Rac-3-Benzoyl-2-methyl-propionic acid and its organic salts: Possibilities of Yang photocyclization in crystals

Article abstract of DOI:10.1107/S0108270108021380

The analysis of the crystal structures of rac-3-benzoyl-2-methyl-propionic acid, C11H12O3, (I), morpholinium rac-3-benzoyl-2-methyl-propionate monohydrate, C4H10NO⁺·C11H11O3 ^-·H2O, (II), pyridinium [hydrogen bis-(rac-3-benzoyl-2-methyl-propionate)], C5H6N⁺· (H⁺·2C11H11O3 ^-), (III), and pyrrolidinium rac-3-benzoyl-2-methyl-propionate rac-3-benzoyl-2-methyl-propionic acid, C4H10N⁺·C11H11O3 ^-·C11H12O3, (IV), has enabled us to predict and understand the behaviour of these compounds in Yang photocyclization. Mol-ecules containing the Ar - CO - C - C - CH fragment can undergo Yang photocyclization in solvents but they can be photoinert in the crystalline state. In the case of the compounds studied here, the long distances between the O atom of the carbonyl group and the -H atom, and between the C atom of the carbonyl group and the -C atom preclude Yang photocyclization in the crystals. Mol-ecules of (I) are deprotonated in a different manner depending on the kind of organic base used. In the crystal structure of (III), strong centrosymmetric O...H...O hydrogen bonds are observed.

Full text of DOI:10.1107/S0108270108021380

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Trzop, 2003). Our present interests are associated with intra-
molecular photochemical processes (Turowska-Tyrk, BaÎko-
wicz, Scheffer & Xia, 2006; Turowska-Tyrk, Trzop, Scheffer &
Chen, 2006; Turowska-Tyrk, BaÎkowicz, Scheffer, 2007;
Turowska-Tyrk, èabeÎcka, Scheffer & Xia, 2007; Trzop &
Turowska-Tyrk, 2008), mainly Yang photocyclization.
ISSN 0108-2701
rac-3-Benzoyl-2-methylpropionic acid
and its organic salts: possibilities of
Yang photocyclization in crystals
A molecule containing a carbonyl group and a ꢀ-H atom
can create a 1,4-hydroxy biradical in a Norrish type II
photoreaction (see scheme above) (Braslavsky, 2007). In the
next step, named Yang photocyclization, a cyclobutane ring
can be formed from such a biradical (Braslavsky, 2007; Chen et
al., 2004; Yang et al., 2005). For instance, Ph±CO±CH2±CH2±
CH2±CH3, Ph±CO±CH2±CH2±CH(CH3)±CH2±CH3 and other
compounds of similar formulae undergo Yang photocycliza-
tion in solvents (Wagner, 1971). Compounds which are
photoactive in solvents can be photoinert in the crystalline
state. In this paper, we analyse the crystal structures of rac-3-
benzoyl-2-methylpropionic acid, (I), morpholinium rac-3-
benzoyl-2-methylpropionate monohydrate, (II), pyridinium
[hydrogen bis(rac-3-benzoyl-2-methylpropionate)], (III), and
pyrrolidinium rac-3-benzoyl-2-methylpropionate rac-3-ben-
zoyl-2-methylpropionic acid, (IV), in order to predict and
understand the behaviour of these compounds in Yang photo-
cyclization in crystals and to check the in¯uence of organic
cations on this reaction. As can be seen in the scheme below,
the compounds may be presented by the general formula
given in the ®rst scheme; potentially, they can form 1,4-
hydroxy biradicals and can undergo Yang photocyclization
(Braga et al., 2004; Chen et al., 2004; Wagner, 1971).
Julia BaÎkowicz and Ilona Turowska-Tyrk*
.
Faculty of Chemistry, Wrocøaw University of Technology, 27 Wybrzeze
Â
Wyspianskiego, 50-370 Wrocøaw, Poland
Correspondence e-mail: ilona.turowska-tyrk@pwr.wroc.pl
Received 30 May 2008
Accepted 9 July 2008
Online 19 July 2008
The analysis of the crystal structures of rac-3-benzoyl-2-
methylpropionic acid, C11H12O3, (I), morpholinium rac-3-
benzoyl-2-methylpropionate
monohydrate,
C4H10NO+Á-
C11H11O3 ÁH2O, (II), pyridinium [hydrogen bis(rac-3-
benzoyl-2-methylpropionate)],
C5H6N+Á(H+Á2C11H11O3 ),
(III), and pyrrolidinium rac-3-benzoyl-2-methylpropionate
rac-3-benzoyl-2-methylpropionic acid, C4H10N+ÁC11H11O3 Á-
C11H12O3, (IV), has enabled us to predict and understand the
behaviour of these compounds in Yang photocyclization.
Molecules containing the ArÐCOÐCÐCÐCH fragment can
undergo Yang photocyclization in solvents but they can be
photoinert in the crystalline state. In the case of the
compounds studied here, the long distances between the O
atom of the carbonyl group and the ꢀ-H atom, and between
the C atom of the carbonyl group and the ꢀ-C atom preclude
Yang photocyclization in the crystals. Molecules of (I) are
deprotonated in a different manner depending on the kind of
organic base used. In the crystal structure of (III), strong
centrosymmetric OÁ Á ÁHÁ Á ÁO hydrogen bonds are observed.
Comment
Many chemists are interested in photochemical reactions in
crystals. The reasons for this are of a practical and theoretical
nature (Boldyreva, 1999). Such reactions are often highly
selective and can serve as a source of pure products impossible
to obtain in solutions. They are environmentally friendly
because they are carried out without the use of solvents (green
chemistry) (Tanaka, 2003). They are also applied in modern
È
technologies (Balzani, 2003; Durr & Bouas-Laurent, 1990;
Irie, 2000).
Figs. 1±4 present views of the crystal lattice fragments and
strong hydrogen bonds for compounds (I)±(IV), respectively.
In the case of compound (I), molecules of the 3-benzoyl-2-
methylpropionic acid form centrosymmetric dimers. The step
between the planes of two carboxylic acid groups in the dimer
Photochemical reactions in crystals are also the subject of
our interest. Our studies concern the step-by-step monitoring
of structural changes during `reactant crystal ! product
crystal' phototransformations. In particular, we study varia-
tions in the reaction centre and the positions of molecules. In
the past, we have studied intermolecular photochemical
reactions (Turowska-Tyrk, 2001, 2003; Turowska-Tyrk &
Ê
is very small, viz. 0.12 and 0.03 A for symmetrically indepen-
dent molecules A and B, respectively. In the crystal structure
of compound (II), all molecules of the acid are deprotonated.
Anions, cations and water molecules are involved in strong
Acta Cryst. (2008). C64, o437±o440
DOI: 10.1107/S0108270108021380
# 2008 International Union of Crystallography o437

