꢀ Quantum chemistry ꢀ Mass spectrometry
Introduction
At the present time, a synthesis of new, physiologically
active compounds derived from sulfonyl-substituted nitro-
gen-containing aromatic systems is actively developed.
The synthesis is based on the high throughput screening
(HTS) technologies [1]. To realize a strategy of this and to
improve the molecular design methods, information on
geometric and electronic structure of arensulfonic acid
amides is needed. Benzenesulfonamide and its various
substituted derivatives (NO –, CH –, Cl–) belong to the
2
2
2
-NBSA at T = 433 (3) K in commensurable amounts.
´
˚
Experimental internuclear distances (A) for the staggered
˚
conformer are (A): r (C–H) = 1.071(9), r (C–C) =
av.
h1
av.
h1
1
.390(4), rh1(C–S) = 1.789(8), rh1(S=O)av. = 1.427(6),
0
r (S–N) = 1.644(6), r (N–O) = 1.221(4), r (C –N) =
h1
h1
av.
h1
1
.487(8), r (N–H) = 1.014. Calculations at B3LYP/cc-
h1 av.
pvtz level were performed to determine the structure and the
energies of the transition states between conformers. It was
shown that the conformer structures of free molecule differ
from those of a molecule stabilized by intermolecular
hydrogen bonds in a crystal. Influence of a substituent X
2
3
basic compounds which contain a sulfonamide group
–SO NH . Since these compounds are the constituents of
2
2
most of the precursors for sulfonamide medicines [2, 3],
any information concerning the structure and conforma-
tional properties is of a great importance for a better
understanding the reactive activity in the processes passing
with the S–N and N–H bonds cleavage.
(
X = –CH , –NO ) on conformational features of the ortho-
3 2
substituted benzenesulfonamide was established.
In processes with participation of substituted benzene-
sulfonamides a change of the aggregate state of the latter
may occur. This arouses interest in knowledge on structure
of molecules in condensed and gaseous phases as well as on
those changes in the molecular structure which accompany
the crystal-to-gas transition. At present, such information is
available only for an unsubstituted benzenesulfonamide
N. I. Giricheva (&) ꢀ Y. S. Medvedeva ꢀ
S. N. Ivanov ꢀ A. V. Bardina ꢀ V. M. Petrov
Department of Physical Chemistry, Ivanovo State University,
Ermak St. 39, Ivanovo, Russia 153025
e-mail: n.i.giricheva@mail.ru
(BSA) and its methyl-derivatives (MBSA). The crystal
structures of BSA [4], ortho-MBSA (or 2-MBSA) [5],
and para-MBSA (or 4-MBSA) [6] were studied by X-ray
diffraction (XRD). Earlier, we reported the results of
G. V. Girichev
Department of Physics, Ivanovo State University of Chemistry
and Technology, F.Engels Av., 7, Ivanovo, Russia 153000
123

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Struct Chem (2011) 22:373–383
gas-phase electron diffraction (GED) study on the molec-
ular structures of free molecules mentioned above [7, 8].
Strong intermolecular hydrogen bonds between O(SO2)
and H(NH ) atoms occur in crystals of BSA, 2-MBSA, and
2
4
-MBSA. These interactions stabilize a certain conforma-
tion of the molecule in a crystal which differs from the
molecular geometry in a free state.
Free molecules of unsubstituted and substituted BSA
have several conformers. BSA [7] and 4-MBSA [8] have
two conformers each: the S–N bond is oriented orthogo-
nally with respect to the benzene ring while the N–H and
S=O bonds of the SO NH groups either eclipse each other
2
2
(
eclipsed conformers) or are in staggered positions (stag-
gered conformers). Unfortunately, the GED method did not
allow to reliably determine a quantitative ratio between the
conformers in case of 4-MBSA because of low scattering
Fig. 1 Intermolecular hydrogen bonds in crystalline structure of
2
-NBSA [9]
power of the hydrogen atom in the NH group.
2
2
-MBSA has four conformers [8] differing by as the
S–N bond orientation around the benzene ring (orthogonal
and planar) as well as by relative orientation of N–H
and S=O bonds of the SO NH group (eclipsed and
properties of the molecules X–C H –SO NH are the sub-
6 4 2 2
jects of this study.
2
2
staggered).
In contrast to MBSA, no information on free nitro-
benzenesulfonamides (NBSA) is available in literature.
Nevertheless, the structure and packing of molecules in
crystalline 2-NBSA [9], 3-NBSA [5], and 4-NBSA [5, 10]
is known from XRD measurements. Intermolecular
hydrogen bond was found to exist in all these molecules.
