Piperonylic anhydride: Isolation and conformational analysis by X-ray crystallography and density functional theory calculations

Article abstract of DOI:10.1016/j.molstruc.2011.02.019

The title compound (1), a symmetrically substituted acyclic anhydride, is shown to crystallise in the monoclinic space group P2₁/n with a = 4.7032(1) , b = 17.8748(6) , c = 15.6869(5) , β = 98.3980(17)° and V = 1304.64(7) ³. There are four molecules in the unit cell. Bond lengths and angles of 1 are comparable to the limited number of benzoic anhydride crystal structures that have been previously disclosed. Compound 1 adapts a syn-conformation in the solid-state with a pseudo-torsion angle for the OC?CO groupings of approximately 25.1°. This structure is compared to other benzoic anhydride (BA) materials that have been structurally elucidated either via single crystal X-ray diffraction methods and/or examined from a theoretical perspective. Calculations at the DFT level (B3LYP 6-311G) for a theoretical gas phase molecule of 1 reveals a similar overall global structure to that observed in the solid-state; these results suggest that crystal packing effects are negligible with respect to the observed ground state syn-conformation in the solid phase. Compound 1 also represents the first structurally characterised di-substituted benzoic anhydride.

Full text of DOI:10.1016/j.molstruc.2011.02.019

Journal of Molecular Structure 991 (2011) 158–161
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Piperonylic anhydride: Isolation and conformational analysis by X-ray
crystallography and density functional theory calculations
Maja W. Chojnacka a, Alan J. Lough b,1, R. Stephen Wylie a, Robert A. Gossage a,
⇑
a Department of Chemistry & Biology, Ryerson University, 350 Victoria Street, Toronto, ON, Canada M5K 2B3
b Department of Chemistry, University of Toronto, Toronto, ON, Canada M5S 3H6
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compound (1), a symmetrically substituted acyclic anhydride, is shown to crystallise in the
monoclinic space group P21/n with a = 4.7032(1) Å, b = 17.8748(6) Å, c = 15.6869(5) Å, b = 98.3980(17)°
and V = 1304.64(7) Å3. There are four molecules in the unit cell. Bond lengths and angles of 1 are compa-
rable to the limited number of benzoic anhydride crystal structures that have been previously disclosed.
Compound 1 adapts a syn-conformation in the solid-state with a pseudo-torsion angle for the O@Cꢀ ꢀ ꢀC@O
groupings of approximately 25.1°. This structure is compared to other benzoic anhydride (BA) materials
that have been structurally elucidated either via single crystal X-ray diffraction methods and/or exam-
ined from a theoretical perspective. Calculations at the DFT level (B3LYP 6-311Gꢁꢁ) for a theoretical gas
phase molecule of 1 reveals a similar overall global structure to that observed in the solid-state; these
results suggest that crystal packing effects are negligible with respect to the observed ground state
syn-conformation in the solid phase. Compound 1 also represents the first structurally characterised
di-substituted benzoic anhydride.
Received 24 January 2011
Received in revised form 9 February 2011
Accepted 9 February 2011
Available online 15 February 2011
Keywords:
Anhydride
X-ray crystal structure
Piperonylic acid
Benzodioxole
Configuration determination
DFT calculations
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
di-substituted symmetric benzoic anhydride to be characterised by
single crystal X-ray diffraction methods. The structure of 1 is com-
Anhydrides represent an important class of organic compounds
which have found widespread use as synthetic intermediates, in
polymer chemistry [1–13] and as precursor molecules for applica-
tions in materials science [14]. The OCAOACO fragment can
engender a large dipole moment to the anhydride and this aspect
has been exploited in, for example, the design of novel liquid crys-
tals [15]. Despite the widespread use of anhydrides, very few di-
aryl anhydrides, i.e., derivatives of the parent compound benzoic
anhydride (BA: Fig. 1) [16], have been crystallographically charac-
terised [17–25].
pared and contrasted to the relatively few benzoic anhydrides that
have been examined in the solid-state (i.e., X-ray) and its gas phase
structure is likewise examined by density functional theory (DFT)
at the B3LYP 6-311Gꢁꢁ level and these data are then compared to
that calculated for BA itself.
