X-ray investigations of sulfur-containing fungicides. II. Intramolecular forces governing the conformation of four novel α-phenylazo- and α-phenylhydrazono-β-ketosulfones

Article abstract of DOI:10.1107/S0108768100013197

The crystal and molecular structures of four novel β-ketosulfones, phenyl benzoyl(phenylhydrazono)methyl sulfone (I), phenyl benzoyl(4-nitrophenylhydrazono)methyl sulfone (II), (benzoyl)(phenyl)(phenylazo)methyl phenyl sulfone (III) and (benzoyl)(phenyl)(3-chlorophenylazo)-methyl 4-tolyl sulfone (IV), have been investigated using X-ray analysis and density functional theory supplemented by ab initio Hartree-Fock calculations. The conformations of (I) and (II) are stabilized by strong intramolecular resonance-assisted hydrogen bonds formed between the sulfonyl and the α-hydrazono moieties. The following increase of a positive charge on the S atoms is compensated via π-conjugation and stereoelectronic back-donation from the nearby β-carbonyl group. Compounds (III) and (IV) adopt a strongly distorted propeller shape with pivotal tetrahedral Cl atoms. Distortion mostly follows from the approximate coplanarity of the α-azophenyl and α-phenyl moieties opposite each other. The main stereoelectronic interactions involve the donation of electron density from the α-azo N2 towards the sulfonyl S and the β-carbonyl C2 atoms.

Full text of DOI:10.1107/S0108768100013197

research papers
Acta Crystallographica Section B
Structural
Science
X-ray investigations of sulfur-containing fungicides.
II.1 Intramolecular forces governing the
conformation of four novel a-phenylazo- and
a-phenylhydrazono-b-ketosulfones
ISSN 0108-7681
Received 2 May 2000
W. M. Wolf
The crystal and molecular structures of four novel ꢀ-
Accepted 26 September 2000
ketosulfones,
phenyl
benzoyl(phenylhydrazono)methyl
sulfone (I), phenyl benzoyl(4-nitrophenylhydrazono)methyl
sulfone (II), (benzoyl)(phenyl)(phenylazo)methyl phenyl
sulfone (III) and (benzoyl)(phenyl)(3-chlorophenylazo)-
methyl 4-tolyl sulfone (IV), have been investigated using X-
ray analysis and density functional theory supplemented by ab
initio Hartree±Fock calculations. The conformations of (I) and
(II) are stabilized by strong intramolecular resonance-assisted
hydrogen bonds formed between the sulfonyl and the ꢁ-
hydrazono moieties. The following increase of a positive
charge on the S atoms is compensated via ꢂ-conjugation and
stereoelectronic back-donation from the nearby ꢀ-carbonyl
group. Compounds (III) and (IV) adopt a strongly distorted
propeller shape with pivotal tetrahedral C1 atoms. Distortion
mostly follows from the approximate coplanarity of the ꢁ-
azophenyl and ꢁ-phenyl moieties opposite each other. The
main stereoelectronic interactions involve the donation of
electron density from the ꢁ-azo N2 towards the sulfonyl S and
the ꢀ-carbonyl C2 atoms.
Institute of General and Ecological Chemistry
.
Â
Â
(I-17), Technical University of èodz, Zwirki 36,
Â
Â
90-924 èodz, Poland
Correspondence e-mail: wmwolf@p.lodz.pl
1. Introduction
The present work is part of a larger project aimed at identi-
fying the molecular properties which are responsible for the
antimycotic activity of the ꢁ-hydrazono- and ꢁ-azo-ꢀ-keto-
sulfones (Wolf, 1999a). A previous scheme of intramolecular
interactions governing molecular conformation was based
solely on the geometrical analysis of 12 X-ray determined
structures (Wolf, 1999b). Its major shortcoming was that no
molecular electronic parameters were taken into considera-
tion. Preliminary experiments have shown that the investi-
gated compounds inhibit the growth of Alternaria alternata,
Aspergillus niger and Rhisoctonia solani. In particular, activity
is signi®cantly increased after exposing fungi colonies with
added fungicide to radiation of daylight characteristics
(Zakrzewski & Kacaøa, 1998; Zakrzewski, 1999, and refer-
ences therein). The latter can be explained by the slow
photodynamic degradation which yields sulfur dioxide and
other products which help to destroy the fungal mycelium.
Negative charge, present on the fungal cell walls, hinders
cationic fungicides passing through and reduces their activity
(Hasall, 1982). Therefore, non-cationic fungicides (such as the
compounds investigated here or sulfur dioxide) should pene-
trate the cell walls of most fungi more easily.
The conformation of ꢀ-ketosulfones is very often controlled
by stereoelectronic effects (Kucsman & Kapovits, 1985;
# 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved
1 Part I: Wolf (1999a).
ꢀ
54 W. M. Wolf Sulfur-containing fungicides. II
Acta Cryst. (2001). B57, 54±62

research papers
2.2. X-ray crystallography
Grossert et al., 1987; Dal Colle et al., 1995; Distefano et al.,
1996, and references therein). These effects tend to reduce the
energy gap between the bonding and non-bonding orbitals of
the respective polar bonds and the lone pairs, and very often
contribute to the HOMO/LUMO barrier (Graczyk & Miko-
øajczyk, 1994; Juaristi & Cuevas, 1995; Cramer, 1996). The
latter is correlated with the excitation energy and therefore
may be regarded as a crude measure of the photodynamic
activity (Fleming, 1976).