In crystalline 4-NBSA [10], the molecules are posi-
tioned by a ‘‘head-to-tail’’ scheme forming intermolecular
Experimental
2-NBSA was synthesized from a commercial sample of
nitrobenzenesulfonylchloride by interaction with ammonia
[11]. The original sulfonylchloride was washed from
hydrochloric acid by water. 2-NBSA recrystallized from a
solvent (20 vol.% propane-2-ol water solution) till the
melting temperature of 465 K (literature: 466 K [12]) has
been reached.
bonds between the hydrogen H(NH ) atom of one molecule
2
and the oxygen O(NO ) atom of the next molecule.
2
The combined GED/MS experiment on saturated vapor
over 2-NBSA was carried using a technique described
earlier [13, 14] which allows the vapor composition to be
in situ monitored during all the diffraction patterns recod-
ing procedure by means the mass spectrometer attached to
the GED apparatus. Sublimation of the sample was carried
out from a stainless steel (X18H10T) cylindrical effusion
cell with the ratio of the cell internal cross section to that of
the effusion canal of about 200. The temperature of the
sample and nozzle was kept at 433(3) K as measured by a
W–Re (5/20) thermocouple. Accurate wavelength of the
electrons was calibrated against diffraction patterns of
polycrystalline ZnO which were recorded just before and
after the exposure of the diffraction patterns series on the
gaseous sample. The scattered electrons were collected on
Kodak Electron Image films SO-163 of the size 9 9
In crystalline 3-NBSA [5], the molecules form layers in
which the –SO NH groups of the adjacent molecules
2
2
directed toward to each other, and every molecule appears
to be connected by two hydrogen bonds with each of the
two neighbors. Intermolecular hydrogen bonds are formed
between H(NH ) in one molecule and O(SO ) of the
2
2
neighbor and vice versa.
In crystalline 2-NBSA [9], each molecule is bound by
hydrogen bonds with four adjacent molecules (see Fig. 1)
due to which the layers consisting of alternating mirror
isomers of 2-NBSA are formed.
In this study, we report the results of synchronous gas-
phase electron diffraction and mass spectrometric (GED/
MS) study of saturated vapors of 2-NBSA. This compound
is a representative of nitro-substituted benzenesulfonamides
in which steric effects between the substituents are
expressed most strongly. A composition of saturated vapor
over 2-NBSA, conformational properties of free molecule,
structural changes in the molecule at the transition from
crystal to a free state, and correlations between the nature of
ortho-substituent X (X = –CH , –NO ) and conformational
2
12 cm . The main conditions of the GED/MS experiment
are listed in Table 1.
From reproducibility of the electron impact mass spectra
recorded during heating the sample one may consider that
2-NBSA sublimes with no decomposition up to the tem-
perature of the GED experiment, 433(3) K. The ion
3
2
1
23

Struct Chem (2011) 22:373–383
375
Table 1 Main conditions of the combined gas-phase electron dif-
sM(s)
fraction and mass spectrometric experiment for 2-NO
2
–C
Camera distance
L = 338 mm L = 598 mm
6 4 2 2
H SO NH
L = 598 mm
Parameter
L = 338 mm
Primary beam current (lA)
Effusion cell temperature (K)
Accelerating voltage (kV)
Ionizing voltage (V)
1.35
0.72
433(3)
74.3
433(3)
78.9
ΔsM(s)
50
50
Exposure time (s)
100
90
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28
-6
-6
Residual pressure in the diffraction
chamber (torr)
1.3 9 10
3.0 9 10
-1
s, Å
-1
)
˚
Scattering angles (A
3.5–26.5
1.2–15.6
Fig. 2 Experimental (dots) and calculated (line) sM(s) functions and
their differences DsM(s) = sM(s)exp - sM(s)theor for the composition
5
2 6 4 2 2
2% (conformer I) and 48% (conformer II) of 2-NO –C H SO NH
Table 2 Electron impact (Uioniz. = 50 V) mass spectrum of satu-
function, sM(s), was evaluated as sM(s) = (I(s)/G(s) - 1)s,
where I(s) is the total electron scattering intensity, G(s) the
experimental background. The background curves were
checked by differentiation to confirm an absence of oscil-
lations with frequencies comparable with those of the
experimental I(s) curves. Experimental and theoretical
sM(s) curves along with their differences DsM(s) are given
in Fig. 2.
rated vapor over 2-NO
experiment
2 6
–C H
SO NH
4 2
2
recorded during the GED/MS
Ion
m/e a.m.u.
Relative abundance (%)
?
[
[
[
[
[
[
[
[
[
[
NO
2
C
C
6
H
4
SO
2
NH
?
2
]
202
186
139
122
108
92
21
100
4
NO
2
H
6 4
SO
?
2
]
6 3 2
C H SO ]
?
NO
2
C
H
6 4
]
2
?
6
C H
4
S]
5
?
NH
2
C
H
6 4
]
12
9
?
Quantum chemical calculations
SO NH
2
2
]
80
?
6
C H
4
]
76
17
43
30
?