2. Results and discussion
2.1. Synthesis and characterisation
During a series of reactions involving the acylation of heterocy-
clic bases involving various benzoyl chlorides (Fig. 2: [26]), we
noted the formation of a minor by-product upon the specific appli-
cation of piperonyloyl chloride (i.e., 3,4-(CH2O2)C6H3COCl). This
product readily crystallised and displayed a high degree of symme-
try via NMR analysis. Furthermore, the compound was devoid of
any molecular fragments of the organic base. Herein, we detail
the solid-state structure of this material which has been identified
as piperonylic anhydride (1). Compound 1 represents the first such
A facile method for the production of acyl enamines (Eq. (1):
Fig. 2) involves the acylation of weakly basic azoles such as benz-
oxazoles, benzothiazoles [26a] or oxazolines [26b] using, for exam-
ple, benzoyl chlorides. The products of this coupling are useful
intermediates for applications in heterocyclic syntheses [26–28].
Using the standard reaction protocols [26b] but employing
2,4,4-trimethyl-2-oxazoline as the azole and piperonyloyl chloride
(Fig. 1: R = C6H3(O2CH2)-3,4), the resulting crude product mixture
contained not only the expected acyl enamine [28] but a second
minor product (isolated yield: 10%). This latter material displayed
a high retention factor (Rf) as shown by TLC analysis (see Section 4).
Isolation of this rapidly mobile material presented a light yellow
solid (1) displaying an IR spectrum with absorbances characteristic
[16] of an anhydride (KBr; cmꢂ1: 1768 m, 1707 m). Benzoic anhy-
⇑
Corresponding author.
E-mail addresses: alough@chem.utoronto.ca (A.J. Lough), gossage@ryerson.ca
(R.A. Gossage).
1
Corresponding author concerning the crystallographic work.
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.02.019

M.W. Chojnacka et al. / Journal of Molecular Structure 991 (2011) 158–161
159
(MeCN) nor the NEt3 used in the reaction mixture. Such protocols
are typically unnecessary to facilitate high yields of the desired
acyl enamines [26–28]. To unequivocally characterise the nature
of 1, we carried out a single crystal X-ray diffraction study of a
sample of the said re-crystallised material.
Fig. 1. The syn- and anti-isomers of benzoic anhydride.
2.2. Structural considerations
Compound 1, piperonyl anhydride (Fig. 4), forms monoclinic
crystals from CHCl3/hexanes mixtures. These crystals are of space
group P21/n with four molecules of 1 in the unit cell. Table 1 con-
tains the general crystal parameters for 1 and Table 2 contains a
list of bond lengths and angles for a unit cell molecule of 1.
Table 1
General crystal parameters for compound 1.
Fig. 2. The general reaction scheme leading to the formation of by-product 1.
Empirical formula
Formula weight
Crystal system
Crystal colour
Crystal size (mm3)
Space group
a (Å)
C16H10O7
314.24
Monoclinic
Pale yellow
0.20 ꢃ 0.12 ꢃ 0.06
P 21/n
4.7032(1)
b (Å)
17.8748(6)
c (Å)
15.6869(5)
a
(°)
90.00
b (°)
98.3980(17)
c
(°)
90.00
1304.64(7)
V (Å3)
Z
4
Density (calc.: g/cm3)
1.600
0.128
648
Abs. coeff. (mmꢂ1
F(0 0 0)
)
Temperature (K)
150(1)
H
(min.–max.)
Dataset [h, k, l]
Total data, unique data, R(int)
Observed data (>2 (I))
2.62–27.49°
ꢂ6/6, ꢂ23/23, ꢂ20/20
11,337, 2967, 0.0465
2967
Fig. 3. Schematic representations of the various hypothetical structural forms 1.
r
Completeness to theta = 27.49°
Absorption correction
Max. and min. transmission
Refinement method
99.3%
Semi-empirical from equivalents
1.002 and 0.904
Full-matrix least-squares on F2
2967, 0, 208
drides can be produced in a number of ways [1,2] but are typically
formed by the stoichiometric treatment of benzoyl chlorides and
the corresponding acid in the presence of base [2] or via benzoic
acid reactions with acetic anhydride [15]. However, such com-
pounds can also be formed by the reaction of benzoyl chlorides
and amine bases in ‘‘wet’’ solvents. This latter scenario appears
to be the case here as we did not pre-dry the reaction solvent
NData, NRestraints, NParameters
GoF (F2)
1.035
Final R indices [I > 2
r
(I)]
R1 = 0.0505, wR2 = 0.1209
R1 = 0.0921, wR2 = 0.1480
0.247, ꢂ0.250
R indices (all data)
Largest diff.: peak, hole (e. Å3)
Fig. 4. ORTEP representation of a molecule of 1 found in the unit cell showing the atomic numbering scheme.