In this paper the main intramolecular interactions which
stabilize the conformation of the four novel ꢁ-phenylhy-
drazono- and ꢁ-phenyl-ꢁ-phenylazo-ꢀ-ketosulfones (I)±(IV)
are described. Their crystal structures have been determined
by X-ray analysis. Electronic properties of the investigated
molecules were calculated at the ab initio molecular orbitals
level using density functional theory and restricted Hartree±
Fock methodologies. The uniform numbering scheme applied
to tables and used throughout the discussion is presented here.
This scheme differs slightly to that which has been employed
during the X-ray structure determinations. The latter is
presented in Fig. 1.
Crystals of (I), (III) and (IV) were obtained by vapour
diffusion. A sample of (I) dissolved in methanol was equili-
brated against pure isopropanol for 2 weeks. Compounds (III)
and (IV) were dissolved in a 3:1 mixture of chloroform and
isopropanol and equilibrated against pure isopropanol for 12
and 6 d, respectively. All the crystallizations described above
were performed at room temperature. Crystals of (II) were
grown in a hot box from the almost saturated methanol
solution over 2 d; the starting temperature was approximately
323 K.
Details of crystal symmetry, data collections, structure
determinations and re®nements are summarized in Table 1.2
All non-H atoms were located on E maps. The H atoms of all
the compounds were routinely located in difference Fourier
maps calculated after three cycles of an anisotropic re®ne-
ment. Their positional and isotropic displacement parameters
were allowed to re®ne freely. In (II) the diffraction data with
2ꢃ > 150ꢁ and one re¯ection ( 1,0,1) identi®ed as an outlier
were not used in the ®nal re®nement. All data were used for
the remaining three crystals.
Standard bond lengths quoted throughout the paper have
been taken from the International Tables for Crystallography
(Allen et al., 1992). Hammett's ꢄp constants were obtained
from Hansch & Leo (1979) and van der Waals' radii from
Bondi (1964).
The interactive molecular graphics programs SYBYL
(TRIPOS Associates Inc., 1996) and XP (Siemens, 1990) were
used for analysis of molecular geometry and the preparation
of drawings.
2.3. Molecular orbital calculations
The molecular structures of the investigated compounds
were optimized and Mayer's bond orders (Mayer, 1986) were
calculated using the DFT (density functional theory) form-
alism (Hohenberg & Kohn, 1964; Levy, 1979), as implemented
in DMOL (Molecular Simulations Inc., 1996). The DNP
double-zeta quality basis set (equivalent to the 6-31G**) and
the gradient-corrected correlation functionals BLYP (Lee et
al., 1988) have been applied. For comparison, (I) has also been
optimized using the 6-31+G(d) basis set, i.e. a split-valence 6-
31G basis set additionally augmented by a set of diffuse
functions and the B3LYP hybrid exchange-correlation func-
tional (Becke, 1993). The ®nal molecular electronic properties
were calculated in a single point using the restricted Hartree±
Fock (RHF) method and the triple zeta 6-311+G(d,p) basis
set. Atomic charges were calculated to ®t the electrostatic
potential at points selected accordingly to the Merz±Singh±
Kollman scheme (Besler et al., 1990; Singh & Kollman, 1984).
The B3LYP geometry optimization and the single point
calculations were performed with the GAUSSIAN98 suite of
programs (Frisch et al., 1998).
2. Experimental
2.1. Synthesis
The compounds were prepared by Dr A. Zakrzewski at the
Department of Technology and Chemical Engineering, Tech-
nical and Agricultural Academy, Bydgoszcz, Poland.
Compounds (I) and (II) were synthesized by a reaction of
benzoylmethyl phenyl sulfone with phenyldiazonium chloride
and p-nitrodiazonium chloride, respectively. Compound (III)
was synthesized using benzoylphenylmethyl phenyl sulfone
and phenyldiazonium chloride, while (IV) was made using
benzoylphenylmethyl p-tolyl sulfone and m-chloro-
phenyldiazonium chloride. All the above reactions were
carried out in alkaline ethyl alcohol solutions (Zakrzewski,
1996).
2 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: OS0056). Services for accessing these data are described
at the back of the journal.
ꢀ
Acta Cryst. (2001). B57, 54±62
W. M. Wolf Sulfur-containing fungicides. II 55

research papers
ꢀ-diketone enols (Bertolasi et al., 1991) and ꢀ-diketoarylhy-
drazones (Bertolasi, Gilli et al., 1994). In the latter compounds
the strength of the intramolecular RAHB is mainly related to
the degree of ꢂ-delocalization existing in the C NÐN frag-
ment of a molecule and modulated by the inductive and non-
bonding interactions. In particular, Bertolasi et al. (1993) have
found that in compounds similar to (VI) the electron-with-
drawing substituents X borne by the phenyl ring bonded to the
hydrazone N atoms tend to reduce the strength of the RAHB,
while the electron-donating substituents act in the opposite
direction.
3. Results and discussion
A view of the compounds investigated with the atom-
numbering scheme used in the X-ray structure determinations
is shown in Fig. 1. Selected geometrical parameters accom-
panied by results of the DFT geometry optimizations are given
in Tables 2 and 3. Electrostatic atomic charges and selected
molecular electronic properties are shown in Table 4.