organic compounds
NÐHÁ Á ÁO and OÐHÁ Á ÁO hydrogen bonds, forming ribbons
along the b crystal axis. Cations are located inside these
ribbons. A very interesting situation takes place in the crystal
of compound (III), namely two symmetrically dependent
anions have contacts with the same H atom located on an
inversion centre and a cationic species lies on a twofold axis.
The distances between this H atom and two neighbouring O
compounds in a Norrish±Yang photoreaction in the crystalline
state is in¯uenced by several geometric parameters (Ihmels &
Scheffer, 1999; Natarajan et al., 2005). Fig. 6 presents a de®-
nition of these parameters, and Table 2 gives their ideal and
average literature values for compounds undergoing this
photoreaction (Natarajan et al., 2005; Xia et al., 2005), and
additionally the values for compounds (I)±(IV). These data
indicate that compounds (I)±(IV) will not undergo Yang
photocyclization in the crystalline state. The distance between
Ê
atoms are both 1.236 (2) A. This short OÁ Á ÁO distance and the
linear OÁ Á ÁHÁ Á ÁO geometry indicate the existence of a strong
hydrogen bond. Symmetric hydrogen bonds have also been
observed in the crystal structures of several other carboxylic
acids and pyridines (Bhogala et al., 2005; Wilson, 2001; Wilson
et al., 2003). OÁ Á ÁHÁ Á ÁO and NÐHÁ Á ÁO hydrogen bonds form
zigzags along the c crystal axis. In the crystal structure of
compound (IV), only half of the molecules of the acid are
dissociated (molecules A) but all molecules of the amine are
protonated. NÐHÁ Á ÁO and OÐHÁ Á ÁO hydrogen bonds form
ribbons along the c crystal axis. The geometry of the hydrogen
bonds in compounds (I)±(IV) is presented in Table 1.
Fig. 5 shows a superposition of the molecules and anions of
compounds (I)±(IV). As can be seen, the presence of organic
cations in the crystal structures of compounds (II)±(IV) does
not cause signi®cant changes in the overall shape of the anions.
The methyl group containing the ꢀ-H atoms and the carbonyl
group are situated on different sides of the chain. This
arrangement has an impact on the reactivity of the compounds
in a Norrish±Yang photoreaction. In general, the reactivity of
Figure 2
A view of the crystal lattice fragment for compound (II), showing the
atom-numbering scheme. Displacement ellipsoids are drawn at the 10%
probability level. H atoms not taking part in hydrogen bonds have been
omitted for clarity. See Table 1 for symmetry codes.
Figure 1
Figure 3
A view of the hydrogen-bonded dimers for compound (I), showing the
atom-numbering scheme. Displacement ellipsoids are drawn at the 10%
probability level. H atoms not taking part in hydrogen bonds have been
omitted for clarity. See Table 1 for symmetry codes.
A view of the crystal lattice fragment for compound (III), showing the
atom-numbering scheme. Displacement ellipsoids are drawn at the 10%
probability level. H atoms not taking part in hydrogen bonds have been
omitted for clarity. See Table 1 for symmetry codes.
ꢀ
o438 BaÎkowicz and Turowska-Tyrk
C11H12O3 and its organic salts
Acta Cryst. (2008). C64, o437±o440

