X-ray investigations of sulfur-containing fungicides. III. Intramolecular forces governing the conformation of a novel orthorhombic polymorph of benzoylmethyl phenyl sulfone, benzoylmethyl 4-chlorophenyl sulfone and benzoylphenylmethyl phenyl sulfone

Article abstract of DOI:10.1107/S0108768101016238

The crystal and molecular structures of three β-ketosulfones: benzoylmethyl phenyl sulfone (I), benzoylmethyl 4-chlorophenyl sulfone (II) and benzoylphenylmethyl phenyl sulfone (III) have been investigated using X-ray analysis and quantum mechanics ab initio calculations. Compound (I) crystallizes in the monoclinic and orthorhombic crystal systems. The crystal structure of the orthorhombic polymorph has not been reported previously. At room temperature and in the presence of daylight the pale yellow orthorhombic crystals undergo transformation to the stable colourless monoclinic polymorph. Hyperconjugative σ(S-C1) - π*(C2=O3) and σ*(S-C1) -π(C2=O3) stabilization energies in benzoylmethyl phenyl sulfones are highly dependent on the central dihedral angle α: S-C1-C2=O3 and arc largest for a gauche arrangement, as found in both crystal forms of (I). The electron density distribution in all compounds (I), (II) and (III) is significantly affected by interactions of oxygen lone pairs with non-bonding orbitals of the adjacent S-C1 and C1-C2 bonds. The latter effect is responsible for back-donation of the electron density from O atoms towards the central part of the molecule.

Full text of DOI:10.1107/S0108768101016238

research papers
Acta Crystallographica Section B
Structural
Science
X-ray investigations of sulfur-containing fungicides.
III. Intramolecular forces governing the conforma-
tion of a novel orthorhombic polymorph of
benzoylmethyl phenyl sulfone, benzoylmethyl 4-
chlorophenyl sulfone and benzoylphenylmethyl
phenyl sulfone
ISSN 0108-7681
Received 17 May 2001
W. M. Wolf
The crystal and molecular structures of three ꢀ-ketosulfones:
benzoylmethyl phenyl sulfone (I), benzoylmethyl 4-chloro-
phenyl sulfone (II) and benzoylphenylmethyl phenyl sulfone
Accepted 2 October 2001
Institute of General and Ecological Chemistry
.
(III) have been investigated using X-ray analysis and quantum
mechanics ab initio calculations. Compound (I) crystallizes in
the monoclinic and orthorhombic crystal systems. The crystal
structure of the orthorhombic polymorph has not been
reported previously. At room temperature and in the presence
of daylight the pale yellow orthorhombic crystals undergo
transformation to the stable colourless monoclinic polymorph.
Hyperconjugative ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) and ꢁ*(SÐC1) ꢁ
ꢂ(C2 O3) stabilization energies in benzoylmethyl phenyl
sulfones are highly dependent on the central dihedral angle ꢃ:
SÐC1ÐC2 O3 and are largest for a gauche arrangement, as
found in both crystal forms of (I). The electron density
distribution in all compounds (I), (II) and (III) is signi®cantly
affected by interactions of oxygen lone pairs with non-bonding
orbitals of the adjacent SÐC1 and C1ÐC2 bonds. The latter
effect is responsible for back-donation of the electron density
from O atoms towards the central part of the molecule.
Part II: see Wolf (2001).
Â
(I-17), Technical University of èod Zwirki 36,
Â
Â
90-924 èodz, Poland
Correspondence e-mail: wmwolf@p.lodz.pl
1. Introduction
Various derivatives of ꢃ-unsubstituted benzoylmethyl phenyl
sulfone have been studied quite intensively over the past years
(Grossert et al., 1988; Kokkou & Cheer, 1986; Krawiec et al.,
1989; Dal Colle et al., 1995; Distefano et al., 1996; Gaødecka &
Gaødecki, 1999). In these compounds two strongly electron-
withdrawing, phenylsulfonyl and benzoyl moieties are sepa-
rated by a methylene group. Photoelectron, NMR and IR
spectroscopy supported by X-ray crystallography and ab initio
quantum mechanics calculations showed that the conforma-
tion of ꢀ-ketosulfones and ꢀ-ketosulfoxides is strongly in¯u-
enced by two cross donor±acceptor interactions existing
between pairs of the sulfonyl or sul®nyl S O and ꢀ-carbonyl
C
O dipoles. These interactions back-donate electron
density from the highly negative O atoms towards the sulfur
and ꢀ-C atoms bearing large positive charge (Distefano et al.,
1991; Olivato et al., 1998, 2000). Dal Colle et al. (1995) argued
that these stereoelectronic interactions prompt the SÐCꢃ
bond to be positioned gauche with respect to the ꢀ-carbonyl
double bond. Indeed, most of the X-ray determined structures
of ꢃ,ꢃ-unsubstituted ꢀ-ketosulfones exist in a gauche confor-
mation (Allen & Kennard, 1993).