3.1. Molecular structure of (I) and (II)
In the crystal structures the S O2 sulfonyl double bonds,
carbonyl groups and phenylhydrazone fragments are
approximately coplanar. The molecular conformations of
these fragments are similar to those observed in 40-
{[benzoyl(4-tolylhydrazono)methyl]sulfonyl}acetanilide (V)
(Wolf, 1999b). Similar conformations have been observed in ꢀ-
ketoarylhydrazones (Bertolasi, Nanni et al., 1994) and were
de®ned as EZE. This three-letter symbol was initially used to
Â
describe the conformation of 2,2-diacylethenamines (Gomez-
Sanchez et al., 1987). In (I), (II) and (V), these three letters
Â
The almost ideal planarity of the six-membered RAHB
rings suggests a high level of ꢂ-delocalization. However, the
X-ray determined SÐC1 bond lengths [1.784 (1) and
indicate the positions of the carbonyl C2 O3, the sulfonyl
S
O2 double bonds as well as the N2ÐC15 bonds bearing
the aryl substituent relative to the C1 N1 bond. Planar
central fragments of the molecules are stabilized by the strong,
cyclic intramolecular hydrogen bonds assisted by resonance
connecting the hydrazone and sulfone moieties, see Table 5 for
details.
The semi-empirical model of resonance-assisted hydrogen
bonding (RAHB) has been formulated by Gilli et al. (1989).
Strong intramolecular RAHBs have been identi®ed in
Ê
1.798 (2) A in (I) and (II), respectively] are larger than values
2
reported both for the Csp ÐS single bonds (1.751 A) and for
Ê
3
the Csp ÐSO2 bonds (1.779 A). The N1 C1 bonds [1.302 (2)
Ê
Ê
and 1.298 (3) A in (I) and (II), respectively] are close to those
Ê
reported for the SÐC NÐX system (1.302 A), but longer
than similar bonds found in the CÐC NÐC moiety
Ê
Ê
(1.279 A). The N1ÐN2 bond in (I) [1.303 (2) A] is slightly
shorter than the similar bond in
Ê
(II) [1.315 (3) A]. Both bonds
are longer than the typical
Ê
N N double bond (1.240 A),
much shorter than planar NÐN
Ê
single bonds (1.401 A) and
close to the partially double
aromatic
nitrogen±nitrogen
Ê
bonds, 1.304 A. The SÐC1
Mayer's bond orders (see Table
6 for the details) in (I) and (II)
are practically the same (1.11
and 1.10, respectively) and
indicate that the in¯uence of
the strongly electron-with-
drawing phenylsulfonyl group
(Hammett's constant, ꢄp = 0.70)
is based on inductive rather
than
conjugation
effects.
However, analysis of bond
orders in the C1 N1ÐN2
fragment shows, as suggested by
the bond length comparison
presented above,
a slightly
higher level of ꢂ-conjugation in
(I) than in (II). The N1 C1
bond orders are 1.59 and 1.62,
Figure 1
View of the compounds investgated, with atom labels which were used during the X-ray structure
determinations.
ꢀ
56 W. M. Wolf Sulfur-containing fungicides. II
Acta Cryst. (2001). B57, 54±62

research papers
Table 1
Experimental details.
(I)
(II)
(III)
(IV)
Crystal data
Chemical formula
Chemical formula weight
Cell setting, space group
Ê
a, b, c (A)
C20H16N2O3S
364.43
Triclinic, P1
5.6784 (7), 11.3204 (15),
14.1087 (19)
102.441 (11), 97.544 (10),
97.447 (11)
866.1 (2)
2
C20H15N3O5S
409.41
Monoclinic, P21=n
14.8351 (7), 6.0456 (5),
21.0161 (12)
C26H20N2O3S
440.5
Monoclinic, P21=c
13.285 (3), 16.577 (3),
11.421 (2)
C27H21ClN2O3S
488.97
Monoclinic, P21=c
14.155 (2), 9.542 (1),
18.822 (1)
ꢁ, ꢀ, ꢅ ꢂꢁ†
90, 98.613 (6), 90
90, 114.80 (3), 90
90, 109.820 (9), 90
3
Ê
V (A )
1863.6 (2)
4
1.459
Cu Kꢁ
82
2283.2 (8)
4
1.281
Mo Kꢁ
48
2391.6 (4)
4
1.358
Mo Kꢁ
26
Z
Dx (Mg m
3
)
Radiation type
1.397
Mo Kꢁ
48
No. of re¯ections for cell
parameters
ꢃ range (ꢁ)
4.7±17.3
0.210
290 (2)
Approximately sphere
shaped, pale yellow
0.25 Â 0.23 Â 0.21
±
9±15
1.892
292 (2)
Prism, pale yellow
5±13.5
0.172
291 (2)
Prism, yellow
4.7±12.0