Since the molecule 2-NBSA possesses three non-rigid
torsion vibration coordinates, it may have several rotational
conformers. Therefore, prior to the structural analysis a
series of quantum chemical calculations were performed to
estimate the conformational composition of the vapor
under investigation and the geometric and vibrational
parameters of the conformers. Two approaches, DFT/
B3LYP (basis sets 6-311?G** and cc-pVTZ [16]) and
MP2/cc-pVTZ (Gaussian-03 package [17]) were applied.
From B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations,
we established that 2-NBSA has four conformers (Fig. 3a)
differing by rotation angles of the SO NH group around
SO
2
]
64
?
4
C H
2
]
50
currents recorded simultaneously with the diffraction pat-
terns exposure are given in Table 2 and evidences for
presence of the only molecular species in the saturated
vapor over 2-NBSA which corresponds to the gross for-
mula of this compound. No associates (dimers, etc.) were
detected in the vapor which means that all hydrogen bonds
undergo a cleaved at ‘‘crystal-to-gas’’ transition. Moreover,
no volatile impurities were found. The mass spectra has a
most intensive ion with m/z = 186 a.m.u. of a stoichiom-
2
2
the C–S bond, the NH group around the S–N bond and the
2
?
etry [NO C H SO ] , along with a series of lighter ions
2
NO group around the C–N bond. On the other hand, the
2
6
4
2
which are the products of a NO C H SO NH molecule
2
B3LYP/6-311?G** calculations discovered three con-
2
6
4
2
dissociative ionization processes. Stoichiometry of the
latter manifests that under electron impact a predominant
cleavage of the bonds takes place between the benzene ring
and the substituents, as well as of the bonds within the
functional groups.
formers only. Torsion angles, relative energies DE, and
relative Gibbs energies DG of the conformers are sum-
0
marized in Table 3. The latter were calculated using the
B3LYP method with 6-311?G** and cc-pVTZ basis sets.
In all the calculations performed the conformers I and II
(see Fig. 3a) were found to be the most stable. From this
one may consider these two conformers to dominate in the
saturated vapor over 2-NBSA at the temperature corre-
sponding to the GED experiment.
The optical densities of the diffraction patterns were
measured by the MD-100 (Carl Zeiss, Jena) microdensi-
tometer modified in our group earlier as to provide it with a
system of computer control [15]. The molecular scattering
123

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Struct Chem (2011) 22:373–383
(
a)
I
II
III
IV
0
0
0
0
ΔG (relative to I):
ΔG (433 K) = 0.1
ΔG (433 K) = 4.4
ΔG (433 K) = 6.2
(
kcal/mol)
(
b)
I
II
ΔG =0
III
ΔG = 0.33
IV
0
0
0
0
ΔG = 1.64 (relative
ΔG = 2.61
to II)
(kcal/mol)
Fig. 3 Geometric structures and relative Gibbs energies (B3LYP/cc-pVTZ) of the conformers of 2-NO
-CH –C SO NH (b)
2
–C
6 4
H SO
2
NH
2
(a) and
2
3
H
6 4
2
2
Table 3 Calculated geometric
parameters (angstroms and
degrees), relative energies
DE and Gibbs energies DG
(kcal/mol), and estimated mole
fractions (%) of the conformers
Method/basis
Parameter
Conf. I
stag.)
Conf. II
(eclips.)
Conf. III
(eclips.)
Conf. IV
(stag.)
(
0
a
a
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
/(C–C–S–N)
76.2
76.7
78.8
1.9
79.7
21.8
–
79.9
20.9
24.1
27.6
of 2-NO
2 6 4
–C H SO
2
NH
2
82.4
23.9
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
/(C–C–S–O)
2.8
92.3
2.7
3.2
91.2
93.8
96.9
–
5.4
5.8
94.2
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
/(C–S–N–H)
/(C–C-N–O)
r(C–S)
-58.5
-58.1
-58.1
-40.5
-40.8
-47.6
1.832
1.825
1.796
1.661
1.652
1.642
0
-86.9
-88.7
-88.4
-36.7
-36.5
-42.8
1.821
1.814
1.786
1.674
1.664
1.653
-0.008
0.26
-130.6
-128.1
-131.4
-42.4
-41.9
-48.4
1.824
1.818
1.790
1.690
1.678
1.664
4.91
-79.2
-76.3
–
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
-45.3
-51.4
–
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
1.825
1.797
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
r(S–N)
1.652
1.643
–
a
Those torsion angles which
are close to 90° were measured
from the bond C2–C1 (see
Fig. 3), i.e., are the angles
C2–C1–S–N(or O). Those
torsion angles which are close to
B3LYP/6-311?G**
B3LYP/cc-pVTZ
MP2/cc-pVTZ
DE
0
5.03
7.26
7.92
–
0
0.23
6.04
0
B3LYP/6-311?G**
B3LYP/cc-pVTZ
DG (298)
0
-0.02
0.09
4.20
0
4.36
6.18
6.83
–
0
° were measured from the bond
b
MP2/cc-pVTZ
0
0.05
5.36
C6–C1, i.e., are the angles
C6–C1–S–N(or O)
B3LYP/6-311?G**
Mole fraction
49.2
52.3
51.4
50.4
0.4
b
Thermal free energies
B3LYP/cc-pVTZ) were used
B3LYP/cc-pVTZ
b
MP2/cc-pVTZ
47.3
0.4
0.0
(
48.5
0.1
0.0
0
for calculating DG (298)
1
23

Struct Chem (2011) 22:373–383
377
Structural analysis
3. All carbon atoms of the benzene ring belong to the
same plane.