The ꢃ,ꢃ-unsubstituted derivatives of benzoylmethyl phenyl
sulfone are examples of molecular systems with the easily
# 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved
ꢀ
806 W. M. Wolf Sulfur-containing fungicides. III
Acta Cryst. (2001). B57, 806±814

research papers
dissociating methylene acidic CÐH bonds (Amel & Marek,
1973). The resulting carbanions are stabilized by the electron
density transfers to the neighbouring highly positive sulfur and
ꢀ-C atoms. The NMR chemical proton shifts of the ꢃ-methy-
lene H atoms are very sensitive to the electron density changes
of their parent C atoms and were used to study the trans-
mission of the substituent effect through the sulfonyl and ꢀ-
carbonyl groups (Borchardt, Kopkowski, Kornacki & Zak-
rzewski, 1990).
theory and the restricted Hartree±Fock methodologies.
Molecular stabilization energies resulting from hyperconju-
gative interactions were calculated using the Weinhold's and
co-workers natural bond orbitals approach (Reed et al., 1988).
2. Experimental
2.1. Preparation
All investigated compounds were synthesized by Dr A.
Zakrzewski at the Department of Technology and Chemical
Engineering, Technical and Agricultural Academy, Bydgoszcz,
Poland. (I), (II) and (III) were obtained by condensation of
the sodium benzenesul®nate with phenacyl bromide, p-
chlorophenacyl bromide and desyl chloride, respectively.
Reactions were carried out in tetrahydrofuran and in the
presence of tetra-n-butylammonium bromide (Borchardt,
Kopkowski, Wasilewski & Zakrzewski, 1990).
Biological tests have shown that the benzoylmethyl phenyl
sulfone and its derivatives effectively inhibit the growth of
Aphanomyces cochlioides and Rhisoctonia solani (Drabik et
al., 1990; Borchardt, Kopkowski, Wasilewski & Zakrzewski,
1990). In particular, fungicidal activity is increased after
exposing samples containing fungi colonies with added
fungicide to radiation of daylight characteristics (Zakrzewski
& Kacaøa, 1998; Zakrzewski, 1999). Wagner & Lindstrom
(1987) have shown that ꢀ-ketosulfones undergo relatively
slow excited radical cleavage to generate ꢃ-keto radicals and
sulfur-centred radicals. Products of this gradual photodynamic
degradation can steadily penetrate the cell walls of fungi
colonies and secure destruction of the mycelium over a longer
period of time. The present work is part of a project aimed at
identi®cation of molecular properties which are responsible
for the antimycotic activity of the selected ꢀ-ketosulfones
(Wolf, 1999a,b, 2000, 2001).
2.2. Crystallization and X-ray structure analysis
Good quality crystals were obtained by vapour diffusion.
Samples of the compounds were dissolved in a 2:1 mixture of
chloroform and 2-propanol and equilibrated against the pure
2-propanol for approximately 1 week. All crystallizations were
performed in darkness at room temperature. Under these
conditions benzoylmethyl phenyl sulfone (I) crystallizes in the
orthorhombic system (space group: P212121) giving pale
yellow crystals. This polymorph is named hereafter as (Io).
Interestingly, when the freshly obtained long pale yellow
prisms of (Io) were left at room temperature in the presence of
daylight for ꢂ2 weeks they underwent a polymorphic trans-
formation yielding the colourless stable crystals of the well
known monoclinic form, named hereafter as (Im). Both
polymorphs have been unequivocally identi®ed by X-ray
structure analysis using the same monocrystal before and after
the conversion. In order to stabilize the fragile orthorhombic
crystal, the X-ray data of (Io) were collected at 110 K. The
Oxford Cryosystem cooling device mounted on the Kuma
Diffraction KM-4 diffractometer was used. Signi®cant decay
(20%) of the diffracting power of (II) re¯ects its photo-
dynamic instability resulting in a completeness of the data set
of only 82%. No polymorphic transformation similar to that
one observed in (Io) was detected in the crystal.
In this paper the main intramolecular interactions which
stabilize the conformation of benzoylmethyl phenyl sulfone
(I) and two novel ꢀ-ketosulfones: benzoylmethyl 4-chloro-
phenyl sulfone (II) and benzoylphenylmethyl phenyl sulfone
(III) are described.
Details of crystal symmetry, data collections, structure
determinations and re®nements are summarized in Table 1.2
All non-H atoms were localized on E maps. The H atoms of all
structures were routinely located in difference Fourier maps
calculated after three cycles of an anisotropic re®nement.
Their positional and isotropic displacement parameters were
Their crystal structures have been determined by X-ray
analysis. The benzoylmethyl phenyl sulfone crystallizes in
either the monoclinic or the orthorhombic crystal system. X-
ray structure determinations of the stable, monoclinic poly-
morph (space group P21/c) have been reported twice so far
(Krawiec et al., 1989; Dal Colle et al., 1995). At room
temperature the pale yellow, fragile orthorhombic crystals
undergo transformation to the colourless monoclinic form.