0.279
291 (2)
1
ꢆ (mm
Temperature (K)
)
Crystal form, colour
Prism, yellow
Crystal size (mm)
Crystal radius (mm)
0.42 Â 0.21 Â 0.12
0.45 Â 0.40 Â 0.25
0.40 Â 0.30 Â 0.15
0.25
±
±
Data collection
Diffractometer
Data collection method
Absorption correction
Tmin
Tmax
No. of measured, indepen-
dent, observed re¯ections
Siemens P3
!±2ꢃ scans
None
Kuma Diffraction KM-4
!±2ꢃ scans
-scan
0.445
0.797
4566, 3710, 2943
Siemens P3
!±2ꢃ scans
None
Siemens P3
!±2ꢃ scans
None
5669, 4010, 3221
6194, 5156, 3703
6942, 5538, 3727
Criterion for observed re¯ec- I > 2ꢄ(I)
tions
I > 2ꢄ(I)
I > 2ꢄ(I)
I > 2ꢄ(I)
Rint
ꢃmax (ꢁ)
Range of h, k, l
0.0565
27.56
0.0204
74.91
18 ! h ! 18
1 ! k ! 7
0 ! l ! 26
3 every 100 re¯ections
0.0329
27.56
1 ! h ! 17
21 ! k ! 1
14 ! l ! 13
3, every 97 re¯ections
0.0284
27.56
1 ! h ! 18
1 ! k ! 12
24 ! l ! 23
3, every 97 re¯ections
2 ! h ! 7
14 ! k ! 14
18 ! l ! 18
No. and frequency of stan-
dard re¯ections
Intensity decay (%)
3 every 97 re¯ections
3
5
5
3
Re®nement
Re®nement on
F2
F2
F2
F2
R‰F2>2ꢄꢂF2†Š, wRꢂF2†, S
No. of re¯ections and para-
meters used in re®nement
H-atom treatment
0.0362, 0.0973, 1.030
4010, 300
0.0488, 0.1459, 0.932
3710, 323
0.0482, 0.1371, 1.028
5156, 366
0.0411, 0.1102, 0.968
5538, 392
All H-atom parameters
re®ned
All H-atom parameters
re®ned
All H-atom parameters
re®ned
All H-atom parameters
re®ned
Weighting scheme
w = 1/[ꢄ2(F2o) + (0.0457P)2 + w = 1/[ꢄ2(F2o) + (0.0759P)2 + w = 1/[ꢄ2(F2o) + (0.0790P)2 + w = 1/[ꢄ2(F2o) + (0.0623P)2],
0.2341P], where P = (Fo2
2F2c)/3
+
1.2875P], where P = (Fo2
2F2c)/3
+
0.2414P], where P = (Fo2
2F2c)/3
+
where P = (F2o + 2Fc2)/3
ꢂÁ=ꢄ†
0.003
0.389, 0.371
SHELXL (Sheldrick, 1997a)
0.007
0.331, 0.488
SHELXL (Sheldrick, 1997a)
0.010
0.543, 0.312
None
±
0.012
0.286, 0.272
SHELXL (Sheldrick, 1997a)
0.0026 (6)
max
3
Ê
Áꢇmax, Áꢇmin (e A
Extinction method
Extinction coef®cient
)
0.020 (2)
0.0019 (3)
² Computer programs used: P3 (Siemens, 1989), KM-4 (Kuma Diffraction, 1991), XDISK (Siemens, 1991), DATAPROC9.0 (Gaødecki et al., 1995), SHELXS97 (Sheldrick, 1997b).
while N1 N2 bond orders are 1.36 and 1.32 for (I) and (II),
respectively.
hand, the already large positive charge located on the sulfur
atom in (I) is even greater in (II) (1.115 and 1.253 e, respec-
tively). Similarly, the negative charge on the O2 atom involved
in the RAHB is slightly larger in (II) than in (I), 0.684 and
0.650 e, respectively. The hydrazone H2 atoms are stripped
of electron density in (II) more than in (I). The positive
charges are 0.335 and 0.265 e, respectively. Subsequently, H
atoms in (II) are more attracted by the sulfonyl O2 atoms and
form stronger intramolecular O2Á Á ÁH2ÐN2 hydrogen bonds.
The in¯uence of the electron-withdrawing p-nitrophenyl
group attached to the hydrazone moiety in (II), as compared
to the almost neutral phenyl group in (I) (Hammett's ꢄp
constants are 0.23 and 0.01, respectively), extends further
than the hydrazone region. The Merz±Singh±Kollman atomic
charge distribution within the N1 N2ÐC1 fragment is more
uniform in (II) than in (I), see Table 4 for details. On the other
ꢀ
Acta Cryst. (2001). B57, 54±62
W. M. Wolf Sulfur-containing fungicides. II 57

research papers
Table 2
Selected geometrical parameters of (I) and (II), as determined by X-ray analysis and accompanied by the
DFT geometry optimization results.
respect to the negative sulfonyl
O1 atoms, at distance
a
Ê
[3.220 (2) and 3.158 (3) A,
respectively], equal or smaller
to the sum of the respective van
(I)
(II)
X-ray
BLYP/DNP
B3LYP/
6-31+G(d)
X-ray
BLYP/DNP
Ê
der Waals radii, 3.22 A.
Ê
Selected bond lengths (A)
A similar pattern of non-
bonding interactions has been
reported by Distefano et al.