160
M.W. Chojnacka et al. / Journal of Molecular Structure 991 (2011) 158–161
Table 2
forms. When compared to the observed solid-state data, DFT (of the
syn-[1,2] form) does a reasonable job at estimating the observed so-
lid-state bond lengths and angles (Table 2) of 1.
Selected bond lengths (Å) and angles (°) for 1 as measured (X-ray) and calculated
(DFT: syn-[1,2] form). Estimated standard deviations are shown in parentheses.
X-ray
DFT (B3LYP 6-311Gꢁꢁ
)
The estimated dipole moment (DFT: B3LYP 6-311Gꢁꢁ) for 1 is
calculated as 5.20 Debye (syn-[1,2] form); a larger value than that
calculated for BA (4.27 Debye) itself.3 This difference is no doubt a
reflexion of the presence of the electron withdrawing O2CH2 groups
bridging both of the meta- and para-aromatic positions of 1. Net
atomic charges (Mulliken: syn-[1,2] form) calculated at oxygen
atoms O3 (ꢂ0.292) and 05 (ꢂ0.293) (Fig. 4) are estimated to be com-
parable to those derived (ꢂ0.285 and ꢂ0.284, respectively2) for BA.
Compound 1 represents the first di-substituted symmetric ben-
zoic anhydride to be crystallographically characterised. However, it
should be noted that a single crystal structure determination of a
tri-substituted material, viz. 3,4,5-trimethoxybenzoic anhydride
has appeared. This compound differs from 1 in the chirality of
the crystal form [15] but the molecules also adapt the syn-confor-
mational isomer in the solid-state.
O(3)AC(8)
O(4)AC(9)
O(4)AC(8)
O(5)AC(9)
C(5)AC(8)
C(9)AC(10)
1.201(2)
1.390(2)
1.395(2)
1.200(2)
1.473(3)
1.476(3)
1.197
1.396
1.395
1.197
1.479
1.480
C(9)AO(4)AC(8)
O(2)AC(1)AO(1)
O(3)AC(8)AO(4)
O(3)AC(8)AC(5)
O(4)AC(8)AC(5)
O(5)AC(9)AO(4)
O(5)AC(9)AC(10)
O(4)AC(9)AC(10)
O(6)AC(13)AO(7)
122.90(16)
107.05(16)
122.88(18)
126.28(17)
110.79(17)
123.85(17)
125.07(18)
111.02(17)
107.74(15)
120.09
107.57
122.26
125.72
111.95
122.27
126.01
111.66
107.55
An ORTEP [29] diagram is presented in Fig. 4 which shows the
atomic numbering scheme. Although it is known that acyclic anhy-
drides can crystallise with almost unrestricted conformations
(Fig. 3) [19,22], compound 1 is shown to adopt a syn-configuration
in relation to the orientation of the two C@O groupings attached to
the central anhydride oxygen atom (i.e., O4). The syn-conforma-
tional isomer is also displayed in the solid-state for several other
related anhydrides such as 5,50-Di(anthracenecarboxylic) anhy-
dride [23], aspirin anhydride [20], and the m-NO2 [21], o-NO2
[19], p-Br [14,17] and p-Cl [18] derivatives of benzoic anhydride
(BA) itself.2 Previously reported molecular calculations [15], at both
the MM2 and AM1 levels of theory, have predicted a higher (gas
phase) stability for the syn-form of BA. Calculations at a higher level
of theory herein (DFT: B3LYP 6-311Gꢁꢁ) of both BA and 1 confirm a
similar global structure to that suggested earlier [15] for BA and
the syn-form observed in the solid-state (see Supplementary mate-
rial) for 1. Unlike the situation with BA, the syn-conformation of 1
can be further differentiated by the orientation of the two, essen-
tially co-planar, aromatic rings; these rotational isomers are de-
picted and denoted in Fig. 3 as the syn-[1,2], syn-[1,1] and syn-
[2,2] forms. Crystallographically characterised 1 takes the syn-[1,2]
form (Fig. 4) with independent and mutually rotated aromatic rings.