According to the mass spectrometric data recorded in this
study (Table 2) the vapor contains the only molecular
species, 2-NBSA, which may, according to the quantum
chemical calculations, have four conformers.
4. The valence angles in the benzene ring were refined in
a group.
5. Because of a low scattering power of the hydrogen
atoms of the NH groups, the N–H bond lengths, the
2
The atom numbering of 2-NBSA is given in Fig. 4. For
the structural analysis a model was chosen which makes it
possible to describe the geometry of any of the four con-
formers. The model included 23 independent parameters
and allowed to take into account the following: (i) an
inequivalence of the C–C bonds in the benzene ring; (ii)
rotation of the SO NH group around the C–S bond; (iii)
valence angles H–N–S and H–N–H and the torsion
angle /(H–N–S–O1) were not refined being kept at the
values given from the quantum chemical calculations.
All geometries were constructed within the r -struc-
h1
ture. The needed vibrational corrections were calculated
with a non-linear relation between Cartesian and internal
coordinates taken into account using the program
SHRINK [18, 19]. The force field yielded by the B3LYP/
2
2
rotation of the NH2 group around the S–N bond; (iv)
rotation of the nitro-group around the C–N bond; (v) pos-
sibility of motion for the S atom out of the benzene ring
plane. Eight interatomic distances (C–H, C–C, C–S, S–N,
S–O, N–H, C–N, and N–O), nine valence angles (C–C–C,
S–C–C, N–S–C, O–S–C, O–S–N, H–N–S, H–N–H, N–C–
C, and O–N–C), and six torsion angles /(S–C–C–C), /(N–
S–C–C), /(H–N–S–O), /(N–C–C–C), /(O–N–C–C), and
6
-311?G** calculations was used as an input for this
program.
Vibration amplitudes for the terms with close internu-
clear distances were refined in groups. The terms were
sorted into the groups according to belonging to the peaks
in the radial distribution function f(r) (see Fig 5; Table 5).
The least-squares analysis was carried out using a modified
program KCED-35 which is analogical to that described in
/(O3–N–C–O4) were taken as independent parameters.
The model had several constraints:
[
20].
The experimental function sM(s) was tested for the fit
1
.
Except the C–H bonds, the lengths of all homotypic
bonds (for example, S1–O1 and S1–O2, all bonds in
benzene ring, etc.) were refined in corresponding
groups. The Dr values which characterized the
inequivalence of homotypic bonds were taken from
the quantum chemical calculations (B3LYP/6-
for conformers I, II, and III of 2-NBSA separately as well
as to fit a mixture of the two most stable conformers I and
II. The differences for interatomic distances and for
valence angles were kept at the quantum chemical values,
whereas the torsional angles /(N–S–C1–C2) and /(O3–N–
C2–C1), which determine the position of the substituents
with respect to the benzene ring, were refined by turns.
Least-squares results are given in Table 4. Six cor-
relation coefficients exceeded 0.75 in absolute value:
3
11?G**) and were not varied in the least-squares
analysis. It is to be noted that the calculations with
different basis sets give practically the same Dr values.
The C–H bonds in the benzene ring were constrained
to be equal and to lie along the bisectors of the
corresponding C–C–C angles.
2
.