(1991, 1996) in a series of papers
concerned with the intramole-
cular interactions in mostly ꢁ,ꢁ-
S
S
O1
O2
1.431 (1)
1.468
1.493
1.852
1.819
1.311
1.316
1.418
1.487
1.241
1.508
1.457
1.476
1.821
1.782
1.301
1.306
1.409
1.484
1.227
1.499
1.435 (2)
1.466
1.491
1.884
1.824
1.309
1.327
1.405
1.494
1.243
1.509
1.444 (1)
1.784 (1)
1.765 (2)
1.302 (2)
1.303 (2)
1.402 (2)
1.476 (2)
1.220 (2)
1.491 (2)
1.446 (2)
1.798 (2)
1.759 (2)
1.298 (3)
1.315 (3)
1.397 (3)
1.492 (3)
1.220 (3)
1.492 (4)
SÐC1
SÐC9
N1 C1
N1ÐN2
N2ÐC15
C1ÐC2
C2 O3
C2ÐC3
unsubstituted
ꢀ-carbonyl
sulfones and sulfoxides (Dal
Colle et al., 1995). In these
compounds the highly polar
CꢁÐS bonds were located
gauche with respect to the
ꢀ-carbonyl groups permitting
the mutual hyperconjugative
Ê
Selected intramolecular non-bonding distances (A)²
SÁ Á ÁO3 [3.32]
O1Á Á ÁC2 [3.22]
SÁ Á ÁN2 [3.35]
O2Á Á ÁN1 [3.07]
O2Á Á ÁN2 [3.07]
2.976 (1)
3.220 (2)
3.107 (2)
2.969 (2)
2.668 (2)
2.957
3.261
3.158
2.937
2.642
2.957
3.250
3.101
2.917
2.596
2.818 (3)
3.158 (3)
3.102 (3)
2.959 (3)
2.642 (3)
2.847
3.309
3.122
2.963
2.596
(Hoffmann, 1971) ꢂC
Selected torsion angles (ꢁ)
ꢁ: SÐC1ÐC2ÐO3
ꢁ0: SÐC1ÐN1ÐN2
ꢀ: O1ÐSÐC1ÐC2
ꢀ0: O1ÐSÐC1ÐN1
ꢅ: O2ÐSÐC1ÐC2
ꢅ0: O2ÐSÐC1ÐN1
C1ÐC2ÐC3ÐC4
O
ꢄ*
and ꢂ*
ꢄCÐS
17.8 (2)
2.3 (2)
53.6 (1)
127.3 (1)
176.7 (1)
2.5 (1)
4.8
4.5
63.2
109.3
167.9
16.6
11.4
4.3
56.8
114.9
174.9
13.3
7.2 (3)
1.6 (3)
54.9 (2)
124.5 (2)
177.0 (2)
3.5 (2)
5.4
4.6
61.9
113.1
170.6
14.4
CÐS
C
O
interactions. Intensive electro-
static charge transfers from the
negatively charged ꢀ-carbonyl
and sulfonyl O atoms towards
the strongly positive sulfur and
ꢀ-carbonyl C atoms were also
detected by the UV photo-
electron spectroscopy supported
by the molecular quantum
135.2 (2)
139.5
148.4
161.9 (2)
169.7
Ê
² Accompanied by the corresponding sums of the van der Waal's radii (A), given in square brackets.
The latter is also supported by the slightly higher Mayer's
O2Á Á ÁH2 bond orders (0.21 and 0.19) and shorter O2Á Á ÁN2
distances, as determined by X-ray analysis. The latter are
mechanic calculations. Therefore, the shortening of the
SÁ Á ÁO(3) and O(1)Á Á ÁC(2) non-bonding distances with respect
to the sum of the van der Waals radii could be used as a rough
measure of stereoelectronic interactions.
Ê
2.642 (3) and 2.668 (2) A in (II) and (I), respectively. Using
the electrostatic potential derived atomic charges to estimate
the strength of the heteronuclear hydrogen bonds seems to be
justi®ed in view of the recent Gilli's et al. (1994) conclusion
that such bonds are mostly of electrostatic nature.
Aromatic rings directly bonded to the hydrazone moieties
are approximately coplanar with the RAHB cyclic systems.
The N2ÐC15 bond lengths in (I) and (II) are practically the
Ê
same [1.402 (2) and 1.397 (3) A, respectively] and smaller than
the typical CÐN bond length reported for the CarÐN
N
Ê
fragment (1.431 A). Mayer's bond orders are very similar (1.23
and 1.24, respectively). However, opposite to above para-
meters, both phenyl rings do not show signi®cant quinoid
character, as indicated by an examination of the respective
bond lengths and angles. Therefore, the in¯uence of the p-
nitrophenyl group in (II) as compared to the unsubstituted
phenyl ring in (I) is based on inductive, rather than ꢂ-delo-
calization effects.
In (I) and (II) the negatively charged carbonyl O3 atoms
are positioned closer to the highly positive S atoms [2.976 (1)
Ê
and 2.818 (3) A, respectively] than the sum of the sulfur and
Ê
oxygen van der Waals radii, 3.32 A. Carbonyl C2 atoms
bearing the substantial positive charge are situated, with
In (I) and (II) the intramolecular hydrogen bonds increase
the semi-polar character of the sulfur oxygen double bonds
and prompt the electron density to be partially transferred
ꢀ
58 W. M. Wolf Sulfur-containing fungicides. II
Acta Cryst. (2001). B57, 54±62

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Table 3
Selected geometrical parameters of (III) and (IV), as determined by X-ray analysis and accompanied by the
DFT geometry optimization results.