Both polymorphs were characterized by single-crystal X-ray
analysis. To the best of my knowledge, this is the ®rst report on
a polymorphic transformation of ꢀ-ketosulfone. Electronic
properties of the investigated molecules were calculated at the
ab initio molecular orbital level using the density functional
ꢀ
allowed to re®ne freely. In (Io) three re¯ections: 1,1,31; 2,1,31;
ꢀ
ꢀ
2,1,32; and in (II) four re¯ections: 3,0,2; 4,3,3; 4,3,1; 3,2,2; all
identi®ed as outliers, were not used in the ®nal re®nement.
Correct chirality of the crystal of (Io) has been assigned by
2 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: OS0077). Services for accessing these data are described
at the back of the journal.
ꢀ
Acta Cryst. (2001). B57, 806±814
W. M. Wolf
Sulfur-containing fungicides. III 807

research papers
Table 1
Experimental details.
(Io)
(Im)
(II)
(III)
Crystal data
Chemical formula
Chemical formula weight
Cell setting, space group
Ê
a, b, c (A)
C14H12O3S
260.3
Orthorhombic, P212121
4.8177 (7), 9.4100 (12),
26.719 (3)
90
1211.3 (3)
4
1.427
Mo Kꢃ
50
C14H12O3S
260.3
Monoclinic, P21=c
9.2145 (9), 5.3594 (6), 25.665
(3)
98.448 (9)
1253.7 (2)
4
1.379
Mo Kꢃ
43
C14H11ClO3S
294.74
Orthorhombic, Pbca
13.469 (1), 7.4580 (1), 26.656
(2)
90
2677.6 (9)
8
C20H16O3S
336.39
Monoclinic, P21=c
9.1282 (8), 17.2532 (19),
10.8670 (11)
105.794 (7)
1646.8 (3)
4
1.357
Mo Kꢃ
48
ꢀ ꢃꢄ†
3
Ê
V (A )
Z
Dx (Mg mꢁ3
)
1.462
Cu Kꢃ
60
Radiation type
No. of re¯ections for cell
parameters
ꢄ range (ꢄ)
5±16
0.264
4.6±14.0
0.255
6±18
4.000
4.1±17.0
0.211
ꢅ (mmꢁ1
)
Temperature (K)
Crystal form, colour
Crystal size (mm)
110 (1)
Plate, pale yellow
0.6 Â 0.4 Â 0.2
290 (2)
Plate, colourless
0.6 Â 0.4 Â 0.2
290 (2)
Needle, colourless
0.50 Â 0.20 Â 0.15
290 (2)
Prism, colourless
0.5 Â 0.4 Â 0.3
Data collection
Diffractometer
Data collection method
Absorption correction
Tmin
Kuma Diffraction KM-4
!±2ꢄ scans
None
Siemens P3
!±2ꢄ scans
None
Kuma Diffraction KM-4
!±2ꢄ scans
Psi-scan
0.514
0.982
3067, 2274, 1761
Siemens P3
!±2ꢄ scans
None
ꢁ
ꢁ
ꢁ
Tmax
ꢁ
ꢁ
ꢁ
No. of measured, indepen-
dent and observed para-
meters
2859, 2633, 2498
4892, 3636, 2755
5033, 3780, 3072
Criterion for observed
re¯ections
Rint
ꢄmax (ꢄ)
I > 2ꢁ(I)
I > 2ꢁ(I)
I > 2ꢁ(I)
I > 2ꢁ(I)
0.0492
30.07
0.0457
30.00
0.0546
74.99
0.0165
27.50
Range of h, k, l
ꢁ1 ! h ! 6
ꢁ1 ! k ! 13
ꢁ1 ! l ! 37
3 every 100 re¯ections
ꢁ12 ! h ! 12
ꢁ1 ! k ! 7
ꢁ1 ! l ! 36
3 every 97 re¯ections
ꢁ1 ! h ! 16
ꢁ9 ! k ! 1
ꢁ1 ! l ! 33
3 every 100 re¯ections
ꢁ11 ! h ! 11
ꢁ22 ! k ! 1
ꢁ14 ! l ! 1
3 every 97 re¯ections
No. and frequency of stan-
dard re¯ections
Intensity decay (%)
2
2
20
2
Re®nement
Re®nement on
F2
F2
F2
F2
R‰F2>2ꢁꢃF2†Š, wRꢃF2†, S
No. of re¯ections and para-
meters used in re®ne-
ment
0.0319, 0.0962, 1.226
2633, 211
0.0408, 0.1199, 1.085
3636, 211
0.0636, 0.1976, 1.051
2274, 217
0.0363, 0.1013, 0.989
3780, 281
H-atom treatment
All H-atom parameters
re®ned
All H-atom parameters
re®ned
All H-atom parameters
re®ned
w = 1/[ꢁ2(F2o) + (0.1429P)2
+ 0.2720P], where P =
(F2o + 2F2c)/3
All H-atom parameters
re®ned
Weighting scheme
w = 1/[ꢁ2(Fo2) + (0.0468P)2
+ 0.5406P], where P =
w = 1/[ꢁ2(F2o) + (0.0684P)2
+ 0.0258P], where P =
w = 1/[ꢁ2(F2o) + (0.0577P)2
+ 0.3264P], where P =
(F2o + 2F2c)/3
(F2o + 2F2c)/3
(F2o + 2F2c)/3
ꢃÁ=ꢁ†
0.027
0.375, ꢁ0.332
0.004
0.313, ꢁ0.289
0.011
0.334, ꢁ0.336
0.001
0.224, ꢁ0.368
max
Ê ꢁ3
Áꢆmax, Áꢆmin (e A
Extinction method
Extinction coef®cient
)
None
±
None
±
SHELXL97
0.0031 (6)
None
±
Computer programs used: KM-4 (Kuma Diffraction, 1991), DATAPROC9.0 (Gaødecki et al., 1995), SHELXS97 (Sheldrick, 1997b), SHELXL97 (Sheldrick, 1997a), P3 (Siemens, 1989),
XDISK (Siemens, 1991).