The pseudo-torsion angle is O3@C8ꢀ ꢀ ꢀC9@O5 in solid 1 is 25.1°
which can be compared to that of, for example, 27.7° found in o-
nitrobenzoic anhydride [19]. As mentioned earlier, the two aromatic
rings of 1 are not truly co-planar; a torsion angle of 17.2° is noted as
measured along the O3AC8AO4AC9 vector. The bond lengths and
angles of 1 (Table 2) are typical in relation to those examples men-
tioned above [15,18–25] and are otherwise unsurprising. Specifi-
cally, the C@O and CAO bonds lengths are well within the
expected ranges [30] for an anhydride. Predictably, the gas phase
calculations of 1 suggests that all three syn-structural forms are very
close in energy (relative energies: [1,1] = 0.00 kcal/mol;
[1,2] = +0.25 kcal/mol and [2,2] = +0.33 kcal/mol) but obviously im-
ply that in the gas phase the syn-[1,1] isomer would be preferred.
In solution (room temperature: CDCl3), only one aromatic group is
noted and hence rapid rotation and/or local symmetry higher than
that of point group C1 (i.e., syn-[1,2]) is present (see Section 4). Of
further interest are the calculated parameters of the syn-[1,1] isomer
which leads to a situation that is characterised (Supplementary
material) as having with the smallest O3AC8AO4AC9 torsion angle,
most constrained O3@C8ꢀ ꢀ ꢀC9@O5 pseudo-torsion angle and result-
ing lowest calculated dipole moment (4.32 Debye) of the three syn-
3. Concluding remarks
The isolation and solid-state (X-ray) characterisation of pipero-
nyl anhydride (1), the first di-substituted symmetric benzoic anhy-
dride, has been carried out. The structure of 1 is shown to be in the
syn-[1,2] conformation isomer (Figs. 3 and 4) with a pseudo-tor-
sion angle about the anhydride functionality of 25.1°. The overall
global structure and properties of various structural isomers of 1
and the parent benzoic acid itself have been further examined by
the DFT level of theory (B3LYP 6-311Gꢁꢁ).
4. Experimental
4.1. General
General procedures and methods were carried out using stan-
dard bench top techniques similar to those described previously
[12]. All reagents were purchased commercially and used as re-
ceived. NMR spectra were recorded at room temperature on a Bru-
ker Avance 400 NMR spectrometer using samples dissolved in
chloroform-d. Coupling constant (J) values are reported in Hertz.
4.2. Isolation of 1
A mixture of 2,4,4-trimethyl-2-oxazoline (1.13 mL: 8.86 mmol),
2.5 mL of NEt3 and 3.26 g of piperonyloyl chloride (17.7 mmol)
were combined together in a 100 mL round-bottomed flask con-
taining ꢄ50 mL of MeCN. This mixture was heated to reflux tem-
perature under an atmosphere of N2(g) for 20 h. After cooling the
resulting orange solution to room temperature, the resulting solids
(presumably [HNEt3]Cl) [26b,27a] were filtered off and washed
with a small amount of MeCN. The acetonitrile fractions were then
combined and all volatile components were removed in vacuo. The
residue was then extracted twice with CHCl3 and water (ꢄ50 mL)
and the organic fractions combined, dried (MgSO4) and then evap-
orated to dryness by rotary evaporation. This procedure yielded a
sticky, semi-solid brown-coloured mass (3.6 g). Analysis of this
material via 1H NMR indicated approximately a 45:55 ratio of the
desired product (2) [28] and a second component 1. A sample of
this crude material (ꢄ0.8 g) was then separated by flash column
chromatography (SiO2; EtOAc/hexanes: 5/8) and the fastest eluting
3
A value of 5.0 Debye was previously calculated for the dipole moment of BA at the
semi-empirical (AM1) level of theory [15]. The other two syn-isomers of 1, i.e., syn-
[1,1] and syn-[2,2], present calculated dipole moments of 4.32 and 5.44 Debye,
respectively. (see Supplementary material). The aforementioned calculations [15] also
yielded Mulliken charge values of –0.29 and –0.32, for O3 and O5 respectively of BA.
2
Although reference [16] details the unit cell and general crystal parameters for
crystalline BA, no bond lengths or angles are reported.

M.W. Chojnacka et al. / Journal of Molecular Structure 991 (2011) 158–161
161
material (Rf = 0.61) was collected and re-crystallised from CHCl3/
Acknowledgements
hexanes (bp 35–60 °C range) to yield approximately 80 mg of pure
1 in the form of pale yellow needles. These needles were deemed to
be suitable for X-ray diffraction methods.
The authors are indebted to the support of Ryerson University
(Dean’s Special Research Fund), The University of Toronto and
nserc (Canada) in the form of a Discovery Grant (RAG) and a NSERC
USRA (MWC). Prof. Derick Rousseau (Ryerson University) is
thanked for his helpful discussions and input.
Yield: 10%; mp: 153–156 °C.