unsubstituted
ꢀ-carbonyl
sulfones and the stereoelec-
tronic charge transfer is mostly
of electrostatic origin. However,
in view of reports on the syn-
anomeric effect (Graczyk &
Mikoøajczyk, 1994; Juaristi &
Cuevas, 1995, and references
quoted therein), the former
contribution of hyperconjuga-
tive interactions cannot be
completely ruled out. Quite
recently Olivato et al. (1998,
(III)
(IV)
X-ray
BLYP/DNP
1.470
X-ray
BLYP/DNP
1.469
S
S
O1
O2
1.420 (2)
1.430 (1)
1.432 (2)
1.878 (2)
1.763 (2)
1.476 (2)
1.243 (2)
1.425 (2)
1.538 (2)
1.521 (2)
1.211 (2)
1.481 (2)
1.473
2.012
1.834
1.465
1.278
1.435
1.563
1.519
1.228
1.515
1.437 (1)
1.885 (2)
1.766 (2)
1.479 (2)
1.247 (2)
1.430 (2)
1.545 (2)
1.515 (2)
1.210 (2)
1.493 (2)
1.474
2.002
1.826
1.466
1.282
1.431
1.568
1.521
1.227
1.517
SÐC1
SÐC9
N1ÐC1
N1 N2
N2ÐC15 [C16 for (IV)]
C1ÐC2
C1ÐC21 [C22 for (IV)]
C2 O3
C2ÐC3
2000) presented
a
multi-
disciplinary study of ꢀ-carbonyl
sulfoxides, in which they have
shown that, similarly to the
investigated compounds (I) and
(II), the syn con®guration of SÐ
Cꢁ and C O bonds is stabilized
by Coulombic and intramole-
cular charge-transfer interac-
tions between the opposite
charged atoms of the C O and
Ê
Selected intramolecular non-bonding distances (A)²
SÁ Á ÁO3 [3.32]
O1Á Á ÁC2 [3.22]
SÁ Á ÁN2 [3.35]
O2Á Á ÁN1 [3.07]
O2Á Á ÁN2 [3.07]
N2Á Á ÁC2 [3.25]
2.910 (2)
3.042
3.337
3.264
2.891
3.638
2.706
2.945 (2)
3.290 (2)
3.234 (2)
2.802 (2)
3.522 (2)
2.623 (2)
3.031
3.306
3.312
2.935
3.739
2.617
3.271 (2)
3.150 (2)
2.773 (2)
3.408 (2)
2.701 (2)
Selected torsion angles (ꢁ)
ꢁ: SÐC1ÐC2ÐO3
10.6 (2)
82.9 (2)
68.1 (1)
168.7 (1)
52.9 (1)
164.7 (1)
41.6 (1)
74.2 (1)
2.9
87.5
61.4
176.8
59.8
169.9
48.1
69.0
8.6 (2)
89.3 (1)
69.2 (1)
168.6 (1)
51.9 (1)
163.2 (1)
41.1 (1)
75.6 (1)
4.9
91.7
62.4
177.3
57.4
168.9
48.6
71.3
ꢁ0: SÐC1ÐN1ÐN2
ꢀ: O1ÐSÐC1ÐC2
ꢀ0: O1ÐSÐC1ÐN1
ꢀ00: O1ÐSÐC1ÐC21 [C22 for (IV)]
ꢅ0: O2ÐSÐC1ÐC2
S
O dipoles.
The terminal benzoyl phenyl
ꢅ : O2ÐSÐC1ÐN1
ring in (I) is more twisted with
respect to the central planar
part of the molecule than in (II).
Both rings are very regular and
show no resemblence to quinoid
structure. Also the C2ÐC3
bond lengths in (I) and (II) are
virtually the same: 1.491 (2) and
ꢅ00: O2ÐSÐC1ÐC21 [C22 for (IV)]
Valency angles (ꢁ) de®ning coordination spheres of the pivotal C1 atoms
SÐC1ÐN1
SÐC1ÐC2
SÐC1ÐC21 [C22 for (IV)]
N1ÐC1ÐC2
N1ÐC1ÐC21 [C22 for (IV)]
C2ÐC1ÐC21 [C22 for (IV)]
104.6 (1)
111.4 (1)
104.4 (1)
113.6 (1)
110.2 (1)
111.9 (1)
101.6
110.7
99.9
114.3
113.8
114.6
105.2 (1)
111.7 (1)
104.0 (1)
112.3 (1)
110.9 (1)
112.1 (1)
102.5
110.6
101.5
112.6
115.7
112.7
Ê
² Accompanied by corresponding sums of the van der Waal's radii (A), given in square brackets.
Ê
1.492 (4) A, respectively. This
suggests that these phenyl rings
are not involved in electron-
density delocalizations and their
from the S towards the O2 atoms, as shown in (VIIb). The
following increase of the positive charge on sulfur can be
compensated via the ꢂ-conjugation as in (VIIc) and (VIId) or
by the stereoelectronic back-donation from the nearby ꢀ-
carbonyl group, as indicated by an arrow in (VIIb). Both
mechanisms take place in (I) and (II). However, in the latter
compound the electron-withdrawing p-nitrophenyl group
attached to the hydrazone moiety destabilizes canonical
structures with the positive charge located on the N atoms to a
larger extent than the almost neutral phenyl group in (I). This
effect intensi®es the stereoelectronic charge transfer from the
ꢀ-carbonyl towards the sulfonyl group and furthermore
strengthens the intramolecular RAHB in (II) compared with
(I). Similar anomeric back-donation of the electron density
triggered by the hydrogen-bond formation has recently been
identi®ed in aminals by Alder et al. (1999).
positions are ®xed by the weak non-bonding van der Waals
interactions.
3.2. Molecular structure of (III) and (IV)
Compounds (III) and (IV) adopt a strongly distorted
propeller shape with the pivotal tetrahedral C(1) atoms.
Distortion mostly follows from the approximate coplanarity of
the oppositely located ꢁ-azophenyl and ꢁ-phenyl moieties.