re®nement of Flack's (1983) absolute structure parameter; its
®nal value was ꢁ0.01 (7).
analysis of molecular geometry and the preparation of draw-
ings.
Standard bond lengths quoted throughout the paper have
been taken from the International Tables for Crystallography
(Allen et al., 1992). The van der Waals radii are from Bondi
(1964).
2.3. Molecular orbital calculations
Final molecular electronic properties have been calculated
in a single point for X-ray determined coordinates. The
restricted Hartree±Fock (RHF) method and the triple zeta 6-
311++G(3df,2p) basis set as implemented in Gaussian98
The interactive molecular graphics programs SYBYL
(Tripos Associates Inc., 1996), InsightII (Molecular Simula-
tions Inc., 1997) and XP (Siemens, 1990) have been used for
ꢀ
808 W. M. Wolf Sulfur-containing fungicides. III
Acta Cryst. (2001). B57, 806±814

research papers
Table 2
Selected geometrical parameters (A, ).
(Frisch et al., 1998) has been applied. Atomic charges were
computed to ®t the electrostatic potential at points selected
accordingly to the high sampling CHELPG scheme
(Breneman & Wiberg, 1990). Mayer's (1986) bond orders
were calculated with the DMOL (Molecular Simulations Inc.,
1996) using the density functional theory formalism (Hohen-
berg & Kohn, 1964; Levy, 1979). The DNP double-zeta quality
basis set (equivalent to the 6-31G**) and the gradient-
corrected correlation functionals BLYP (Lee et al., 1988) were
applied.
Natural bond orbital calculations were performed using
Version 3.1 of the NBO program (Glendening et al., 1992), as
implemented in Gaussian98 (Frisch et al., 1998). Due to the
restriction of the maximum number of orbitals which can be
evaluated by the NBO program, all natural bond analyses
were performed in the 6-31G(d,p) basis.
ꢄ
Ê
(Io)
(Im)
(II)
(III)
Ê
Bond lengths (A)
S
S
O1
O2
1.437 (1)
1.443 (1)
1.789 (2)
1.757 (2)
1.519 (3)
±
1.209 (3)
1.491 (3)
±
1.433 (1)
1.434 (1)
1.785 (2)
1.762 (2)
1.523 (2)
±
1.209 (2)
1.481 (4)
±
1.425 (2)
1.443 (3)
1.773 (4)
1.767 (3)
1.517 (5)
±
1.219 (5)
1.484 (5)
1.730 (4)
1.439 (1)
1.438 (1)
1.820 (1)
1.768 (1)
1.539 (2)
1.516 (2)
1.213 (2)
1.486 (2)
±
SÐC1
SÐC9
C1ÐC2
C1ÐC15
C2 O3
C2ÐC3
C12ÐCl
Ê
Intramolecular non-bonding distances (A), accompanied by corresponding
Ê
sums of the van der Waal's radii (A) given in square brackets
SÁ Á ÁO3 [3.32]
O1Á Á ÁC2 [3.22]
O2Á Á ÁC2 [3.22]
3.188 (2)
3.340 (3)
2.836 (3)
3.428 (1)
3.913 (2)
3.309 (2)
2.926 (3)
3.254 (4)
3.186 (5)
2.894 (1)
3.116 (2)
3.272 (2)
Valency and torsion angles (ꢄ)
SÐC1ÐC2
107.5 (1)
ꢁ76.0 (2)
114.6 (1)
89.8 (2)
ꢁ158.7 (1)
±
72.3 (1)
±
113.9 (3)
ꢁ4.1 (5)
70.4 (3)
±
110.0 (1)
18.7 (2)
60.4 (1)
ꢁ175.1 (1)
ꢁ71.0 (1)
53.4 (1)
ꢃ: SÐC1ÐC2ÐO3
ꢀ: O1ÐSÐC1ÐC2
ꢀ0: O1ÐSÐC1ÐC15
ꢇ: O2ÐSÐC1ÐC2
ꢇ0: O2ÐSÐC1ÐC15
3. Results and discussion
88.9 (1)
±
A view of the compounds investigated with the atom-
numbering scheme is shown in Fig. 1. Relevant geometrical
parameters are given in Table 2. Electrostatic-potential-
derived atomic charges and selected molecular electronic
properties are summarized in Table 3. Mayer's bond orders
are in Table 4.