IR (KBr: cmꢂ1): 3128 (s, br), 2923 (m), 2853 (m), 1768 (m), 1707
(m), 1605 (m), 1503 (m), 1489 (m), 1444 (m), 1400 (vs), 1254 (m),
1192 (w), 1136 (w), 1114 (w), 1095 (m), 1029 (m), 909 (m), 812
(w), 767 (w), 744 (w), 714 (w), 621 (w).
References
1H NMR (400 MHz) dH/ppm: 7.76 (dd, 1H, J = 8.3, 1.8, ArH), 7.54
(dd, 1H, J = 1.7, 0.3, ArH), 6.90 (d, 1H, J = 8.4, ArH), 6.10 (s, 2H, CH2).
13C{1H} NMR (75 MHz) dC/ppm: 161.3, 153.4, 148.6, 127.1, 122.7,
110.1, 108.4, 102.2.
[1] R.C. Larock, Comprehensive Organic Transformations: A Guide to Functional
Group Preparations, 2nd ed., Wiley–VCH, Weinheim, 1999. Sections 2.58, 3.5,
5.3, 8.27 and 9.13-9.16.
[2] R. Sustmann, in: B.M. Trost, I. Fleming (Eds.), Comprehensive Organic
Synthesis: Selectivity, Strategy and Efficiency in Modern Organic Chemistry,
vol. 6, Elsevier, Amsterdam, 1991. Section 2.1.
[3] G.D. Yadav, S.S. Naik, Org. Proc. Res. Develop. 4 (2000) 141.
[4] P.-W. Tseng, S.-W. Yeh, C.-H. Chou, J. Org. Chem. 73 (2008) 3481.
[5] A.J. Carmichael, M.J. Earle, J.D. Holbrey, P.B. McCormac, K.R. Seddon, Org. Lett. 1
(1999) 997.
[6] A. Orita, C. Tanahashi, A. Kakuda, J. Otera, J. Org. Chem. 66 (2001) 8926.
[7] C.-T. Chen, J.-H. Kuo, V.D. Pawar, Y.S. Munot, S.-S. Weng, C.-H. Ku, C.-Y. Liu, J.
Org. Chem. 70 (2005) 1188.
[8] P. Goodrich, C. Hardacre, H. Mehdi, P. Nancarrow, D.W. Rooney, J.M. Thompson,
Ind. Eng. Chem. Res. 45 (2006) 6640.
[9] H. Mitsuhashi, H. Miyazaki, Y. Kawamura, H. Nakamura, K. Arata, Chem. Mater.
13 (2001) 3038.
[10] C. Hardacre, P. Nancarrow, D.W. Rooney, J.M. Thompson, Org. Proc. Res.
Develop. 12 (2008) 1156.
[11] C.J. Wilson, S.S. Husain, E.R. Stimson, L.J. Dangott, K.W. Miller, J.E. Maggio,
Biochemistry 36 (1997) 4542.
[12] R.A. Gossage, in: H.W. Roesky, D.K. Kennepohl (Eds.), Experiments in Green
and Sustainable Chemistry, Wiley–VCH, Weinheim, 2009, pp. 19–24. Chapter
4.
[13] C. Kanta De, E.G. Klauber, D. Seidel, J. Am. Chem. Soc. 131 (2009) 17060.
[14] For example E.N. Duesler, R.B. Kress, C.-T. Lin, W.-I. Shiau, I.C. Paul, D.Y. Curtin,
J. Am. Chem. Soc. 103 (1981) 875.
4.3. Single crystal X-ray structure determination of 1
X-ray diffraction data were recorded on a Nonius Kappa CCD
diffractometer using Mo K
a radiation (k = 0.71073 Å) and the
resulting data collection obtained using Collect [31]. All estimated
standard deviations (esds), except the esd in the dihedral angle be-
tween two l.s. planes, are estimated using the full covariance ma-
trix. The cell esds are taken into account individually in the
estimation of esds in distances, angles and torsion angles; correla-
tions between esds in cell parameters are only used when they are
defined by crystal symmetry. An approximate (isotropic) treat-
ment of cell esds is used for estimating esds involving l.s. planes.
The cell refinement and data reduction was performed with Den-
zo–smn [32]. The structure solution employed sir-92 [33] and
the structure refinement was carried out with shelxtl 6.1 [34].
The molecular graphics were obtained using platon [35] and the
publication materials were generated utilising shelxtl 6.1 [34].