organic compounds
the carbonyl C atom and the ꢀ-C atom, parameter D, is too
Ê
large (ca 3.9 A) in comparison with the average literature
Experimental
Compound (I) was purchased from Sigma±Aldrich. Organic salts
(II)±(IV) were prepared by us. Morpholine (0.1 ml, 0.0011 mol) was
added to compound (I) (0.192 g, 0.0010 mol) dissolved in toluene
(10 ml). The mixture was left for evaporation at room temperature.
After 1 d, colourless crystals of (II) were collected. Pyridine (0.0435 g,
0.00055 mol) and pyrrolidine (0.03912 g, 0.00055 mol) were added to
compound (I) (0.100 g, 0.0005 mol) dissolved in toluene (10 ml).
After several days, colourless crystalline products, (III) and (IV),
were collected and recrystallized from toluene.
Ê
value (3.0 A). Yang photocyclization was not observed in
Ê
crystals where D was larger than 3.2 A (Xia et al., 2005). The
carbonyl O and ꢀ-H atoms are also too far from each other;
Ê
parameter d is larger than 4.5 A (average literature value is ca
Ê
2.6 A). The values of these two parameters preclude the
possibility of Yang photocyclization of compounds (I)±(IV) in
the crystalline state.
Compound (I)
Crystal data
3
Ê
C11H12O3
Mr = 192.21
V = 2033.4 (6) A
Z = 8
Monoclinic, P21=c
Mo Kꢂ radiation
ꢃ = 0.09 mm
T = 299 (2) K
0.40 Â 0.20 Â 0.20 mm
1
Ê
a = 14.951 (3) A
Ê
b = 6.0452 (9) A
Ê
c = 22.935 (4) A
ꢁ = 101.201 (17)ꢁ
Data collection
Kuma KM-4-CCD diffractometer
10560 measured re¯ections
3550 independent re¯ections
1715 re¯ections with I > 2ꢄ(I)
Rint = 0.056
Re®nement
R[F2 > 2ꢄ(F2)] = 0.053
wR(F2) = 0.139
S = 0.95
3550 re¯ections
261 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
Figure 4
A view of the crystal lattice fragment for compound (IV), showing the
atom-numbering scheme. Displacement ellipsoids are drawn at the 10%
probability level. H atoms not taking part in hydrogen bonds have been
omitted for clarity. See Table 1 for symmetry code.
3
Ê
Áꢅmax = 0.16 e A
3
Ê
0.15 e A
Áꢅmin
=
Compound (II)
Crystal data
C4H10NO+ÁC11H11O3 ÁH2O
3
Ê
V = 1589.3 (9) A
Z = 4
Mr = 297.34
Monoclinic, P21=n
Figure 5
Superposition of the molecules and anions of compounds (I)±(IV).
Mo Kꢂ radiation
1
Ê
a = 15.010 (5) A
ꢃ = 0.09 mm
T = 299 (2) K
Ê
b = 6.697 (2) A
Ê
c = 16.017 (5) A
0.50 Â 0.20 Â 0.10 mm
ꢁ = 99.21 (3)ꢁ
Data collection
Kuma KM-4-CCD diffractometer
8314 measured re¯ections
2746 independent re¯ections
1366 re¯ections with I > 2ꢄ(I)
Rint = 0.060
Re®nement
R[F2 > 2ꢄ(F2)] = 0.055
wR(F2) = 0.128
S = 0.96
2746 re¯ections
198 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
3
Ê
Áꢅmax = 0.12 e A
3
Ê
0.17 e A
Áꢅmin
=
Compound (III)
Crystal data
C5H6N+ÁH+Á2C11H11O3
3
Ê
V = 2545.8 (9) A
Z = 4
Mr = 463.51
Monoclinic, C2=c
Mo Kꢂ radiation
1
Ê
a = 25.759 (6) A
ꢃ = 0.09 mm
T = 299 (2) K
Ê
b = 10.172 (2) A
Figure 6
De®nition of the parameters in¯uencing the reactivity of compounds in a
Norrish±Yang photoreaction in the crystalline state.
Ê
c = 9.776 (2) A
0.60 Â 0.30 Â 0.15 mm
ꢁ = 96.34 (2)ꢁ
ꢀ
Acta Cryst. (2008). C64, o437±o440
BaÎkowicz and Turowska-Tyrk
C11H12O3 and its organic salts o439