Examination of dihedral angles as speci®ed in Table 3
clearly shows that the X-ray determined as well as the DFT-
minimized conformations of (III) and (IV) generate a large
number of cis and gauche interactions involving the highly
polar sulfonyl, ꢁ-azo and ꢀ-carbonyl groups. All these groups
incorporate electronegative N and O atoms bearing non-
bonding lone pairs. The highly positive S atoms (see Table 4
for the atomic charges) are located closer to the neighbouring
carbonyl O3 and the azo N2 atoms bearing negative charge
than the sum of SÁ Á ÁO and SÁ Á ÁN van der Waals radii. Also, the
The SÐC1 bonds are positioned syn with respect to the
carbonyl C2 O3 group. This suggests that hyperconjugation
is substantially weaker than in gauche conformers of the ꢁ,ꢁ-
ꢀ
Acta Cryst. (2001). B57, 54±62
W. M. Wolf Sulfur-containing fungicides. II 59

research papers
Table 4
indicates that the steric strain induced deformations (such as
È
Selected Merz±Singh±Kollman electrostatic atomic charges (e), overall
Hartree±Fock molecular energy (H), dipole moments (D), HOMO and
LUMO energies (eV) calculated at the HF/6-311+G(d,p) level.
those described by Ruchardt & Beckhaus, 1985) cannot be a
major reason for the elongation of SÐC1 bonds. This suggests
that the real molecules are to a larger extent represented by
canonical structures with the broken SÐC1 bond, i.e. (VIIIb)
and (VIIId) than by (VIIIc), in which SÐC1 is a double bond.
(I)
(II)
(III)
(IV)
S
O1
O2
O3
N1
N2
H2
C1
C2
C3
C9
C15
C21
E(HF)
Dm
1.115
0.591
0.650
0.503
0.310
0.054
0.265
0.137
0.343
0.165
0.082
0.225
±
1.253
0.617
0.684
0.504
0.130
0.190
0.335
0.095
0.512
0.092
0.107
0.269
±
1.261
0.622
0.627
0.424
0.240
0.135
±
0.256
0.362
0.165
0.241
0.430
0.360
1.181
0.618
0.637
0.413
0.267
0.154
±
0.136
0.158
0.113
0.180
0.194
0.238
Ê
However, the C1ÐC2 bonds [1.538 (2) and 1.545 (2) A in the
X-ray structures of (III) and (IV), respectively] are longer
than the single carbon±carbon bonds, as found in aliphatic
Ê
ketones CÐC(O)ÐC (1.511 A), and suggests that the
contribution of structure (VIIIb) with the double C1ÐC2
bond is less signi®cant.
1497.58
6.79
1701.13
5.95
1726.95
6.76
2224.99
7.31
HOMO
LUMO
8.506
0.121
9.361
0.378
9.083
1.211
9.031
0.950
Table 5
The resonance-assisted intramolecular hydrogen-bond parameters in (I)
and (II), as determined by an X-ray analysis and accompanied by the
DFT geometry optimization results.
(I)
(II)
BLYP/ B3LYP/
DNP
BLYP/
DNP
X-ray
6-31+G(d) X-ray
Ê
Ê
N2ÐH2 (A)
0.84 (2)
1.98 (2)
1.06
1.788
1.03
1.76
136.0
2.596
0.06
0.89 (3)
1.92 (2)
136.9 (1.6) 141.1
1.06
1.685
O2Á Á ÁH2 (A)
O2Á Á ÁH2ÐN2 (ꢁ) 136.6 (1) 135.0
Ê
O2Á Á ÁN2 (A)
2.668 (2) 2.642
0.02
2.642 (2)
0.01
2.596
0.07
Ê
d² (A)
0.12
² RMS (root mean square) deviation from the least-squares optimized O2, S, C1, N1, N2,
H2 mean plane.
positively charged C2 atoms of the ꢀ-carbonyl groups form
short intramolecular contacts to the sulfonyl O1 and the azo
N2 atoms. Details on interatomic distances accompanied by
the corresponding van der Waals radii are summarized in
Table 3. This suggests that the pattern of stereoelectronic
interactions in (III) and (IV) is more complicated than in (I)
and (II). It can be conveniently characterized using the
concept of the `double bond ± no bond resonance' initially
introduced by Brockway (1937) and Roberts et al. (1950), and
further widely applied to the visualization of an anomeric
effect (Graczyk & Mikoøajczyk, 1994; Juaristi & Cuevas, 1995,
and references therein). In addition to the interactions already
described in (I) and (II), and involving the sulfonyl and the ꢀ-
carbonyl groups, represented by canonical structures (VIIIb)
and (VIIIc), the ꢁ-azo moieties can also participate in the
stereoelectronic charge transfer as indicated by (VIIId) and
(VIIIe).
This simple analysis leads to the conclusion that the main
stereoelectronic interactions are represented by structures
(VIIId) and (VIIIe) and involve the donation of electron
density from the azo N2 towards the S and C2 atoms. The
latter two structures may be additionally stabilized by conju-
gation of the ꢁ-phenyl ring directly bonded to the C1 atom
with the C1ÐN1 double bond. It explains the odd confor-
mation of (III) and (IV) in which the ꢁ-phenylazo fragments
are roughly coplanar with the oppositely located ꢁ-phenyl
rings. The coordination spheres around the C1 atoms are
deformed in such a manner that the SÐC1ÐN1 and SÐC1Ð
C21 bond angles are signi®cantly smaller than the remaining
four angles, Table 3. Considering steric interactions, the
phenylsulfonyl group is the largest of all the substituents
Important evidence of stereoelectronic interactions are
Ê
unusual SÐC1 bonds [1.878 (2) and 1.885 (2) A in the X-ray
structures of (III) and (IV), respectively], which are much
longer than the normally observed single carbon±sulfur bond,
Ê
1.78 A. Analysis of non-bonding intramolecular distances
ꢀ
60 W. M. Wolf Sulfur-containing fungicides. II
Acta Cryst. (2001). B57, 54±62

research papers
Table 6
Mayers's bond orders of selected bonds as calculated at the BLYP/DNP
level.