The refinement of F2 is against ALL reflections. The weighted R-fac-
tor wR and GoFs are based on F2, conventional R-factors R are based
on F, with F set to zero for negative F2. The threshold expression of
[15] K. Kishikawa, S. Furusawa, T. Yamaki, S. Kohmoto, M. Yamamoto, K.
Yamaguchi, J. Am. Chem. Soc. 124 (2002) 1597.
[16] G. van Alen, J. Kraube, Z. Chem. 4 (1964) 193.
[17] C.S. McCammon, J. Trotter, Acta Cryst. 17 (1964) 1333.
[18] M. Calleri, G. Ferrais, D. Viterbo, Atti Accad. Sci. Torino 100 (1966) 145.
[19] G. Huelgas, L. Quintero, C. Anaya de Parrodi, S. Bernès, Acta Cryst. E62 (2006)
o3191.
F2 > 2 (F2) is used only for calculating R-factors (gt), etc. and is not
r
relevant to the choice of reflections for refinement. R-factors based
on F2 are statistically about twice as large as those based on F, and
R-factors based on ALL data will be even larger.
[20] S.R. Bryn, P.Y. Siew, J. Pharma. Sci. 70 (1981) 280.
[21] M.L. Głowka, I. Iwanicka, I. Król, J. Crystallogr. Spec. Res. 20 (1990) 519.
[22] J.K. Maurin, Polish J. Chem. 68 (1994) 1795.
[23] A.J. Blake, R.S. Grimditch, M. Schröder, Acta Cryst. C51 (1995) 1472.
[24] D.E. Lynch, R. Hayer, S. Bagga, S. Parsons, Aust. J. Chem. 53 (2000) 593.
[25] G.-F. Liu, Y.-W. Luo, D.-B. Qin, Acta. Cryst. E65 (2009) o1043.
[26] (a) Gh. Ciurdaru, M. Ciuciu, J. Prakt. Chem. 321 (1979) 320;
(b) Y. Tohda, T. Kawashima, M. Ariga, R. Akiyama, H. Shudoh, Y. Mori, Bull.
Chem. Soc. Jpn. 57 (1984) 2329;
(c) A. Zhou, C.U. Pittman Jr., Tetrahedron Lett. 45 (2004) 8899;
(d) A. Zhou, C.U. Pittman Jr., Tetrahedron Lett. 46 (2005) 2045;
(e) G. Ye, S. Chatterjee, M. Li, A. Zhou, Y. Song, B. Lloyd Barker, C. Chen, D.J.
Beard, W.P. Henry, C.U. Pittman, Tetrahedron 66 (2010) 2919.
[27] (a) Y. Tohda, T. Yanagidani, S. Hiramatsu, N. Nishiwaki, K. Tani, M. Ariga, Bull.
Chem. Soc. Jpn. 70 (1997) 2781;
4.4. Molecular calculations of 1
The gas phase molecular calculations of BA and 1 were carried
out using the Spartan 8.0 (Wavefunction Inc., Irvine CA, 2008) suite
of software programs.
(b) A. Zhou, C.U. Pittman Jr., Synthesis (2006) 37.
Supplementary material
[28] Details on the optimization of Equation 1 (Figure 2) for the azole 2,4,4-
trimethyl-2-oxazoline and R =–C6H3(O2CH2)-3,4 will be reported separately;
M.W. Chojnacka, A.J. Lough, R.A. Gossage et al., unpublished observations.
[29] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[30] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, G. Orpen, R. Taylor, J. Chem.
Soc., Perkin Trans. 2 (1987) S1.
[31] ‘‘Collect’’: Data Collection Software. Nonius B.V., Delft, The Netherlands, 1997–
2002.
[32] Z. Otwinowski, W. Minor, Meth. Enzymol. 276 (1997) 307.
[33] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori,
M. Camalli, J. Appl. Cryst. 27 (1994) 435.
Crystallographic data (excluding structure factors) have been
deposited in the Cambridge Crystallographic Data Centre as Sup-
plementary publication No. ccdc 776757. Copies of these data
can be obtained free of charge on application to ccdc, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336 033; e-mail: de-
posit@ccdc.cam.ac.uk). Supplementary data associated with this
article (i.e., .cif file of 1 and files, in .mol2 format, containing the
structures of BA and 1 derived from the DFT treatment of these
materials) can be found, in the online version, at doi:10.1016/
j.molstruc.xxxx.xx.xxx or requested directly from the authors.
[34] G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
[35] A.L. Spek, Acta Cryst. D65 (2009) 148.