p /p = -0.82, p /p = -0.81, p /p = 0.78, p /p =
10
1
0
16
2
5
12 13
9
-0.85, l /p = 0.97, l /p = 0.76 (subscript numbering
4
12
4
13
f(r)
Δf(r)
Conformers I and II
a
b
Conformer III
0
1
2
3
4
5
6
7
8
r, Å
Fig. 5 Experimental (dots) and calculated (line) radial distribution
curves f(r) and their differences Df(r) = f(r)exp - f(r)theor for 2-NO
SO NH : (a) difference curve when the mixture of conformers
2
–
C
H
6 4
2
2
I (52%) and II (48%) are modeled; (b) difference curve when
conformer III is modeled
Fig. 4 Atom numbering in the molecule 2-nitrobenzenesulfonamide
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Struct Chem (2011) 22:373–383
Table 4 Geometric parameters of the conformer I of 2-NO
2
–C
6
H
4
SO
2
NH
2
(angstroms and degrees)
B3LYP/cc-pVTZ
Parameter
GED rh1-structure
B3LYP/6-311?G**
MP2/cc-pVTZ
XRD [9]
a
1.071(9) p
C–H
1
1.082
1.401
1.393
1.832
1.661
1.452
1.458
1.015
1.013
1.481
1.226
1.217
118.4
121.3
125.0
108.8
106.3
108.0
112.7
114.5
122.8
117.6
172.4
76.2
1.079
1.397
1.390
1.825
1.652
1.444
1.449
1.013
1.011
1.479
1.224
1.215
118.3
121.3
125.0
108.3
106.4
108.1
112.3
114.5
122.9
117.7
172.6
76.7
1.080
1.396
1.392
1.796
1.642
1.442
1.445
1.013
1.011
1.464
1.231
1.226
118.4
121.5
123.9
107.4
106.3
107.7
111.3
113.8
122.3
117.4
173.4
78.8
0.930
1.386
1.387
1.786
1.606
1.433
1.432
0.883
0.883
1.466
1.220
1.223
118.4
122.0
124.1
108.8
107.7
108.8
b
C1–C2
1.398(4) p
1.390(4) (p
2
(
C–C)cp.
2
)
C–S
1.789(8) p
1.644(6) p
1.424(4) p
3
S–N1
S–O1
S–O2
N1–H1
N1–H2
C–N2
N–O3
N–O4
4
5
1.430(4) (p
1.015 p
1.013 (p
5
)
6
6
)
1.487(8) p
1.226(4) p
7
8
1.217(4) (p
117.3 (9) p
121.5(9) (p
8
9
9
)
\
\
\
\
\
\
\
\
\
\
C2–C1–C6
C1–C2–C3
S–C1–C2
N1–S–C1
O1–S–C1
O1–S–N1
H–N–S
)
125.2(18) p10
107.7(32) p11
106.3(18) p12
108.9(33) p13
112.8 p14
113.5 p15
121.7(21) p16
116.0(3) p17
173(2) p18
74 (8) p19
56.5 p20
H–N–H
N2–C2–C1
O3–N2–C2
121.9
118.0
/S–C1–C2–C3
/N1–S–C1–C2
/(H–N–S–O1)
/N–C2–C1–C6
/O3–N2–C2–C1
/O3–N–C–O4
89.9
56.4
56.8
56.0
179(6) p21
-42(6) p22
177.5 p23
2.0(3)
177.8
-40.5
176.9
2.128
49.2
177.8
-40.8
176.9
2.123
52.3
178.2
-47.6
176.9
2.110
51.4
-47.6
2.578
2.02
O3(N2)ꢀꢀꢀH1(N1)
Mole fraction (%)
52
R
f
(%)
2.48
See Fig. 4 for atom numbering
a
2
2 0.5
Uncertainties were calculated as [(2.5rL-S) ? (0.002 ꢀ r) ] for internuclear distances, 3rL–S for valence angles and rL–S for torsion angles.
The parameters given without uncertainties were fixed in the refinement
b
i i
p parameter refined independently; (p ) parameter refined in the i-group
of the parameters p and of the root-mean-square amplitudes
l are listed in Tables 4 and 5, respectively).
respectively (B3LYP/cc-pVTZ). These geometric values
indicate that the intramolecular hydrogen bond is formed
and stabilizes the conformers I and II as compared to the
conformers III and IV in which this bond is absent.
In conformers I and II, the S–N bond is in a position
close to orthogonal and deviates from it due to intramo-
lecular hydrogen bond. In this case one of the S=O bonds
almost eclipses the C–C bond in benzene ring. In con-
formers III and IV the S=O bond is orthogonal to the
benzene ring.
Discussion
Conformers of 2-NBSA
According to the quantum chemical calculations the mol-
ecule 2-NBSA has four conformers (Fig. 3a). The distances
between the H atom of the NH group and the O atom of
2
˚
the NO2 group are 2.12 and 2.25 A, and the angles
Orientation of the NO2 group about the skeleton is
practically the same for all conformers and is probably
determined by keeping the longest distances between the
\
NHꢀꢀꢀO are 133.3° and 118.2° in conformers I and II,
1
23

Struct Chem (2011) 22:373–383
379
Table 5 Internuclear distances, experimental and theoretical vibra-
tion amplitudes and vibrational corrections (excluding the non-
bonded atom pairs containing hydrogen atoms) for the conformer I
O(NO ) atom and the two most adjacent electronegative
2
oxygen and nitrogen atoms (conformers I and II) or two
oxygen atoms (conformers III and IV) of the sulfonamide
2 6 4 2 2
of 2-NO –C H SO NH
group. In all four conformers these distances are
˚
Parameter
r
a
l
exp
l
calc
Dr = rh1 - r
a
Group
2
.87–3.17 A.