organic compounds
Data collection
Table 2
Values of geometric parameters in¯uencing Yang photocyclization.
Kuma KM-4-CCD diffractometer
6670 measured re¯ections
2199 independent re¯ections
1454 re¯ections with I > 2ꢄ(I)
Rint = 0.040
! (ꢁ)
Á (ꢁ)
 (ꢁ)
Ê
d (A)
Ê
D (A)
Ideal value
Average literature
value²
(IA)
(IB)
(II)
(III)
(IVA)
(IVB)
<2.7
2.64 (8)
0
54 (10)
90±120
82 (8)
180
116 (3)
Re®nement
3.00 (9)
R[F2 > 2ꢄ(F2)] = 0.063
wR(F2) = 0.210
S = 1.11
2199 re¯ections
156 parameters
7 restraints
H-atom parameters constrained
4.58
4.59
4.60
5.31
4.58
4.57
3.87
3.86
3.85
3.85
3.86
3.86
17.8
14.1
9.5
14.3
13.3
13.2
56.9
57.4
58.0
57.7
56.9
57.7
64.3
63.9
63.6
68.0
65.8
65.7
3
Ê
Áꢅmax = 0.22 e A
3
Ê
0.20 e A
Áꢅmin
=
Compound (IV)
² The mean values of d, !, Á and  are given for 54 aromatic ketones undergoing Yang
photocyclization (Natarajan et al., 2005) and that of D for 53 structures (Xia et al.,
2005).
Crystal data
C4H10N+ÁC11H11O3 ÁC11H12O3
3
Ê
V = 2464.8 (14) A
Z = 4
Mr = 455.53
Monoclinic, P21=c
Mo Kꢂ radiation
For all four compounds, data collection: CrysAlis CCD (Oxford
Diffraction, 2003); cell re®nement: CrysAlis CCD; data reduction:
CrysAlis RED (Oxford Diffraction, 2003); program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to re®ne
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
ORTEP-3 for Windows (Farrugia, 1997); software used to prepare
material for publication: SHELXL97.
1
Ê
a = 26.249 (9) A
ꢃ = 0.09 mm
T = 299 (2) K
Ê
b = 9.556 (3) A
Ê
c = 9.869 (3) A
0.35 Â 0.25 Â 0.20 mm
ꢁ = 95.32 (3)ꢁ
Data collection
Kuma KM-4-CCD diffractometer
12988 measured re¯ections
4295 independent re¯ections
1733 re¯ections with I > 2ꢄ(I)
Rint = 0.062
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SK3242). Services for accessing these data are
described at the back of the journal.
Re®nement
R[F2 > 2ꢄ(F2)] = 0.063
wR(F2) = 0.199
S = 0.96
4295 re¯ections
310 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
3
Ê
Áꢅmax = 0.22 e A
3
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Ê
0.18 e A
Áꢅmin
=
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Ê
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130
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1
2
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Ê
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ꢀ
o440 BaÎkowicz and Turowska-Tyrk
C11H12O3 and its organic salts
Acta Cryst. (2008). C64, o437±o440