ꢁ39.3 (2)
ꢁ60.8 (3)
±
±
Table 3
Selected CHELPG (Breneman & Wiberg, 1990) electrostatic atomic
charges (e), overall Hartree±Fock molecular energy E(HF) (H), dipole
moments Dm (D), HOMO and LUMO energies (eV); all properties were
calculated at the HF/6-311++G(2df,2p) level.
3.1. Molecular structure of (Io) and (Im)
In the crystal both polymorphs (Io) and (Im) adopt a
different conformation, see Fig. 2 for comparison. The ꢃ: SÐ
C1ÐC2ÐO3 dihedral angles in (Io) and (Im) [ꢁ76.0 (2) and
89.8 (2)ꢄ, respectively] indicate that the ꢀ-carbonyl groups are
approximately gauche with respect to the SÐC1 bonds. The
(Io)
(Im)
(II)
(III)
S
O1
O2
O3
C1
H1
1.128
1.066
1.158
1.124
ꢁ0.600
ꢁ0.599
ꢁ0.529
ꢁ0.161
0.029
ꢁ0.595
ꢁ0.599
ꢁ0.575
ꢁ0.097
0.061
ꢁ0.592
ꢁ0.603
ꢁ0.509
ꢁ0.266
0.049
ꢁ0.600
ꢁ0.598
ꢁ0.483
ꢁ0.191
0.051
S
O1 and S O2 bonds, when referring to the central C1Ð
C2 bonds, are either gauche, gauche [as in (Io)] or anti, gauche
[as in (Im)].
H2
C2
C3
C9
C15
Cl
E(HF)
Dm
0.076
0.561
ꢁ0.066
ꢁ0.164
±
0.065
0.570
ꢁ0.146
ꢁ0.157
±
0.061
0.652
ꢁ0.184
ꢁ0.117
±
ꢁ0.130
ꢁ1618.24110
7.68
±
0.566
ꢁ0.079
ꢁ0.159
0.158
The electrostatic-potential-derived atomic charge distribu-
tion is quite similar in both polymorphs. All O atoms bear
substantial negative atomic charges, while the S and C2 atoms
are positively charged. This charge arrangement favours
electrostatic interactions between the oppositely charged
atoms of the S O and C O bonds. Indeed, the conformation
of the unstable orthorhombic (Io) polymorph is controlled by
two cross, intramolecular SÁ Á ÁO3 and C2Á Á ÁO2 contacts which
±
±
±
ꢁ1159.31555
ꢁ1159.32013
ꢁ1388.81764
8.27
ꢁ10.052
0.691
4.15
ꢁ9.814
1.431
8.45
ꢁ9.592
0.727
HOMO
LUMO
ꢁ9.777
0.672
Ê
Table 4
Mayers's bond orders of selected bonds as calculated at the BLYP/DNP
level.
are signi®cantly shorter [3.188 (2) and 2.836 (3) A, respec-
tively] than the respective sums of the van der Waals radii
Ê
(3.32 and 3.22 A). During the daylight-induced polymorphic
transformation from (Io) to the more stable (Im), these
distances have undergone signi®cant elongation [to 3.428 (1)
Ê
and 3.309 (2) A, respectively] and are extended out of the van
der Waals limits. The SÐC1ÐC2 valency angle de®ned
around the pivotal C1 atom is more restricted in (Io)
(Io)
(Im)
(II)
(III)
S
S
O1
O2
1.89
1.88
1.17
1.14
1.03
0.61
0.59
±
1.88
1.90
1.26
1.15
1.11
0.50
0.61
±
1.92
1.90
1.16
1.12
1.06
0.60
0.61
±
1.89
1.88
1.12
1.13
1.02
0.38
±
1.08
1.91
1.01
±
SÐC1
SÐC9
C1ÐC2
C1ÐH1
C1ÐH2
C1ÐC15
C2 O3
C2ÐC3
C12ÐCl
Ê
Ê
[107.5 (1) A] than in (Im) [114.6 (1) A] and indicates the more
relaxed conformation of the latter polymorph. Negative
charges are located on the C1 atoms (ꢁ0.161 and ꢁ0.097 e,
respectively), while the methylene H1 and H2 atoms are
positively charged. The C1ÐH1 and C1ÐH2 Mayer's bond
1.89
1.01
±
1.86
1.02
±
1.90
1.02
1.17
ꢀ
Acta Cryst. (2001). B57, 806±814
W. M. Wolf
Sulfur-containing fungicides. III 809

research papers
orders [0.61, 0.59 and 0.50, 0.61 for (Io) and (Im), respectively]
are much smaller than unity, indicating weak bonds which are
prone to electrolytic dissociation. This conclusion is in good
agreement with the earlier experimental observations which
had shown that in the ethanol solution benzoylmethyl phenyl
sulfones exhibit acid properties. Amel & Marek (1973) had
suggested that in the resulting carboanion (IV)
distances slightly shorter than the respective van der Waals
limits involve methylene H1 and H2 and O atoms (details are
summarized in Table 5). According to a liberal de®nition of
Desiraju & Steiner (1999) these contacts can be classi®ed as
very weak hydrogen bonds. The observed polymorphic
transformation introduces signi®cant changes to the overall
crystal symmetry (from P212121 to P21/c). If no bonds had
been broken during the transformation it would have required
large translations and rotations of entire molecules in the
crystal. Detailed analysis of the crystal packing shows that in
the crystal there is no ample space for such complex move-
ments. Furthermore, long and complicated motions are unli-
kely because they would have generated high tensions which
could eventually destroy the crystal. Therefore, the
mechanism of the observed transformation is presumably
based on the initial photochemical cleavage of the SÐC1
bonds. The resulting free radicals migrate in the crystal and
further recombine to give the stable polymorph (Im). The free
radical SÐC1 bond splitting has often been observed during
the photodegradation of benzoylmethyl phenyl sulfones
(Wagner & Lindstrom, 1987). The photochemical origin of the
above described polymorphic transformation is additionally
supported by the fact that this reaction does not proceed
without the presence of daylight.