Conformers I and II differing by mutual orientation of
the NH and SO groups may just tentatively be attributed
N–H1
1.010(1)
1.066(4)
1.224(1)
1.387(1)
1.388(1)
1.423(1)
1.485(3)
1.642(2)
1.787(3)
0.072(3)
0.076(3)
0.045(1)
0.051(1)
0.051(1)
0.042(1)
0.059(1)
0.062(4)
0.070(4)
0.071
0.075
0.039
0.045
0.045
0.036
0.053
0.050
0.058
0.004
0.005
0.001
0.000
0.001
0.000
0.001
0.001
0.001
1
1
2
2
C–H
as staggered (conformer I) and eclipsed (conformer II)
since in any of them the NH group turns, due to the
N2–O3
C4–C5
C3–C4
S–O1
2
2
2
intramolecular hydrogen bond formed, that favors the
distance between H(NH ) and O(NO ) atoms to shorten.
2
2
2
2
The second pair of conformers, III and IV, also differs
mostly by relative positions of the NH group, and the
C2–N2
N1–S1
C1–S1
H–O1
2
2
3
steric factors make the conformer IV to be less favorable
relative to III.
3
2.315(32) 0.182(2)
0.190 -0.005
4
As it may be seen from Table 3, the Gibbs energies of
the conformers I and II are similar, while those of the
conformers III and IV are much higher.
C2–C6
C3–C5
N1–O2
C1–O2
C1–O1
H1–O1
C2–C5
C3–C6
H–S1
2.374(5)
2.401(2)
0.049(2)
0.048(2)
0.057
0.056
0.074
0.077
0.087
0.180
0.064
0.064
0.146
0.116
0.131
0.006
0.004
0.004
0.004
0.005
0.020
0.008
0.006
0.011
0.006
0.010
4
4
2.461(17) 0.066(2)
2.564(10) 0.069(2)
2.574(10) 0.079(2)
2.726(21) 0.187(3)
4
4
Pathways of conformational transitions
4
5
Geometry of the conformers and transition states (TS)
between them are shown in Fig. 6. It might be noted that
the transition from the staggered to the eclipsed conformer
2.766(3)
2.754(7)
0.071(3)
0.071(3)
5
5
2.771(16) 0.153(3)
3.215(6) 0.130(9)
5
(
I ? II or III ? IV) can be realized by as internal rota-
N2–S1
C2–N1
H–O3
6
tion of the NH group around the S–N bond, as well as by
2
3.501(49) 0.145(9)
3.476(99) 0.257(9)
3.734(64) 0.144(4)
6
pyramidal inversion of the N atom around the plane
H1H2S. Barriers of the transitions between the conformers
are shown in Fig. 7. Apparently, the pyramidal inversion
0.243 -0.014
6
C5–N1
C2–O2
C5–S1
C4–O4
C3–S1
O2–O3
C4–S1
N2–O2
C3–N1
C5–O4
C3–O2
C4–O2
C4–H1
C4–N1
C4–H2
0.138
0.082
0.073
0.121
0.078
0.017
0.015
0.015
0.012
0.015
7
3.880(6)
4.026(7)
0.088(4)
0.090(2)
7
via planar structure of the SNH fragment is the most
2
8
energetically favorable.
4.130(27) 0.139(2)
4.097(6) 0.096(2)
4.441(27) 0.186(2)
8
Each of the transition states shown in Fig. 6 is a first-
order saddle point on the potential energy surface. Struc-
tures of the transition states TS(I ? II) and TS(III ? IV)
are characterized by one imaginary frequency each corre-
sponding to the pyramidal inversion motion, while in cases
TS(II ? III) and TS(IV ? I) by one imaginary frequency
each corresponding to the correlated internal rotation of the
NO and SO NH substituents. In the TS(II ? III) and
8
0.167 -0.007
9
4.569(4)
4.551(8)
0.095(2)
0.130(2)
0.077
0.112
0.153
0.099
0.092
0.111
0.019
0.017
0.021
0.024
0.023
0.023
0.009
0.028
0.020
0.033
0.051
0.036
9
9
4.786(39) 0.165(8)
4.869(35) 0.112(8)
10
10
10
10
11
11
11
11
11
11
4.958(6)
0.104(8)
2
2
2
5.072(11) 0.123(8)
TS(IV ? I) structures, the S–N bond lies in a plane of the
5.383(24) 0.334(18) 0.271
5.396(19) 0.226(18) 0.163
5.498(27) 0.375(18) 0.313
benzene ring and a plane of the NO group is in either
2
perpendicular or co-planar to the benzene ring position.