bonded to C1. Therefore, in contrast to the results of the X-ray
structure determination, all three bond angles involving the S
atoms should be larger or at least equal to the remaining three
angles. The existing deformation accounts for the signi®cant
contribution of resonance structure (VIIId) with the N1ÐC1
double and C1ÐC2 single bonds accompanied by the broken
C1ÐS bond. In this structure the bond angles N1ÐC1ÐC2,
N1ÐC1ÐC21 and C2ÐC1ÐC21 should adopt values close to
120ꢁ. The larger SÐC1ÐC2 angle observed may result from
the electrostatic repulsion between the negatively charged O
atoms of the sulfonyl and carbonyl groups. Indeed, in the X-
ray structures of (III) and (IV) the intramolecular non-
(I)
(II)
(III)
(IV)
SÐO1
SÐO2
SÐC1
SÐC9
C1ÐC2
C1ÐC21
C2ÐC3
C2ÐO3
N1ÐC1
N1ÐN2
N2ÐC15
N2ÐH2
O2Á Á ÁH2
1.87
1.77
1.11
1.14
1.05
±
1.01
1.87
1.59
1.36
1.23
0.72
0.19
1.86
1.75
1.10
1.15
1.02
±
1.05
1.81
1.62
1.32
1.24
0.69
0.21
1.89
1.88
0.97
1.14
0.92
0.96
1.05
1.87
1.04
1.87
1.12
±
1.89
1.87
0.96
1.14
0.92
0.96
1.04
1.88
1.05
1.87
1.12
±
Ê
bonding O1Á Á ÁO3 distances [3.015 (3) and 3.077 (2) A, in (III)
and (IV), respectively] are very close to the sum of the
Ê
corresponding van der Waals radii, 3.04 A. Therefore, the
±
±
contribution of (VIIIe) should be less signi®cant than that of
(VIIId) and donation of the electron density from N2 to the S
atoms seems to be the dominating stereoelectronic interaction
in (III) and (IV). On the other hand, Mayer's bond orders of
the C1ÐC2 bonds are the same in (III) and (IV) (equal to
0.92) and smaller than those of the SÐC1 bonds (0.97 and
0.96, respectively). This suggest that (VIIIe) cannot be
completely ruled out. Anomeric interactions represented by
the `double bond ± no bond resonance' structures (VIIIb)±
(VIIIe) increase the charge separation within the molecule.
They are accompanied by the Coulombic electrostatic
attraction of atoms bearing opposite charges. The latter,
indicated by arrows in (VIIIb)±(VIIIe), are mostly responsible
for the number of short intramolecular distances existing in
(III) and (IV).
lized by the Coulombic attraction coupled with the
intramolecular charge transfer between negatively charged
carbonyl O and positively charged sul®nyl S atoms. The DFT
optimized and the X-ray determined structures are similar, the
main difference being lengthening (in comparison with the X-
ray determined structures) of polar bonds as well as the
intramolecular non-bonding distances affected by stereoelec-
tronic effects in the DFT minimized molecules. This elonga-
tion reduces steric strain and therefore can lead to an
underestimation of the stereoelectronic interactions in the
DFT optimized species. The planarity of the six-membered
ring closed by the resonance-assisted hydrogen bonds formed
between the sulfonyl and ꢁ-hydrazono moieties in (I) and (II)
is better preserved in the X-ray determined structures than in
their DFT minimized analogues.
Contrary to the SÐC1 bonds, in all compounds (I)±(IV) the
SÐC9 bond lengths determined by X-ray analysis are very
Ê
similar: 1.765 (2), 1.759 (2), 1.763 (2) and 1.766 (2) A, respec-
tively. They all are very close to a value reported for the single
Ê
SÐC bond found in the CarÐSO2ÐC systems, 1.763 A. Also
Mayer's bond orders are practically the same: 1.14, 1.15, 1.14
and 1.14, respectively. This suggests that the terminal phenyl
moieties borne by the sulfonyl groups are not involved in
stereoelectronic interactions.
The author is indebted to Dr Andrzej Zakrzewski (Tech-
nical and Agricultural Academy, Bydgoszcz, Poland) for his
valuable comments and samples of (I)±(IV). Quantum
chemical calculations were performed in the ACK
Â
CYFRONET Krakow, Poland; support through computa-
tional grants 030/1999 and 050/1999 is gratefully acknowl-
edged.
4. Conclusions
Comparison of the crystallographic and quantum chemical
calculations suggests that the conformations of (I)±(IV) are
in¯uenced by stereoelectronic interactions. These effects
induce a number of short intramolecular contacts between the
sulfonyl, ꢁ-azo and ꢀ-carbonyl groups. The Merz±Singh±
Kollman electrostatic charge distribution, calculated at the
HF/6-311+G(d,p) level, clearly shows that the largest positive
charge is located on S atoms and indicates that sulfur is the
best acceptor of the stereoelectronic electron-density back-
donation from neighbouring negatively charged atoms. The
latter partially counteracts the strong electron-withdrawing
capacity of the sulfonyl group. Similar interactions have been
recently observed by Distefano et al. (1996) and Olivato et al.
(1998, 2000). They have found that in ꢁ-alkylsul®nylaceto-
phenones the cis1 conformation in the solid state was stabi-
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