the negative charge formally located on a methylene C1 atom
is redistributed to the sulfonyl and carbonyl O atoms in a
fashion illustrated by the resonance structures similar to (V)
and (VI).
3.2. Molecular structure of (II) and (III)
In the crystal both compounds (II) and (III) adopt an
extended conformation, see Fig. 4 for a comparison. The
central SÐC1 bonds are positioned syn when related to the ꢀ-
The dipole moment of the (Im) molecule is much lower than
that of (Io) (4.15 and 8.27 D, respectively). As already
mentioned above, in (Io) the C1 negative charge is larger than
in (Im). The SÐC1 and C1ÐC2
Mayer's bond orders in (Im) (1.26 and
1.11, respectively) are larger than in
(Io) (1.17 and 1.03, respectively). The
carbonyl C2 O3 bond order in (Im)
(1.86) is slightly smaller than that in
(Io) (1.89). No similar simple relation
is observed for the sulfonyl S
O
bonds. The latter bonds exhibit
pronounced dipolar character (Oae,
1985) and therefore their Mayer's
bond orders are less prone to changes
resulting from the electron density
variations (Wolf, 2001). The above
simple comparison indicates that the
®rm (Im) polymorph is to a larger
extent than (Io) stabilized by the
electron density delocalizations as
described by structures (IV) and (V).
Comparison of the overall molecular
SCF energy, as calculated at the HF/6-
311++G(2df,2p) level shows that the
energy of (Im) is only 12.14 kJ molꢁ1
lower than that of (Io).
Crystal packing diagrams of both
polymorphs (Io) and (Im) are
presented in Fig. 3. Intermolecular
Figure 1
View of investigated compounds. Thermal ellipsoids were drawn at the 50% probability level.
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810 W. M. Wolf Sulfur-containing fungicides. III
Acta Cryst. (2001). B57, 806±814

research papers
Ê
stretched [1.820 (1) A] than the normally observed SÐC
Ê
single bond 1.78 A. It is also longer than the corresponding
bonds in (Io), (Im) and (II) [1.789 (2), 1.785 (2) and
Ê
1.773 (4) A, respectively]. Furthermore, comparison of the
non-bonding distances clearly shows that steric repulsions like
Ã
those described by Ruchardt & Beckhaus (1985) cannot be a
major reason for the SÐC1 bond elongation in (III). The SÐ
C1 and C1ÐC2 bond orders in (II) (1.16 and 1.06, respec-
tively) and (III) (1.12 and 1.02, respectively) are smaller than
their analogues observed in the stable polymorph (Im) (1.26
and 1.11, respectively). This simple analysis suggests that the
electron density delocalizations in (II) and especially in (III)
are less intensive than in (Im). Examination of the relevant
intramolecular distances summarized in Table 2 shows that
interactions between the oppositely charged S and O3 atoms
are stronger in (II) and (III) than in (Io). On the other hand,
the O2Á Á ÁC2 attraction is stronger in (Io).
Crystal packing diagrams of compounds (II) and (III) are
presented in Fig. 5. As in previously characterized crystals of
(Io) and (Im), very weak intermolecular hydrogen bonds link
H atoms at the pivotal C1 atoms with the sulfonyl group O
atoms.
Figure 2
Superposition of (Io) and (Im) polymorphs as indicated by empty and
solid lines, respectively. Both conformations were plotted using atom
coordinates determined by an X-ray crystallography. The least-squares ®t
was based on S, O1, O2, C1, C2, C9, C10, C11, C12, C13 and C14 atoms,
3.3. Hyperconjugative interactions
Ê
and the root mean-square deviation was 0.12 A.
In addition to the already characterized, intramolecular,
electrostatic attraction between the oppositely charged atoms
of the sulfonyl and carbonyl groups, conformation of ꢀ-keto-
sulfones is often in¯uenced by the mutual hyperconjugative
(Hoffmann, 1971) ꢁ*(SÐC1) ꢁ ꢂ(C2 O3) and ꢁ(SÐC1) ꢁ
ꢂ*(C2 O3) interactions. In particular, these effects were
identi®ed by Distefano et al. (1991, 1996) and Dal Colle et al.