The barrier of the transition between the two existing in
N1–H(C3) 5.504(61) 0.252(18) 0.189
O2–O4 5.467(31) 0.286(18) 0.223
S1–H(C4) 5.623(6) 0.168(18) 0.105
the gas conformers of 2-NBSA phase, I and II, exceeds the
-1
thermal energy RT = 0.86 kcal mol
which is an evi-
dence of hindered inversion of the N atom in the S-NH2
fragment. This makes it possible to carry out the structural
analysis in a ‘‘traditional’’ way, i.e., without a dynamic
model approach.
See Fig. 4 for atom numbering
a
All parameters given in angstroms. Uncertainties in parentheses are
the rL–S values
123

3
80
Struct Chem (2011) 22:373–383
Fig. 6 Geometric structure and
relative energies (kcal/mol) of
the conformers and transition
2 6 4 2 2
states for 2-NO –C H SO NH
from theoretical calculations
B3LYP/cc-pVTZ
TS III →IV (inv)
E = 7.33
Conformer IV
Conformer III
E = 7.26
E = 5.03
TS IV →I
E = 8.43
TS II →III
E = 7.66
TS I →II (inv)
E = 1.41
Conformer II
Conformer I
E = 0.26
0
Conformational composition of the saturated vapor.
Limitations and abilities of gas electron diffraction
Alongside with the hypothesis about predominant presence
of conformers I and II in the saturated vapor (based on the
results of quantum chemical calculations) we also tested a
possibility to discover a conformer III in the gas phase. In
this refinement scheme of a least-squares procedure all
geometric parameters of the conformer III were refined
except the torsion angle N–S–C–C which was fixed at the
value of -20.9° (B3LYP/cc-pVTZ). Figure 5 and the dis-
As it may be estimated from the results of the B3LYP/
cc-pVTZ calculations, the relative concentrations of the
conformers at the temperature of the GED experiment is
expected to be 52.3:47.3:0.4:0.0, according to which in a
saturated vapor over condensed phase of 2-NBSA the
conformers I and II are to present in comparable amounts,
while the conformers III and IV are to be poorly abundant.
These expectations have been supported by the results of
the GED data interpretation. Due to low scattering power
agreement factor value of R = 4.5% (which in this case is
f
twice as much as that for the optimal vapor composition)
illustrate that a geometry of the conformer III does not fit
the GED data collected. Thus, the GED experiment sup-
ports the theoretical predictions about the maximal stability
of the conformers I and II relative to that of the conformers
III and IV. Experimental and calculated geometries of the
conformer I are summarized in Table 4, main parameters
of the other conformers are given in Table 3. Within error
limits, most of the experimental geometric parameters are
consistent with those calculated by different methods. The
only exceptions are the S=O bond lengths for which the
of the hydrogen atoms of the NH groups an accurate
2
position determination of the N–H and S=O bonds in the
SO NH group is quite problematic. That, in turn, might
2
2
bear difficulties in distinguishing between conformers I and
II. Indeed, an attempt to refine the ratio between the
abundances of these two conformers yielded 0.44(25)
instead of theoretical value 0.52 accompanied by insig-
nificant increase of the disagreement factor Rf.
˚
calculated values are larger by ca. 0.02 A. It is to be noted
Nevertheless, the GED method is able to distinguish the
conformers I and II from the conformers III and IV.
that only the S–C bond distance is essentially dependent on
1
23

Struct Chem (2011) 22:373–383
381
2-MBSA are represented in the same sequence determined
by orientation of the sulfonamide group as in the case of
E,
(b)
6
5
4
3
2
1
0
kcal/mol
2-NBSA.
As it was mentioned above, a common feature of the
V
0(rot) = 5.8
conformers of 2-NBSA is that one of the oxygen atoms of
the NO group is located at a maximal distance away from
2
the oxygen (or nitrogen) atom of the SO NH group. In
2
2
contrast, for the conformers of 2-MBSA, a tendency to a
minimal distance between two H atoms of CH group and
3
O and N (or N) atoms of SO NH group was observed. In
2
2
(a)
all four conformers of 2-MBSA one of the bonds (S=O or
S–N) of the sulfonamide group eclipses the C–C bond of
the benzene ring, in contrast to the conformers of 2-NBSA
where one of the bonds (S=O or S–N) strive to occupy an
orthogonal position relative to the benzene ring plane (see
Table 3). In 2-MBSA, the eclipsed around the bonds (S=O
and S–N) conformers II and III appeared to be more stable
than the staggered conformers I and IV, because the H
V0(inv) = 1.4
Conformer II
Conformer I
Fig. 7 Barriers of transitions from the ‘staggered’ conformer I to the
‘eclipsed’’ conformer II of 2-NO -C SO NH : a pyramidal inver-
sion; b rotation of the NH group around the N–S bond
‘
2
6
H
4
2
2
atoms in the NH group are either most distanced away
2
2
from the nearest H atoms of the CH group, or from the H
3
atom of the benzene fragment. Effect of a substituent on
the method of calculation—the difference was up to
˚
.04 A. The MP2/cc-pVTZ combination reproduces the
geometry of the SO NH group is reflected in Table 6.
2 2
0
Valence angles S–C–C(X) and C–C–X exceed 120° which
is due to steric interaction of the substituents and is more
expressed in 2-NBSA. The average bond distance C–C in
experimental bond lengths best of all.
Influence of nature of a substituent on conformational
properties of ortho-substituted benzenesulfonamide
the benzene ring increases as the donor substituent CH is
3
introduced and decreases as the acceptor substituent NO is
2
introduced.
The non-substituted molecule of benzenesulfonamide,
BSA, has two conformers, both with orthogonal position of
the S–N bond with respect to the benzene ring plane but
differing by staggered and eclipsed orientations of the N–H
and S=O bonds in the SO NH fragment [7]. When a
0
Difference in the DG value for the most and the least
stable conformers is essentially lower in 2-MBSA than in
2-NBSA.
2
2
Change of the hydrogen bond type in 2-NBSA
at the transition ‘‘crystal-to-gas’’
substituent X (where X = CH , NO ) is introduced into
3
2
ortho-position, the number of conformers increases to four.
Along with the conformers of 2-NBSA studied in this
work, the conformers of 2-MBSA are also shown in Fig. 3;
geometries of the latter were determined in study [8]
by GED and quantum chemical methods. Conformers of
It was mentioned before that in conformers I and II of free
2-NBSA molecule an intramolecular hydrogen bond exists.
According to the X-ray results [9], a crystalline 2-NBSA is
a
Table 6 Experimental geometries (angstroms and degrees) of the most stable conformers of X–C
6
H
–SO NH
4 2
2
(X = NO
2 3
, CH )
Parameter
2-NBSA, conformer I
staggered) X = NO , this work
2-NBSA, conformer II
(eclipsed) X = NO , this work
2-MBSA, conformer II
(eclipsed) X = CH , [8]
3
(
2
2
(
C–C)average
1.390(4)
1.789(8)
1.424(4)
1.390(4)
1.778(8)
1.428(4)
1.432(4)
1.657(6)
1.398(4)
125.3(18)
121.6(21)
1.406(3)
1.770(7)
1.429(3)
1.430(3)
1.682(5)
1.398(4)
121.8(11)
123.7(23)
C–S
S=O
1
.430(4)
S–N
1.644(6)
1.398(4)
125.2(18)
121.7(21)
C(S)–C(X)
S–C–C(X)
C–C–X
a
Models of the conformers are shown in Fig. 3
123

3
82
Struct Chem (2011) 22:373–383
built from alternating layers of mirror isomers. The latter
are connected to each other by intermolecular hydrogen
Geometric parameters of the conformers were determined
experimentally and quantum chemical calculations were
performed for all possible conformers of this compound, as
well as transitions states between those.
bonds (Fig. 1). Each hydrogen atom of the NH group of
2
one molecule forms a hydrogen bond with one of the
oxygen atoms of the SO group of the adjacent molecule,
2
It was established that the nature of the ortho-substituent
in benzenesulfonamides governs not only the geometry but
also the conformational vapor composition.
and each oxygen atom of the SO group of a first molecule
2
forms a hydrogen bond with one of the hydrogen atoms of
the NH groups of the other adjacent molecule. As a result,
2
Trends in the geometric structure change of 2-NBSA at
the transition ‘‘crystal-to-gas’’ were considered.
each molecule in the crystal is connected to four sur-
rounding molecules. By means of the intermolecular
hydrogen bonds in the crystal a conformation becomes
stabile which may be to some extent considered ‘‘orthog-
onal’’ as for the position of the S–N bond relative to the
benzene ring plane and staggered as for mutual orientation
of the S=O and N–H bonds in the SO NH group. The
Acknowledgments We thank the Russian Foundation for Basic
Research, RFBR (Grant 09-03-00796a) for financial support of this
work.
2
2
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four conformers of free 2-NBSA molecule. Geometric
parameters of the molecule in crystal are compared with
those of the conformer I in Table 4. Most of the bond
lengths in the crystal and free molecule are close to each
other, except the bond S–N which is shorter in the crystal
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1
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6
1
1
1
1
2
2
2
4
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Conclusion
A combined gas-phase electron diffraction and mass
spectrometric study showed that 2-nitrobenzenesulfona-
mide sublimes in vacuo with no decomposition at least up
to the temperature of the GED/MS experiment carried out
in this work, 433(3) K. The saturated vapor consisted of
monomeric molecules and was a mixture of two con-
formers. Intramolecular hydrogen bond was found to exist
in these conformers which connect the H atom of the
SO NH group and the O atom of the NO2 group.
2
2
1
23

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