(1995) to be responsible for the predominant gauche confor-
mation of the central SÐC1ÐC2 O3 fragment, as found in
several ꢀ-benzoylmethyl phenyl sulfones (Gaødecka &
Gaødecki, 1999; Grossert et al., 1988; Kokkou & Cheer, 1986;
Krawiec et al., 1989). In the present work, calculations of the
hyperconjugative stabilization energies in (Io), (Im), (II) and
(III) were performed using Weinhold's et al. natural bond
carbonyl group, while the sulfonyl S O1 and S O2 bonds
are both gauche with respect to the C1ÐC2 bonds.
The atomic charge arrangement is similar to that observed
in the previously discussed polymorphs (Io) and (Im). The SÐ
C1 bond in the X-ray determined structure of (III) is more
Figure 3
Figure 4
Superposition of (II) and (III) molecules as determined by an X-ray
analysis. The least-squares ®t was based on S, O1, O2, O3, C1, C2, C3 and
Perspective drawings of the (Io) and (Im) crystal structures viewed
parallel to the a and b axes, respectively. Very weak hydrogen bonds are
indicated with dashed lines.
Ê
C9 atoms, the root mean-square deviation was 0.17 A.
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Acta Cryst. (2001). B57, 806±814
W. M. Wolf
Sulfur-containing fungicides. III 811

research papers
Table 5
Hydrogen-bonding geometry (A, ) for (Io), (Im), (II) and (III).
to (Im), in (Io) more electron density is transferred from SÐ
C1 towards the C2 O3 bond. Consequently, in (Io) the
former bond becomes weaker and the latter becomes stronger.
Very small ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) and ꢁ*(SÐC1) ꢁ
ꢂ(C2 O3) stabilization energies in (II) and (III) follow from
the synperiplanar arrangement of the SÐC1 and C2 O3
bonds. The intensities of these interactions in benzoylmethyl
phenyl sulfones are highly dependent on ꢃ, i.e. the central SÐ
C1ÐC2ÐO3 dihedral angle. This relationship is clearly visible
in Fig. 6. The ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) and ꢁ*(SÐC1) ꢁ
ꢂ(C2 O3) stabilization energies, calculated for the
systematic ꢃ scans and (Im) as a starting conformer, reached
the highest values at two ꢃ torsion angles ꢁ105 and 105ꢄ,
respectively. For the synperiplanar rotamer hyperconjugative
stabilization energies are close to zero. These results are
consistent with the general observation that the anomeric
effect is the most effective when interacting polar bonds are
positioned gauche with respect to each other (Graczyk &
Mikoøajczyk, 1994; Juaristi & Cuevas, 1995, and references
therein). The so-called syn-anomeric effect (Irwin et al., 1990)
plays only a marginal role in the investigated compounds (II)
and (III).
Electron density distribution in (Io), (Im), (II) and (III) is
signi®cantly affected by interactions of the oxygen lone pairs
with non-bonding orbitals of the adjacent SÐC1 and C1ÐC2
bonds. The resulting stabilization energies are summarized in
Table 6. Contradictory to the previously analysed ꢁ*(SÐC1)
ꢁ ꢂ(C2 O3) and ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) hyperconjuga-
tion, the intensity of these interactions is similar in all inves-
tigated compounds and does not signi®cantly depend on the ꢃ
dihedral angle. See Fig. 7 for a comparison. This effect is to a
ꢄ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
< (DÐHÁ Á ÁA)
(Io)
C1ÐH1Á Á ÁO2i
0.99 (2)
1.02 (3)
2.44 (2)
2.38 (3)
3.413 (2)
3.347 (3)
170 (2)
158 (2)
C1ÐH2Á Á ÁO1ii
(Im)
C1ÐH2Á Á ÁO2iii
0.91 (2)
2.38 (2)
3.282 (2)
170 (2)
(II)
C1ÐH1Á Á ÁO2iv
0.99 (3)
1.00 (5)
2.27 (3)
2.32 (5)
3.247 (5)
3.280 (5)
169 (2)
161 (4)
C1ÐH2Á Á ÁO1v
(III)
C1ÐH1Á Á ÁO2vi
0.95 (2)
2.45 (2)
3.398 (2)
170 (2)
Symmetry codes: (i) 1 ‡ x; y; z; (ii) 12 ‡ x; 23 ꢁ y; ꢁz; (iii) x; 1 ‡ y; z; (iv) 32 ꢁ x; ꢁ ‡ y; z;
1
2
1
(v) 2 ꢁ x; ꢁ ‡ y; 12 ꢁ z; (vi) x; 21 ꢁ y; 12 ‡ z.
2
orbital (NBO) analysis of the Hartree±Fock wavefunctions
(Reed et al., 1988). The NBO deletion procedure (Glendening
et al., 1992; Reed & Schleyer, 1987; Salzner & Schleyer, 1993)
was applied. Results of these calculations are summarized in
Table 6.
The ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) stabilization in (Io) is slightly
larger than that in (Im), while the reverse back-donation
ꢁ*(SÐC1) ꢁ ꢂ(C2 O3) is weaker. It means that as compared
Figure 6
The ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) and ꢁ*(SÐC1) ꢁ ꢂ(C2 O3) NBO
stabilization energies (kJ molꢁ1) plotted as a function of ꢃ: SÐC1Ð
C2 O3 dihedral angle (ꢄ). Energies were calculated for the systematic ꢃ
scans (Áꢃ = Æ15ꢄ) and the X-ray structure of (Im) as a starting
conformer. Due to severe steric clashes of the terminal phenyl rings, only
ꢁ150 ꢅ ꢃ ꢅ 150 values were allowed.
Figure 5
Perspective drawings of the (II) and (III) crystal structures viewed
parallel to the b and a axes, respectively. Hydrogen bonds are indicated
with dashed lines.
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812 W. M. Wolf Sulfur-containing fungicides. III
Acta Cryst. (2001). B57, 806±814

research papers
Table 6
(II) and (III) the natural population
analysis (NPA) calculated within the
NBO framework showed that d orbi-
tals participate in hybrids describing
the electronic con®gurations of S
atoms for all bonds of the sulfur
coordination sphere in less than 3%.
Their contribution to the overall
stabilization energy was close to zero.
The NBO stabilization energies in (kJ molꢁ1) of the selected pairs of the bonding and non-bonding
natural orbitals, as calculated with the natural bond orbital deletion procedure (Glendening et al.,
1992).
Non-bonding orbitals are indicated by stars. The symbol n(O1,O2) represents the natural orbitals de®ning
lone pairs of the sulfonyl group O1 and O2 atoms; n(O3) represents the related orbitals of the carbonyl group
O3 atom.
ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) ꢁ*(SÐC1) ꢁ ꢂ(C2 O3) n(O1,O2) ꢁ ꢁ*(SÐC1) n(O3) ꢁ ꢁ*(SÐC1)
(Io) 21.256
(Im) 18.669
(II) 1.402
(III) 2.031
6.624
10.053
0.201
0.251
170.650
165.739
174.677
175.171
96.083
93.562
97.477
97.636
Therefore, the
S atom electron
density back-donation is mostly
realised through the n(O1,O2) ꢁ
ꢁ*(SÐC1) and n(O3) ꢁ ꢁ*(SÐC1)
interactions and proceeds without
large extent responsible for back-donation of the electron
density from the O atoms towards the central part of a
molecule. It partially counteracts the strongly electron-with-
drawing character of the benzoylmethyl and especially
phenylsulfonyl moieties, as con®rmed by highly positive values
of their Hammett's ꢁp constants 0.43 and 0.70, respectively
(Hansch & Leo, 1979).
signi®cant involvement of the non-bonding sulfur d orbitals.
4. Conclusions
In all the compounds investigated, (Io), (Im), (II) and (III),
the electron density distribution favours electrostatic attrac-
tion between the oppositely charged atoms of the S O and
The nature of the S atom electron density back-donation
has been a matter of controversy over a long period of time.
Traditional interpretation assumed overlapping of the sulfur
non-bonding d orbitals with ꢂ orbitals of the adjacent bonds
(Kwart & King, 1977, and references therein). In (Io), (Im),
C
O bonds. These interactions constrain the conformations
of (Io), (II) and (III) by contracting the SÁ Á ÁO3 and C2Á Á ÁO2
intramolecular distances below the respective van der Waals
limits. However, the restrained conformation of the fragile
orthorhombic polymorph (Io) is relieved during the light-
induced solid-state transformation which ®nally gives the
stable monoclinic crystals of (Im). Conformation of the latter
polymorph is to a larger extent than (Io) stabilized by the
electron density delocalizations.
Hyperconjugative ꢁ(SÐC1) ꢁ ꢂ*(C2 O3) and ꢁ*(SÐC1)
ꢁ ꢂ(C2 O3) stabilization energies in benzoylmethyl phenyl
sulfones are highly dependent on ꢃ: SÐC1ÐC2 O3 (central
dihedral angle) and are largest for the gauche arrangement, as
found in (Io) and (Im). For the synperiplanar conformation [as
in (II) and (III)] these energies are approaching zero. The
electron density distribution in all compounds (Io), (Im), (II)
and (III) is signi®cantly affected by interactions of the oxygen
lone pairs with non-bonding orbitals of the adjacent SÐC1
and C1ÐC2 bonds. This effect is responsible for back-dona-
tion of the electron density from the O atoms towards the
central part of a molecule and counteracts the strongly elec-
tron-withdrawing character of the benzoylmethyl and espe-
cially phenylsulfonyl moieties.
The author is indebted to Dr Andrzej Zakrzewski (Tech-
nical and Agricultural Academy, Bydgoszcz, Poland) for his
valuable comments and samples of (I)±(III). 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.
Figure 7
The n(O1,O2) ꢁ ꢁ*(SÐC1) and n(O3) ꢁ ꢁ*(SÐC1) NBO stabilization
energies (kJ molꢁ1) plotted as a function of ꢃ: SÐC1ÐC2 O3 dihedral
angle (ꢄ). Energies were calculated in the same way as described in the
legend to Fig. 6. The n(O1,O2) and n(O3) symbols are the same as
characterized in Table 6.
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